Design of a MedEvac UAV for Operation in Physically ...

Design of a MedEvac UAV for

Operation in Physically Constrained

Environments

Multi-Disciplinary Design Project 2012-13

14th

January 2013

Group 1:

Wasim Aslam (Medical Engineer); Michael Collison (Aerospace Engineer);

Sarad Limbu Lawati (Aerospace Engineer); Matthew Temple (Electrical

Engineer); Maria Wood (Mechanical Engineer); Dela Yohuno (Medical

Engineer)

Supervisors:

Chris Newbold (Qinetiq); Prof. Roger Webb (University of Surrey); Dr. Andrew

Pennycott (University of Surrey)

Design of MedEvac UAV for Operation in physically constrained environments

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Contents

1 Executive Summary ............................................................................................................... 1-8

2 Introduction ......................................................................................................................... 2-10

3 Aircraft Configuration ......................................................................................................... 3-11

3.1 Single and Coaxial Rotor Configurations Rejection ................................................... 3-11

3.2 Fixed wing design rejection ......................................................................................... 3-11

3.3 Tilt rotor design rejection ............................................................................................ 3-12

3.4 Chosen Configuration .................................................................................................. 3-13

4 Duct design .......................................................................................................................... 4-14

4.1 Double Ducted Fan concept ........................................................................................ 4-15

4.2 Stator Vanes & Flaps ................................................................................................... 4-19

5 Fan/Rotor design ................................................................................................................. 5-20

5.1 Blade Element Theory (Leishman, 2006) .................................................................... 5-22

5.2 Materials and Stress analysis ....................................................................................... 5-24

6 Transmission........................................................................................................................ 6-25

6.1 Transmission Concept 1 .............................................................................................. 6-26



6.4 Transmission Design ................................................................................................... 6-30

7 UAV dimensions ................................................................................................................. 7-34

8 Structures ............................................................................................................................. 8-34

8.1 Main Spar .................................................................................................................... 8-34

8.2 Skin and Bulkheads ..................................................................................................... 8-35

8.3 Frames and Stringers ................................................................................................... 8-36

8.4 Floor and Ceiling ......................................................................................................... 8-36

8.5 Landing Gear ............................................................................................................... 8-37

8.6 Miscellaneous .............................................................................................................. 8-38

8.7 Cabin Door .................................................................................................................. 8-38

8.8 Structural CAD Representation ................................................................................... 8-38


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9 Flight modes ........................................................................................................................ 9-39

10 Drag Estimation ............................................................................................................. 10-40

11 Power requirements ....................................................................................................... 11-41

11.1 Induced Power ........................................................................................................... 11-41

11.2 Blade Profile Power ................................................................................................... 11-43

11.3 Total, and Available Power Analysis ........................................................................ 11-43

11.4 Flight Envelope ......................................................................................................... 11-44

12 MTOW mass iteration using fuel and structural mass................................................... 12-46

13 Operational Flight Profile .............................................................................................. 13-47

13.1 Acceleration ............................................................................................................... 13-47

13.2 Climb Performance .................................................................................................... 13-48

13.3 Overall Mission Profile ............................................................................................. 13-49

14 Performance ................................................................................................................... 14-50

14.1 Disk Loading ............................................................................................................. 14-50

14.2 Range ......................................................................................................................... 14-50

14.3 Centre of Gravity & Stability .................................................................................... 14-51

15 Processors ...................................................................................................................... 15-51

16 Sensors ........................................................................................................................... 16-52

16.1 Terrain Mapping ........................................................................................................ 16-52

16.2 Colour Camera........................................................................................................... 16-56

16.3 Attitude Determination Sensors................................................................................. 16-57

16.4 Altitude Determination .............................................................................................. 16-59

16.5 Tachometer ................................................................................................................ 16-59

17 Electrical Bus Layout .................................................................................................... 17-60

18 Navigation and Flight Operations.................................................................................. 18-61

19 Communication ............................................................................................................. 19-62

19.1 Operating Frequency ................................................................................................. 19-63

19.2 Satellite Networks ..................................................................................................... 19-63

19.3 Modulation, Error Correction and Polarisation ......................................................... 19-64


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19.4 Encryption ................................................................................................................. 19-65

19.5 Antenna Design ......................................................................................................... 19-65

20 Electrical Power Generation .......................................................................................... 20-68

21 Ground Control Station ................................................................................................. 21-70

21.1 Pilot Control Station .................................................................................................. 21-71

21.2 Medic Control Station ............................................................................................... 21-71

22 Environmental Control .................................................................................................. 22-72

23 Fuel Tank Protection ..................................................................................................... 23-73

23.1 Minimising Explosion Risks ..................................................................................... 23-73

23.2 Stopping Leaks from Punctured Fuel Tanks ............................................................. 23-74

24 Defence systems ............................................................................................................ 24-75

24.1 CROSSHAIRS .......................................................................................................... 24-75

24.2 Basic Countermeasures ............................................................................................. 24-76

24.3 RAFAEL Trophy Family .......................................................................................... 24-76

25 Transportation of UAV .................................................................................................. 25-76

25.1 Air Transportation ..................................................................................................... 25-76

25.2 Land Transportation .................................................................................................. 25-77

26 Regulations .................................................................................................................... 26-78

26.1 Training Requirements .............................................................................................. 26-78

26.2 Sense and Avoid Criteria ........................................................................................... 26-78

26.3 Redundant Engines .................................................................................................... 26-78

26.4 Emergency Landings Procedures .............................................................................. 26-79

27 Casualty Movement ....................................................................................................... 27-79

28 Initial preliminary research (Battlefield injuries) .......................................................... 28-81

28.1 Choosing the injuries to treat ..................................................................................... 28-82

29 Adapting Medical treatments and diagnostics for the UAV .......................................... 29-83

29.1 Deciding on Medical treatments and diagnostics ...................................................... 29-83

30 Casualty Diagnostics ..................................................................................................... 30-84

30.1 Pulse Oximetry .......................................................................................................... 30-84


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30.2 Blood Pressure ........................................................................................................... 30-86

31 Insertion of a Line for injection of fluids ...................................................................... 31-87

32 Blood Transfusion ......................................................................................................... 32-89

33 Injuries and Treatments ................................................................................................. 33-91

33.1 Occurrence ................................................................................................................. 33-91

33.2 Specific Injuries ......................................................................................................... 33-93

33.2.1 Open wounds ..................................................................................................... 33-93

33.2.2 Potential solutions ............................................................................................. 33-95

33.2.3 Burn Injuries ...................................................................................................... 33-99

33.2.4 Chemical and Radiation Injuries ..................................................................... 33-100

34 Fractures ...................................................................................................................... 34-106

34.1 Open fractures ......................................................................................................... 34-106

34.2 Closed fractures ....................................................................................................... 34-107

35 CPR ............................................................................................................................. 35-107

35.1 Chest compressions ................................................................................................. 35-107

35.2 Automatic External Defibrillator (AED) ................................................................. 35-108

36 Open chest wounds ...................................................................................................... 36-109

37 Airway management .................................................................................................... 37-110

37.1 Blocked airway ........................................................................................................ 37-110

37.2 Medical portable ventilation .................................................................................... 37-111

38 Casualty Compartment ................................................................................................ 38-113

39 Effects of altitude on patient ........................................................................................ 39-114

40 Disinfection ................................................................................................................. 40-115

41 Patient cabin layout ..................................................................................................... 41-116

41.1 Patient stretcher platform ........................................................................................ 41-116

41.2 Medical device layout .............................................................................................. 41-117

42 Robot Arm ................................................................................................................... 42-120

42.1 Possible Options ...................................................................................................... 42-120

42.2 Robotic Arm Sensors ............................................................................................... 42-121


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42.3 Layout ...................................................................................................................... 42-122

43 Robotic tools ................................................................................................................ 43-124

44 Program Costs ............................................................................................................. 44-128

45 Overall CAD Technical Drawing ................................................................................ 45-130

46 Specification ................................................................................................................ 46-132

46.1 Performance ............................................................................................................. 46-132

46.2 Control and Stability ................................................................................................ 46-132

46.3 Operation ................................................................................................................. 46-132

46.4 Powerplant ............................................................................................................... 46-133

46.5 Aircraft Systems ...................................................................................................... 46-133

46.6 Flight Controls ......................................................................................................... 46-133

46.7 Sensing .................................................................................................................... 46-133

46.8 Communication ....................................................................................................... 46-134

46.9 Remote Control ....................................................................................................... 46-134

46.10 Casualty Loading ................................................................................................. 46-134

46.11 Medical ................................................................................................................ 46-134

46.11.1 Operation ..................................................................................................... 46-134

46.11.2 Diagnosis ..................................................................................................... 46-135

46.11.3 Treatment ..................................................................................................... 46-135

46.12 Regulatory/Safety ................................................................................................ 46-135

46.13 Assumptions ........................................................................................................ 46-136

47 Medical Treatment ....................................................................................................... 47-136

48 Medical Training ......................................................................................................... 48-139

49 Mass, Size and Power Estimation................................................................................ 49-140

50 Financial Analysis ....................................................................................................... 50-142

50.1 Development Program Costs ................................................................................... 50-142

50.2 Operational Costs .................................................................................................... 50-144

51 Project Management .................................................................................................... 51-147

52 Conclusion ................................................................................................................... 52-149


1-7

54 Bibliography ................................................................................................................ 54-150

Appendix A – Current Aircraft Data ....................................................................................... 54-159

Appendix B .............................................................................................................................. 54-160

Appendix C – Gear Terminology ............................................................................................ 54-168

Appendix D – Satellite Communication Equations ...................................................................... 169

Appendix E – Finance Equations ................................................................................................. 170

Electronics Development Cost Estimate .................................................................................. 170

Analytical Spreading Function for Research and Development Projects ................................. 170

Appendix F - Flowcharts .............................................................................................................. 171

Communications System .......................................................................................................... 171

Flight Operations ................................................................................................................. 54-172

Medical Operations ............................................................................................................. 54-174

Appendix G - Communication Bus Diagram .......................................................................... 54-180

Appendix H - Failure Mode Effect Analysis ........................................................................... 54-181


Author: Group 1-8

1 Executive Summary

A Medical Evacuation Unmanned Aerial Vehicle (MedEvac UAV) preliminary design solution is

discussed and presented herein, which is able to fulfil an MOD need for a UAV that is capable of

operating in a physically constrained urban environment and providing not only casualty

extraction to a field hospital, but also autonomous medical diagnosis and treatment at the scene

and in transit.

The chosen UAV configuration is an innovative double ducted fan configuration, using a series of

flaps and vanes to give the desired control and stability movements. This configuration was

chosen in order to be able to land in physically constrained urban environments, whereby a small

UAV footprint allows more potential landing zones to be accessed. For example, the ducted fan

UAV with a footprint of 2.91m x 7.59m allows it to land on a single lane road, whereas a standard

helicopter or fixed wing configuration would not be able to operate in these conditions.

The secondary duct enables the UAV to fly level with the fans perpendicular to the oncoming

airflow due to their presence creating a flow of air around the duct lip, which prevents separation

occurring at this point as would normally happen in this flight condition without the secondary

duct. Furthermore, the fans themselves are designed with stators to straighten the flow by

removing the swirl, along with the blade design reducing the noise and vibration levels of the

UAV. The two fans need to be able to alter their speed independently to overcome the effects of

UAV pitch disturbances, therefore the transmission of power from the engines to the fans will be

transferred via a differential gearbox, similar to that used in the rear axle of a vehicle.

The UAV has dual redundant engines in case of failure which allow the UAV to have a ceiling of

5000m with a cruise speed of 57m/s (205km/h) at sea level and a maximum flight speed of 71m/s

(256km/h) at 4500m, this is slightly slower than a typical helicopter but is limited by the choice of

configuration to give a small landing footprint. The semi-monocoque UAV structure contains a

central pressurised casualty cabin section and a fan at either end, with the drive shafts, engines

and other equipment stowed internally above the cabin ceiling, or below the cabin floor.

There is sufficient technology currently available on the market to enable the UAV to operate as

an autonomously controlled aircraft. A complete flight control system is assembled from the

following units, which are controlled with a single field programmable gate array. The sensors

provided in the UAV are: a Global Positioning System (GPS), to sense geographic position and

velocity of the UAV; an Inertial Measurement Unit (IMU), to sense the attitude of the UAV; and

a pressure sensor, to sense the altitude of the UAV. These components provide all of the

necessary sensory data to accurately determine the position and attitude of the UAV. When

combined with other sensors to measure the fan speed and flap positions the on-board computer

has sufficient data to control the aircraft, and fly the UAV to the desired locations without the

need of a constant control signal from the ground station.


Author: Group 1-9

To aid in the autonomous operations of the aircraft a Light Detection and Ranging (LiDAR)

system can be used to not only detect obstacles around the UAV, but also scan nearby terrain for

suitable landing sites from high altitude. A remote robotic arm controlled by medics on the

ground then completes the package.

The MedEvac is designed to only carry the NATO stretcher since it is currently used on the

battlefield due to it being lightweight and having the ability to collapse to the size of a rucksack,

and can be inter-operable with other military vehicles which can also carry the stretcher.

Detachable wheels will be provided to clamp onto the handles on one side of the stretcher so it

can be manoeuvred by one person.

Since no medic will be on board the UAV, non-invasive diagnostic equipment will play an

essential role in the treatment of the casualty. To measure and record the blood pressure of the

casualty, an adhesive blood pressure patch will be utilised, and to measure the blood oxygen

levels, a forehead pulse oximeter will be applied.

One of the major issues for the MedEvac is the treatment of open wounds and the blood loss that

results as a consequence. The proposed solution is the use of a haemostatic powder (Celox) which

would be applied by a robotic arm with a specialised attachment to any open wounds; the powder

would then form a gel like clot. Fluid resuscitation is also implemented via a fluid and medication

delivery system using the intraosseous (IO) method to maintain blood volume at sufficient levels

for tissue perfusion to occur. Medications such as morphine for pain relief and tranexamic acid to

reduce the severity of bleeding can be implemented through the IO fluid delivery system within

the UAV. Furthermore a ventilator is implemented to provide support for those with breathing

problems. Several specialised attachments are designed for use by the robotic arm to allow for

treatment of several conditions including a spring loaded needle attachment which is designed for

the treatment of pneumothorax, a potentially fatal condition.

The production quantity of 50 UAVs gives rise to program costs associated with the research,

development, design and manufacture of the UAV to be £132million, giving a unit cost of

£2.6million for each operational aircraft.

The solution provided removes the risks involved with committing extra personnel to a dangerous

situation as is the case with current military MedEvacs. It is also able to integrate with current

operations with minimal training requirements, and provide a cost effective upgrade to current

MedEvacs with added capabilities such as accessing physically constrained locations for casualty

extraction.


Author: Group 2-10

2 Introduction

Air ambulances are an important and crucial part of the medical services provided worldwide

particularly in military settings. However in military use where air ambulances usually have to

enter conflict zones they are putting themselves at danger, this risk to the personnel of the air

ambulance is an important part of the decision to deploy air ambulances. With 6311 aeromedical

evacuations occurring over the period covering the 1 January 2006 to 31 October 2012 (Gov.co,

2012), it can be seen that medical personnel are risking their lives on numerous occasions. It is for

this reason that interest in the development of MedEvac UAVs is so high, the potential to remove

the risk to medical personnel while still being able to evacuate wounded soldiers and provide

treatment is one that the military is very interested in. Also with warfare having moved on from

large scale wars fought in the open to smaller battles fought in smaller areas such as towns and

cities it is important that the UAV is able to operate within these physically constrained

environments.

A successful design which meets these requirements will provide numerous benefits to both the

MOD and to the soldiers who risk their lives. It also has the potential to save more lives compared

to the current MedEvac fleet which would not be allowed to undertake any missions which are

deemed too dangerous for the personnel on board the aircraft. It also has the potential for use in

civilian applications in the instance of environmental disasters, extreme weather and other

hazardous environments.

This report details the design of a MedEvac UAV designed specifically for small constrained

spaces such as urban environments for the UK MOD. It covers the specific aircraft configuration,

the medical systems implemented, the electronic systems and operational procedures all of which

should be able to be monitored and controlled autonomously. The proposed solution is intended

for an entry in to service of 5 years, and should integrate with current operations as much as

possible.

Design of a MedEvac UAV for Operation in Physically Constrained Environments

Author: Michael Collison and Sarad Limbu Lawati 3-11

3 Aircraft Configuration

UAV systems have a wide range of applications (military or civil) due to their advanced

capabilities and some distinct advantages over manned aircraft. However, the design and

capabilities of the UAV system is specifically determined by its role.

Casualty rescue operations, particularly in hostile or difficult urban environment are the focal

design requirements for the MedEvac UAV design proposed by the UK mod. Taking the

operational constraints into consideration, the aspects that offered the optimal base concept for the

mission requirement were narrowed down to a UAV system providing good manoeuvrability,

stability, control and minimal footprint.

Prior to the selection of the VTOL ducted fan design for the MedEvac, an incomprehensive

analysis of a fixed-wing (HTOL) and tilt-rotor aircraft (hybrid) design were conducted to decide

on most suitable solution.

3.1 Single and Coaxial Rotor Configurations Rejection

Using the data for helicopters with a similar MTOW as the UAV presented in Table 28 it can be

seen that the average rotor diameter is 10.1m, and that the average disk loading is 252N/m2;

assuming that the consistency of these values across all the helicopters implies that the values are

near optimal, then both of these values present limits on the minimum footprint of the UAV due

to the size of the rotor disk diameter. Even if a coaxial rotor is used to provide the same amount of

lift then the diameter is typically only reduced by a factor of √ , in this case to 7.1m. However,

even this diameter restricts the UAV footprint to greater than the 3.7m required as stated in

specification point ‎46.3.‎1 and therefore in order to meet this requirement it is deemed that it is not

viable to use a single or coaxial rotor configuration for the UAV.

3.2 Fixed wing design rejection

Figure 1: MQ-1B Predator Fixed wing UAV(Keller, 2012)

Typical HTOL (Horizontal Take-off and Landing) aircrafts are of fixed wing configurations

which require a strip of runway for take-off and landing. The wings generate majority of the

aerodynamic lift that keeps the aircraft afloat as it moves forward through air powered by thrust

produced from its engines.



Fixed wing aircrafts are designed to have low aerodynamic drag in order to obtain long range and

mostly cruise at higher altitudes. Parasitic drag is less at higher altitudes because the air density is

low.‎ It‎ comprises‎ of‎ drag‎ that‎ originate‎ from‎ the‎ aircraft’s‎ skin‎ friction,‎ form,‎ momentum,‎

interference and cooling factors but can be minimised by innovative airframe design and limiting

the aircraft to fly at low speeds (minimum drag speed). However, induced drag is higher if the air

density is low unless wing span loading for the aircraft is low i.e. longer but optimal wing span is

required. Although fixed wing aircrafts have a high disposable load fraction acquired by taking

advantages of advanced materials and careful structural design, this disposable load needs to be

shared between the payload and fuel to be carried when designing for long range. Fixed wing

aircrafts usually have high response to atmospheric turbulence because of its large surface area to

mass ratio which is easily disturbed by air gusts far more than an aircraft with high mass to

surface area. Aircraft with high mass, therefore high inertia is less affected by the acceleration

resulting from an imposed force(Austin, 2010). Figure 87 in Appendix B shows Aircraft vertical

response to a vertical gust derived from simple calculations.

3.3 Tilt rotor design rejection

Figure 2: V22 Osprey tilt rotor design(Anon., 2005)

Helicopters fly at lower flight speeds and their rotors have large diameter blades with relatively

less twist that operate at lesser RPMs compared to propellers. They have better efficiency because

of low disk loading and drag created from rotors is minimised. Conversely, propellers need

operate at higher RPMs to generate sufficient thrust for airplanes to be able to fly at higher

speeds. So, they require much smaller diameter blades (high disk loading) with more twist to

maximise the mass flow rate of air to generate enough thrust. The propeller blades are also

designed to be swept to deal with conditions that arise with blade tips operating at supersonic

speeds.

Tilt rotors are a hybrid concept that combines both HTOL fixed wing capabilities of a propeller

airplane and the VTOL (Vertical Take-off and Landing) capabilities of helicopter. In vertical

flight the rotors are horizontal, but for cruise flight they tilt forward through 90 degrees to behave

as propellers. (Austin, 2010)However, the enhanced performances gained from a design

compromise‎ between‎ a‎ helicopter’s‎ rotor‎ and‎ an‎ airplane’s‎ propeller‎ has‎ a‎ downside‎ to‎ it.‎



Inclusive of all the design characteristics associated with fixed wing aircraft for HTOL

comparison, a tilt rotor airplane has much more drag because of its short span and high wing

thickness than for an airplane. Furthermore, the huge prop rotors create more drag and are less

efficient‎at‎higher‎speeds‎which‎affect‎the‎aircraft’s‎fuel‎efficiency‎and‎range.‎Therefore,‎not‎only‎

are tilt rotors less efficient but also have neither the payload ranges nor capacity of a similar sized

airplane or a helicopter.

The calculations that were carried out using basic aerodynamic formulae to analyse the suitability

of both fixed wing and tilt rotors are shown in Table 29 & Table 30. A symmetrical and cambered

aerofoil profile (Figure 88) was used to obtain the CL values for lift from the wing.

Including the aspects of both designs discussed above, the main reasons for the rejecting the two

concepts are:

Both designs require very large wingspans, tilt rotors even more because the prop rotor

radius is included.

Apart from the VTOL capability that tilt rotors provide, its other characteristics are

similar to fixed wings HTOL aircrafts. They are less manoeuvrable and have low control

response if the aircraft is designed to be light weight and stable. To increase the aircrafts

control and manoeuvrability the aircraft needs to be statically and dynamically less stable

and requires better structural integrity (i.e. added weight) to be able to bear the loads

during various manoeuvres.

A VTOL capability is more appropriate to fulfil our mission requirements (close-range

battlefield aircraft). Flying at low altitudes means flight is affected by air turbulence but

yet a stable platform is required to sense ground targets and maintain desired attitude for

the aircraft.(Austin, 2010)

Tilt rotors lack efficient transition between hover to forward flight mode and vice versa

whereas fixed wing aircrafts require runways for take-off and landings.

As a result, the ducted fan VTOL design, with thrust vectoring was selected for our MedEvac

UAV design because its performance characteristics offer the closest solution for the design

requirements, as explained in section ‎3.4.

3.4 Chosen Configuration

Due to the high footprint requirements of the fixed wing, tilt-rotor, single rotor and coaxial rotor

configurations, it was necessary for the design of this UAV to find an alternative solution to

provide the performance whilst keeping the footprint below the 3.7m width requirement.

Therefore ducted fans were considered due to their high disk loading, (thrust output per unit area),

which suits the UAV design criteria.

Therefore the configuration chosen to be used for the UAV was a ducted fan design whereby the

same fans are used for both lift and forward propulsion. This is achieved by not utilising a tilted



fan as some aircraft do, for example the Bell X-22, but by maintaining the fans in a horizontal

position relative to the flight path and then altering the flow direction by angling the stator flaps in

the fan exit flow so as to give a thrust vector with both lift and forward flight components.

The advantages of not tilting the fans are that the mechanical complexity associated with doing

this is negated especially with regards to maintaining the transmission connection, and also there

is a significant mass saving due to there being no need for a heavy tilting mechanism. However

there are still issues with the configuration, such as ensuring that the fan flow is deflected to the

correct level and that whilst in forward flight the flow entering the fan does not become separated,

these issues and there solutions are discussed in Sections ‎4 and ‎5. The main disadvantage of this

configuration is that there is a maximum to how much the flow can be deflected, around 40

degrees, and hence there is a maximum amount of thrust that can be produced in the forward

direction. This limits the maximum attainable speed which can be achieved by the UAV, and the

chosen configuration therefore has a lower cruise speed than a standard helicopter, however the

magnitude of difference is not large, the UAV top speed is approximately 200km/h compared to

other helicopters which are normally between 200-300km/h, see Table 28.

4 Duct design

The design for the ducted fan is comprised of combination of a few concepts that have been

successfully tested and some of which are already in use in real applications. Implementation of

these design concepts is to overcome the major problems associated with the performance of

standard ducted fans.

Most of the problems that arise are a result of the primary problem i.e. upstream inlet lip

separation in forward flight. In forward flight or crosswinds, the flow separates on the upstream

duct lip which distorts the inlet flow into the fan rotor (as shown in Figure 3 below). As a result of

this occurrence the thrust generation is reduced from the upstream side of the duct which gives

rise to asymmetric loading. The flow separation creates an imbalance in the fluid momentum

entering the duct at the leading and trailing edges which give rise to severe static pressure field

inside the duct leading edge and also the excess noise and vibrations from the fan rotor. The

power requirement and fuel consumption are also affected while trying to maintain the operational

requirements. All these factors make the standard ducted fan configuration very inefficient at

horizontal forward flight.(C. Camci, 2010)


Author: Sarad Limbu Lawati 4-15

Figure 3: Inlet flow separation (left) and

total pressure distribution (right)

4.1 Double Ducted Fan concept

The double duct concept simply comprises of a second annular duct surrounding the standard

duct. The second duct has a cambered airfoil shape lip (NACA8412) and a much shorter axial

chord length that the standard duct which forms a converging-diverging channel with the standard

duct. The dynamic pressure of the inlet flow into the converging diverging duct is self-adjusting

and‎ proportional‎ to‎ the‎ square‎ of‎ the‎ vehicle’s‎ forward‎ flight‎ velocity.‎With‎ the‎ selection‎ of‎ a‎

suitable value for the lip diameter (DL) for the standard duct the whole DDF geometry can be

constructed as shown in Figure 4.

The vertical distance between the second duct and the main duct is 0.33DL to achieve the

appropriate control of lip separation. In fact, all the orientations, positions and dimensions of the

elements for the DDF concept are extremely important for improving the flow near the leading

edge or upstream if the duct.(C. Camci, 2010)



Figure 4: a) Standard duct b) DDF geometry with recommended dimensions(C. Camci,

2010)

Figure 5: Reduction in flow distortion in the leading and trailing edge for the selected

(CASE B) design (C. Camci, 2010)

The DDF configuration (CASE B) in Figure 5 shows improvement in pressure deficit of the

standard duct caused by the inlet lip separation. It also improves the thrust performance and

reduces the amount of pitching moment generated by the imbalance in total pressure or thrust

between the leading and trailing edge of the rotor (shown Figure 8).



Figure 6: Comparison of inlet flow/velocity magnitude between standard and DDF concept

at 20m/s (C. Camci, 2010)

Similar, to the flow accelerating over the top surface of an airfoil, the flow at the leading edge of

the secondary duct is accelerated and directed into the duct. This is possible because of the

positioning of the second duct at a height slightly above the standard duct. The fluid that enters

through the converging-diverging duct remains attached to the surface of the standard duct (due to

the nature of the whole arrangement) and automatically adjusts the dynamic pressure and fluid

momentum thereby, reducing flow distortion.

The DDF geometry improves the performance of the standard ducted fan in forward flight

conditions by maintaining low loss of mass flow rate which otherwise would have dropped by

33%. The mass flow rate on the standard duct alone drops very rapidly with increase in forward

flight velocity and suffers a high level of inlet flow distortion, Figure 7.



Figure 7: Rotor disk MFR versus forward flight speed(C. Camci, 2010)

Figure 8: Total Pressure distribution through duct (bottom) and at rotor

exit plane (top) for the standard and DDF types(C. Camci, 2010)

Ducted fans generate a greater static thrust compared to isolated propellers. The shroud provides a

supplementary safety feature by enclosing the high RPM rotating fan and also an option for



including noise treatments inside the duct. The fan produces lift vertically by drawing the air into

the duct. Altering the axial chord length of the standard duct has no change in the lift generated.

The air flow divides at a stagnation point at the ducts leading edge and the duct cross-section

behaves similar to an airfoil. Therefore the resultant lift vectors of the duct are strongly canted

towards the centre while the vertical lift components provide additional lift. This allows for

effective‎thrust‎vectoring‎by‎using‎flaps‎at‎the‎duct’s‎exit‎to‎generate‎the‎desired‎control moments

to manoeuvre the aircraft(Anita I. Abrego, n.d.).

4.2 Stator Vanes & Flaps

The stators provide structural support to the duct and hub while also assisting to align the swirl

from the flow at the fan exit. The flaps are positioned at the end of the duct at a suitable distance

away from the centre of mass of the vehicle and help to generate the required control moments by

deflecting the flow at the exit by ± 40 degrees.

Figure 9: Stator Vanes and flaps

The stators have a specific design to achieve maximum noise reduction and are positioned within

2.5 -10‎cm‎from‎the‎fan‎to‎remove‎the‎existing‎swirl‎in‎the‎flow.‎“The‎stators‎are‎lean‎in‎a‎plane‎

of fan rotation and swept in a plane normal to fan rotation to create the optimum amount of noise

reduction in the ducted fan air-vehicle.” (Burdisso, 2010) Sweep is the axial displacement of

stator leading edge that varies span wise and lean is the circumferential displacement of the stator.

The angle of sweep on the stators should be between 0-20 degrees downward while a maximum

lean of 20 degrees in the direction of fan rotation (Figure 10 and Figure 11 respectively). These

orientations are important because opposite direction leads to increase in noise rather than its

reduction. The lean and sweep on the stator introduces a phase variation in the upwash velocity

which is responsible for the loud noise. The phase variation results in strong cancellation between

contributions to the noise field from different locations along the stator span.(Burdisso, 2010)



Figure 10: Span wise sweep on the stator vanes along its leading edge

Figure 11: Lean on stator vanes

5 Fan/Rotor design

The axial flow fan has 5 airfoil shaped blades (NACA 4412) and is 2 m in diameter with the hub

diameter of 0.6 m. The blade has a pitch of 30 degree at the hub and a gradual linear twist which

terminates at the blade tip at 15degrees. The fan blades generate lift similar to a wing generates

lift except the air flow over the blade root is lower compared to the blade tip because the

tangential velocity is greater at the blade tip than at its root. Therefore, the chord length and blade

pitch are gradually reduced towards the blade tip in order to remove variation in loads across the

blade’s‎span‎which‎could‎generate‎huge‎deflection‎on‎the‎blade‎tip‎and‎affect‎the‎performance‎of‎

the fan. (Shown in Figure 90)

Reducing fan noise and vibration were important consideration for the design even though the

thrust requirements could have been achieved by changing the fan diameter and RPM. But a fan

with small diameter would have to spin at higher RPMs to generate the equivalent thrust and

would also increase the power requirement and noise and vibration. Conversely, a larger diameter

fan can generate the same thrust spinning at lesser RPM and also minimizing the noise levels but

requires more torque than power. Fan operating at higher RPM also give rise to design

complications: the blade tip speed operating at supersonic Mach speeds requires the blade design



to have sweep and smaller chord length to cope with the operating conditions. The noise level is

proportional to the tip speed, for a given pressure while also roughly proportional to the pressure

developed regardless of the blade type. Three of the fan laws below describe the relation between

fan speed, pressure, power and therefore noise levels.

1. The capacity is directly proportional to the fan speed.

2. The pressure (static, total, or velocity) is proportional to the square of the fan speed.

3. The power required is proportional to the cube of the fan speed. (BASF Corporation, n.d.)

Therefore, the tip speed of the fan blades has been limited to Mach 0.8 however the airfoil profile

(NACA 4412) for the blade operates fine in transonic conditions.

Figure 12: Complete Double Ducted Fan assembly

If the fan blade stalls during flight, it can be corrected by increasing the rotor speed or by reducing

the flight altitude which helps to regain the airflow. The variable pitch blades option was

discarded because there is other simpler solution.



Hub diameter was set to 30% of the total fan diameter which is a typical value.

The number of blades was chosen to be 5 because it provides better airflow stress distribution

properties (Figure 92). However, more than 5 blades can provide better airflow and thrust but

with added torque and power requirements.

Chord thickness (0.3 m) was determined by Equation 1.

Equation 1

Where, c = chord length; Dh = hub diameter and Nb = number of blades

The‎Separation‎gap‎between‎the‎rotor‎blade‎tip‎and‎the‎duct‎was‎set‎to‎2%‎of‎the‎fan’s‎radius‎i.e.‎

0.02 m because it provides the best thrust coefficient value at the RPM the fan operates in, Figure

91.

5.1 Blade Element Theory (Leishman, 2006)

Figure 13: a) A strip of blade element b) Incident velocities and

aerodynamic environment at a typical blade element(Leishman, 2006)

The blade element theory was used to predict the thrust generated and power required for the fan.

The results show that the MedEvac UAV can hover at sea level with both the fans operating at

1800 RPM and is capable of cruising at 55 m/s at an altitude of 5000m at 2500 RPM.

The blade element theory predicts the performance of a propeller/fan by dividing the blade into a

number of independent sections along the length. Using a set of non-linear equations shown

below the values of thrust, torque and power can be calculated for each section and summed up to



get the whole value. The values obtained for these calculations are represented in Table 31: fan

Parameters to Table 35in the appendix.

In Figure 13 a) above R = blade radius; dy = blade element length

UR = radial velocity; UT = tangential velocity and U = resultant velocity

And in Figure 13 b) dL, dD and dM represent blade element lift, drag and moment respectively.

Θ‎=‎Blade‎pitch‎angle;‎α‎=‎angle‎of‎attack;‎φ=‎induced‎angle of attack

Equation 2 Resultant velocity, √

Equation 3 Where,

Local plane resultant velocity on any element

Equation 4

Equation 5

Equation 6 √

Where, T = half of total thrust required and A = rotor disc area.

Assumptions made:

Constant lift curve slope, ao = 6.2832 /rad based on NACA4412 CL curve

Linear blade angle distribution (linear twist)

Near hub region (r < 0.37) of the fan blade does not generate thrust

Step-by-Step Calculation for Table 7:

Step 1

For each blade element

Equation 7 Calculate induced angle of attack, (

)

Where UT and UP are obtained from Equation 3and Equation 4

Step 2

Equation 8 Solidity of blades is given by,

Step 3

Blade‎pitch‎angle,‎θ‎provided‎in‎Table 33 in radians.

Equation 9 Then, blade angle of attack,

Step 4

Equation 10 Coefficient of lift,

Step 5



Equation 11 Increment in Thrust,

Equation 12 Where element lift,

Equation 13

Where U is obtained from Equation 2 and c is the blade chord length

Step 6

Equation 14 Power increment,

Equation 15 Where,

And dL and dD are obtained from Equation 11and Equation 12

Step 7

Calculate‎element‎thrust‎(∑T)‎and‎element‎power‎(∑P)‎required‎using Trapezium Rule

Equation 16 ∫ ( )

( )

( ) ( )

Repeat Steps 1-7‎for‎the‎remaining‎sections‎of‎the‎blade‎and‎add‎together‎(∑T)‎for‎each‎section‎to‎

get‎the‎total‎thrust‎and‎(∑P)‎to‎get‎the‎total‎power‎for‎a‎single blade. Multiply these values by the

number if blades (Nb) to obtain the thrust and power for the fan. Finally, multiply by 2 (because

two ducted fans) to obtain the total thrust Generated and Power required for the MedEvac UAV.

All Equation are obtained from Blade element analysis (Leishman, 2006)

5.2 Materials and Stress analysis

All the components of the DDF will be constructed from carbon fibre composites. Carbon fibre

composites are an extremely durable material and have high strength-to-weight ratio and stiffness,

thereby a strong light weight solution. The ultimate tensile strength for carbon fibre range

between 4130MPa-63 GPa where the higher strength limits are for carbon nano-tubes. The

material is stronger in the direction of the fibre and can be manufactured in different

configurations to optimize the strength, rigidity and other material properties such as high

temperature and corrosion resistance.(F. Li, 2000)

Figure 14 and Figure 17 below show the deformation on the Fan blades and Stator vanes

respectively at maximum operation (2350 RPM). The maximum deformations are on the fan

blade tips and in the hub on the stator vanes. These deformations are minimal and should not

hugely affect the performance of the ducted fan.


Author: Maria Wood 6-25

Figure 14 Total deformation at maximum

operation

Figure 15 Stresses on fan ant 2350 RPM

Likewise, Figure 15 and Figure 16 represent the level of stresses on different areas of the fan and

the support stator vanes. The stresses are more concentrated towards the blade roots on the fan

whereas at the tip ends of the stator vanes which are attached to the duct. The Equivalent (Von-

Mises) Stress was used for analysing the structural integrity of the ducted fan components, which

calculates whether the combination of principal stresses in three dimensions (x, y, z on a single

element) at a given point will cause a failure.

Equation 17 ( ) ( ) ( )

Von-Mises Stress Formula, where S1, S2 and S3 are the three principal stresses and Se is the

equivalent/Von-Mises Stress.(efunda Inc., 2013)

Figure 16 Maximum Stresses on stator vanes

Figure 17 Stator Vane Deformation

6 Transmission

The purpose of the drive train in the UAV is to transmit power from the engines to the fans. The

drive train consists of all the components from the engine to the gear box to the rotor. General

requirements of the transmission system are its performance, reliability, maintainability and



survivability. Performance considers the weight of the system, its efficiency, the size of the

system and the noise level produced.

To design the drive train of the UAV, first the torque required was calculated using Equation 18.

Equation 18

⁄

The Turbomeca Tm333 has a shaft output speed of 628.3 rad/s and a continuous power of 736 kW

which produces a continuous torque of 1171 Nm (Safran Turbomeca, 2010). For hover, the

required fan speed is 1750 rpm with a torque of 2500 Nm. For safe decent with one engine

inoperable, the maximum torque available at 736 kW and fan speed of 1750 rpm is 4016 Nm,

which is sufficient to overcome the torque of the fans. For cruise at 5000 m, the fans require a

torque of 4500 Nm at 2350 rpm. The engines are able to provide a maximum continuous power

of 1472 Nm at 2350 rpm fan speed which produces a maximum continuous torque of 5982 Nm,

sufficient to overcome the torque of the fans.

To reduce weight, the driveshaft shall be made from a high strength material such as carbon fibre.

As explained in section ‎26.3, two engines are required for redundancy purposes, therefore the

transmission must include a method to connect the drive of the engines together, since both

engines will be operating at the same time else there would be a lag time between an engine

failing and the second engine starting up. The propulsion is given by two ducted fans, which

require individual speed control to overcome unbalances in the pitch angle; therefore the fans

cannot be directly connected to the engines. Also, one engine cannot drive one fan, since if one

engine fails, the UAV cannot fly with one fan in operation.

6.1 Transmission Concept 1

The initial concept was to use a planetary gear box contained within the hub of each fan, as used

in the Chinook depicted in Figure 19. Planetary gears are often used in aircrafts due to their

compact structure and high torque to weight ratio (Dudley, 1984). Simple planetary gears consist

of a sun gear, planetary gears on a carrier and the ring gear as displayed in Figure 18. By

changing which gear is the input, the output or held stationary the output shaft speed can be

varied; this gives two forward gear ratios and one reverse gear ratio. Compound planetary gears,

as used in automatic vehicle transmissions, consist of two sun gears, two sets of planetary gears

and one ring gear; this gives four forward gear ratios and one reverse (Nice, n.d.). The advantage

of this gearbox is they offer a much larger gear reduction ratio; can transmit a higher torque and

can achieve more configurations (Guo, 2011). A reverse gear would not be necessary in this

application. Also, the fans only need to operate within a narrow speed range, between 1500 rpm

and 2500 rpm, therefore several gear ratios would not be required. Transition between gears

would not be smooth and it requires varying the speed of the engines. A progression from using

an epicyclic gear box is to include a split torque system to distribute the torque to allow for

smaller, lighter gears to be used, as in the Mi-26 Helicopter (Hameer, 2009). Epicyclic gear trains



are also known for high vibration levels (Guo, 2011) which can mean a short life time for the

gears and discomfort to the casualty within the UAV.

Figure 18: A schematic of a Planetary Gear set (Oriental Motor USA Corp., 2006)

Figure 19: The Chinook CH-47D Drive Train utilising planetary gearboxes for each rotor

(Company H, 4th Battalion, 7th Aviation Regiment, 2012)


The second concept looked into the use of continuous variable transmission (CVT). This would

allow a constant, smooth transition of the output speed of the fans, whilst allowing the engine to

operate at its most efficient condition. Some types of CVT also offer an infinitesimal range of

gear ratios which would allow both fans to operate at the required speed. There are several types

of CVT systems available; frictional types such as the variable diameter pulley CVT whereby the

drive pulley is made from two cones at a 20o pitch angle attached via a belt to the driven pulley

(Harris, n.d.). There is an inverse relationship between the diameter, D, of the pulleys and the

output speed, as expressed in Equation 19. Problems with frictional CVTs are their low

efficiency, low reliability, high weight, high vibration levels and lower power capacity, therefore

is unsuitable for this application.



Equation 19 (Hameer, 2009)

Another‎type‎is‎the‎hydrostatic‎CVT‎which‎“transmits‎power‎through‎the‎use‎of‎high‎pressure‎oil”‎

(Beachley & Frank, 1979). It utilises a hydrostatic pump to produce hydraulic power by

transferring the rotational motion of the engine to move fluid around a circuit to a hydraulic

motor, which transfers the pressure from the fluid into a rotational output. Output speed is varied

by altering the displacement of the fluid by changing the angle of the vanes within the pump

and/or motor. It can produce an infinite range of gear ratios (Beachley & Frank, 1979). Electric

systems are analogous to hydrostatic systems, except use an electric alternator and an electric

motor to vary the output speed by altering the either the frequency of current or the electric flux

(Renius, 2005). However they need complex controllers(Beachley & Frank, 1979) and are better

suited to hybrid or electric vehicles. Both these systems are used in heavy machinery, such as

tractors (Renius, 2005).

After analysing the common types of CVT, the hydrostatic system seemed the most appropriate

for integration into the UAV. A preliminary design can be viewed in Figure 20. A hydraulic

pump was connected to each engine which pumped the fluid around to a control point where the

fluid was then distributed between two hydraulic motors, each connected to a propulsion rotor.

The pumps were positive displacement pumps, to allow the engine to operate at its most efficient

condition. The motors were variable vane displacement, allowing the speed of the fans to vary.

The control point would also control the amount of fluid distributed to each motor, allowing the

fans to vary independently of each other. The configuration of the hydrostatic CVT allows for

one engine inoperable, and also for a fault in one of the hydraulic lines. It also eliminates the

need for drive shafts and gears. The disadvantages of this system are the size and weight of the

pumps and motors that would be required to transmit the torque required. This would also lead to

the necessity of a cooling system for the hydraulic fluid. Also, it is only a moderately efficient

system. However if further study was made into the hydraulic system so smaller pumps and

motors could transmit a higher power, there is the possibility for this to be an effective

transmission. It may also be more beneficial for a single rotor aircraft, since there would only be

a need for one pump and one motor.



Figure 20: The Preliminary Design of the Hydraulic CVT System


After establishing that the hydrostatic CVT drive train was not suitable for this application, the

necessity of having the ability to vary the speed of the fans independently was questioned. Since

this is only required to overcome the change in angle of the UAV, the difference in speed between

the fans does not have to be great. Therefore the possibility of controlling this through a

differential type gearbox system seemed possible. The benefit between this gearing system and

using a gear box is that only one set of gears is required. Also, there will be no jerk from a gear

change and continuous variation of engine speed through acceleration or deceleration.

Differential systems are widely used on vehicles to allow the rear wheels to rotate at differing

speeds whilst travelling around a corner. Open differentials consist of a gear driven from the

power source; pinion gears and side gears, as shown in Figure 21. When the fans on the UAV

need to operate at the same speed, the pinion gears do not rotate, Figure 21 a). However, when

there needs to be a difference in the speed of the fans, the pinion gear rotates, transferring more

power to one shaft than the other, but at the same torque so the speed of that fan increases, Figure

21 b). One issue with open differentials is they distribute the torque equally between the drive

axles, which, on poor terrain, can mean the vehicles wheel slips (Nice, n.d.); however this should

not be an issue for the UAV. Being a simple system, it allows for low maintenance and low

manufacturing costs. The differential will be controlled mechanically by a gyroscope that was

already selected for the UAV.



a) b)

Figure 21: Arrangement of a Differential Gear Box, a) the half shafts are rotating at the

same speed, b) the half shafts are rotating at different speeds (Wikipedia, n.d.)

6.4 Transmission Design

First, the maximum torque from the engines was calculated. The Turbomeca Tm333 has a

maximum power (One Engine Inoperable, OEI) of 910 kW (Safram Turbomeca, 2010) and the

minimum shaft speed the engine will operate at is 3600 rpm or 377 rad/s. Therefore the

maximum torque from the engines is 2414 Nm, calculated from Equation 18. There is a reduction

in speed between the engines and fans of ratio 2.4:1. Therefore the maximum torque output from

the gearbox at 910 kW and 157 rad/s is 5796 Nm. The reduction ratio of 2.4 was calculated from

a nominal engine rotation speed of 6000 rpm and maximum fan speed of 2500 rpm, which is a

reduction of 2.4.

The engines will connect to the main drive shaft via a spur gear drive train, which encompasses

the reduction gear. Since two engines are required, this seemed the most simple and efficient

method to connect both engines to the drive shaft. There will be an override clutch between each

engine and the spur gear should an engine fail, therefore power would not be wasted turning an

inoperable engine (Dreier, 2001). This configuration is typical for two engine helicopters as

depicted in Figure 22. The differential and drive to the fans will be a bevel gear train.

Figure 22: Typical Drive Train Arrangement for a Single Main Rotor Helicopter with Two

Engines (Dreier, 2001)

An initial design to the size of the gear required can be calculated by approxmating the teeth as

cantilever beams and determing the safe working stress, as used in the Lewis Stress Formula. The

http://en.wikipedia.org/wiki/File:Differential_free.png

http://en.wikipedia.org/wiki/File:Differential_locked-2.png



Lewis Stress Formula for spur gears is given in Equation 20. The terminology of the spur gear

can be seen in Figure 93.

Equation 20 (Stokes, 1970)

The impact from the gears rotating can be included into this equation using the Barth Equation for

milled, hellical gears.

Equation 21 (RoyMech, 2011)

Where V is the Pitch Line Velocity and can be calculated from Equation 22.


This transforms the Lewis Equation to Equation 23.


The Lewis form factor for 20o pressure angle, full depth teeth is found from Equation 24.


Tangential load on teeth is calcualted from Equation 25


The module is defined as the ratio between the pitch diameter of the gear and the number of teeth

(RoyMech, 2011).

The differential and drive between the main drive shaft and fans will be transmitted via spiral

bevel gears. The terminology of the bevel gear is given in Figure 94. The Lewis Formula has

been modified to apply to bevel gears, Equation 26 .


The lewis form factor is the same as Equation 24 , however the number of teeth used is

determined by finding the equivalent number of teeth on a spur wheel, Equation 27 .


The main drive shaft has been calculated to minimise twist, Equation 28, and shear stress,

Equation 29.



Equation 28 (The Engineering Toolboox, n.d.)

(

) (

)

Equation 29 (The Engineering Toolboox, n.d.)

(

)

A schematic of the differential transmission arrangement is found in Figure 23. It was found that

the shafts from the bevel gear to the fan would not be required since the fan is at the correct height

to connect directly to the gear.

Figure 23: Differential Transmission Schematic for the MedEvac UAV

The gears will be manufactured from titanium alloy (Ti-8-1-1) since this has a high tensile stress

(1070 MPa) but lower density (4370 Kg/m3) than steel alloys commonly used, which is required

to keep the mass of the UAV as low as possible (Aerospace Specification Metals Inc., n.d.). This

material allows a minimum safety factor of 35% though the design of the gears, however it would

be preferable for this value to be higher. Due to the application of the UAV, noise and vibration

will have to be kept a minimum, therefore double helical gears will be used instead of spur gears

and spiral bevel gears replacing straight bevel gears, Figure 24. These gears are around 98%-99%

efficient.

Figure 24: Double-Helical Gear and Spiral Bevel Gear (Coord 3 Metrology, 2012)

The drive shaft shall be made from carbon fibre tube at fibre directions of (+/-450). The modulus

of rigidity for this material is 330 GPa, shear strength of 260 MPa and density 1600 kg/m3

(Performance Composites Ltd., n.d.). The angular shaft defelction has to be below that permitted



by support bearings. For bearings that would be suitable in this application, a maximum angular

defelection of 2o is permitted (RoyMech, 2011).

Table 1 displays the determined values for the gear train and drive shaft based on the equations

above. The pinion spur gear is attached to the shaft from the engine and the wheel spur gear is

attached to the main drive shaft. An iterative procedure was used to obtain the best design, the

cells highlighted portray the variables.

Table 1: The Design of the Gears used in the Transmission of the UAV

Pinion Spur Gear

Torque Transmitted [Nm] 2414

Angular Speed [rad/s] 377

Pitch line Velocity [m/s] 37.7

Pitch Circle Diameter [m] 0.2

Module [mm] 20

Number of Gear Teeth 10

Diametrical Pitch 50

Circular Pitch 0.06

Width of Teeth [mm] 200

Tangential Load on Teeth [N] 24140

Lewis Form Factor 0.063

Velocity Factor 7.18

Lewis Formula [MPa] 690.0

Volume [m3] 0.0027

Density [kg/m3] 4370

Mass [kg] 12.01

Wheel Spur Gear


Angular Speed [rad/s] 157

Pitch line Velocity [m/s] 37.7

Pitch Circle Diameter [m] 0.48

Module [mm] 20

Number of Gear Teeth 24


Circular Pitch 0.06

Width of Teeth [mm] 200

Tangential Load on Teeth [N] 39046


Velocity Factor 7.18

Lewis Formula [MPa] 604.2

Volume [m3] 0.0327


Mass [kg] 142.71

Bevel Gear


Pitch Circle Radius [m] 0.18

Tangential Load [N] 26033

Outside Pitch Radius [m] 0.18

Inside Pitch Radius [m] 0.08

Mean Pitch Radius [m] 0.13


Tooth Width [m] 0.1


Circular Pitch 0.06

Number of Bevel Gear Teeth 18

Pitch Cone Angle [rad] 1.57

Number of Teeth Equiv Spur 11.46

Safe Working Stress [MPa] 593.0

Volume [m3] 0.0149


Mass [kg] 65.31

Drive Shaft

Torque [Nm] 9371

Length [m] 2.5

Outer Radius [m] 0.075

Inner Radius [m] 0.06

Modulus of Rigidity [Pa] 3.30E+10

Twist [rad] 0.024

Twist [deg] 1.39

Shear Stress [MPa] 23.95

Volume [m3] 0.016


Mass [kg] 25.45


Author: Michael Collison 8-34

The total mass of the system is 675 kg, which is much higher than anticipated, even with the use

of high strength to weight materials. This mass of the gear system was not used in the propulsion

calculations, therefore will require consideration in the future design of the MedEvac UAV. This

transmisison design also requires consideration of the lubrication system, gear housing and

bearing design.

7 UAV dimensions

The exterior dimensions of the UAV were determined mainly from the size of the casualty

stretcher, (2.29 m x 0.58 m) and the duct diameter from fan diameter, section ‎5, to give sufficient

thrust. Therefore the width of the cabin cross section was determined as 2.5m to match the duct

size, and the height of the cabin cross section was chosen as 1.5m to give sufficient head room for

the casualty and to also allow room for the engines and other equipment. The length of the cabin

section was chosen to be 2.5m to allow the casualty stretcher to be placed longitudinally, therefore

the UAV length totals approximately 7.5m.

8 Structures

The structural elements of the UAV are chosen to have a similar layout to that of a semi-

monocoque aircraft fuselage which uses the combination of the skin, frames and stringers to resist

the forces from pressurisation and bending moments and maintain the fuselage shape. In the

following sections the structural analysis is undertaken for an UAV mass of 1500kg which was an

initial estimate, the structural mass will then be iterated using mass fractions to obtain the final

UAV mass.

8.1 Main Spar

In the case of this UAV, there are strong longitudinal bending moments produced by the fans on

the cabin, somewhat like a wing on a standard aircraft; two I-beam main spars will run the length

of the cabin section between the two fans in order to handle these loads, and the spars will meet as

they follow the circumference of the ducts at either end to add further structural rigidity. The free

body diagram of the level flight condition is shown in Figure 25 from which the maximum shear

force and bending moments were found to be 16.6kN and 3.72x107Nmm respectively using a load

factor of 2.25 from 1.5 for maximum thrust and 1.5 for g number, as well as 4500mm for L which

is the distance between centres of both fans.



Figure 25: Free Body Diagram and Maximum Bending Moment and Shear Force

A particular I-beam section is then chosen to handle these loads with a second moment of area of

1.13x107mm

4 and a cross sectional area of 1390mm

2. The maximum shear stress, Equation 30,

and compressive/tensile stress, Equation 31, can then be found using beam bending theory.

Equation 30

Equation 31

The spars are to be made from aluminium alloy 7075-T6 because of its high strength and

toughness properties; this material has a yield strength and shear strength of 503N/mm2 and

331N/mm2 respectively, with a density of 2810kg/m

3. Therefore comparing the maximum stresses

in the spar with the material strengths there is a safety factor of 2.4 in yield and 27.9 in shear

which are satisfactory. The length of I-beam required is twice the straight length plus the fan

circumference, giving a length of 16.1m, which combined with the beam cross sectional area and

material density, gives a mass for the I-beam spar of 62.9kg.

8.2 Skin and Bulkheads

Due to the requirement that the cabin needs to be pressurised for the casualty and equipment, from

a structural point of view the elliptical cross section can be treated as a pressure vessel. Typically

a cabin needs to be pressurised to an altitude of 2440m (8000ft) at which the ambient pressure is

0.0753N/mm2, whereas at the UAV ceiling of 5000m the ambient pressure is 0.0540N/mm2;

However due to the medical requirements of the patient it is more beneficial to pressurise the

cabin to sea level (0.101N/mm2) which gives a pressure differential of 0.0473N/mm

2 which will

produce longitudinal and hoop stresses which for the elliptical section are calculated from

Equation 32and Equation 33 using standard pressure vessel relationships, noting that the highest

hoop stress will occur at the sides of the cross section due to the higher radius of curvature in that

region.

Equation 32

Equation 33

L T=W/2

W

T=W/2



The skin thickness was chosen as 1mm mostly due to it being the minimum gauge to resist

indentations, because the pressurisation stresses were not significant with a minimum safety

factor of 4.8 on the yield stress of 345N/mm2 for the aluminium alloy 2024-T3, which was

chosen for the skin as it is generally used on pressure critical skins. The same skin will be used for

the ducts and bulkheads (which are at each end of the cabin) as well as the cabin, and therefore

using an estimate of the total surface area and the 2024-T3 density of 2780kg/m3 the skin mass is

estimated to be 128kg and the bulkhead mass to be 20kg. These skin and bulkhead estimations

also include a 10mm layer of insulating foam material with a density of 100kg/m3 around the

casualty cabin section to shield the casualty from external noise and temperatures. Because the

main spar is deemed to carry all the bending moments produced by the fan an analysis of these

moments on the skin is not carried out here.

8.3 Frames and Stringers

In order to help hold the shape of the cabin and ducts, as well as to prevent catastrophic failure of

the skin in the event of a local skin failure, a series of cross sectional frames and longitudinal

stringers are used to stiffen the structure. These frames and stringers are made from 2024-T3

aluminium‎alloy‎with‎ a‎ ‘C-section’,‎ side‎ length‎ of‎ 10mm‎and‎ a‎wall‎ thickness‎ of‎ 1mm.‎ In‎ the‎

cabin section the frame spacing is 250mm and the stringer spacing is approximately every 400mm

around the circumference so that the pillowing of the skin between each set of frames and

stringers is kept to a minimum. This effective sectioning of the skin also means that if a puncture

to the skin occurs, for example from a bullet, then the skin will only tear and fail in that section,

meaning that the structural integrity is retained, though the cabin will depressurise. In the

unpressurised duct regions, there are much less forces on the skin and therefore the spacing of the

frames is increased to 500mm and there is only a stringer on the top and bottom extremes.

Therefore the total length of frames and stringers can be estimated, from which using the C-

section cross sectional area of 28mm2 and the density of the material, the mass of the frames and

stringers can be estimated as 11.6kg.

Furthermore, any cut-outs in the skin for reasons such as landing gear hatches, engine intakes and

doors reduce the strength of the skin. Therefore strengthening frame follows the edges of these

cut-outs which diverts the skin stresses along the frames so that the skin can continue to function

against the loads. The cut-out frames have the same properties as the normal frames, but with

double wall thickness of the C-section, and therefore their mass is estimated as 1.0kg which

covers the landing gear, door, engine intakes and engine exhaust cut-outs.

8.4 Floor and Ceiling

Using the initial mass estimates, it was determined that the floor and ceiling would have to carry

masses of 319kg and 762kg respectively. For the purposes of this analysis these loads were

deemed to be evenly distributed over the rectangular surface areas, therefore a constrained edge,

uniformly loaded, rectangular plate stress analysis can be undertaken as described below.



Figure 26: Constrained and Uniformly Loaded Rectangular Flat Plate Stress Analysis

(Beardmore, 2011)

In order to effectively handle these loads a sandwich panel is used with CFRP skins and the same

insulating material as discussed in ‎8.2 as the core. For the purposes of this analysis only the

thickness of the CFRP is considered due to the core having negligible strength; the CFRP has a

Young’s‎Modulus‎of‎400GPa and a density of 1800kg/m3. Therefore the thickness of the skins is

determined by specifying a maximum centre deflection of 5mm, and then the maximum stress can

be calculated from this thickness, a summary of the results is shown in Table 2.

Table 2: Properties of the Floor and Ceiling

p (N/m2) a (mm) b (mm) t (mm) σm (N/mm

2) ym (mm)

Floor 0.92x10-3

2500 1360 3.5 69 5

Ceiling 1.55x10-3

2500 1930 6 67 5

The mass of the floor and ceiling can then be calculated from the CFRP and core thicknesses and

densities, (note the core thickness is again 10mm), giving the floor mass as 24.8kg, and the ceiling

mass as 56.9kg.

8.5 Landing Gear

The first component of the landing gear is the vertical strut, which is required to be 400mm in

length to give sufficient clearance for the UAV and tyres. To determine the required diameter of

the strut it is necessary to consider the buckling and yielding failure modes when it is assumed the

whole UAV mass is transferred through one strut with a load factor of 2, for example in a rough

landing, which equates to a load of 29.4kN. Therefore using a 28mm diameter, 1mm thin wall

tube, the critical buckling load can be calculated from Equation 34.

Equation 34

With the strut made out of high strength steel, which has a yield strength of 2000N/mm2 and

Young’s‎Modulus‎of‎210GPa,‎the‎yield‎stress‎can‎also‎be‎calculated‎from Equation 35.

Equation 35

This means the safety factors in buckling and yield are 4.3 and 5.7 respectively. Using the

maximum mass on each tyre of 3000kg (6600lb), suitable tyres can be selected that can withstand



this mass; using (Goodyear, 2002) the 504T41-2 type tyre was chosen which has a diameter of

337mm, a width of 128mm, and a mass of 2.9kg each. Therefore assuming that the landing strut

length is doubled for a supporting strut, the landing gear strut mass is 2.7kg, with the four tyres

being 11.6kg.

8.6 Miscellaneous

The remaining structural weight such as the fan hubs and stators are not calculated in this report,

but are estimated at 35kg for the purposes of mass iteration.

8.7 Cabin Door

The cabin door is deemed to not require any extra structure, however due to its large area it will

require‎ a‎ solid‎ securing‎ system‎ so‎ that‎ it‎ doesn’t‎ weaken‎ the‎ pressure‎ vessel,‎ a‎ securing‎

mechanism similar to aircraft doors is suggested here which has multiple automatically securing

latches. To allow good access for loading/unloading the casualty, the cabin door will be the length

of the cabin section and its height will be between the floor and ceiling; when opened it can rotate

down to rest on the floor as shown in Figure 27.

Figure 27: Cabin Door Open

8.8 Structural CAD Representation

Figure 28 below shows the layout of the cabin structural elements, without the skin shown so that

the other elements can be seen.



Figure 28: CAD Representation of the UAV Structure (note – skin excluded)

9 Flight modes

The UAV is able to achieve the same flight modes as a standard helicopter, namely hover

including translation in all directions, forward flight, descent and climb. However the transition

between the various flight modes is achieved by a mixture of change in front and rear fan speeds,

as well as stator flap deflections; a summary of how the UAV achieves specific movements is

shown in Table 3 for both hover and forward flight.



Table 3: Methods of Flight Movement

Hover Forward Flight

Translation Longitudinal and spanwise

stator flaps deflection to

translate whilst in hover.

N/A

Roll Duct side wall deflection to maintain level flight and to correct

any undesirable roll moments, such as from cross winds.

Pitch Use of main shaft differential combined with engine speed

adjustments as necessary to achieve front and rear fan rpm

difference to maintain level flight and to correct any undesirable

pitch moments, such as from wind gusts or duct drag.

Yaw Opposite deflection of front and rear fan longitudinal stator flaps

to correct any undesirable yaw moments. Also allows

directional control in hover and forward flight.

Acceleration/Deceleration N/A Deflection of both front and

rear spanwise stator flaps

backwards (acceleration) or

forwards (deceleration).

Climb/Descent Change in both front and rear fan speeds by increasing (climb),

or decreasing (descent) engine rpm output. Can be used for axial

climb/descent and also in combination with forward flight.

Note that all flight movements described in Table 3, involving stator flap deflections require an

increase in both fan speeds (see climb/descent), in proportion to the level of deflection required,

as the thrust vector is altered from vertical and thus the increase is needed so as to maintain the

same magnitude of lift force.

Potentially the most troublesome flight mode of the UAV is the transition to forward flight from

hover. This transition would be achieved by gradual simultaneous increase in both stator flap

deflection and fan speeds to provide a component of the thrust vector in the forward flight

direction, and to maintain the vertical component at a constant level respectively. Any undesirable

effects of the manoeuvre, such as roll, pitch or yaw moments will be corrected as described in

Table 3.

10 Drag Estimation

Due to the clean shape of the UAV, it was modelled as fuselage body for drag estimation

purposes, with the length of the body estimated as the distance between the midpoint of the two



fans, due to the presence of the fans removing surfaces from the body that would otherwise be

prone to drag. Based on this characteristic length and the kinematic viscosity at 5000m ISA of

2.21x10-5

the Reynolds number of the aircraft at its design cruise speed of 200km/h (55m/s) was

calculated as 1.12x107. From this Reynolds number the friction coefficient can be estimated using

(Roskam, 1971, p. 3.9) as 0.0028, this value of friction coefficient is solely based on the Reynolds

number which is defined from the worst case scenario – notably the maximum cruise altitude,

however the Reynolds number, and hence skin coefficient values are largely unaffected by the

range of altitudes; therefore the value of 0.0028 and the corresponding CD value are used

throughout the drag analysis at all altitudes and flight speeds.

The drag of the aircraft is deemed to be solely due to the fuselage body, due to the fans not

directly seeing the oncoming flow, therefore the drag coefficient is equal solely to the parasitic

drag, as the fuselage body produces no induced drag, CD=CD0. The parasitic drag coefficient of a

fuselage body can be estimated following the process defined in (Raymer, 1992, p. 283) to

include both the skin friction and form drag, by means of a form factor, FF, which is calculated

from Equation 36 and Equation 37. In order to calculate the form factor and drag coefficient it is

also necessary to calculate the wetted area and frontal area of the UAV. The frontal area was

simply taken as the maximum cross sectional area that the flow sees, equivalent to the fuselage

elliptical cross section as 2.95m2. The total wetted area was taken as the external surfaces of the

fuselage, and was determined from the CAD model as 22.9m2. The fineness ratio is also required

to calculate the form factor, and is equal to the length divided by the cross section diameter.

Equation 36

Equation 37

This form factor is then used with the friction coefficient, wetted area and frontal area to calculate

the parasitic drag coefficient, Equation 38.

Equation 38 (

)

11 Power requirements

The power requirements of the UAV have three components, induced power to provide the thrust,

the power required to maintain forward flight, and the blade profile power to overcome the drag

of the fan blades; any excess power can be used for climb.

11.1 Induced Power

The power required to maintain forward flight is modelled as an increase in induced power by

requiring an increased amount of thrust, due to there being no vertical air flow speed because of

the aircraft flying level even in forward flight. At each flight speed, the equivalent thrust is

calculated from the horizontal force required to overcome the drag at that constant flight speed



(TH=D) and the vertical force to overcome the UAV weight (TV=W). The equivalent thrust

required and the stator flap deflection required to achieve that thrust can then be calculated using

Pythagoras’‎theorem,‎as‎shown‎below:

Figure 29: Diagram of Fan Thrust Components

Equation 39 √

Equation 40 (

)

This configuration means that there is a maximum amount of horizontal thrust that can be

produced‎dependent‎on‎the‎stator‎flap‎angle,‎θ,‎and‎the‎vertical‎thrust‎required‎which‎is‎equal‎to‎

the weight of the UAV in level flight. Therefore the maximum horizontal thrust available in level

flight is defined with the maximum take-off weight of 1350kg and the maximum stator flap

deflection angle of 40°, Equation 41.

Equation 41

The effects of this maximum horizontal thrust on the maximum attainable flight speeds are

discussed in Section ‎11.4.

To calculate the induced power requirement based on the required thrust, a helicopter approach is

used as described in (Leishman, 2006, p. 83), with the adjustment that a ducted fan consumes a

factor of √ less power than an open rotor (Leishman, 2006, p. 323). The induced power

required is then related to the induced velocity, vi, including an efficiency factor, k, to account for

non-ideal losses, Equation 42and Equation 43.

Equation 42 √

Equation 43

⁄

√

√

Where the area used in the above equation is determined from the fan diameter, scaled by a tip

loss factor, B, minus the hub area which for ducted fans have a diameter of 0.3 times the fan

diameter section ‎4; therefore using a tip loss factor 0.98 for the ducted fan due to the presence of

the duct reducing the effect of the tip loss vortices the equivalent disk area is given by Equation

44.

Tequiv TV

TH

θ



Equation 44

For the 2m diameter fan chosen for the UAV, this gives a disk area of 2.73m. It should be noted

that the induced power requirement increases with respect to both altitude, due to decreased air

density, and forward flight speed, due to increased equivalent thrust requirement. Furthermore the

result of this simplification is very close to the actual result using blade element theory.

11.2 Blade Profile Power

The power required to overcome the fan blades drag is calculated using aerofoil theory, where for

the purposes of this analysis the fan blade is treated as having constant properties throughout its

length. Therefore assuming the blade is rectangular in platform, and the drag coefficient of the

blade aerofoil is constant, then the blade profile power for each fan can be calculated as in

(Leishman, 2006, p. 69), where Nb is the number of blades, c is the blade chord, and R is the blade

radius.

Equation 45

The angular velocity for the purposes of this analysis was determined from the maximum rpm

required of 2350, and the other values are fixed as described in section ‎5.

11.3 Total, and Available Power Analysis

The total power required was then calculated by summing the induced power and blade profile

power at a range of altitudes and flight speeds. Using the fixed parameters and the estimated

maximum take-off weight, the most demanding power requirement is found at the cruise speed at

5000m altitude. In order to choose the turboshaft engines with the correct power rating, it was

determined that it was necessary for one of the two engines to be able to continue this mode of

flight for a short amount of time. This is known as One Engine Inoperative (OEI), and the

selected Turbomeca TM333 engines have various OEI ratings each referring to a different time

period for which the single engine can safely be used at this power rating without the need for

maintenance action; a summary of the power ratings of the Turbomeca TM333 is shown in Table

4.

Table 4: Turbomeca TM333 Power Output Data (Turbomeca, n.d.)

All engines operative, maximum continuous power 736kW

One engine inoperative – power for 30 minutes 807kW

One engine inoperative – power for 2 minutes 841kW

One engine inoperative – power for 30 seconds 910kW

These engine powers are then calculated at a range of altitudes by using the ISA pressure and

temperature ratios at each altitude using the relationship as described in Equation 46 (Leishman,



2006, p. 232) where PMSL is the power available at sea level and Palt is the equivalent power at

altitude.

Equation 46 (

) (

⁄

⁄)

11.4 Flight Envelope

Combining the available power curves at each altitude with the required power curves at each

altitude to maintain hover and for cruise (55m/s) gives the results as shown in Figure 30.

Figure 30: Available and Required Power against Altitude

It can be seen from Figure 30 that in the event of an engine failure, even the most demanding

flight regime of 55m/s flight at 5000m can be maintained for 30 seconds, and therefore this

altitude‎is‎taken‎as‎the‎UAV’s‎ceiling, despite it being able to achieve a ceiling of 8400m when

both engines are operating normally. However it can also be seen that the engine cannot provide

the amount of power required to maintain this flight mode for a prolonged period of time, and

therefore to maintain the flight speed the UAV must descend to 4500m within 30 seconds of the

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000200

400

600

800

1000

1200

1400

1600

altitude (m)

pow

er

(kW

)

Cruise (55m/s) Power Req

Hover (0m/s) Power Req

OEI 30sec Power Available

OEI 2min Power Available

OEI 30min Power Available

AEO max. cont. Power Available



engine failure and to 4000m within 2 minutes so as to not damage the engines and maintain a safe

flight. Even taking these precautions in to account, it is advisable to land the UAV within 30

minutes, as the risk mitigations are reduced.

By using the OEI power availability case to determine the flight envelope, as described above for

the ceiling classification, the rest of the flight envelope in terms of maximum speeds at each

altitude can be determined. The maximum speed at each altitude is either restricted by the power

available, or by the maximum thrust available to counter drag. The maximum speed due to drag

restrictions can be calculated using the drag equation and the value of the drag coefficient

presented in Section ‎10, but instead using the maximum available horizontal thrust as the value

for drag, and then solving for forward flight speed, Umax, as shown in Equation 47.

Equation 47 √

The results of this analysis are summarised in Figure 31 which shows that the flight envelope to

allow safe transition to OEI operation gives a maximum attainable forward flight speed of

approximately 71m/s (256km/h) at 4500m. At this altitude of 4500m, the UAV is therefore able to

achieve higher flight speeds, more equivalent to those delivered by helicopters. Therefore it is

desirable to fly at higher altitudes in terms of achieving a faster forward flight speed, however in

terms of operational risks this may not be advisable as it will be easier for the enemy to identify

and attack the UAV. It can also be seen that at SL the maximum speed is 57m/s (205km/h), with

the maximum speeds being restricted by drag up to 4500m, after which the maximum attainable

speed falls rapidly to zero due to OEI available power restrictions.



Figure 31: UAV Flight Envelope of Maximum Flight Speed against Altitude

12 MTOW mass iteration using fuel and structural mass

If it is assumed that the structural mass fraction of the UAV will stay constant, i.e. it will vary as

UAV MTOW varies, however due to the power requirements not varying much over the range of

MTOWs expected the total fuel mass is deemed constant here. Therefore using the non-variable

masses such as equipment, including fuel totalling 1031kg, the MTOW can be iterated using the

structural mass fraction gained from Section ‎8 as shown in Table 5. This mass fraction is

calculated from summing the structural mass components, which total 354.5kg, and dividing it by

the MTOW of 1500kg which these structural masses were calculated for, giving a structural mass

fraction of 0.236.

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

20

40

60

80

100

120

altitude (m)

flig

ht

speed (

m/s

)

Drag restricted

Power restricted



Table 5: MTOW and Structural Mass Iteration

MTOW Non-Variable

Structural = 0.236 x

MTOW

1500 1031 354

1385 1031 327

1358 1031 320

1351 1031 319

1350 1031 319

1350 1031 319

Therefore from Table 5 it can be seen that the iteration converges to giving an MTOW of 1350kg,

and structural mass of 319kg. This MTOW will be used for further analysis.

13 Operational Flight Profile

13.1 Acceleration

The acceleration of the UAV is important for two reasons, the first being that it is desirable to get

to the maximum flight speed as quickly as possible to get out of the danger area rapidly, and the

second being that if the acceleration is too high, then the g forces imparted on the casualty may

inhibit their recovery and any medical procedures that are being undertaken. Therefore a

maximum limit of 1.25g was imposed on the flight profile, which means that the acceleration to

maximum flight speed must be gradual; the profile of speed, acceleration and g were calculated

against time from a stationary start as shown in Figure 32, with the thrust linearly increased from

zero to maximum over a period of 40 seconds. The acceleration at each epoch was calculated

using the difference in thrust and drag at each epoch, divided by the UAV mass.



Figure 32: Speed, Acceleration and g Number Profile Against Time at Sea Level

It can be seen from Figure 32 that it takes approximately 50 seconds for the UAV to reach its top

speed at sea level, with the maximum g at approximately 1.22. The Flight Control System (FCS)

would be designed to accelerate as quickly as possible whilst adhering to this g limit.

13.2 Climb Performance

The climb performance of the UAV can be simply modelled by taking the excess power in any

flight condition and dividing it by the weight of the aircraft for the maximum rate of climb; if the

available power is less than the required power to maintain level flight then the climb rate is

negative (i.e. a descent). If the performance is considered with all engines operative, with which

the minimum excess power is 400kW, then in all regions of the flight envelope the UAV is

capable of climb rates up to 30m/s. However, as for the forward acceleration the acceleration to

the climb rates needs to be kept within the 1.25g boundary, this means that the acceleration to this

climb velocity needs to take place over 20 seconds, with the maximum climb velocity being

achieved within approximately 30 seconds. This climb rate is significantly higher than a typical

0 10 20 30 40 50 60 700

20

40

60

time (s)

forw

ard

flig

ht

speed (

m/s

)

0 10 20 30 40 50 60 700

1

2

3

time (s)

accele

ration (

m/s

2)

0 10 20 30 40 50 60 701

1.1

1.2

1.3

1.4

time (s)

g n

um

ber



helicopter climb rate of around 8m/s, however if the excess power available to climb is limited to

100kW due to the possibility of OEI operation, then the maximum climb rate is 7.5m/s, which is

more comparable to helicopters. At higher altitudes the excess power decreases and ergo so does

the maximum achievable climb rate, until the service ceiling where climb rate is zero. It follows

from the above analysis that in order to descend at 7.5m/s then the power produced should be

100kW less than the power required for level flight.

13.3 Overall Mission Profile

The UAV Gross Still Air Range (GSAR) of 299km can be used for two distinctly different typical

mission profiles assuming that the UAV can be transported on the ground before it is used. The

first option is to have a mission radius of 100km from the main medical base, or the second option

would be to take the UAV to the battlefield if it is greater than 100km away from the base so that

it only has to fly one way virtually. The second option effectively increases the mission radius of

the UAV to around 250km and it also verifies that the MTOW should include the maximum fuel

mass and casualty mass together. However this second option would be difficult to employ widely

as it would need a UAV and the supporting ground transport team for each battlefield, but there

would be occasions where this mission profile would be beneficial such as distant battlefields

which are expected to incur casualties. Also the 250km distance will take more than an hour to

cover even at top speed, therefore the UAV could be used to just take the casualty to an

intermediate manned medical vehicle (either helicopter or truck) so that human intervention can

be given quicker whilst the UAV is still used to avoid the extraction danger; or alternatively if it is

deemed safe to do, or there is no other option the casualty could be flown the 250km back to the

medical base as there will be immediate medical action provided due to the UAV being at the

scene of battle.

The actual profile of any flight will be such that the UAV will always be fully fuelled, medically

supplied, and ready to depart with a ground control mission commander and ground control medic

on standby at all times. When a call is received the mission commander will input the location to

be flown to and return to and tell the UAV to depart. At this point the UAV will use its LIDAR

system to avoid obstacles, whilst the FCS allows the fully automated flight to the selected

location. The flight will typically consist of a small time climbing and increasing forward flight

speed to the maximum, then cruising at this speed to the target location, upon reaching which the

UAV will spend a small time decelerating to a hover before automatically detecting a suitable

landing zone and descending to it. The casualty will then be loaded with engines idling to allow a

quick turnaround and the above process will be repeated to fly to the return location. Although

flying at higher altitudes allows for increased flight speeds as discussed in Section ‎11.4 in order to

avoid enemy detection as much as possible the height flown above the local terrain will be kept to

a few hundred metres, furthermore if there are known danger areas on the route then the mission

commander may add waypoints to the flight path so as to avoid these areas.



14 Performance

14.1 Disk Loading

The disk loading of the UAV is calculated by dividing the weight of the aircraft by the equivalent

area of the fan disks as shown in Equation 48.

Equation 48

Comparing this value to data of other helicopters in Table 28, it can be seen that it is a lot higher

than the average value of 252N/m2, however it is in the range of the ducted fan aircraft, especially

the Urban Aero Airmule (2710N/m2) which is a similar style of aircraft; The other ducted fan

aircraft have disk loadings up to 6300N/m2, this shows that the disk loading of the UAV, whilst

high, is not at an unphysical level.

14.2 Range

Specification point ‎46.1.‎1 gives a 100km mission radius requirement which equates to a minimum

GSAR of 200km, but more ideally 300km to allow for landings, take-offs, and any indirect

routings.‎Firstly‎the‎size‎of‎the‎UAV’s‎fuel‎tanks‎was‎calculated‎to‎achieve‎a‎300km‎GSAR‎at‎an‎

average power consumption of 360kW per engine, which was determined from the average of the

sea-level equivalent power for cruise flight at 0m (264kW per engine) and 5000m (455kW per

engine) altitude, taken from Figure 30. Noting that the value of specific fuel consumption (SFC)

varies with power as shown in (Leishman, 2006, p. 232) from the TM333 maximum continuous

power reference value of 0.322kg/kWhr (Meier, 2005), and that the fuel mass flow rate varies

linearly with power from the reference value of 119kg/hr, it is possible to calculate the SFC at any

power as follows, shown here for the 360kW case:

Equation 49 (

) (

)

Equation 50

Where a and b are constants dependent on the engine, and here are modelled as 50 and 0.5

respectively to give the SFC-power curve the same shape as that described above. Using this

value of SFC the fuel mass value can be calculated to obtain a 300km GSAR from Equation 51.

Equation 51

If the fuel mass flow rate and SFC are plotted for this engine it can be seen from Figure 33 that

although the engine runs less efficiently (with a higher SFC) at power outputs below its

maximum, because the fuel mass flow rate reduces linearly the maximum range actually increases

with reduced power from the same quantity of fuel; range is calculated by re-arranging Equation

51.



Figure 33: Variation of Fuel Mass Flow Rate, SFC and Range with Engine Power

It can be seen that a range of greater than 200km is achievable for all engine powers below

800kW, which means that under all normal flight conditions with all engines operative this range

is achievable by the UAV.

14.3 Centre of Gravity & Stability

In order for the UAV to be stable in flight it is necessary for the centre of gravity (CG) of the

UAV to be at or near to the midpoint between the two fans. With the UAV being mostly

symmetrical about this mid-point this is not a big issue, as the extra front mass of the 2nd

duct can

be offset by moving the engines slightly aft. The main issue is maintaining the CG throughout the

flight, as fuel is burnt, and also if there is a casualty loaded or not. To mitigate the effects of these

variable masses, it was decided to ensure that the CG of these components is at the desired CG of

the UAV; hence the fuel tanks and casualty position are centred around the UAV CG so that as

their masses vary there is no change in the global UAV CG.

15 Processors

There are several options for the type of processors that could be used for this type of aircraft.

These range from Application Specific Integrated Circuits (ASIC) such as the IBM PPC750FL to

Field Programmable Gate Array (FPGA) type processors.

A FPGA is a semiconductor integrated circuit containing a matrix of configurable logic blocks

(CLB) that are connected together by software defined connections. This has the advantage over

ASIC processors that the entire FPGA can be reconfigured as needed and on the fly if

circumstances change whilst in flight (e.g. damage sustained etc.). There are‎also‎specific‎FPGA’s‎

that are military rated to survive radiation, such as an electromagnetic pulse. The ASIC based

system offers a similarly high performance low mass system, however the inputs to the processor


Author: Matthew Temple 16-52

and how the processor operates cannot be changed. Therefore as the types of sensors on the

aircraft will be constantly evolving over time a reprogrammable processor approach is to be

preferred to afford maximum flexibility in both design and operation of the aircraft.

The type of processor that is programmed onto a FPGA is called an Intellectual Property (IP)

core. This is because the processor can be downloaded from a number of companies other than the

manufacturer of the FPGA device itself, and as the software description of the processor is unique

it can be patented in a similar way to a microprocessor die. The advantage of the FPGA approach

is that once the software description of the processor is loaded onto the FPGA, the inputs and

outputs of the FPGA can be dynamically reconfigured as required. This means that if in the future

a new/additional sensor is needed it can be connected directly to the processor by simply

reprogramming the FPGA to allow a new communication port. The only limitation to this

approach is that there needs to be a physical connection on the circuit board to connect the sensor

to the processor.

Due‎ to‎ the‎ rapidly‎ increasing‎popularity‎of‎FPGA’s‎ as‎processors‎more‎ and‎more‎ IP‎Cores‎ are‎

being released with greater speed and functionality and occupying an ever decreasing amount of

space on the FPGA. This means that multiple processors can be programmed onto a single FPGA

to create multiple cores allowing parallel processing and all that this offers in terms of increased

processing speed. This means that for the flight computer all of the raw data from the sensors can

be processed live before being combined to determine the aircrafts exact orientation. This allows

for far greater processing power and flexibility than using ASIC based processors. For this reason

most of the computers on the aircraft should be FPGA based as this allows for a custom designed

computer that can be reconfigured as new equipment is added and the

performance/functionality/design of the aircraft is changed over the operating life time.

The other advantage of‎FPGA’s‎is‎that‎as‎the‎device‎can‎be‎reprogrammed‎whilst‎the‎aircraft‎is‎in‎

operation by uploading a new program over the communication system, if a processor fails

another processor can be reprogrammed to take over operations as needed provided there is a

sufficient level of redundancy on the aircraft. This would allow the aircraft to safely return to base

to receive repairs.

16 Sensors

Sensors on the aircraft fall into two distinct functional categories; those to inform and control

flight operation and those to inform and control medical operations.

This section details the flight control sensors only, (see Section ‎29 and ‎30 for medical sensor

details).

16.1 Terrain Mapping

To identifying optimal landing sites for the UAV, the UAV needs to be able to accurately map the

ground. There are two main sensor options for doing this, either Light Detection or Ranging



(LiDAR) or Synthetic Aperture Radar (SAR) sensors. Both sensor types are capable of mapping

the terrain however SARs generally have greater power requirements, an example of a SAR unit

power consumption is shown in (Sandia National Laboratories, 2005), and transmit radio waves at

similar frequencies to the communications antenna which could increase the noise and therefore

decrease performance of the communication system of the aircraft, and possible ground based

systems near the aircraft. Consequently an alternate sensor system that minimises these issues,

such as a LiDAR based system would be preferred for this UAV.

LiDAR Systems work by using a laser and a rotating mirror / housing to scan the area around the

unit. By measuring the time it takes for a transmitted laser pulse to return to the issuing LiDAR

unit an image can be built up of the distance to various points around the LiDAR unit. There are

several potential LiDAR units that could be used on this aircraft, each offering different benefits.

A unit such as the Velodyne HDL-32E LiDAR unit could be used to scan in one plane to detect

obstacles around the aircraft; as the unit is small enough to fit on top of the aircraft without

affecting airflow. However this unit would not be suitable for scanning for landing sites, because

the maximum range of the unit is 70m and the cruise altitude of this aircraft is typically between 3

and 5km. The specification for this LiDAR unit can be found in (Velodyne, 2012). This unit uses

a rotating housing to scan the area around the sensor, giving a 360 degree view around the LiDAR

scanner.

To enable the aircraft to map the landing sites from higher altitudes (3 – 5km), a different LiDAR

unit is needed. At these altitudes more sophisticated processing is required because at high

altitude the time between a laser pulse leaving the unit and the return being received is so long

that some of the laser pulses could be interpreted incorrectly, for this reason several sophisticated

algorithms are needed to identify which pulse is which and to combine the necessary information

to create the 3D image. For mapping potential landing sites at high altitude a LiDAR unit such as

the Ingenieur-Gesellschaft für Interfaces (IGI) – LiteMapper 6800 is a good candidate. This

LiDAR unit has been specifically designed for aerial use, unlike the Velodyne system which is for

close range obstacle detection, making it ideal for mapping potential landing sites from higher

altitudes. High altitude operation is a feature essential for this application as if the aircraft has to

drop to low altitude to scan for landing sites the risk to the aircraft and the patient is dramatically

increased. These risks are either from physical obstacles such as electrical pylons, cables, bridges

etc. or weapons fire which could bring down the aircraft.

The IGI – LiteMapper 6800 can be used from altitudes as high as 3 km if the unit is mounted

vertically underneath the aircraft, according to (Ingenieur-Gesellschaft für Interfaces, 2012). This

means that to survey an area for a potential landing site the aircraft would need to fly in a pattern

over the area to map all the candidate areas before making a decision on which one to land at. The

image is formed by panning a laser across an area to produce a set of range data points, the unit

then needs to be moved before repeating this process. Each pan produces a linear set of data that



when combined with the location of the sensor when taken can be used to create an artificial array

of range data points to generate a three dimensional image of the area scanned.

The IGI LiDAR Unit is shown in Figure 34.

Figure 34: IGI LiteMapper 6800 LiDAR Unit (http://www.igi.eu/lm-6800.html)

To speed selection of a suitable landing area, using this type of LiDAR unit, a single pass of the

aircraft over an area could map the terrain as long as the field of view of the sensor was sufficient

to allow for one pass. By using the maximum range of this LiDAR unit (3 km), the maximum

possible swath width and optimum altitude can be calculated using simple trigonometry. The

maximum swath width can be calculated using Equation 52, using the data supplied in the

products datasheet.

Equation 52: Calculating Maximum Swath Width of LiDAR Unit

[ (

) ]

Using Equation 52, the maximum swath width is calculated as 3 km. In a similar way the

optimum altitude that the sensor can be used at to get the widest field of view, can be calculated

using trigonometry as shown in Equation 53.

Equation 53: Calculating Optimum Altitude for LiDAR

(

)

Using Equation 53 and substituting the necessary values the optimum altitude that the scanner

needs to operate at to get the best possible field of view can be calculated. For this scanner the

UAV would need to fly at an altitude of 2.59 km.

Then by processing the image produced all of the areas large enough for the aircraft to land could

be calculated. To do this the 3D image would need to be processed, by the on board computer,

looking for areas of ground which are not only smooth enough for a safe landing, but are large

enough for the UAV to land in. An example of this is shown in Figure 35 of the Petronas Twin

Towers in Kuala Lumpur.

http://www.igi.eu/lm-6800.html



Figure 35: LiDAR Image generate by LiteMapper 6800 (http://www.igi.eu/lm-6800.html)

Once a potential landing site has been identified, the aircraft needs to be able to photograph the

site to relay an image back to the ground station to get permission to land at that location. A visual

image is needed because although the LiDAR might interpret an area as smooth it might not be a

suitable‎for‎landing‎the‎aircraft,‎for‎example‎it‎might‎be‎smooth‎because‎it’s‎a‎glass‎roof!

For the LiDAR Unit to be able to produce an image such as the one shown in Figure 35, the

processor‎ needs‎ to‎ be‎ able‎ to‎ accurately‎ determine‎ the‎ scanner’s‎ forward‎ velocity,‎ and‎ its‎ roll,‎

pitch and yaw angles with respect to the ground. To determine these parameters and hence the

attitude of the sensor a device such as a gyroscope is needed to accurately determine the sensors

orientation to the ground. The IGI – LiteMapper 6800 unit has an optional Inertial Measurement

Unit (IMU), effectively a series of sensors including a gyroscope based system that can be

incorporated into a custom anti-shock housing to ensure that the orientation of the sensor can be

accurately calculated and reported. This means that to have one of the IGI – LiteMapper 6800

units on the MedEvac UAV, the total mass will be as shown in Table 6.

Possible Landing Site

http://www.igi.eu/lm-6800.html



Table 6: IGI - LiteMapper 6800 LiDAR Unit Masses

Item Dimensions Weight

Laser Scanner Unit 480 x 212 x 230 mm 17.5 kg

Data Recorder DR560 337 x 178 x 197 mm 7.0 kg

LiteMapper Control 270 x 162 x 62 mm 2.2 kg

AERO Control 250 x 209 x 132 mm 1.8 kg

IMU – IIe 146.5 x 126.5 x 98 mm 2.2 kg

Total 30.7 kg

Although this is a significant amount of mass to add to the aircraft, the accuracy that this system

offers is far superior to the Velodyne system, as it gives a range resolution of 20mm when looking

straight down. This level of accuracy means that the aircraft can identify individual people on the

ground, as the sensor can detect a 20mm object whilst at high altitude and as long as the distance

between each point is small enough the shape of a person could be detected, allowing the aircraft

to actually pick up the location of personnel if they are out in the open. This would enable the

aircraft to prioritise the landing site to ensure that it lands as close as possible to the injured

casualty or friendly forces.

16.2 Colour Camera

The purpose of this camera is to provide a high resolution image of an identified potential landing

site by the LiDAR unit so that the ground staff can make an informed decision on whether the

potential site is suitable. This means that the camera needs to be mounted next to the LiDAR unit

in similar orientation i.e. directly facing downward and mounted on a shock proof platform to

achieve stable images.

The company, IGI that make the LiDAR unit also make several high resolution cameras for aerial

photography, and these can be integrated into the same control computer and sensors used for the

LiDAR unit so that the exact position and orientation of the camera can be calculated. This means

that the camera can be aimed at exactly the same area as the LiDAR unit. One such example is the

IGI-DigiCAM, which can be configured in several different ways to change the type of image that

can be taken depending on if the camera is aligned along or across the flight track. There are also

three different resolutions for the IGI-DigiCAM 40, 50 or 60 Megapixel. It is important to use the

highest possible resolution so that the image can be magnified without loss of quality. The

specification for these cameras can be found in (Ingenieur-Gesellschaft für Interfaces , 2012). An

example of the image quality produced by these cameras from altitude is shown in Figure 36.



Figure 36: IGI-DigiCAM Example Photograph (http://www.igi.eu/single-digicam.html)

The ground areas that can be imaged can be calculated for the different lenses by using Equation

54 and Equation 55.

Equation 54: Coverage width of DigiCAM

( ) ( )

Equation 55: Coverage Width per Pixel

( ) (

)

If the aircraft uses a 60 Megapixel camera at the optimum cruise altitude of 2.6 km, then the

number of pixels in each direction is 8956 x 6708. Using Equation 54 and 4, the results in Table 7

have been calculated for a range of different lenses.

Table 7: DigiCAM Ground Resolutions

The results in Table 7 shows that to be able to accurately image the landing site the camera would

need to have the 300mm lens to make sure that the images produced can show as much detail as

possible from typical cruise altitude. If however it was more important to photograph a large area

then one of the small lenses could be used to get a large area photograph, but the individual streets

could be missed if operating over an urban area.

16.3 Attitude Determination Sensors

In order to determine the exact location and orientation of the aircraft, data from several different

sensors‎is‎required.‎The‎most‎common‎method‎of‎determining‎the‎aircraft’s‎geographic‎location‎is‎

to use a Global Positioning System (GPS), however because of the risk of enemy forces

Focal Length (m) Field of View (Degrees) Coverage Width (km)

Along Track Cross Track

0.028 70 363.73 40.61 54.22

0.035 59 306.57 34.23 45.70

0.05 44 228.63 25.53 34.08

0.08 27 140.30 15.67 20.91

0.1 23 119.51 13.34 17.82

0.15 15 77.94 8.70 11.62

0.21 11 57.16 6.38 8.52

0.3 8 41.57 4.64 6.20

Coverage Width Per Pixel (m)

http://www.igi.eu/single-digicam.html



interrupting the signal and causing the UAV to crash or divert GPS cannot be the only method of

determining position.

GPS units are available in two different formats: civilian and military. A GPS satellite transmits

two different signals: Course Acquisition code and Precision Code. Course Acquisition code is

available to civilian users and is accurate to a couple of meters in latitude and longitude, however

military users can have access to the Precision code which is capable of determining the position

to within a couple of centimetres. There are two main issues to consider when using GPS, firstly,

as the GPS system is maintained by the American Military they can turn off the GPS signal or

degrade performance at will, secondly; GPS is not accurate at determining altitude. Consequently

whilst GPS could be used on this aircraft to primarily determine the position and velocity of the

aircraft, a backup/secondary confirmatory system is advised. The new Galileo system would be a

better candidate for determining the positioning of the aircraft as this system is maintained by

European Space Agency and is based on significantly more advanced technology than the ageing

GPS system offering improved accuracy and performance. Galileo is therefore a better choice for

this aircraft, however as Galileo is not due to go operational until 2014 / 2015 initially the aircraft

would need to use GPS for testing. As Galileo and GPS data feeds and utilisation are similar

changing‎between‎the‎two‎shouldn’t‎need‎much more than a simple hardware change to change

the receiver from GPS to Galileo.

To accurately determine the aircrafts attitudinal position an inertial measurement unit (IMU)

could be used in conjunction with the GPS / Galileo system. An IMU consist of a combination of

gyroscope, accelerometers and magnetometer sensors. To calculate the current acceleration in

each direction using accelerometers and the rotational changes in roll, pitch and yaw using a

gyroscope. Both the gyroscope and magnetometer have inaccuracies which can cause the position

and orientation sensed by the IMU to drift. For this reason an IMU is traditionally combined with

a GPS transceiver to calibrate out these errors.

The biggest source of error is the gyroscope in the IMU as these have a tendency to drift rapidly

when operating. There are two main types of gyroscope that could be used; a mechanical or an

optical based gyroscope. The mechanical gyroscope is now more likely to be based on a vibrating

structure, such as an oscillating crystal, rather than a spinning mass, so that as the device changes

direction the vibration changes and can be used to determine the change in direction. These are

now so cheap that they can be used on small remote control helicopters. However an optical

gyroscope works by injecting two laser beams into a fibre optic cable in opposite directions,

therefore as the gyroscope experiences a rotation the time delay of each pulse is altered due to the

Sagnac effect, this effect is shown in (Post, 1967). Therefore using interferometry the difference

can be measured and the rotation calculated. However both gyroscope types suffer from

significant drift over small periods of time, as much as 0.02 degrees per second for the Sensonor

SAR100 IMU commercial unit. This would not be suitable for use on this aircraft as it is vital that



the‎aircraft’s‎position‎can‎be‎sensed‎accurately,‎therefore‎a‎higher‎grade‎unit‎specifically‎built‎for‎

the military would be needed, such as the MOOG Crossbow VG700MB Fibre Optic Vertical

Gyro. The advantage of the MOOG Crossbow is that the IMU is military hardened and tested

making it more robust for battlefield operations meaning that less development time is needed to

make a working system. This unit has a built in processor to automatically calibrate out the errors

to provide a complete IMU that can simply be connected to the flight computer to give the

aircraft’s‎ orientation‎ and‎ a‎ crude‎ estimation‎ of‎ its‎ position‎ using‎ flight‎ time‎ and‎ direction‎

information.

By combining an IMU and a GPS type system then even if the GPS fails then the flight computer

can still have a reasonable estimation of the position of the aircraft. This means that even if

someone manages to tamper with the GPS signal then the flight computer can detect this and still

manage to navigate itself back close enough to a suitable site where a ground pilot could land the

aircraft safely.

16.4 Altitude Determination

The only other sensor that is needed to accurately determine the position of the aircraft is a

method of calculating the altitude. On small aircraft this is done by using a barometric pressure

sensor to detect the difference in pressure between sea level and the current air pressure around

the aircraft. Air pressure changes with altitude at a rate of 100 hectopascals per 800 meters, giving

a total change in pressure, between sea level and the maximum cruise altitude of 5 km, of 625

hectopascals. An example of such as sensor is the Bosch BMP085 sensor that can sense altitudes

up to a maximum of 9 km and itself measures just 5 x 5 x 1.2 mm in size. At lower altitudes (less

than 3 km), the data produced by this sensor can be double checked with the LiDAR system

pointing straight down.

16.5 Tachometer

In order for the flight computer to be able to measure the speed of each of the fans described in

section ‎4,‎it‎must‎be‎able‎to‎sense‎the‎rotational‎speed‎of‎each‎of‎the‎fans’‎drive‎shafts.‎The‎easiest‎

way to do this is to use a tachometer. There are two main types of tachometer: mechanical or

optical. The mechanical tachometer uses a rotating magnet to induce a current in a Hall Effect

transistor. The mechanical tachometer requires a physical mechanical connection to the object that

is to be measured (the wheel of the tachometer and the drive shaft need to be in contact), which

would wear out and need replacing at regular intervals and requires mounting the sensor at exactly

the correct distance from the rotating object.

For this reason an optical tachometer is preferred for this application of measuring the rotational

speed of the drive shaft, as the optical tachometer will not wear out as quickly and will allow for

vibrations in the drive shaft whilst still measuring the speed accurately. The optical tachometer

works by measuring the intensity of a laser reflection off the surface of the rotating object. By

using a mark on the drive shaft as a target, as the shaft rotates the reflection will change which can



be picked up and the rotational speed calculated accurately by the tachometer. An example of this

type of tachometer is the LaserTach -ICP Laser Tachometer as shown in (LaserTach, 2006).

17 Electrical Bus Layout

To enable all of the different systems on the aircraft to be connected together, there needs to be

several different communication buses to transfer the data needed between the various devices to

perform all of the operations on the aircraft. There are several different communication buses that

could be used however each Communication Bus type has different performance characteristics.

Most of the navigational flight sensors such as the IMU and GPS systems have a low data rate,

but need a high reliability therefore for this an RS232 communication system is needed. This

should be used as there are several military grade terminal nodes that could be used to connect the

sensors via the RS232 Bus to the flight computer. The RS232 Bus should be used for the

navigation sensors as it has been proven reliable for military operations.

However the LiDAR and the camera feeds need a significantly higher data rate capacity to

transmit their data output to the central flight computer and if they used the RS232 bus too then

all of the other sensor data (such as the IMU or GPS) would be blocked, while transmitting the

LiDAR or Camera Data. Therefore keeping the navigational sensors on their own specific bus

means that there is little chance of the bus jamming and stopping the data from reaching the flight

computer. By jamming the RS232 (navigational) communication bus this could cause the aircraft

to become unstable and possibly even crash therefore a secondary high speed bus is required. For

the LiDAR and Camera sensors an Ethernet bus is proposed as it allows for a simple high speed

communication bus that also can be implemented on the FPGA.

The majority of the Medical system sensors have a low data rate, and because the connections to

the processor need to be mechanically flexible in order to allow the sensors to be placed on the

patient a communication bus with a small number of wires is needed. For this reason an Inter

Integrated Circuit (I2C) bus could be used. This is a simple and reliable communication system

that only requires two wires. This bus also allows for new nodes (sensors) to be added, without

the need to change the wiring inside the aircraft and a simple software update to enable them and

make them work.

A basic wiring diagram for the UAV is shown in Figure 104, using this layout the three main

computers on the UAV are connected on a common bus. The use of a common bus means that the

three main computers can share information without needing to pass through another device,

therefore increasing the data throughput of the entire system. However using this communication

bus layout means that there is only one root for data to enter and leave the UAV, this makes the

communication computer the master control computer on the UAV. The master control computer

handles the flow of information around the UAV and out to the Ground stations, and needs to be



able to monitor the status of the other devices on the UAV to ensure that the UAV is operating

correctly.

18 Navigation and Flight Operations

To simplify the control of the aircraft most of the flight operations will be performed on board the

aircraft. For this to work the ground controller or medic will need to load the co-ordinates where

the UAV needs to fly to onto the aircrafts flight computer at outset, the aircraft will then create a

flight path that avoids areas where friendly ground forces were recently engaged. This is to avoid

endangering the aircraft as much as possible, by keeping away from the most dangerous areas on

the battlefield as much as possible.

To protect the aircraft from weapons fire, there needs to be a system to detect incoming projectiles

and deploy countermeasures such as chaff or move the UAV out of the way if possible. This

system is further described in section ‎24. The data produced by the anti-weapon system then

needs‎to‎be‎fed‎into‎the‎flight‎computer‎to‎redirect‎the‎aircraft‎out‎of‎harm’s‎way.‎The‎process‎of‎

generating a flight path is shown in Figure 97.

When the aircraft approaches the co-ordinates uploaded by the dispatching medic the flight

computer checks to see if the co-ordinates indicated a medical facility landing site or a casualty

pick up location. If they indicate a casualty pick up location then the aircraft needs to image the

area with the LiDAR and Colour camera system to identify possible landing sites within a

specified radius of the given co-ordinates. The identified sites are then ranked in terms of size,

space around the landing site and distance from the co-ordinates supplied. This information is

then relayed back to the ground controller who has to authorise the landing site selected by the on

board computer. This is to keep the complex variety of additional considerations under human

control, eventually this could be replaced by Artificial Intelligence or inference engines.

In special circumstances the UAV can be flown by the ground controller to fit into areas that the

auto‎pilot‎isn’t‎calibrated‎to‎permit‎to‎do‎so.‎The‎biggest issue when operating in this mode is the

time‎delay‎between‎the‎UAV‎and‎the‎ground‎controller’s‎commands.‎In‎these‎situations‎the‎UAV‎

has to switch into a hover mode and using the LiDAR system make sure that there are no

obstacles within half a meter around the aircraft. The Auto pilot function is shown in Figure 96.

If the UAV loses its communication link with the ground control station or is waiting for

authorisation, then the UAV should fly in a random pattern to make it hard for hostile forces to

target the aircraft. If however the aircraft is flying between buildings then the aircraft cannot fly in

a pattern without the risk of hitting an obstacle, therefore in these conditions the aircraft would

have to automatically be able to retrace its flight path until the communication link is restored.

The flight computer must be able to monitor the strength of the communication link, so that when

it starts to degrade and before it reaches a certain breakdown threshold the UAV must warn the

ground station before carrying out the command in case the signal is subsequently lost.



The entire flight computer can be programmed into a single Field Programmable Gate Array

(FPGA) such as the AeroControl Integral 2X AutoPilot unit. This autopilot has most of the

functions described in sections ‎16.3 and ‎16.4 built in including gyroscopes, accelerometers and a

GPS based navigation system. The whole of this computer i.e. the FPGA fits into a box just 66 x

98 x 35mm. this is shown in (AeroControl Inc, 2012). This system uses two software defined 64

MHz processors to operate, one to perform the auto pilot functions and one for payload sensors.

The AeroControl Integral 2X Auto Pilot system‎was‎originally‎designed‎for‎use‎on‎small‎UAV’s‎

that are launched by either a rail or thrown by hand. An Example of the AeroControl unit is

shown in Figure 37.

Figure 37: Integral 2X Flight Control System (http://www.aerocontrol.com/products)

This shows how for this aircraft even using all of the sensors described above, the entire flight

computer for this aircraft can be programmed onto a single FPGA. Therefore to speed up

development, a company that produces a FPGA based auto pilot (like AeroControl) could be

hired to modify their existing system to work with the MedEvac UAV, and all of the sensors

specified to produce a flight worthy system that could be produced within five years. The biggest

time constraint is to achieve regulatory approval that the system is safe to operate over populated

areas such as towns and cities.

19 Communication

To communicate with the UAV, there needs to be a communication system with sufficient

bandwidth to stream two video feeds and telemetry information at the same time back to a ground

control station. Due to the urban environment that this aircraft is going to be operating in, the

communication system needs to work in two different modes: Line of Sight (LOS) and Beyond

Line of Sight (BLOS). Both LOS and BLOS systems can operate on the same frequency using the

sane equipment, the only difference between these two systems is the transmission power needed

and the sensitivity of the receiver. BLOS uses either a geostationary communication satellite to

relay the information from the UAV back to the ground station, or the signal can be relayed via

another aircraft to avoid obstacles such as buildings or natural features, whereas LOS

communication is used in cases where the satellite or another aircraft cannot be seen. The data

produced by the UAV needs to be processed to create a linear data stream for transmission to the



ground control station; this process is shown in Figure 95. This shows how the data is combined

by the processor to create a linear data stream that is sent back to the ground station, ensuring that

all of the data is received by the ground station in sufficient time for the ground controller to

operate the aircraft. The on-board computer also has to be able to decode the commands returning

from the ground station. To be able to mix all of this data and carry out all of the other

communication system operations in real time, a processor such as a Field Programmable Gate

Array (FPGA) PowerPC (IP Core) could be used.

If the satellite communication link is lost and cannot be automatically restored, then the UAV

must switch to a LOS operation by turning down the power of the communication system to a

lower power setting. This would enable the ground personnel to bring a mobile control station

into range of the UAV to enable the aircraft to be rescued and moved to a position where the

satellite communication link can be restored; once the satellite link is restored the UAV can return

to normal operation and switch back to BLOS operation.

19.1 Operating Frequency

There are several different radio frequencies available for military use; these are selected

depending on the performance and availability required by the system in question. For the UAV a

large bandwidth is needed with a high data rate in order to stream all of the data live, including

two video feeds and telemetry data. X-Band radio frequencies support these requirements, and

therefore should be used as there is a sufficient amount of hardware currently used by the UK

Ministry of Defence to choose from, X-Band also offers a higher data rate than C-Band (civilian

satellite communication systems) and other lower frequency communication systems. The X-

Band hardware systems range from mobile terminals for the infantry to ground control stations for

UAV drones, this means that if the MedEvac UAV were to use these frequencies there would be

no need to develop a new unit for the infantry or a satellite receiver system.

The X-Band frequencies cover 7 – 11.2 GHz, this means that there is a limited risk that rain will

affect this communication link as rain only becomes a problem at frequencies above 15 GHz.

Rain drops can attenuate a radio wave, by either absorbing the energy or scattering the signal, the

amount of attenuation is related to the size of the rain drops and the wavelength of the radio wave.

However the average size of rain drops is too small to affect radio waves less than 15 GHz; this

means that the availability of the communication link is sufficiently higher than if using a higher

frequency, higher data rate system such as Ku-Band (~20 GHz).

19.2 Satellite Networks

Currently there are only a couple of satellites that use X-Band in orbit; this means that there is a

large separation between the satellites making it ideal for communication on the move, as there is

no need to worry about interfering with neighbouring communication satellites. Skynet 5 is

currently being deployed to increase the capacity of X-Band communication networks around the

world. Skynet 5 provides a large bandwidth capable system with protection from interference and



attack from hostile forces. Skynet 5 was built by Astrium and started deployment in 2007, this

network has been designed to operate for 15 years and to provide secure military satellite

communication for UK Ministry of Defence systems around the world.

19.3 Modulation, Error Correction and Polarisation

To encode the data on to a Radio Frequency Carrier Wave there are several different methods that

could be employed, these work by changing the amplitude, phase or frequency of the carrier

wave. The most common of these for satellite communication is phase shift keying. To get the

best possible performance out of the communication link the encoding rate (number of symbols,

each symbol represents a certain amount of data to be transmitted) of the signal needs to be able

to dynamically change with the signal strength. The performance of the communication link is

measured in the terms of carrier to noise power, as this ratio starts to degrade due to the noise

level increasing the number of symbols used to encode the data needs to reduce increasing the

tolerance to noise. When flying between buildings or close to obstacles the signal can bounce off

these obstacles and increase the amount of noise at the antenna. Therefore by using an adaptive

modulation scheme the tolerance to the amount of noise that this communication system can

tolerate before failing is significantly higher than using a fixed modulation scheme. This also

means that when there is a small amount of noise, the data rate can be significantly increased to

transfer more data providing the ground control station with extra information. However when

operating in a noisy environment, only mission critical data can be sent as the data rate is

significantly lower than optimum.

To protect against errors, redundancy bits need to be added to the data stream so that error

correction programs can be used to identify and correct errors. The simplest method for this is to

use forward error correction, where algorithms are used on the data to generate redundancy bits,

which are then added to the data stream at the transmitter end. At the receiver the data and

redundancy bits are separated and by using the same algorithms the redundancy bits generated can

be checked against the ones received. If the redundancy bits match then there is a high possibility

that there were no errors in the received data stream. Depending on the number of errors in the

data set, the errors can either be corrected or if there are too many errors in the data set they

cannot be corrected but can be identified. Just like modulation the strength of the error protection

(number of redundancy bits) needs to be able to change dynamically to balance an acceptable data

rate for error protection of data. This means that as the signal level degrades the encoding rate

needs to reduce and the amount of error protection needs to increase to ensure that the probability

of the communication link failing (too many errors in received data) is reduced.

There are three different types of polarisation (orientation of electric field vector): circular,

horizontal or vertical. For this communication system circular polarisation is best as this means

that‎ the‎ antenna‎ doesn’t‎ have‎ to‎ be‎ aligned‎ as‎ carefully‎ with‎ the‎ satellite,‎ this‎means‎ that‎ the‎

motion/attitude of the aircraft will not affect the performance of the antenna on the aircraft.



19.4 Encryption

To ensure that the communication signals to and from the aircraft cannot be intercepted or

interfered with the signal need to be encrypted. There are several different types of data

encryption that could be used on the communication system, both software or hardware based

techniques.

A software based encryption system reduces the data throughput of the communication system

significantly as the processor has to deal with not only the data that needs to be sent but the

encryption program to scramble the data also. This means that the encryption process introduces a

significant bottleneck on the processor that could mean that not all of the information from the

UAV can be sent back to the ground station in sufficient time.

For this reason a hardware based encryption system has several advantages. With hardware

encryption there needs to be a physical processor just to deal with the encryption process, adding

a small amount of mass to the whole system. Again the use of encryption will decrease the data

rate of the system but as there is a separate processor just for the encryption, the data can be

scrambled live meaning that there is no bottleneck introduced. One such example of this

encryption technique is called the Tactically Unbreakable Communication Security (TUC). This

encryption uses an Asymmetric Key Establishment Scheme that enables the secret and public

keys to be levered as needed creating a real time encryption scheme that is suited for encrypting a

communication for a moving vehicle.

The FPGA Company Xilinx has been working with defence solution developers and governments

to develop a single chip encryption method, which can be used on moving vehicles such as

UAV’s‎ using‎ a‎ single‎Field‎Programmable‎Gate‎Array‎ (FPGA).‎For‎ this‎ encryption‎method‎ to‎

work the encrypted and unencrypted data must be kept separate at all times with the encryption

processor sitting between the two. This entire encryption process has been demonstrated on a

Xilinx Vertex 5, using a Power PC processor core in the FPGA. This process has been

successfully‎demonstrated‎on‎UAV’s‎and‎further‎information‎can‎be‎found‎in‎(Anderson, 2011).

This type of encryption is suitable for encrypting both video and telemetry data from the aircraft.

By using this technique to encrypt the communications from the UAV only a single chip would be

needed to encrypt the data without significantly reducing the data rate of the system, or increasing

the power consumed by the communication system.

19.5 Antenna Design

There are several different types of antenna that could be used for this aircrafts communication

system, these are: Dipole, Helix or Dish antennas. Dish antennas offer the best performance as

they produce a highly directional beam; however they require a large physical size and weigh

considerably more than the alternatives. Therefore for this aircraft a dish antenna is not suitable.

Dipole antennas on the other hand provide an Omni-directional radiation pattern which would be



fine for line of sight communication, however there is insufficient directionality to enable the

aircraft to transmit and receive data from a Geostationary Satellite network.

For these reasons a helical antenna should be used as it offers a lightweight antenna that produces

a directional radiation pattern that could reach a satellite if BLOS or LOS were required, another

reason for choosing helical antennas is because they are used on portable Sat-Phone systems,

demonstrating their effectiveness for communicating with geostationary satellite systems.

To calculate the size and performance characteristics of the antenna needed for the UAV, the

following calculations are needed. The best antenna performance is obtained when the antenna is

exactly matched to the operating frequency, but since that is not known at the present time an

average frequency of (centre of the X-Band frequency range) will be used to estimate the

size of the antenna needed. There are several other inputs needed to calculate the size of this

antenna, they are the number of turns in the helical antenna, and the amount of power to be

transmitted by the communication system.

The spacing between the turns of the antenna is calculated using Equation 56.

Equation 56: Calculating the spacing between turns of a Helical Antenna

When using the 9 GHz operating frequency, Equation 56 gives a spacing of 0.008m. Now the

diameter of the coils in the antenna can then be calculated using Equation 57.

Equation 57: Calculating the diameter of the coils in a Helical Antenna

Equation 57 therefore gives a diameter of 0.01m for this antenna. Therefore the total length of the

antenna can then be calculated using Equation 58.

Equation 58: Calculating the length of a Helical Antenna

Now using Equation 58, the total length of the antenna is calculated as 0.08m. The circumference

of the antenna can then be calculated using Equation 59.

Equation 59: Calculating the circumference of a Helical Antenna

Using Equation 59, the circumference of the antenna is calculated as 0.03m. Using the

circumference, the Half Power Beam Width can now be calculated using Equation 60.

Equation 60: Calculating the half power beam width of a Helical Antenna

( )

(

)

For this antenna the Half Power Beam Width is calculated as 26 degrees, this means that this

antenna sends half of the power in a cone 26 degrees around the Boresight (centre) of the antenna.



The other performance characteristic of importance is the gain of the antenna; this can be

calculated using Equation 61.

Equation 61: Calculating the gain of a Helical Antenna

(

)

The gain of this antenna is calculated as 11.9dB, this indicates a reasonable gain antenna for its

physical size. The only other characteristic of interest is the Effective Isotropic Radiated Power

(EIRP); this can be calculated by Equation 62.

Equation 62: Calculating the EIRP of a Helical Antenna

( )

Using a transmit power of 10 Watts, this gives an EIRP of 21.9dB for this antenna system. This

means that the communication system is going to rely on the amplification power of the Skynet 5

satellite rather than the antenna on the UAV to minimise the amount of power that needs to be

transmitted by the UAV. The only other factor that is going to affect the antenna design is the

orientation that it needs to point to reach the satellites in the network. These calculations will be

based on the uplink from the UAV to the Satellite at two RAF bases; the results are shown in

Table 8.

Table 8: Antenna Pointing Data

The variations in the elevation angle required means that antenna will need to be mounted on a

platform that can track the satellite while the UAV is flying; therefore to protect the antenna from

damage it will need to be placed inside a Radome. A basic design for the UAV antenna is shown

in Figure 38.

Satellite Information Units RAF Dounreay Camp Bastion

Name Skynet 5C Skynet 5B

Longitude (+ve E) -17.8 52.8

Altitude km 35786 35786

UAV Information Units

Longitude (+ve E) degrees -3.43 64.13

Latitude (N) degrees 58.35 31.24

Antenna Pointing Units

Latitude Angle degrees 59.45 33.03

Azimuth degrees 196.75 201.12

Elevation degrees 22.52 51.57



Figure 38: Custom Antenna with and without Radome

For the tracking system to work the communications processor needs to be able to find the exact

position and orientation of the UAV and calculate the elevation and azimuth needed to point the

antenna at the satellite with the best possible view of the UAV, the processor also needs to be able

to switch between satellites as needed to ensure that the communication link is maintained as the

UAV is travelling.

Communicating with a Geostationary Satellite introduces a significant time delay between the

UAV and the ground station; this is because of the massive distance that the radio wave needs to

travel between the transmitter and receiver. The following calculations (shown in Table 9) are

based on the UAV and the Ground Station being in the same location i.e. same distance from the

satellite.

Table 9: Propagation Delay Calculations

Table 9 shows that for these two geographic locations there is a quarter second delay between the

two ends of the link, this means that there will be at least a half a second delay between anything

being detected on the UAV to an operation happening after being authorised by the ground

station.

20 Electrical Power Generation

There are several options for generating power on this type of aircraft. These are: turning a

dynamo to generate power, fuel cells or rechargeable battery packs. The rechargeable battery

packs offer a good power to mass ratio but require large amounts of time to recharge the battery

when they have been used. The packs also have to be replaced at intervals as the storage capacity

degrades over time. This makes batteries unsuitable for the aircraft as the primary power source,

as there would be insufficient warning to charge the battery before launching the aircraft. The

only choice would be to leave the aircraft charging all of the time wasting power. The batteries

Propagation Delay Units RAF Dounreay Camp Bastion

Maximum Range km 39306.97 36980.65

Time Delay seconds 0.26 0.25



could be used however to store excess power that is produced by other means, and provide the

high current needed to start the turbine.

A dynamo could be used on this aircraft to provide a continuous supply of power whilst the

propulsion turbine is running. However the size of the dynamo required to provide the amount of

power specified in Table 20 and survive the amount of torque generated by the turbines in the

aircraft would weigh too much for the aircraft to lift without sacrificing space for the patient or

medical equipment.

For this reason to save space and mass, a fuel cell could be used as this offers a high energy

density and can be recharged by simply replacing a fuel tank. A system like the Horizon Aeropak

could be used where a tank is filled with water, generating hydrogen gas. This hydrogen is then

combined with oxygen in a Polymer Electrolyte Membrane (PEM) which generates power as

needed. An example of this can be seen in Figure 39.

Figure 39: Aeropak Hydrogen Fuel Cell

Although these Fuel Cells have a limited operating life time they can be recharged by simply

replacing the water in the tank allowing the aircraft to be recharged anywhere without the need to

worry about needing special fuel. This means that apart from the fuel to power the turbine the

only other fuel that the aircraft needs is water available everywhere where the soldiers might be

stationed.

For this aircraft two of these Aeropak Fuel Cells would be needed to provide sufficient power to

operate the equipment on the aircraft. These Hydrogen fuel cells are small in size, and only weigh

3.5kg when fully hydrated. The Aeropak generator needs to be replaced after 500 hours of

continuous use, sufficient for at least 250 flights (based on a standard mission lasting for 2 hours)

before needing to be replaced. Using the Type II fuel cartridge one of these systems could supply

the necessary power to the aircraft for at least 10 hours. This can be seen in(Horizon, 2010).

To deliver the power generated to the various parts of the aircraft all of the elements need to be

connected to the power source, however connecting them directly to the fuel cell would mean that

if one element fails it could draw too much power and cause the whole power system to fail. To



avoid this microprocessor is needed that is able to turn individual elements on and off. This is

done by using a latching switching circuit, an example of this is shown in Figure 40.

InputVoltage

OutputVoltage

+10 V

0 V

CommandSignal

Figure 40: Power Switch with Safety Cut off

The circuit in Figure 40 not only allows the microprocessor to turn individual elements on and

off, but if one of the components tries to draw too much power then it will cause the voltage on

the transistors bias pins to fall, at a certain point (set by bias resistors) the transistors will switch

off, which will then cut the power to the element turning it off before any damage can be done.

There also needs to be a power regulation system to make sure that the voltage in the aircraft is

safe, and to ensure that each element is supplied with the correct voltage. There are several ways

to do this: regulating the voltage at each element on the aircraft, or using a central power regulator

that supplies a regulated bus to the aircraft which each element can connect to. The central power

regulating method is safer as none of the elements have direct access to the fuel cell, meaning that

they cannot drop the entire power in one unit allowing the aircraft to continue operating even if

one element fails.

21 Ground Control Station

By making the MedEvac UAV mostly autonomous, the ground control station can be simplified

compared to other UAV control stations such as the ground control station used by the Predator

UAV. This aircraft would need two control computers one for the pilot to control the flight of the

aircraft and one for a medic to control all of the medical equipment on board the UAV.

As most of the control operations are carried out on board the UAV, the ground control stations

can simply be a modified laptop connected to a satellite communication system. Such as the (L-3

Unmanned Systems, 2010) Ground SATCOM system which can be connected to a laptop to

communicate with the UAV for a small and mobile ground station that could be placed inside

existing building such as field hospitals or Forward Operating Bases. If the ground station is to be

located in a building with an existing satellite communication system, then the computer to

control the UAV can be connected to an existing satellite connection and the information passed

into the control computers for this aircraft.



21.1 Pilot Control Station

For the pilot control computer all that is needed is a video feed from the front facing camera on

the‎UAV‎and‎a‎set‎of‎sensor‎read‎outs‎showing‎the‎UAV’s‎position‎and‎orientation similar to the

screen shown in Figure 41.

Figure 41: Draganfly Heads-up Video Screen (www.draganfly.com)

Figure 41 shows‎how‎all‎of‎the‎information‎about‎the‎aircraft’s‎sensors‎can‎be‎shown‎along‎with‎a‎

live video feed allowing the ground controller to remotely fly the aircraft if needed.

The pilot also needs to be able to switch to a map screen during flight. When landing the front

facing camera feed can be swapped to show the data produced by the LiDAR sensor. This is to

make sure that the ground controller has an accurate image of the landing site in 3D to make the

best possible decision on where to land the aircraft. When the UAV is on the ground the video

feed needs to switch to the inner-cabin video feed so the pilot can see what is going on in the

patient cabin and when it is safe to lift off.

There will also need to be a joystick to manually control the UAV in case the on board computer

fails, or for unusual operations which cannot be simply programmed into the UAV using the

normal procedures. To fly the UAV to a specific location the pilot simply needs to put down a

waypoint on the map and then specify whether the UAV has to land or simply fly to the waypoint.

This will then be sent to the UAV which will work out how the UAV needs to move to reach this

waypoint.

21.2 Medic Control Station

Similar to the Pilot Control Station all that is needed is a modified laptop and a joy stick. The

joystick is needed to control the robotic arm. The laptop has to be able to show the feed from the

cameras inside the UAV one at a time switching when commanded by the operator. There also

has to be buttons to operate the various pieces of medical equipment on board. When one of the

pieces of equipment is requesting authorisation a pop up will be displayed on the screen of the

control station.

A similar screen as shown in Figure 41 will be shown on the Medics terminal but instead of the

flight dials the status of the medical sensors will be shown. This would enable the ground medic

http://www.draganfly.com/



to see the status of all of the medical equipment on the UAV along with the video feed from one

of the on board video systems either: the cabin view, the robot camera or the thermal imaging

camera feed. This would enable the medic to monitor the patient’s‎health‎and‎make‎sure‎that‎the‎

patient is not suffering more than necessary.

For the medics terminal there also needs to be a microphone and speaker to enable the medic to

talk to and listen to either the patient or the medic at the pickup location. All of this equipment

needs to be placed in a single case so that it is easy to move around when needed. Therefore the

control computer would look similar to the computer shown in Figure 42.

Figure 42: UAV Ground Station Terminal (www.armedforces-int.com/article/mini-

unmanned-aerial-vehicle.html)

Figure 42 shows a rugged laptop with a joystick and control pad contained within a shockproof

case; this means that the components would be protected from shock and damage when the

terminal is being shipped. With all of the equipment inside one case the whole terminal could be

moved quickly as needed, including shipping the terminal out to the battlefield.

22 Environmental Control

To ensure that the patient cabin within the aircraft remains at a constant temperature, an

environmental control system is needed.

Commonly on aircraft a device called an Air Cycle Machine is used as the turbine used to power

the aircraft can be used to also power the environmental control system without needing another

heavy compressor system like in traditional air conditioning units.

An air cycle machine works by taking a portion of the hot bleed air from the turbine, this air is

normally at around 150oC. This hot air is then mixed with air from outside the aircraft in a heat

exchanger and cooled (1). This cooled air is then passed into a compressor which raises the

temperature up to around 250oC (2). This heated air is then passed through another heat exchanger

to reduce the temperature again using the external air as a coolant (3). At this point the

compressed air is still warmer than the outside temperature, to cool this down the compressed air

http://www.armedforces-int.com/article/mini-unmanned-aerial-vehicle.html

http://www.armedforces-int.com/article/mini-unmanned-aerial-vehicle.html



is then passed into an expansion chamber which drops the temperature to around -20oC (4). At

this point the cooled air contains significant amounts of water vapour which can be removed by a

centrifugal turbine which separates the water vapour from the air. This cooled air can now be

mixed with a controlled amount of hot air from the turbine to produce the desired temperature (5),

which can be introduced into the patient cabin. This can be seen in Figure 43.

Figure 43: Air Cycle Machine (http://thisisecs.com/blog/2008/12/09/air-cycle/)

Air Cycle machines are compact, so for the MedEvac UAV only one would be needed to control

the temperature inside the patient cabin. A second Air Cycle Machine could be used on the

aircraft to cool a storage box down to the desired temperature for storing medication and blood

needed to carry out the operations on board the aircraft.

These Air Cycle Machines have a high performance to weight ratio and reliability which is why

most aircraft use these devices, from large passenger aircraft down to small private business

aircraft. These devices are custom built for each aircraft, therefore there is no standard unit that

could be simply plugged into the MedEvac UAV meaning that a custom unit would need to be

designed and built for this application. However due to the simplicity of the design the

development time should be short compared to the other systems on the aircraft. The proportional

valve that lets the hot air into the mixing chamber can be controlled simply by a microprocessor

with temperature sensors in the compartment where the temperature control is needed.

23 Fuel Tank Protection

The fuel tanks on the MedEvac pose a large amount of risk to the aircraft, if punctured by a bullet

or shrapnel. There are two main risks with the fuel tanks, these are: risk of the fuel leaking over

the aircraft; and the risk of the fuel exploding. These are common problems with most fuel tanks

on military vehicles giving rise to the military standard (United States Air Force (USAF), 1973)

for suppressing fuel tank explosions by placing foam or baffles inside the fuel tank.

23.1 Minimising Explosion Risks

By placing specially constructed foam inside the fuel tank the structure of the foam act as a three

dimensional fire screen that will stop fire from spreading into the fuel tank creating a chain

http://thisisecs.com/blog/2008/12/09/air-cycle/



reaction that could detonate the fuel tank. The foam also reduces the sloshing effect of the fuel

during flight making it easier to control the aircraft in flight.

There are several different types of this foam on the market to reduce the risk of fire /explosion,

being used in military vehicles, boats and racing cars for the same reasons. One such example of

this foam is called TSS Safety Foam, which can be retrofitted to existing fuel tanks. By adding

this foam to the fuel tank the total capacity of the tank is reduced by only 3%, however the risk of

the tank exploding is significantly reduced. This is shown by (TSS International BV, 2012); an

example of a converted fuel tank is shown in Figure 44.

Figure 44: TSS ProtecTank - Explosion-Suppressant Fuel Tank

The fuel is stored within the foam and slowly diffuses into the centre where it can be withdrawn

as needed. Figure 44 also has a built in Fuel level indicator that can be connected to existing

gauges and meters.

23.2 Stopping Leaks from Punctured Fuel Tanks

There are two main techniques to stop the fuel leaking when the tank has been punctured; the first

is to introduce a layer of a rubber like material to the surface of the fuel tank. This rubber coating

means that as the projectile passes through the tank the hole naturally wants to close sealing the

hole as long as the projectile is small. This rubber coating closes around the puncture quick

enough that for small projectiles very little fuel is released from the tank before the hole is sealed.

However if the projectile is too large then the rubber coating will not be able to reseal the hole left

by the projectile, therefore a second material is needed that is capable of actively resealing the

hole caused by the projectile. This is normally done by a chemical coating that when exposed to

the fuel in the tank swells sealing the hole left by the projectile. This means that much larger holes

can be sealed compared to the rubber coating. Unlike the rubber coating though this process will

take some time allowing more fuel to leak from the tank compared to the rubber coating.

Both of these can be applied to existing fuel tanks, however there will be a slight increase in the

mass of the fuel tank when these coatings are applied the amount of mass added to the tank

depends on the level of protection required. One such example of this technique is ARM-R-

COAT this is shown in (Aircraft Rubber Manufacturing Inc, 2010), where the amount of mass of

the material needed to protect against different projectiles is given.



As the main objective of this UAV is to go into situations under heavy fire, a level IV protection

is needed to try and best protect the fuel tank against the majority of projectiles and ensure that

the patient is safe inside the UAV from most projectiles up to and including a .50 calibre round

while increasing the total mass by 15.6kg/m2 according to the manufactures datasheet.

24 Defence systems

The defence systems installed in the MedEvac UAV were determined focusing on battlefield

scenarios in urban areas i.e. the UAV will be vulnerable to a range of attacks mainly from small

firearms such as bullets, rocket-propelled Grenades (RPG), anti-tank guided missiles (ATGM)

and direct fire mortars.

The defence systems implemented on the MedEvac comprises of sense and avoiding systems

(‎24.1) and basic countermeasures. Other defence systems that were considered (‎24.3 Trophy APS

Family and Add-on armour from RAFAEL) have been ignored because of their mass (200-500

kg) which affect the unit and operational cost. However, these systems can be integrated on board

if the UK mod considers that they are imperative but they require further testing in airborne

operations and selection of power plant to adjust to power requirements due to added weight.

These factors limit the level of protection to the casualty, therefore capable of protection from

attacks only when airborne at higher altitudes. It simply detects the hot zones in the battlefield and

takes a safer route to its destination while providing protection against ATGMs and heat seeking

missiles using countermeasures such as flares, chaffs and electro/optical jammers (E/O jammer).

The highest risk to the UAV and other personnel (medic and casualty) is whilst loading the

casualty onto the MedEvac but it has been assumed that other soldiers present in the field would

provide cover fire for protection.

24.1 CROSSHAIRS

CROSSHAIRS is a counter-shooter‎detection‎and‎location‎system‎comprised‎of‎Mustang’s‎radar‎

sensor which detects subsonic weapons (RPGs, ATGMs etc.) using radio waves and the

Boomerang acoustic sensor system for detecting supersonic weapons (such as bullets). It provides

a 360degree effective coverage whilst stationary and also on the move. The system also provides

real-time data on geo-location of the shooter which can be shared with other vehicles and tactical

operations centre (TOC). It also provides an interface for integration of Active Protection Systems

(APS) for threat neutralization.(England, 2009-12)



Figure 45: CROSSHAIRS counter-shooter detection and neutralization system(England,

2009-12)

24.2 Basic Countermeasures

Flares are very effective against IR (infra-red) missiles. They burn at temperatures much higher

than that of jet engine exhausts and confuse the IR sensors from seeking the actual target.

The Shock Absorber is a man-portable Active Protection System weighing only about 25 kg

developed by the Israeli Military Industries Ltd. While also being able to determine the launch

position of the threats it provides Soft Kill protection against second generation ATGMs using

directional E/O jammer.(Israeli Military Industries, Land system Division, 2012)

24.3 RAFAEL Trophy Family

The RAFAEL trophy family consists of Active Protection Systems for a range of armoured

vehicles and provide 360 degree protection from a wide range of simultaneous threats using both

Hard Kill and Soft Kill countermeasures. These systems detect, track and intercept the threat

before it reaches its target. Hard Kill countermeasures work by firing multiple explosive Formed

Penetrators (MFRP) or energetic blades while the Soft Kill counter measures jam the sensors on

the incoming threat. (RAFAEL Defense System Ltd., 2010) A List of Technical Specifications is

in the Appendix Figure 89.

25 Transportation of UAV

25.1 Air Transportation

The‎mod’s‎ RAF‎Air‎ Transportation‎ (AT)‎ fleet‎ has‎ a‎ range‎ of‎ transportation‎ aircrafts‎ that‎ can‎

deliver the MedEvac UAV to battlefield operation bases worldwide. The AT fleet comprises of



the C-17 A Globemaster III which is a heavy-lift transport aircraft for long range missions and a

range of C 130 Hercules tactical transport aircraft. Both aircrafts have a huge payload capacity

and can accommodate a range of payloads from troops to a range of wheeled or tracked combat

vehicles.

The C-17A Globemaster III is designed to operate in difficult terrain and unfavourable weather

conditions. With the ability to perform high-angled steep approaches at very low speeds and a

small turning radius on the ground, the aircraft can operate effectively in airfields and short

runways. (Royal Air Force, n.d.)

Table 10: Payload Comparison between C-17A and C 130(Boeing, n.d.)

C-17A Globemaster III C 130 Hercules Family

Payload Capacity (kg) 45,360 20,000

Range (km) 8,334 3,704

Cargo bay Length (m) 20.78 12.3 – 19.9

Loadable Height (m) 3.76 2.74

Loadable Width (m) 5.49 3.12

No. of UAVs it can contain 4-8 (5,200 – 10,400 kg) 1-2 (1,300 – 2,600 kg)

The C130 Hercules family has a much smaller payload compared to the C-17A Globemaster III

but with a range of freight sizes and can operated round the clock from unprepared to semi-

prepared surfaces.(Royal Air Force, n.d.)

25.2 Land Transportation

Figure 46: HET by OSKOSH (British Army Website, n.d.)

Heavy Equipment Transporters (HET) by OSKOSH Defence consists of an Oshkosh 1070F 8 x 8

tractor truck and a King Trailer GTS 100 seven axle semi-trailer and is capable of carrying 72

tonnes of either tanks or light armoured vehicles within a range of 300 miles at. It can have

transport 2 MedEvac UAVs on board while also towing the mobile Ground Control Station



(GTC) behind it. It delivers the equipment to its destination much quicker and in mission ready

condition.(Oshkosh Defence, n.d.)

26 Regulations

Regulations and standard documents specifically for the design and operations of the UAVS

(Unmanned Aerial Vehicle Systems) have not been fully established because of their relatively

recent emergence in battlefield applications. Therefore, the guidance documents for design and

operations of UAVS compiled by the UK mod and CAA indicate that the UAVS should meet the

same airworthiness and safety requirements to that of manned aircrafts. Thereby, requiring

compliance with current CAA and military regulations:

1. UK MOD Defence Standard 00970 – Volume 1 and 2.(Defence Standards 00970, 1999)

2. Regulatory Articles 1000-5000 series by the MAA(Military Aviation Authority, 2012)

3. THE UK APPROACH TO UNMANNED AIRCRAFT SYSTEMS -Joint Doctrine Note

2/11(Defence, 2011)

4. CAP 722 Unmanned Aerial Vehicle Operations in UK Airspace – Guidance, to allow

training operations to be carried out in the UK.(Directorate of Airspace Policy, 2002)

Some of the essential design and operation aspects demanded by the regulations and UAV

guidance documents (discussed below) have been considered in the design of the MedEvac UAV.

26.1 Training Requirements

Additional training, required qualifications and knowledge necessary to operate the UAVS should

be outlined in the (Flight) Operations Manual.(Directorate of Airspace Policy, 2002) The

following aspects for MedEvac UAV have been discussed in detail in relevant sections.

Training requirements for Medical personnel and operation of equipment section ‎48.

Communication Procedures, section ‎19.

Information of Flight Critical Systems.

UAV flight information, section ‎9.

26.2 Sense and Avoid Criteria

UAVS are required to have reliable sense and avoid systems to be allowed to operate in

unsegregated airspace. Currently, range of parameters such as specific distances, or time factors

by which a UAV should avoid other airborne objects have yet to be established. Nonetheless, the

CAA has provided guidance on factors that need to be considered for the development of Sense

and avoid systems.(Directorate of Airspace Policy, 2002)

26.3 Redundant Engines

There are no specific statements that require aircrafts to have redundant engines. However, the

aircraft (either single or twin engine) must be able to perform controlled landing manoeuvres in

case of an engine failure. This is inevitable specially when operating over populated areas. So, a



twin engine configuration with a single drive shaft that powers both fans was selected because

ducted fans rotors do not auto rotate like helicopters for controlled landing. (MAA - Military

Aviation Authority, 2010)

26.4 Emergency Landings Procedures

There are well established landing procedures and control manoeuvres for both single and twin

engine fixed wing airplanes and rotor crafts. Since, the ducted fan MedEvac UAV design has

novel control manoeuvres and flight performance it is imperative that its emergency landing

procedures and manoeuvres are provided. See Section ‎13.

In case a fan failure occurs rather than an engine failure, the UAV will not be able to carry out any

of the operations mentioned for a safe landing. Therefore, the UAV can implement the steerable

parachute controlled by GPS that current UAVS use for a safe landing approach while airbags can

be deployed to reduce the impact on the aircraft due the landing.(Rogers, 1999)

27 Casualty Movement

One of the main purposes of the MedEvac UAV is to transport casualties from the battlefield to a

safe place where they can receive specialist medical treatment. This may mean that they are not

taken directly to a field hospital, but to a safer space where they can be further transported by a

manned vehicle. Therefore, due to its current use in the military, the NATO stretcher, Figure 47,

was chosen to be utilised in the design of the MedEvac. It has the benefits of being a lightweight

stretcher, able to fold down to the size of a rucksack making it easy to be carried by a soldier and

most military emergency vehicles and field hospitals are equipped to accommodate the NATO

stretcher. Although, if the casualty has sustained a spinal injury a spinal board is able to give the

additional support required, the use of multiple stretchers is outweighed by the damage that can be

caused by moving a casualty between stretchers; i.e. it is highly likely that the casualty will be

placed onto a NATO stretcher in the first instance, therefore could be an increased risk of adding

severity‎ to‎ the‎ casualty’s‎ injuries‎ by‎moving‎ them‎ onto‎ different‎ stretchers, especially if other

medical vehicles are not able to secure other types of stretchers. A NATO stretcher shall be

carried on board the MedEvac to replace the one used by the soldier.



Figure 47: The NATO Stretcher (Nodin Aviation AS, 2012)

This type of stretcher would normally require at least two people to carry it. However, since it

would be beneficial to assume only one additional soldier will be on the ground with the casualty,

another method for moving the casualty on the stretcher to the MedEvac will be required. In the

Inception report (Wood, et al., 2012), the Roadless Stretcher was considered, which utilises tracks

on one end of the stretcher and handles at the opposite end so the soldier could push the casualty

along. Applying this design, it was decided to carry on board the MedEvac wheels capable of

being clamped over the handles on one end of the NATO stretcher, allowing one soldier to push

the casualty onto the UAV. The clamp that could be used is similar to that used in the building of

scaffolding. It uses a small nut and threaded bar to clamp the poles of the scaffolding together.

This small nut would be tightened by hand to increase the grip of the clamp over the handle of the

stretcher as portrayed in Figure 48. The wheels used would need to be operable over a variety of

terrains. The wheels to attach to the stretcher will be kept separate, i.e. not attached to a common

axle, since the diameter of the stretcher will alter depending upon the build of the casualty on the

stretcher. Further research would be required to determine the most appropriate height the wheels

should raise the stretcher to ensure the patient is not raised to a high angle and the soldier can

comfortable push the stretcher.

Figure 48: Arrangement for the attachment of wheels to the handles of the NATO stretcher

(Scaffolding Direct, 2011)

To place the casualty inside the MedEvac, a platform will slide out from the casualty

compartment. The casualty will then be pushed onto the platform, via a ramp, length ways. This

Stretcher Handle

Wheel Axle

http://images.scaffolding-direct.co.uk/large-299-PRDB.jpg



means minimal space is required for loading the casualty, keeping the footprint of the UAV low,

which is a requirement in the specification ‎46.3.

Since the NATO stretcher is only a cloth supporting the casualty, one concern is if the casualty

has sustained a spinal injury, no stabilisation of the spine is given. Therefore, the floor of the

MedEvac shall be flat and hard to give the necessary support. It will be necessary to support the

head and neck of the casualty during transport to reduce the possibility of secondary cervical

spinal damage (James, et al., 2004).

28 Initial preliminary research (Battlefield injuries)

It is important to specify which medical interventions to incorporate within the MedEvac UAV

this will be based upon the likely injuries which will be encountered in an urban battlefield

environment. Research was done into common battlefield injuries, data was taken from previous

conflicts, data on the type of injuries and the anatomical region of the injuries from the Vietnam,

World War I, II and Iraq and Afghanistan conflicts (2002-2006) was collected and a decision on

which treatments to focus on was made based on the most frequently occurring injuries and the

severity of these injuries.

Table 11: Injury likelihood and severity chart data from (Dougherty & Mohrle,

2009)(clifford & Cloonan, n.d.)

Table 11 shows that the most common type of injuries in Iraq and Afghanistan on the battlefield

were open wounds, 50% of the injuries were open wounds, the second most frequently occurring

injury were fractures, 19% and the third most frequently occurring injury were contusions with

9.2% (Dougherty & Mohrle, 2009). Data was taken from a study performed in Iraq and

Afghanistan between 2002-2006.


Author: Dela Yohuno 28-82

The injuries highlighted in blue are injuries that would be focused on, injuries in green we will

provide some care to and injuries in the red we will not focus on treating.

Additionally more research was done on the most common region that injury occurs and the

severity of the injury sustained on that body part. The result of this research is shown in Table 12,

the data for this taken from two separate studies of the WWI, WWII and the Vietnam war, it was

found that the most common injuries were sustained in the lower extremity with 35% of soldiers

having these injuries the second most common type of injury was upper extremity injuries with

31% other common injuries were head and neck injuries 17% and chest injuries 13% (clifford &

Cloonan, n.d.). The severity of the injuries sustained was also shown in the table. With head and

neck injuries being the most fatal with 40% of these injuries being fatal in one study(clifford &

Cloonan, n.d.) and 31% in another study (Parsons, 2005). 22% of lower extremity injuries were

fatal and 10% of upper extremity injuries were fatal. As a result of this study it was decided that

we would focus on treating injuries in the blue and green. The decision of which injuries to treat

was a compromise between the likelihood of the injury occurring and probability of the soldier

surviving the injury once the injury has been sustained for example head, face and neck injuries

are in most cases fatal therefore the MedEvac would provide some level of intervention to these

injuries but will be more likely to successfully treat less fatal/severe injuries such as chest injuries

or upper/ lower extremity injuries.

Table 12: Anatomical Region of Injury likelihood and severity

28.1 Choosing the injuries to treat

After the preliminary research into the likely injuries that will need to be treated on the battlefield

a table was drawn that had listed each common injury and how we plan to diagnose, treat the

injury as well as the equipment needed to provide treatment. A copy of this can be found in



section ‎47. The list of injuries we plan on treating is listed in the left hand column, they include:

Open wounds, contusions, fractures, Pneumothorax, Burns, Dislocations, Strains and Sprains and

Amputations. The table details potential issues with each treatment in the context of treating the

casualty using an unmanned vehicle without the assistance of medic and also the problem of

operating in a hostile urban environment. Automation of the treatment would be one solution in

overcoming the issue of needing continuous medical assistance, in the table it is shown whether or

not we could automate each treatment. After considering the likelihood of encountering the injury

and the potential issues in the treatment of each injury a decision was made whether the MedEvac

was going to provide treatment for the injury and how we were going to treat each injury this is

shown‎in‎‘treat?’‎column,‎the‎rows‎highlighted‎in‎green‎we‎would‎focus‎on‎providing‎treatment‎

for whereas the yellow rows the MedEvac would only provide some treatment to an the red rows

we would not be treated.

29 Adapting Medical treatments and diagnostics for the UAV

There were numerous problems in designing, creating treatments for an unmanned aerial vehicle

where there is minimal contact with the medic during air transit. As a result of the complications

which arise, it is not possible to incorporate all the treatments, it was decided not to incorporate

invasive airway management procedures during transit such as jaw thrusts or endotracheal tubes

as‎there‎is‎some‎risk‎associated‎with‎them‎and‎a‎chance‎that‎the‎patient’s‎condition‎can‎be‎made‎

worse. Similarly treating nerve injuries without medic to supervise the treatment will result in

further damage to the injured patient due to the fragile nature of nerves. It was initially proposed

that a x- ray machine should be used in the MedEvac for diagnostic screening for fractured bones

however a suitable portable x-ray machine was not found for the UAV, the weight and the power

requirements of the x-ray machine were reasons for not including the x-ray machine additionally

x-ray machine could cause interference with electronic equipment.

29.1 Deciding on Medical treatments and diagnostics

One of the main spec points of the MedEvac UAV was that treatment should be administered

quickly with the aid of the standard NATO stretcher, the main priority of the UAV is to provide

some level of intervention to the casualty, to stabilize the patient and transport the patient to a

medical field hospital as soon as possible, time on the ground should be minimized, as a result

treatments have had to be modified, and adapted to suit rapid treatment and evacuation of

deployment zone. For instance for treatment of fractures, vacuum splinting has been favoured in

place of Sagar- traction splints. Vacuum splints are easy and quickly applied to the casualty for

immobilisation of the patients injured limbs they can be applied by 1 medic whilst traction splints

require 2 medics. CPR treatment was adapted for rapid treatment by semi – automating the

treatment using automatic chest compression equipment – Autopulse™,‎ ventilator‎ and‎ AED‎

Defibrillator which has an inbuilt algorithm to guide the medic through the CPR procedure. Flow



charts were developed to link the 3 systems for effective and quick delivery of CPR during transit.

Time is spent on the ground primarily attaching the equipment to the patient which is a quick

process. Open chest wounds caused by penetrating trauma such as bullets, shrapnel and knives

can cause lung issues and breathing problems the focus in treating this is to stabilise the patient

stop further complications due to the injury such as pneumothorax, tension pneumothorax caused

by air in the pleural cavity which will make it difficult for the patient to breath. An easy way to do

this is to apply the Bolin chest seal this can be done quickly by the medic and diagnosed by

cameras inside the MedEvac. Airway management and oxygen therapy can be administered

quickly provided the medic has inserted the nasophyneal airway to the casualty in case of a

blocked airway air can be given to the patient through an oxygen mask via the ventilator.

30 Casualty Diagnostics

Since no medic will be aboard the MedEvac UAV, patient diagnostics will play a vital role in

ensuring the correct treatment is given to the casualty. Non-invasive diagnostics have the

advantages of minimising the risk transmission of infections and few complications (Northrop,

2002). Diagnostic equipment will be applied to every casualty that is transported via the

MedEvac UAV. If the equipment is inoperable or producing poor signals, spare equipment will

be kept inside the casualty compartment. However, it will be at the discretion of the soldier on

the ground with the casualty and the ground station medic as to whether the UAV can take off

with the diagnostic equipment inoperable. The balance between fast transport to the field hospital

for expert treatment or spending time to ensure their condition can be monitored will have to be

made.

30.1 Pulse Oximetry

Pulse oximetry (SpO2) is a continuous, non-invasive‎ procedure‎ to‎ measure‎ the‎ “percentage‎ of‎

haemoglobin that is oxygen saturated”‎ (Borton, 2010), which is used to assess and monitor the

respiratory status of a casualty (Fernandez, et al., 2007). For a healthy person, the reading should

be between 95% and 100%. A low oxygen alarm default setting is at 90% since below this the

oxyhaemoglobin dissociation curve rapidly increases as the partial pressure of oxygen diminishes

(Borton, 2010). The pulse oximeter can be used to measure the amount of oxygen the casualty

requires to return the saturation level to at least 90%, at which point the oxygen can be stopped or

the rate reduced, which will avoid wasting oxygen (Borton, 2010).

The pulse oximeter, typically placed on a finger, ear lobe or toe, operates by applying two light

emitting diodes, one radiating red light and the other infrared light, on an area of the body where

there‎is‎“good‎local‎blood‎flow”‎(Fernandez, et al., 2007). A detector on the opposite side of the

sensor receives the information, which is then sent to a signal processing unit to calculate the

oxygen saturation in the blood (Fernandez, et al., 2007).‎‎“The‎amount‎of‎light‎absorbed‎at‎each‎

frequency is recorded and compared to compute the oxygen saturation. This measurement is



directly related to the partial pressure of oxygen in haemoglobin which determines how well

oxygen is delivered to cell tissues‎in‎the‎body”‎(Wendelken, 2004).

Pulse‎oximeters‎may‎lose‎accuracy‎or‎have‎‘drop-out’‎readings‎due‎to‎movement;‎low‎blood‎flow‎

due to low body temperature; sensor adherence (Fernandez, et al., 2007). Another type of pulse

oximeter can be placed on the forehead, which would improve accuracy and reliability due to the

effects of movement, as depicted in Figure 49 (Fernandez, et al., 2007). The forehead pulse

oximeter is a reflectance sensor, whereby instead of having the emitter and detector on opposing

sides of the application area; they are adjacent (Fernandez, et al., 2007).

Figure 49: OxiMax Max-Fast Forehead Sensor (Nellcor Puritan Bennett LLC, 2013)

In a report comparing the traditional pulse oximeter to the forehead sensor, it was found that the

forehead sensor tracked (SpO2) with increased accuracy due to the tissue blood flow in the

forehead being less affected by thermoregulatory vasoconstriction (blood vessels closing to

conserve the heat of the body) compared to peripheral sites (Fernandez, et al., 2007). It also

appears to respond faster to changes in oxygen saturation than traditional methods (Shelley, et al.,

2005). However the forehead sensor requires pressure to ensure complex waveforms are not

produced (Shelley, et al., 2005).

The Max-Fast forehead sensor produced by OxiMax contains a chip inside the sensor which

contains the calibration information and specific operating characteristics (Nellcor Technical

Staff, 2011). The monitor displaying the information can also display trouble shooting tips to

ensure correct use of the equipment, such as reposition sensor; warm application site; clean sensor

site; secure the cable or bandage the assembly (Nellcor Technical Staff, 2011).

Errors may arise with pulse oximetry readings since the sensors are unable to differentiate

between different types of haemoglobin; environmental interference such as vibration; cold skin;

the use of intravascular dyes (Borton, 2010).

Due to the possibility of amputation of limbs, it will be more beneficial to utilise the forehead

pulse oximetry sensor to monitor the casualty whilst on board the MedEvac UAV. Also since it is

less sensitive to movement and thermoregulatory vasoconstriction, the reading will be more

accurate and reliable than traditional pulse oximetry methods. One issue could be from external

javascript:ViewImage(246, '')



vibrations of the UAV which could affect the sensor. The additional pressure required across the

sensor could come from a securing strap inside the aircraft. The forehead sensors are can be used

for up to 2 days with regular checks of the application site (Nellcor Technical Staff, 2011). The

flowchart for the application of the pulse oximeter can be found in Figure 98.

30.2 Blood Pressure

Blood pressure (BP) is another non-invasive diagnostic procedure which will be used to identify if

the casualty is in shock or has a sucking chest wound. Traditionally to measure the blood

pressure of a patient, a sphygmomanometer is used (Northrop, 2002). This is a cuff which is

wrapped around the upper arm; a bladder inside the cuff is inflated to exert a pressure on the

upper arm, above the pressure required to collapse the brachial artery (Northrop, 2002). The

pressures of the tissues in the upper arm are assumed to be the same as the air pressure inside the

cuff (Northrop, 2002). The cuff pressure is then slowly released through a valve at 2 mm Hg/sec

(Northrop, 2002). A stethoscope is then used to listen for the first of what is known as the

korotkoff‎sounds.‎‎The‎systolic‎BP‎is‎when‎a‎‘thump’‎is‎sounded‎through‎the‎stethoscope,‎when‎

the‎ “upper‎ artery‎ forces‎ the‎ artery‎ open‎ momentarily‎ allowing‎ a‎ bolus‎ of‎ blood‎ to‎ flow”‎

(Northrop, 2002).‎‎The‎‘thumps’‎sound‎periodically‎but‎gradually‎fade‎away‎as‎the‎pressure‎inside‎

the cuff reduces. The disappearance of this sound is the diastolic BP, when blood flow returns to

normal (Northrop, 2002). Issues associated with this method of obtaining BP readings are it is not

taken in a beat by beat manner, not dynamic; takes around 1 minute to take a measurement;

constant use of the pressure cuff on one arm may decrease the accuracy of the readings by

blocking the venous return from the lower part of that arm and it is possible to miss the systolic

BP (underestimated by 5-15 mm Hg) and the diastolic pressure (overestimated by 10-20 mm Hg)

due to the periodic events (Northrop, 2002). Errors may also occur if a small cuff is used on a

large arm, since the pressure is concentrated to a point instead of evenly distributed around the

arm (Northrop, 2002). The only advancement in the method of obtaining the blood pressure is to

automate the procedure.

An adhesive, disposable blood pressure patch which operates in a similar method to a pulse

oximeter is currently undergoing clinical trials is portrayed in Figure 50. Red and infrared LEDs

are‎used‎to‎irradiate‎an‎artery‎lying‎below‎the‎patch‎which‎generates‎an‎optical‎signal‎and‎a‎“horse‎

shoe-shaped metal electrode surrounds these optical components and generates an electrical

waveform”‎ (Banet, 2005). A processing module determines the systolic and diastolic pressures

from the electrical and optical waveforms, which is sent to a wireless component (Banet, 2005).

The change in the volume of blood changes the amount of the light the blood cells absorb and

transmit (Banet, 2005). An electrical signal is transmitted from the heart to the BP patch almost

immediately after a heartbeat. There is a time delay between the electrical and optical signals

which correlates to the systolic and diastolic blood pressure (Banet, 2005). Advantages of this

method are it increases the accuracy of BP measurement by being continuous; is cuffless; and



does not require specialist communication devices (Banet, 2005). It can also be programmed to

calculate heart rate and blood oxygen saturation.

Figure 50: The continuous measurement blood pressure patch (Medgadget LLC, 2012)

The application of the blood pressure patch to monitor the blood pressure of the casualty whilst in

the MedEvac will be much easier than applying a pressure cuff. It is also smaller and lighter than

the traditional equipment utilised. Although the patch was designed to monitor the blood pressure

of someone during their daily tasks, it could be most beneficial in this application. Since the

patch is not yet commercially available, the cost is unknown. The flowchart for the application of

the blood pressure patch can be found in Figure 99.

31 Insertion of a Line for injection of fluids

In emergency situations, immediate access may be required for the administration of vital drugs

and‎fluids‎into‎the‎casualty’s‎circulation‎to‎aid‎their‎recovery.‎‎Traditionally‎an‎intravenous‎(IV)‎

line is inserted into the vein of the casualty; however there are several cases where this method

can be inappropriate. The most common reasons are that a vein cannot be found or the procedure

is too time consuming (Wayne, 2009). An alternative procedure is to insert a hollow needle into

the bone marrow of the casualty. This is known as intraosseous (IO). It was first widely used

during the Second World War; however advancements have since been made to assist in the

application (Wayne, 2009). Research suggests that drugs and fluids are absorbed into the

casualty’s‎blood stream as quickly as if a central intravenous line was used and faster than if a

peripheral intravenous line was inserted (Wayne, 2009). Some situations where IV access is

urgently required but most difficult to administer include trauma, cardiac arrest, profound shock,

haemodynamic instability, overwhelming sepsis, severe respiratory distress, severe burns, severe

agitation, severe dehydration or toxic conditions where an antidote is urgently required (Wayne,

2009). Many of these conditions could be seen within the battle zone within which the MedEvac



will operate. The use of IO will also be beneficial on board the MedEvac due to the type of

trauma that will be encountered, the need for rapid insertion of drugs, fluids and blood and the

evacuation method (Harcke, et al., 2001).

Complications‎associated‎with‎the‎insertion‎of‎the‎IO‎line‎are‎“extravasations‎into‎the‎soft‎tissues‎

surrounding the insertion site; dislodgement of the needle; embolism; compartment syndrome;

fracture or chipping of the bone during insertion; pain related to the infusion of drugs/fluids;

infection/osteomyelitis”‎ (Resuscitation Council (UK), 2011). Contraindications (reasons as to

why‎a‎medical‎procedure‎ is‎ inadvisable)‎ ‎ include‎“fracture‎in‎ the‎ targeted‎bone‎proximal‎ to‎ the‎

insertion site; recent IO in the same limb (past 24 – 48 hours); signs of infections at insertion site;

inability to locate landmarks‎ or‎ excessive‎ tissue”‎ (Resuscitation Council (UK), 2011). The

maximum time an IO line should be left in position is 24 hours (Resuscitation Council (UK),

2011); therefore if one is applied within the MedEvac, once the casualty has been admitted into

the field hospital, it should be replaced with an intravenous central line.

Common insertion sites for IO are the proximal tibia, proximal humerous or the sternum (Wayne,

2009). US Military medics are currently trained to insert an IO line into the sternum in most

severe situations (Harcke, et al., 2001). There are currently three main devices, pictured in Figure

51, used to insert the IO line; each has a specific site for operation. EZ-IO is a reusable, battery

operated power drill; the depth of insertion is controlled by the operator; it can be used in the

proximal tibia, distal tibia or proximal humerous (Resuscitation Council (UK), 2011). This

device will not be used on the MedEvac since it is the largest of the three devices; needs

assembling prior to use and is more difficult to remove the cannula (Day, 2011). The Bone

Injection Gun (BIG) is a disposable, spring loaded injection gun which can also be used in the

proximal tibia and humorous however the depth is set prior to insertion (Resuscitation Council

(UK), 2011). This device is small and compact so can easily be stored (Day, 2011). The third

type is known as FAST, another small, compact device with automatic depth control; however it

can only be used in the sternum. It utilises stabilizer points to assist with the insertion of the

cannula. A target patch is also supplied to ensure the correct insertion site is used. By inserting

the cannula in the sternum, it avoids sites where lifesaving interventions are applied.



Figure 51: The Intraosseous Devices, EZ-IO, BIG and FAST respectively (Day, 2011)

In the report by (Harcke, et al., 2001) a sample of consecutive deaths in theatre were examined

where a tibial IO was placed and a 95% success rate of correct positioning of the IO needle was

found. In another report by (Reades, et al., 2011) comparing the effectiveness between IO and IV,

“frequency‎ of‎ first‎ attempt‎ success‎ at‎ the‎ tibial‎ intraosseous‎ route‎ exceeded‎ that‎ of‎ both‎ the‎

humeral IO and peripheral IV routes by greater than 40%. Time to initial needle placement was

decreased and needle dislodgements occurred less often when the tibial intraosseous route was

used‎for‎initial‎vascular‎access”.‎‎

Pain associated with the insertion of fluids or drugs into the casualty through an IO line has been

said to be similar to the associate pain through a central line (Wayne, 2009). Time to insert an IO

line much faster than IV line, which is important since it will be the soldier with the casualty that

will have to insert the IO line, and since the time the UAV is on the ground needs to be

minimised, IO is a better route than IV.

An IO line will be required for any soldier with severe blood loss, requiring fluid resuscitation,

pain relief or if they are unconscious. For other injuries cases it will be recommended that an IO

line‎is‎inserted‎since‎the‎casualty’s‎condition‎may‎worsen‎during‎the‎flight,‎however‎it‎will‎not‎be‎

compulsory if the casualty strongly objects and only has a minor injury. The only IO devices that

will be utilised within the MedEvac will be the BIG and FAST since they are easy to store,

require no assembly prior to use and are disposable, reducing the spread of infection. Although

medics are already trained in the insertion of an IO line in the sternum of a casualty, it will be

required that all soldiers are trained in the insertion of an IO line using the BIG and FAST

devices. It will be at the discretion of the soldier with the casualty as to which method they use,

although the BIG cannula is small and so can be easily knocked if it is not noticed. The flowchart

for the insertion of the intraosseous cannula can be found in Figure 100.

32 Blood Transfusion

The typical wounds found within the military can lead to severe blood loss. Although blood

clotting agents will be used to slow down the blood loss, it may be necessary to offer a blood

transfusion if excessive amounts of blood is lost and to reduce the possibility of the casualty going

into shock.



Each person belongs to a specific blood group; A, B, AB or O (National Heart Lung and Blood

Institute, 2012). These groups are further divided into Rh-positive and Rh-negative (National

Heart Lung and Blood Institute, 2012). For blood transfusion, the blood type must be compatible

with‎the‎blood‎group‎of‎the‎casualty.‎‎It‎is‎beneficial‎if‎the‎casualty’s‎blood‎can‎be‎tested‎to‎ensure‎

a compatible blood type is transfused, however in the case of the MedEvac UAV, it will not be

possible to identify and obtain a blood match unless it is known prior to the UAV taking off.

However, almost everyone can accept type O blood (National Heart Lung and Blood Institute,

2012). Also, those with Rh-positive blood can accept both Rh-positive and Rh-negative blood,

but those with Rh-negative blood are only compatible with this type (National Heart Lung and

Blood Institute, 2012). Therefore the type of blood that will be transported within the MedEvac

will be of type O Rh-negative.

Blood is made up of individual parts; each has a specific role to play in a transfusion. Blood can

be transfused as a whole or in its individual parts. Red blood cells are transfused if the casualty

has lost a lot of blood (National Heart Lung and Blood Institute, 2012). Therefore, this will be

required in the MedEvac. Red blood cells carry oxygen to the lungs and other organs and remove

carbon dioxide (National Heart Lung and Blood Institute, 2012). Therefore a reduction in the

number of red blood cells can be fatal. Platelets help the blood to clot to stop bleeding, both

internally and externally (National Heart Lung and Blood Institute, 2012). There are other

methods being utilised on board the MedEvac to help external wounds to clot, therefore platelets

will not be required. Plasma transfusions may be required if the casualty has suffered severe

burns or a severe infection. It contains proteins, clotting factors, hormones, vitamins, cholesterol,

sugar, sodium, potassium, calcium etc. (National Heart Lung and Blood Institute, 2012).

There are strict quality control procedures which must be adhered to when obtaining blood from a

donor, the transportation and storage of blood and the transfusion into the casualty (Overfield, et

al., 2008). Standards and regulations must also be followed for the processing of the components

within blood (Overfield, et al., 2008). One procedure that must be followed is the traceability of

the blood (Overfield, et al., 2008). Red blood cells must be stored at 4-6 oC which is cold enough

to kill most types of bacteria. However there are still some bacteria that can grow if the blood is

removed from the refrigerator and begins to warm. Therefore a transfusion of the red blood cells

must start within 30 minutes and be completed within 4 hours of removing from the refrigerator

(Overfield, et al., 2008). Red blood cells have a shelf life of 35-42 days, since the oxygen

carrying capacity decreases over time (Overfield, et al., 2008). However, often blood bags have

to be opened, to remove plasma or for the attachment of leucocyte depletion filter, which means

that the blood has to be used within 12 hours being stored between 4-6 oC (Overfield, et al.,

2008).

There are risks associated with blood transfusions; some are visible almost immediately however

some can take hours to develop. These risks include allergic reaction; virus or infectious disease



carried in the donor blood (it is screened for HIV, Hepatitis B, Hepatitis C and Human T-cell

Lyphotropic virus); fever; iron overload; lung injury; acute immune haemolytic reaction, the body

attacks the new blood cells usually because the blood is‎not‎compatible‎with‎the‎casualty’s‎blood‎

type; delayed immune haemolytic reaction, a delayed reaction to the previous; graft-versus-host

disease,‎ the‎white‎ blood‎ cells‎ attack‎ he‎ patient’s‎ body‎ tissue‎ (National Heart Lung and Blood

Institute, 2012). The temperature of the blood and speed of the transfusion has to be monitored

since if it is too cold and too fast there is a risk of the casualty developing hypothermia or cardiac

arrest. A heater will be required to heat the blood up to 35 oC before entering the body, however

if the blood is transfused slowly, the blood can be cooler than this (Lippincott, et al., 2008). One

unit is the same as one bag of blood which can be transfused between 1-4 hours; therefore only

one bag of blood would be required on board the MedEvac.

In‎ compliance‎ with‎ the‎ British‎ Standard‎ regulation‎ for‎ ‘Electrically‎ Operated‎ Blood‎ Storage‎

Refrigerators’,‎the‎refrigerator‎must‎be‎of‎a‎type‎1;‎“refrigerator‎fitted‎with‎a‎single refrigeration

system”;‎or‎type‎2;‎refrigerator‎fitted‎with‎two‎independent‎refrigerating‎systems”‎which‎can‎be‎

changed over in the occurrence of a failure (British Standard 4376-1, 1991). It must also have a

temperature read out and alarm system if the temperature is not maintained. Something similar to

the AcuTemp mobile refrigerator, Figure 52, will be used. This product meets the military

specifications MIL-STD and MIL-STD461E (AcuTemp, 2013). It is small and compact so will

be easy to transport within the UAV and since only one unit of blood is required per flight, other

drugs which required refrigeration could be stored also.

Figure 52: AcuTemp Mobile Refrigerator and Freezer (AcuTemp, 2013)

33 Injuries and Treatments

33.1 Occurrence

The operating conditions of the MedEvac have to be considered carefully when it comes to the

medical procedures required. The nature of the situations and the areas of operation of the

MedEvac mean that it will be dealing with specific sets of circumstances unique to military use

which will be the primary area of use of the MedEvac. This required a more in depth look at the

special requirements for an air ambulance in the military.


Author: Wasim Aslam 33-92

The types of injury and how often they occur was looked at in detail. A table detailing this

information and more was created in section ‎47. Looking at the types of injury and their

incidence as seen in (Arul Ramasamy, 2009), an investigation into the types of injury found at a

British field hospital, a better view and understanding of the requirements of the MedEvac can be

obtained.

Table 13

Diagnosis IED Mortars RPG Small

Arms

Other Total %

Open wounds 72 36 1 26 2 137 59.1

Fractures 16 3 1 14 0 34 14.7

Burns 6 0 0 0 0 6 2.6

Amputations 3 0 2 0 0 5 2.2

Contusions 0 0 0 0 1 1 0.4

Acute post-haemorrhagic anaemia 5 2 1 5 0 13 5.6

Superficial injuries 4 2 0 0 1 7 3.0

Intracranial injuries 1 1 0 1 0 3 1.3

Hearing loss 6 1 0 2 0 9 3.9

Nerve injuries 1 1 0 4 0 6 2.6

blindness, visual disturbances 2 0 0 0 0 2 0.9

Internal injury of thorax, abdomen

and pelvis

0 1 0 8 0 9 3.9

Total 116 47 5 60 4 232 100

Patients 42 18 2 20 4 86

Diagnosis per patient 2.82 2.61 2.5 3 1 2.70

What was found was that the most common type of injury was an open wound, which can be

clearly seen in Table 13 with an incidence of 59.1%. The second most common injury was found

to be fractures with an incidence of 14.7% while the remaining injury types had incidences of less

than 6%. This showed that the MedEvac will need to be able to treat open wounds and any

complications arising from them as a priority as this will be the main type of injury encountered.

The main issues arising from open wounds is blood loss, which can range from being either

insignificant or life threatening. Our main concern medically is haemorrhagic and hypovolemic

shock, which occurs if a large volume of blood, is lost from the circulatory system which can

result in decreased tissue perfusion throughout the body (a lack of oxygen and nutrients being

supplied to the cells of the body). This can be potentially fatal.



This means that the MedEvac will need to be able to stem or slow blood flow from any open

wounds as well as being able to increase or maintain the volume of fluid in the circulatory system

at a sufficient level for adequate tissue perfusion throughout the body. Other potential issues that

could arise are hypothermia and cardiac arrest due to the lack of heating provided by the

circulatory system as well as oxygen deprivation to the heart.

Most of the other injuries listed in Table 13 have a very small incidence so the benefit/case for

treating them all is limited. However for the conditions that could be potentially fatal such as

amputations, burns and internal injuries some level of care should be provided as they could prove

fatal unlike the other injuries listed.

A full list of the injuries that could occur can be seen in section ‎47 which also lists the

considerations and issues with each injury type as well as the likelihood of the injury occurring

and the severity if it did occur. Weighing up these two factors the decision was made if the

MedEvac would provide treatment for that injury or not, the decisions can be seen in the table.

The viability of the treatment options was also considered in this decision. By doing this we were

able to specify what the MedEvac should be able to do and the issues with implementing these.

33.2 Specific Injuries

33.2.1 Open wounds

Open wounds as mentioned earlier are the most common types of injury found on the battlefield

and therefore something the MedEvac needs a solution for. Open wounds can range in severity

from minor injuries such as a small cut or scrape to severe or critical injuries such as a deep cut to

an artery. It is for these moderate to severe cases that a solution is required.

As mentioned earlier the main danger from open wounds occurs due to the occurrence of shock

due to the blood loss sustained. There are many stages of shock and specific signs for each stage,

with these being shown in Table 14. Each‎stage‎is‎progressively‎worse‎with‎a‎casualty’s‎chance‎

of survival continually decreasing; as a result it is important to identify shock as early as possible.



Table 14

CLASSIFICATIONS OF HEMORRHAGIC SHOCK

Class I Class II Class III Class IV

Amount of

Blood Loss

(% total blood

volume)

<750ml

(<15%)

750-

1500ml

(15%- 30%)

1500-2000ml

(30%- 40%)

>2000ml

(>40%)

Heart rate Normal or

minimally

increased

>100 >120 >140

Pulse

(quality)

Normal Thready Thready/ very

weak

No Radial/ thready

Carotid

Capillary

Refill

Normal Delayed

(3-5 seconds)

Delayed

(>5 seconds)

Delayed

(>5 seconds)

Respiratory

Rate

Normal 20-30 30-40 >35

SBP Normal Normal Decreased

(<80 mmHg)

Greatly Decreased

(approx. 60 mmHg)

Skin Colour Pink Pale White

extremities/

Ashen Gray

White extremities/

Ashen Gray/

Cyanotic

Skin

Temperature

Cool Cool, Moist Cool

Extremities

Cold Extremities

Mental Status Normal Anxiety Fright Severe Anxiety

Confused

Lethargic

Unconscious

One of the first actions or treatments that should be carried out for an open wound is to prevent

further blood loss or slow the rate of bleeding down. For small to moderate wounds the body is

perfectly capable of doing this on its own given time however for more serious cases either the

body’s‎ own‎ defences‎ are‎ not‎ enough‎ or‎ can’t‎ take‎ effect‎ quick‎ enough.‎ In‎ this‎ case‎ pressure‎

should be applied to the area usually with a bandage or dressing in place. In the military the

standard response is to apply a bandage to the area and apply pressure until a clot forms on its

own, pressure bandages are also used in which case once the dressing is applied a self-sustained

pressure is applied to the wound. For more serious cases where an artery has been cut for example

haemostatic dressings have been used, these are dressings which promote clot growth either by

boosting‎the‎body’s‎own‎system‎or‎by‎a‎method‎independent‎of‎the‎body’s‎immune‎system.‎



The other important treatment for open wounds and more specifically shock is fluid resuscitation;

this is the replacement of lost fluid from the body. It is important for the more severe cases where

shock has occurred or the casualty is in danger of going into shock. The initial or basic type of

fluid resuscitation is to bring the volume of fluid in the circulatory system up to a sufficient level

so that it can perform its intended function of delivering oxygen to the cells of the body.

This is done by the injection of crystalloid or colloid solutions into the circulatory system both

can be used but crystalloid is the most commonly used on the battlefield because of its

effectiveness and comparatively lower price. These solutions make up the volume deficit in the

circulatory system and are also isotonic to blood meaning that they have a similar make up and

properties compared to blood plasma, this ensures that the normal fluid balance and transfer

across the arterial walls is maintained.

The use of crystalloid and colloid solutions is enough in many cases to stabilise and improve a

casualty’s‎status,‎however‎in‎the‎most‎severe‎cases‎when‎the‎casualty‎is‎in‎stage‎III‎or‎IV‎shock‎

too much blood has been lost for crystalloid and colloid solutions too be enough on their own to

stabilise‎and‎improve‎the‎patient’s‎condition.‎This‎is‎because too much red blood cells have been

lost‎ and‎ the‎ body’s‎ ability‎ to‎ transport‎ oxygen‎ has‎ been‎ severely‎ affected.‎ In‎ this‎ case‎ the‎

injection of oxygen carrying fluids is required, although much research has been carried out into

oxygen carrying blood substitutes there are no real alternatives to blood and so blood transfusions

are required if the casualty has reached stage III or IV shock.

Blood transfusions have only recently been implemented on the battlefield and in air ambulances

mainly for the storage requirements. Blood packs need to be kept frozen which was a problem on

the‎battlefield‎and‎in‎air‎ambulances.‎The‎recent‎introduction‎of‎‘golden‎hour‎boxes’‎which‎keep‎

blood packs frozen for up to 72 hours has allowed for their use mainly in battlefield hospitals.

33.2.2 Potential solutions

One potential solution/treatment that was considered was the use of the IT clamp, which was a

clamp with curved spikes along the jaw of the clamp which when applied to a wound site would

draw the wound into the clamp applying a pressure to the wound and allowing a clot to form

underneath it, Figure 53 shows the IT clamp in use. The benefits of this device were that it was

effective even on severe arterial cuts and it was very quick to apply. However its usage was

limited by its size and the location of the wounds, any wounds bigger than its 5cm length

wouldn’t‎be‎treated‎as‎effectively‎as‎possible.‎It‎would‎also‎be‎difficult to implement unmanned

as it would be difficult to accurately place and apply, while determining correct placement would

also be difficult. It could have been applied by the person on the ground but overall considering

its limited use and the difficulty in its application it was rejected.



Figure 53: The IT Clamp

Another potential solution that was considered was the use of photochemical bonding, which uses

a special dye which when exposed too light of a certain wavelength forms crosslinks which can

bond surfaces together. In practice the dye would be applied to the area of a wound and a specific

wavelength (green) of light would be applied which would activate the dye and seal the wound.

The main problem with this solution was that the technology was relatively new and had only

been proven to be effective for small and thin wounds. There was the potential to use it as an

alternative‎to‎sutures‎but‎it‎wouldn’t‎be‎viable‎for‎larger‎wounds,‎also‎for‎openly‎bleeding‎wounds‎

the application of the dye could be difficult. As a result this solution was also rejected.

Another potential solution was the use of haemostatic dressings and powders. Haemostatic

dressings are currently used in the army due to their effectiveness compared to traditional

dressings. Haemostatic agents are agents that help stop bleeding through several different

methods, they have been in use in the military for some time and have a very good record even for

very serious and life threatening wounds. There are several forms of haemostatic agent with the

most common being in powder form or as dressings impregnated with a haemostatic powder. The

haemostatic dressings tend to be used in military operations due to their ease of use; they are

usually in the form of a gauze bandage which can be unrolled and applied quickly to any wounds

either by wrapping it around the area or by packing it into the wound.

The haemostatic powders usually come in packs of a predetermined amount and can be poured

into a wound where the powder helps cause rapid clot formation. The method through which they

act‎can‎either‎be‎dependent‎upon‎the‎body’s‎natural‎clotting‎processes‎or‎independent.‎

It was decided that haemostatic agents would be used in the MedEvac to prevent further blood

loss from any wounds due to their effectiveness; they are able to form rapid clots even for arterial



bleeding, and also because of their practicality. They can be applied to any open wounds and are

relatively easy to apply.

It was decided that we would use Celox powder as our choice of haemostatic agent. It was felt

that a powder would be able to be applied much more easily in our unmanned MedEvac and the

powders offer additional advantages compared to the dressings in that they can be used to treat

penetrating trauma, such as gunshot or shrapnel wounds, which the dressings were not as effective

at treating.

Celox gauze is also part of the standard equipment for the MOD so a product from the same line

is already in use in the British military. It has been in use since 2006 so the product has been

proven‎to‎work.‎It‎also‎works‎independently‎of‎the‎body’s‎natural‎clotting‎methods‎and‎forms‎a‎

gel like clot with any blood it comes into contact with within 30 seconds. This was seen as an

advantage in the case of any radiation exposure as there would be no negative impact to the

treatment of open wounds, more detail can be found in section ‎33.2.4 .

It was decided that this was the best option and so a method to apply the powder was needed,

alongside a method to apply a pressure to the wound site. The solution can be found in section ‎43.

It was decided that the use of fluid resuscitation and blood transfusion should be implemented in

the MedEvac so a fluid delivery system was designed, which is discussed in section ‎31. A flow

diagram was also made which shows how the on board sensors would detect the presence of

shock and how the appropriate response would be decided. The flow diagram can be seen in

Figure 54, all decisions would go through the ground medic initially who would confirm the

decisions made by the system. A time limit could be placed after which the system would carry

out the action if there had been no response which could be useful in the case of a loss of

communication.

With‎ the‎fluid‎delivery‎system‎able‎ to‎deliver‎fluids‎and‎other‎drugs‎ to‎a‎patient’s‎body,‎ it‎was‎

decided that other medications would be used that could provide some benefit. The first of these

was the use of pain killers, such as morphine to provide relief to casualties who will be suffering

from severe and most likely painful injuries. Tranexamic acid was also incorporated into the

MedEvac, tranexamic acid is a drug that is used to prevent or reduce heavy bleeding. It works by

preventing the breakdown of blood clots that your body forms. This is an advantage for both

severe haemorrhaging and internal bleeding which is otherwise hard to treat or prevent. This is

because in severe injuries the immediate response is the application of fluid resuscitation to

stabilise blood volume, however this dilutes the blood and its clotting factors causing blood clots

to breakdown more easily. Tranexamic acid prevents this from happening and allows blood clots

to form quickly which is of particular use for internal bleeding.



Figure 54: Flowchart showing how shock would be treated within the MedEvac



33.2.3 Burn Injuries

Burn‎injuries‎aren’t‎very‎common‎on‎the‎battlefield as can be seen from Table 13 which showed

an incidence of 2.6%. However burn injuries have the potential to be very serious and potentially

fatal injuries. Also burn injuries are a big potential risk if chemical or radiation weapons were to

be used, more detail on radiation and chemical warfare can be found in section ‎33.2.4. This is why

potential solutions for this type of injury were considered.

Burn injuries like open wounds can range in severity from minor inconveniences to potentially

fatal wounds. The severity of the wound depends upon the thickness of the burn and the extent of

it. First degree burns are those that only involve the top layer of skin, the epidermis, and are

usually not very serious although they can be painful. The more serious types of burns are second

and third degree burns with these involving either part or all of the dermis respectively. Second

degree burns can still be painful but third degree burns are usually accompanied by a lack of pain

or feeling in the area affected as the nerves in the skin have been damaged. The most severe type

of burn is fourth degree burns which extend through the skin to the muscles and bone beneath.

The other factor affecting the severity of the wound is the surface area affected by the burn. A

burn covering more than 15% of the body will usually require some treatment however this also

depends upon the thickness of the burn.

The main concern with burn injuries is the affect it has on the vascular system at a local level.

Burns cause damage to cell structure and can cause cell death, it is in this way that it affects the

blood vessels in the area of the burn. This causes structural damage to the blood vessels and

increases their permeability resulting in fluid leakage and also increased blood viscosity. As a

result there is a fluid build-up at the site of the burn, otherwise known as an edema. This causes a

decrease in the volume of circulating blood while also increasing the resistance of blood at the site

of injury. If the burn is severe enough it can result in shock in a similar manner as that of severe

open wounds, the treatment required is the same as that mentioned earlier with the maintenance of

blood‎volume‎at‎sufficient‎levels‎for‎tissue‎perfusion.‎However‎usually‎lactated‎ringer’s‎solution‎

is enough and blood transfusions are not required, Table 15 shows the formula for determining the

right amount of fluid required for casualties suffering from burns. The extent of the fluid loss is

mainly dependent upon the surface area of the body affected with burns affecting large areas of

the body causing large widespread edema and therefore large blood volume decreases.



Table 15: Taken from (US Army, 2000)

33.2.4 Chemical and Radiation Injuries

Although chemical and radiation injuries are rarely seen in the military, radiation more so than

chemical injuries, the risk of chemical and nuclear warfare being used is taken very seriously by

the military. With more countries having access to both nuclear and chemical weapons the

potential for their use is there, this coupled with the potential for chemical and nuclear weapons to

cause large scale destruction and massive numbers of casualties means that methods to deal with

the consequences are needed. Also the very nature of chemical and nuclear weapons means that

there are risks to any personnel who either enter an area where they have been used or interact

with a casualty who has been wounded or come into contact with them. This is why it was

decided that the MedEvac should be able to deal with injuries caused by chemical and nuclear

weapons, because if a moment came were either of these were used a unmanned MedEvac would

be of great use as it would allow for quick evacuation while maintaining any casualties conditions

and it would also prevent other personnel having to be sent in and exposing themselves to

potential risks.

There are essentially 6 classes of chemical agents which describe the symptoms and effects of the

chemicals which come under its category. These are nerve, blister, blood, chocking, incapacitation

and riot control agents.

Nerve agents are an extremely potent chemical weapon and considered a major threat. They work

by inhibiting choline esterase and preventing it from hydrolysing acetylcholine, a neurotransmitter

which activates skeletal muscle and has an inhibitory affect in cardiac tissue where it slows heart

rate. Nerve agents can cause a wide range of symptoms and effects some of which include nausea;

vomiting; increased secretion by glands in the airway; convulsions; muscle fatigue and flaccidity;

a decreased heart rate and apnea (stopping of respiration). Nerve agents can come in either vapour

or liquid form and depending upon the dosage can be fatal within minutes, however there is



usually a latent period with no symptoms when contact is made with the liquid form. Treatment

for nerve agents requires rapid injection of atropine to block the effects of excess acetylcholine

alongside injection of pralidoxime chloride to reactivate cholinesterase. Diazepam can also be

administered to reduce convulsions and prevent brain damage due to seizures. Soldiers will carry

both atropine and pralidoxime chloride on them for injection if they come into contact with nerve

agents. Due to the rapid onset of symptoms and the likelihood of death it is unlikely that the

MedEvac will be able to reach and treat a casualty suffering from exposure to large amounts of

nerve agents, it is more likely that a casualty exposed to nerve agents will have already been

treated if they are still alive to be picked up by the MedEvac. The MedEvac could potentially

carry these antidotes if required and apply them through the same method as that used for

administering fluid resuscitation as mentioned in section ‎31. The other potential treatments that

could be required would be removal of any secretion through prone turning as well as the use of

automated ventilation which are mentioned in detail in ‎37.

Blister agents also known as mustard gas are a group of chemicals which primarily cause

irritation to exposed skin and the formation of blisters. It can be in either liquid or vapour form

and can affect skin through thin layers of clothing. It is quickly absorbed through the skin with

heat and moisture increasing the diffusion rate; this makes it more of an issue in hotter countries.

The main symptoms and effects of blister agents are painful blisters forming on exposed skin

along with irritation of the eyes and respiratory tract. In severe cases pulmonary edemas can form

along with airway obstruction, there can also be some neurological affects although‎ they‎aren’t‎

well understood. There are no specific therapies for blister agents, only treatments for the

symptoms. Decontamination should occur immediately after exposure or as soon as possible, this

involves washing of the eyes and skin with cool water with possible a mild soap for the skin.

Early use of CPAP ventilation as well as oxygen therapy is recommended if the respiratory tract is

affected. Blister agents unlike nerve agents have a large latent period where symptoms do not

occur which can last from between 2 to 48 hours depending upon dosage. Blister agents generally

don’t‎cause‎life‎threatening‎injuries‎unless‎a‎severe‎dose‎has‎been‎given‎in‎which‎case‎death‎can‎

occur through respiratory failure however this is a rarity. It was decided that the MedEvac would

only need to treat the effects of the agent on the airway which are covered by the use of a

ventilator, as mentioned in section ‎37, as these are the only potentially fatal injuries that could

occur as a result of blister agents and in the majority of cases of exposure a MedEvac would not

be required. However it was decided that a method to decontaminate chemical injuries would be

needed, a way to wash the patient’s skin and eyes to prevent further damage if any casualties with

chemical injuries were collected by the MedEvac.

Choking agents are another group of chemical weapons which mainly affect the lungs of

casualties by affecting the membrane between the alveoli and the capillaries. The permeability of

this membrane is affected which causes a build-up of fluid in the alveoli and lungs known as a



pulmonary edema. Choking agents generally manifest themselves as dense low hanging gases

which‎ are‎ very‎ noticeable;‎ they‎ don’t‎ have‎ an‎ immediate‎ impact‎ but‎ a‎ delayed‎ one.‎ Choking‎

agents generally cause eye and airway irritation, coughing, breathlessness, pulmonary edema and

hypoxemia (low blood oxygen levels). Again there is no specific treatment for choking agents just

of the symptoms experienced, firstly decontamination to prevent worsening of the condition as

well as to prevent contamination of others. The primary concern is the respiratory distress which

means that ventilation of the casualty is usually required; this also helps prevent and treat

hypoxia. Also the airway secretions must be allowed to be expelled either through draining it or

placing the casualty in a position so that he may expel them easily himself. Choking agents are

another delayed onset chemical and symptoms can be delayed by up to 24 hours with severe cases

having symptoms appear after 4. The MedEvac would‎ require‎ no‎ new‎ treatments‎ that‎ haven’t‎

been mentioned already, only decontamination and use of a ventilator.

Blood agents are a potentially lethal group of chemical agents which include cyanide. They work

by inhibiting aerobic metabolism in cells; this is done by inhibiting the enzyme cytochrome

oxidase which is responsible for the formation of ATP via hydrolysis of oxygen. As a result

aerobic respiration in cells comes to a stop meaning that cells have no energy for their normal

processes and eventually cell death can occur. Typical symptoms and effects include an increased

rate of breathing, feelings of weakness, nausea, muscular trembling, convulsions, decreased heart

rate and eventually cessation of a heartbeat. Blood agents have a rapid onset with symptoms

occurring as quickly as 15 seconds after exposure and death occurring within 6 to 8 minutes after

exposure for a strong dose. Casualties exposed to blood agents should be removed from the

source immediately and then offered treatment. Removal of wet clothing and cleaning of the skin

where liquid is likely to be found should be done quickly to prevent further damage or

contamination. Ventilation and 100% oxygen therapy can help to provide relief and can be

enough for the patient to recover. For severe patients specific antidotes are recommended such as

sodium nitrite which causes cyanide to attach to it over cytochrome oxidase freeing the enzyme

and allowing aerobic respiration to occur again. A sulphur donor such as sodium thiosulphate is

then administered which breaks the agent such as cyanide down into a less damaging form.

Although blood agents are extremely dangerous with severe effects on a person due to its nature

unless a high dose is administered few symptoms are experienced with their severity being

reduced. It was decided that no additional treatments or therapies would be needed to treat

patients exposed to blood agents as due to its rapid onset and the time for death to occur it is

unlikely for the MedEvac to reach that patient in time, if a patient with blood agent exposure is

picked up it is most likely that they have received antidotal treatment already and therefore are not

critical.

Incapacitation agents are a group of chemicals which affect the nervous system of a casualty, they

can cause a wide range of effects and are extremely debilitating. They suppress nerve activity



through competing with acetylcholine, the neurotransmitter. Incapacitation agents bind to the

acetylcholine binding sites at the ends of neurons which results in a reduced or lack of stimulation

of the nerve. Incapacitation agents have a wide range of symptoms and effects which include

confusion, disorientation, decreased levels of consciousness, hallucinations, impaired memory,

slurred speech and paranoia. It can also cause hyperthermia due to the reduction or failure of the

body’s‎ normal‎ temperature‎ regulation‎methods,‎ reduction‎ or‎ cessation of sweating is common

alongside vasodilation of the extremity blood vessels. Effects and symptoms can occur from

between 30 minutes to 20 hours with these being able to last up to 96 hours. Again

decontamination of the patient is required to prevent further deterioration, there is also an

antidotal treatment which can be applied called carbamate anticholinesterase physostigmine

which boosts the amount of cholinesterase at the ends of neurons. The other important

consideration is the maintenance of the‎casualty’s‎body‎ temperature‎ to‎prevent‎hyperthermia.‎ It‎

was decided that we would have a temperature controlled patient cabin to allow us to maintain a

good body temperature for the patient in this case and also due to the temperature differences at

varying altitudes. A more in depth look can be found in section ‎22. Overall the effects of

incapacitation agents are very debilitating but they are not potentially life threatening, therefore it

was decided that other than temperature control and decontamination of the patient other

treatments‎weren’t‎necessary.‎

The final group of chemical agents is riot control agents which include tear gas and are usually

used by police forces. Symptoms of riot control agents typically include irritation of the eyes,

nose‎and‎skin‎as‎well‎as‎the‎airways.‎The‎symptoms‎produced‎by‎these‎agents‎aren’t‎particularly‎

harmful and the agents are self-limiting and do not usually last for more than 15 minutes. There

aren’t‎ any‎ specific‎ treatments‎ required‎ for‎ this‎ agent‎ apart‎ from‎ perhaps‎ gentle‎ rinsing‎ and‎

washing of the eyes.

The use of nuclear weapons introduces many new concerns and problems that have to be thought

about. Not only are there the potential injuries that could occur but the scale of the injuries that

would occur if a nuclear weapon were to go off. Nuclear weapons possess large amounts of

energy and can cause widespread destruction. They have three primary methods of causing harm

which are thermal radiation, the initial blast and ionising radiation.

If a nuclear weapon is used there is likely to be a large number of casualties who have received

burn injuries due to the high temperatures caused by the explosion and the speed at which this

thermal radiation travels which allows it to cause burns at large distances from the epicentre of the

explosion. This means it is even more important that the MedEvac can treat burn injuries as

shown in section ‎33.2.3.

Another concern is the effect of the initial blast caused by the nuclear weapon. Injuries could

occur either due to the primary blast wave (direct) or due to the accompanying wind (indirect).

Direct injuries would be rare as any casualties close enough to the epicentre would most likely



receive immediately fatal injuries. Indirect injuries are to be more likely with many casualties

suffering from missile induced injuries due to the accompanying winds. As a result it is important

that‎good‎care‎is‎received‎for‎any‎serious‎open‎wounds.‎Blast‎injuries‎aren’t‎likely‎to‎cause‎any‎

potentially serious injuries on their own but may complicate the treatment of other more severe

injuries.

Ionising radiation is the major concern when it comes to nuclear weapons; this is due in part to its

prolonged effects. At the time of detonation radiation in the form of alpha, beta, gamma and

neutron radiation is present in great amounts and it can persist for large amounts of time

depending on the half-life of the nuclear materials. Although the levels of radiation decrease over

time the length of time for it to reach safe levels is usually great, this causes many problems

operationally as sending in evacuation or medical teams introduces them to the risk associated

with radiation exposure.

The main cause for concern is the damage and effect ionising radiation can have on the body of

anyone exposed to it. The extent of the damage caused is mainly down to the amounts of radiation

present or that the person is exposed to along with the time that they are exposed to it, this means

rapid evacuation is extremely important to prevent further deterioration of casualties in the field.

Radiation sickness is not usually immediately fatal but depending upon the dose death can occur

from anywhere between a few days to a few weeks after exposure. The effects of radiation

exposure and radiation sickness can be divided into three different syndromes which describe the

dosage received, the primary organ affected and which are progressive meanings that if a person

suffers from the effects of the second syndrome he also has the symptoms of the first. The

response of the body to radiation injury follows a similar pattern independent of the dosage

received and has 3 stages. There is an initial response which is generally independent of the

dosage which is followed by a latent period and finally the clinical stage which is different

dependent upon the dosage received. The initial response of the body occurs within a few hours

after exposure and generally consists of weakness, anorexia, vomiting, diarrhoea and generally

feeling unwell. This can last for up to a few hours and during this time it is difficult to determine

the dosage and severity of exposure. This is then followed by a period where there are no

symptoms which can be negligible or last up to 6 weeks dependent upon the dose received. There

are no obvious signs during this time and the patient typically feels well. The final stage known as

the clinical stage is unique dependent upon the dose received and is marked by one or more of the

three syndromes mentioned earlier.

The primary syndrome known as hematopoietic syndrome affects mainly the bone marrow of

patients by causing bone marrow depression which affects blood cell creation. This means that

there is a decrease in the number of red blood cells, white blood cells and platelets. As a result

they are more prone to infection, have a reduced or non-existent clotting response and become

prone to bleeding. Patients normally develop haemorrhaging throughout the body which coupled



with the lowered immune system of the patient can cause many difficulties. Infections become

common and are the usual cause of death with treatment usually limited to the use of antibiotics

and fluid therapy. There is a chance of recovery depending upon the ability of the bone marrow to

recover. The latent period is usually around 2 to 3 weeks.

The secondary syndrome known as gastrointestinal syndrome is caused by doses of about

1000cGy. As well as the effects seen in the hematopoietic syndrome this syndrome also affects

the gastrointestinal tract severely with severe bloody diarrhoea within 4 to 5 days. This combined

with the aforementioned symptoms results in large fluid and electrolyte losses as well as large

blood losses. Bone marrow recovery is unlikely and bone marrow depression will usually

deteriorate to a fatal level. Survival is unlikely with death occurring early unless fluid therapy is

provided to deal with the massive fluid and blood losses in which case death will usually occur

due to severe bone marrow injury.

The final syndrome is neurovascular syndrome which typically requires doses of 3000cGy. The

patient’s‎ mental‎ facilities will start to deteriorate with this taking the form of an increasing

depression which leads to a coma and eventually death. Convulsions are also frequent with ataxia

(inability to coordinate muscle movement) occurring early on. Symptoms usually occur after 5 to

6 hours without the symptoms of the previous two syndromes occurring apart from diarrhoea due

to the rapid onset of other symptoms and death. Patients are not expected to survive this syndrome

with death occurring rapidly.

Nuclear weapons introduce many issues and concerns that need to be considered and that the

MedEvac will need to be able to cope with. The first are the primary injuries which are extremely

dangerous and have the potential to cause many fatalities, the main concern here is the internal

bleeding that occurs as well as the fluid losses. There are no real methods available and practical

that the MedEvac can use to stop the bleeding unlike open wounds, however the effects caused by

it can be treated similarly by the use of fluid therapy as mentioned in section ‎33.2.1.

Unfortunately there are no real treatments that the MedEvac can provide for the patients with

neurovascular syndrome apart from treating any other injuries. Although the likelihood of patients

with burns injuries is likely to increase in the case of a nuclear weapon being used the MedEvac is

already equipped to deal with it as mentioned in section ‎33.2.3. A major concern for radiation

injuries is the effect it has on the immune system, the damage done to the bone marrow means

that wound healing is slowed in all cases with clot formation being delayed and infections

becoming a greater threat.‎Although‎there‎isn’t‎a‎direct‎solution‎or‎treatment‎for‎this‎problem‎it‎

was considered when looking at solutions for other injuries, for example one of the reasons celox

powder was used to treat open wounds was that it worked independently of the body’s‎immune‎

system‎meaning‎that‎its‎effectiveness‎wouldn’t‎be‎effected‎by‎the‎lowered‎immune‎system‎due‎to‎

radiation sickness. The main concern was the symptoms of the initial stage which will always

occur, the main concern here is the nausea and the vomiting that accompanies it. Although it



doesn’t‎seem‎an‎overly‎serious‎condition‎but‎due‎to‎the‎fact‎that‎there‎are‎no‎medics‎aboard‎and‎

the patient will be strapped into the patient cabin on their back the potential for the patient to

suffocate on their vomit is there. Therefore it was decided to provide the patient with Dolasetron,

a drug used to treat nausea and patients at risk of vomiting. Although this would reduce the

likelihood‎of‎patients‎vomiting‎ it‎wouldn’t‎eliminate‎ the‎ risk.‎Therefore‎ it‎was‎decided that the

patient platform in the patient cabin would be able to rotate 90 degrees so that the patient would

be in a position where he could freely vomit if required.

34 Fractures

Fractures are to be treated using splints, with the main aim of treatment being to treat for shock,

control haemorrhaging in the case of open or closed fractures, provide some pain relief and

immobilize the injured limb to prepare the patient for transportation. Upon arrival at the scene of

the‎ injury‎ the‎ medic‎ should‎ carry‎ out‎ an‎ assessment‎ of‎ the‎ casualty’s‎ Airway,‎ Breathing‎ and‎

circulation‎(ABC’s).‎The‎initial‎assessment‎will‎be‎common‎for‎all‎casualties‎at‎the‎scene‎of‎the‎

injury. After this initial assessment the casualty should be moved onto the standard military

NATO stretcher and transported to the patient cabin in the MedEvac. Diagnosis of the fractures

should be made by examination of the fracture site, indications of fractures include swelling,

bruising, deformity and angulation(Ian Greaves, 2011) these can be seen by the medic before

transportation or with internal cameras.

34.1 Open fractures

Open fractures are easier to diagnose than closed fractures, they feature bone exiting and

penetrating the skin and can be visibly diagnosed by the medic or cameras within the MedEvac.

In cases of open fractures a sterile dressing should be applied on the site of the injury to control

haemorrhaging, this can be done on the scene of the injury with the use of the bandages available

in‎the‎medics’‎first‎aid‎kit.‎Spare‎bandages‎are‎available‎as‎consumables‎in‎the‎MedEvac UAV. A

vacuum splint supplied by the MedEvac UAV should then be applied on the casualty to

immobilize the injured limb. The Evac- U-Splint® shown in Figure 55. The Evac-U-Splint can be

applied around the injured limb, air is removed from the splint manually or via the suction pump,

the vacuum splint forms a ridged mould around the patient’s limb for immobilization. After

immobilization the pulse and Oxygen saturation levels should be monitored using pulse oximetry

during transit. Oxygen therapy should also be given to the patient using the portable ventilator.

Additional immobilization of the neck and spine can achieve using Maimi J® cervical collar. A

flowchart of the treatment procedure for fractures is shown in Figure 101.



Figure 55: Evac-U-Splint vacuum splint for immobilisation

34.2 Closed fractures

Closed fractures are often more difficult to diagnose than open fractures. There is no penetrating

trauma in closed fractures and the rigid ends of the bones fracture site can do significant damage

to underlying tissue and blood vessels causing pain and blood loss. Although diagnosis of closed

fracture is not as easy as open fractures there are some distinguishing features of closed wounds

such as pain, swelling, tenderness, angulation of fracture site and loss of function (Ian Greaves,

2011). All of these symptoms can be observed by the medic on the ground or by cameras in the

MedEvac UAV. After the diagnosis of a closed fracture has been made the limb can be

immobilized by the Evac-U-Splint vacuum splint and be treated for shock by administering 100%

oxygen using the ventilator, the pulse and oxygen saturation levels should be monitored using the

pulse oximeter the distal pulse of the limb should also be measured. The casualty is likely to be in

pain therefore a local anaesthetic can be administered to the site fracture, the closed fracture

procedure is covered in Figure 101.

35 CPR

The main aim in CPR is to maintain breathing and circulation in a casualty who is unconscious

and without a pulse. The airway, breathing and circulation –ABC5 should be checked on arrival at

the scene of the injury. In the case of a blocked airway the airway must be opened by lifting the

chin and tilting the head. A nasopharyngeal tube can be used by the ground medic carrying a first

aid kit, nasopharyngeal tube spares can be found within the MedEvac UAV. In the case of head

and neck trauma movement in these areas can cause further harm, use of the Miami J cervical

collars can help protect the victim from further harm.

35.1 Chest compressions

Chest compressions should be started, 30 compressions should be administered at a rate of 100

compressions per minute. After 30 compressions 2 rescue breaths should be delivered this can be

done using the Autopulse® shown in Figure 56. The Autopulse is placed underneath the patient



platform and the patient will be strapped in using the lifeband as shown in Figure 66. The

Autopulse will have the ability to slide up and down underneath the patient platform so that it can

be adjusted for different patients. The lifeband is a disposable strap that tightens around the

patient thorax and will be used to secure the patient. The Autopulse is able to deliver 30

compressions after which there will be a pause for two breaths to be given to the patient using the

ventilator. One of the main disadvantages of using the Autopulse is that it can cause disruptions to

ECG monitoring and it must be paused and interrupted to avoid an ECG motion artefact and

incorrect ECG trail, the Autopulse will be paused remotely when the assessment of heart rhythm

is needed. The oxygen ventilation can be given using the ventilator after 30 compressions during

the breathing period; use of the Autopulse is detailed in Figure 102.

Figure 56: Autopulse Chest Compressions Equipment

35.2 Automatic External Defibrillator (AED)

An automatic external defibrillator will be used as part of the CPR equipment to deliver

defibrillation to patients suffering a cardiac arrest caused by heart arrhythmias, the Zoll AED

Pro® will be used to deliver defibrillation Figure 57, the AED will be connected to the patient

using CPR-D-Padz® defibrillation electrodes. The 2 electrodes are contained within a large pad

for‎2‎lead‎ECG‎monitoring‎and‎can‎be‎easily‎located‎and‎placed‎on‎the‎patient’s‎chest‎using‎the‎

crosshairs on the pads(ZOLL Medical Corporation, 2011), the pads should be placed before the

chest straps are secured. The AED is located on the floor next to the patient platform and is within

reach of the medic. The AED issues prompts for each stage of CPR, it prompts the rescuer when a

shock is advisable after monitoring the rhythm of the patient it is then up to the rescuer to press

the button and shock the patient however the shock will be administered remotely by the remote

hospital. If a shock is not advised, chest compressions will be resumed by the Autopulse, the

remote hospital will be notified during each stage of CPR occurring in the MedEvac. A flowchart

of the treatment procedure for CPR is shown in Figure 102.



Figure 57: CPR Zoll AED

36 Open chest wounds

One of the most common occurring injuries on the battlefield was open and closed chest wounds,

according to one source 13% of injuries on the battlefield are open chest wounds(clifford &

Cloonan, n.d.) As a result of knife or gunshot wounds traffic accidents and falls(Ian Greaves,

2011). Open chest wounds cause sucking chest wounds where air enters the pleural space during

inspiration through the open wound this can lead to a collapsed lung or

pneumothorax.(About.com, 2004) One solution to this would be to place a seal over the open

chest wound; this will stop air entering through the open wound site. The Bolin® chest seal

shown in Figure 58will be one solution to treat open chest wounds, one of the main benefit of the

Bolin chest seal is that air can be made to leave the pleural space, this reduces the risk and

likelihood of the collapse lung developing into a more severe case of tension pneumothorax which

can be life threatening and cause significant reductions in blood oxygen levels.(Ian Greaves,

2011). The Bolin chest seal has a triple valve design to allow air and blood to escape the pleural

space and reduce the build-up of pressure in the pleural space causing collapsed lungs. Indications

of a tension pneumothorax are uneven left and right chest movement of the chest, shortness of

breath, low blood oxygen levels and blood pressure which can be diagnosed by the ground medic,

cameras, pulse oximetry and blood pressure sensors in the MedEvac. The chest seals will be

placed as spare consumables in the MedEvac UAV. Flowcharts for the treatment of

pneumothorax, tension pneumothorax are shown in Figure 103.



Figure 58: Bolin chest seal for open chest wound

37 Airway management

Management of the casualties airway will be an essential task to be performed before the patient

is prepared and stabilized for transit to the hospital. The patient is likely to require assistance in

breathing if they are suffering from unconscious, cardiac arrest and respitory depression caused

by trauma. Additionally alternative methods in maintaining a casualties airway and breathing will

be required if the airway is blocked by blood or vomit, however suction using a portable suction

device of the upper airway can be done to remove these obstructions(Manitoba Health, 2011).

37.1 Blocked airway

In the case of a unconscious patient with a blocked airway and no breathing the head tilt

manoeuvre should be performed to open the airway, the breathing rate should then be reassessed.

If the airway is still blocked and there is injury to the mouth or clenched teeth, a naso phalyngeal

tube can be inserted in through the nostril as a passage for administering oxygen. The NPA

(Figure 59) comes as part of first aid medical kit, and can be adapted with the addition of a

medical ventilator to administer artificial oxygen and support the breathing of a patient(Manitoba

Health, 2011). The MedEvac will provide spares of the NPA. Some contraindications to the use of

the NPA tube are if there are skull and facial fractures. Additionally the chance of vomiting and

gastric distension increases.

Figure 59: Nasopharyngeal airway, medical device for airway access

In the case that casualty finds it difficult to breath due to obstruction of the airway as a result of

blood, vomit in the oral cavity a portable suction pump in the MedEvac should be used to suction,



blood vomit, the breathing should be re assessed and the supplemental oxygen should be

administered if required. Flowchart of the airway management procedure is shown in Figure 60.

The Bag valve mask can be used with a nasopharyngeal tube or a laryngeal mask, the soldier can

provide manual air to the patient through the compression of the bag. 100% oxygen can also be

administered to the patient by using the oxygen reservoir at the rear of the bag which can be

attached to oxygen tank, indications for use include:

No chest movement casualty is not breathing by him/herself

During CPR

Airway management flowchart

Attach diagnostic

equipment

Remove

clothing

Perform ABC

Assesment (Check

airway, breathing

and circulation)

Is the airway

blocked

Is the

patient

breathing

No

Yes

Carefully tilt the chin

up to open the airway

and open mounth with

jaw thrust

No

Use the Medical

ventilator to administer

postive pressure

ventilation 50-100%

No

Does the

patient have

pulse heart

beat? (ECG/

Pulse Ox)

Administer

CPRNo

Use portable

suction device

to remove

blood in the

chest cavity/

oral cavity/

trachea

Is the patient airway still blocked?

Yes

Insert the

Nasopharynge

al tube

Is it possible

to use the

mouth as the

airway?

No

Yes

Figure 60: Flowchart for airway management

37.2 Medical portable ventilation

The flight 60® medical ventilator will be used to provide oxygen to the patient, in the case that

the patient finds it difficult to breath indicated by low breathing rate or not breathing

spontaneously, the Assist control mode will be used to provide assistance in helping the patient

inspire air, the patient initiates a mechanical breath delivered by the machine and the machine aids

the patient. If the patient is not capable of initiating a breath the machine will take control.

Indications of the patient requiring ventilator assistance are:

Respitory distress

Breathing rate is 8 BPM or less

Breathing rate is 30 BPM or more

Signs and symptoms of hypoxia (Manitoba Health, 2011).



Other diagnostic equipment such as the pulse oximetry and blood pressure sensor will help

determine what to set the respitory rate, the FiO2 oxygen percentage and PEEP on the ventilator

to keep the patient breathing.(Advanced Patient Education, 2010-2012), the settings and readings

on the ventilator should be controlled and monitored remotely during transit.

Figure 61: Flight 60 mechanical ventilator

An oxygen tank must be attached to the ventilator to supply the inspired oxygen, the required

volume of oxygen to take in the MedEvac should be calculated, from Equation 63 there must be

enough oxygen for the patient during transit:

Equation 63

( ) ( ( ) ( )

( )

For a healthy young adult the average tidal volume is: 500ml

Average normal breathing rate is: 30 bpm

The transport time is likely to be: 40min

Safety factor: 1.5

Oxygen required for the single journey from the battlefield to the hospital is equal to: 360 L, this

value is likely to be slightly less because the FiO2 percentage given to the patient should be

reduced during transit to less than 60% to avoid oxygen poisoning. The oxygen cylinder tank to

be used will be a 1000L tanks supplied by Quirumed® enough oxygen will be stored within the

MedEvac for transport of two patients on the medical ventilator. A portable suction unit such as

the laerdal suction unit in Figure 62 will be supplied in the patient cabin for suctioning of the

patients airway when the airway is blocked, suctioning should be administered to the patient by

the medic before the transporting the casualty, suctioning during transit will be potentially

dangerous therefore the procedure will not be automated.



Figure 62: Laerdal suction unit manufactured by Laerdal

38 Casualty Compartment

The casualty compartment within the MedEvac must be able to sustain certain conditions to

provide as comfortable journey as possible. In accordance with (British Standard 13718-2, 2008),

there should be a heating system which is capable of raising the temperature from 0 oC to 18

oC

within 20 minutes; the compartment must have a lighting system capable of changing between 10

lx and 200 lx, which is brighter than a dark, overcast day (100 lx) but dimmer than office lighting

(320 lx); the noise exposure must be kept below 85 dB which is equivalent to city traffic inside a

car but louder than a telephone dial tone (Glaren Carol Audio, 2007). Following the guidelines

given by the HSE, vibration should be kept below 5 m/s2 for a maximum exposure time of 2 hours

to keep discomfort of the casualty to a minimum as portrayed in Figure 63 (Health and Safety

Executive, n.d.). Therefore it will be essential to insulate the walls, floor and ceiling of the

casualty compartment with anti-noise and anti-vibration protection and also mount the power

plant on anti-vibration mounts.

Figure 63: Guidance to Maximum Vibration Exposure against Time of Exposure (Health

and Safety Executive, n.d.)



39 Effects of altitude on patient

The effect of low blood oxygen saturation levels are hypoxia and hypocania, arterial oxygen

partial pressure of less than 80mmHg in room air can cause hypoxia and trigger symptoms in

individuals due to low oxygen saturation levels. Hypoxia frequently occurs in personnel who

operate at high altitudes 4572m- 6096m (1500-2000) ft. In this operating range the saturation of

arterial blood SaO2 is 70-80%(Ian Greaves, 2011). Figure 64 below shows the variation of Partial

pressure of oxygen outside and inside the human body at various altitudes, values of partial

pressure were calculated assuming PaCO2 expired remains the same at 37mm Hg a

Figure 64: Variation of PaO2 at different altitudes at different environments

The arterial blood pressure range for a healthy individual ranges from 75mm Hg -100mHg as

shown by the dashed lines in Figure 64. A PaO2 of less than 60 mmHg suggests supplemental

oxygen should be administered and a PaO2 below 26mm Hg will put an individual at risk of

death(Wikipedia, 2012). At the operating altitude of 5000, the partial pressure of arterial blood is

roughly 20 mmHg, this will vary slightly from individual depending on age, fitness etc. However

if the MedEvac is to operate in these high altitude, it will be essential that the casualty should be

given supplemental oxygen via a portable ventilator or otherwise systems should be put in place

to pressurize the cabin. The oxygen deficit causes symptoms such as: head ache, amnesia,

decreased level of consciousness, nausea, weakness numbness and tingling as well as other

symptoms. Additionally the casualty is likely to experience some discomfort in ascent due to

expansion of gases in gas containing organs/ cavities. Pressurised cabin will solve this problem.

In addition to the physiological effects on the personnel medical diagnostic equipment is also

susceptible to malfunction and loss of accuracy (Ian Greaves, 2011) due to the change in altitude.

The list includes:

-40

-20

0

20

40

60

80

100

120

140

160

180

0 50

0

10

00

15

00

20

00

25

00

30

00

35

00

40

00

45

00

50

00

55

00

60

00

65

00

70

00

75

00

80

00

85

00

90

00

Par

tial

pre

ssu

re o

f o

xyge

n P

aO2

Altitude m

PaO2 variation in different environments PaO2 inAir

Pa O2inTrachea

Pa O2in lungs

PaO2arterialblood



Gas intravenous fluid bottles

Pressure bags

Chest drainage bags

Pneumatic shock garments

Air splints.

The values of atmospheric pressure at varying altitudes were calculated using:

Equation 64 (society, 2004) (

)

The partial pressure of oxygen in the air is 0.21 times the atmospheric pressure:

Equation 65 ( )

The partial pressure of oxygen in the trachea is 47mmHg less than the expired air:

Equation 66 ( )

The partial pressure of oxygen in the aveoli is equal to:

Equation 67 ( )

Partial pressure of oxygen in the blood:

Equation 68 ( )

Where 10.75 in the Aveoli- arterial gradient.

40 Disinfection

Another issue that we faced in the MedEvac was the disinfection and sterilisation of the patient

compartment and the medical devices contained within. The normal procedure would be the use

of disinfectants and manually cleaning the surfaces within the compartment but this could take too

long if there is a demand for the services of the MedEvac and could affect redeployment time.

The main purpose of disinfection and sterilisation is to prevent the spread of infection which can

be a major concern for some of the casualties that the MedEvac is likely to see, for example

casualties with radiation sickness who have lowered immune systems as well as those with open

wounds which may be more susceptible to picking up these infections.

Therefore it was decided that UV sterilisation could be used to decrease the time for

redeployment. UV light works by disrupting the chemical bonds present in DNA, if bacteria and

other pathogens are exposed long enough the damage is permanent. However for UV sterilisation

to be successful there has to be line of sight between the UV source and the surface. UV light can

also be dangerous to people as it can damage the eyes and skin. Therefore in order for it to be

used the layout of the lights have to be arranged precisely to cover all of the areas that are

required, in our case this would be the passenger bed and the surfaces that the patient will be in

contact with. Precautions would have to be taken to prevent anyone from being harmed by the UV

light, such as preventing the activation of UV lights if the compartment doors are open as well as



checking‎for‎any‎people‎in‎the‎cabin‎by‎the‎use‎of‎the‎on‎board‎sensors‎and‎camera’s‎before‎UV‎

sterilisation begins.

41 Patient cabin layout

The cabin where the patient will be placed during transit to the field hospital is shown in Figure

68. The dimensions of the cabin space are 2.5m × 1.7m × 0.8m, it is a relatively small

compartment and only one casualty/ person can occupy the space at any one time. However the

small cabin space allows for the necessary equipment to be accessible from outside of the

MedEvac. Additionally it reduces the length of medical leads required for attachment to the

patient such as ECG lead or connections between equipment such as the ventilator and the oxygen

cylinders.‎The‎casualty’s‎condition‎will‎be monitored using the medical equipment and treatment

will be administered to the patient when necessary to stabilise the patient’s condition. The settings

of the medical device will be able to be set by the medic at the pick-up location, additionally the

patients physiological condition,: heart rate, ECG trails, respitory rate, oxygen saturation levels,

blood pressure will be transmitted to the ground station using the Xilinx Artix computer, the

medic at the base station will be able to change the medical equipment setting from the ground

base station using the communication with the computer when the patient requires a change in

delivery dose. In addition the diagnostic and treatment devices there are various compartments

and cabinets for storage of: medications, consumables such as the Bolin® chest seal and combat

lifesaver first aid kit, spares and splints

41.1 Patient stretcher platform

The patient platform is located at the centre of the cabin space and is shown in Figure 67 the

dimensions of the platform are 2.0m × 0.6m which is enough to hold the army NATO stretcher.

The NATO stretcher will be secured to the platform to stop the stretcher from dropping off; the

platform is linked to rotory servo motors on either end of the platform to allow the platform to

pivot about the Y axis as shown in Figure 67. A servo motor brake such as the one shown in

Figure 65, can be fitted to the rotary servo motor to hold the platform at the desired angles using

a spring applied electromagnetic brake, the brake is engaged when power is turned off and is

disengaged when voltage is applied to the motor(Mendolia, n.d.) holding torques of 180Nm can

be provided by each of the 2 brakes which is possible using a 1EB60 servo motor bake

manufactured by matrix international (Matrix international, 2009).



Figure 65: Matrix international servo motor brake for angle positioning of platform

This tilt mechanism will be controlled remotely by the ground medic in case the unconscious

patient vomits during transit and needs to be tilted to allow the vomit to be expired. The patient

platform sits on rails on the floor of the MedEvac and is able to slide towards the cabin door for

the loading phase of the patient transport. The Platform will then slide back into the MedEvac and

be secured; the position of the platform is suited to provide access to all of the medical devices.

The Autopulse chest compression medical device will be attached underneath the stretcher using a

slider and rail mechanism to allow it to be adjusted to the patient as shown in Figure 66.

Figure 66: Autopulse rail mechanism

Figure 67: Patient platform tilt mechanism

41.2 Medical device layout

The layout of the patient cabin is shown in Figure 68, most of the devices are located nearer to the

cabin door, this is because of the ease of which the devices can be accessed. The equipment need

to be at least within arm’s‎reach of the medic loading the casualty. The ventilator and the oxygen

cylinders have been positioned close to each other because the oxygen tank will feed the

ventilator oxygen therefore the output and input ports must be in reach of each other for the feed

lines to reach. Additionally the ventilator will sit in a compartment and be moved and secured by

an overhead rail as shown in Figure 70 this will allow the medic to choose the appropriate setting

and position the gas mask on the patient then slide the ventilator back to where the platform is



secured. The oxygen cylinder will be secured by onto the cabin wall by sheet metal which can be

attached to the wall with screws.

Figure 68: Internal cabin layout

Figure 69: Internal cabin layout section view



Figure 70: Medical ventilator location and rail

The AED defibrillator will be positioned in a metal compartment on the floor of the MedEvac

bellow the patient platform. This will allow the defibrillator pads to be in reaching distance of the

patient’s chest and easy placement. The AED compartment is within reaching distance from the

cabin door and can be taken out of the compartment if needed.

The 3 channel IV pump will be attached using a clamp to the pole protruding from side of the

patient platform as in Figure 71 the pump can be moved along the platform slightly to suit the

patient’s‎needs.‎ The drug dosage parameters can be set by the medic when the platform slides

towards the cabin door. The close proximity of the IV pump to the patient will allow the IV lines

easy access to the patient and intraosseous devices. Additionally the IV bags will be on a pole

which will be on a sliding rail attached to the patient platform as in Figure 72 the pole will be

height adjustable such IV poles are available from suppliers ( Scimthz and Shöne). 4 IV bags can

be attached on the pole so drug administration can be done simultaneously. The IV bags will

supply the IV pump with the required medicine.

Figure 71: IV Pump pole and clamp



Figure 72: IV pole hooks and IV pump

The Evac- U splint ® vacuum splints along with the manual suction pump come in a duffle style

carry case and will be stored in a compartment at the roof of the cabin. There will be two

partitions to the cabinet the second smaller space will be for storage of the Miami J cervical

collars. Drugs and medical consumables such as the chest seals will be stored in a medical cabinet

on the right of the patient cabin. The location of the medication cabinet is close to the cabin door

so it is easy for the medic to access.

42 Robot Arm

During the flight from the pickup location to the hospital there are several problems that could

arise with the patient. Most commonly these would be: lung collapse and rapid blood loss, both of

which could kill the patient in a very short amount of time. Therefore a method of treatment is

needed, for this particular UAV a specialised robot arm is proposed the design of which is such

that it could provide the lifesaving treatment‎needed‎to‎sustain‎the‎patient’s‎life‎until‎the‎UAV‎has‎

landed at the designated medical treatment centre.

42.1 Possible Options

The first option considered was a robot similar to the Festo ExoHand as shown in Figure 73.

Figure 73: Festo ExoHand (http://www.popsci.com/technology/article/2012-04/video-3-d-

printed-exoskeletal-glove-provides-precision-control-super-strong-robot-arm)

http://www.popsci.com/technology/article/2012-04/video-3-d-printed-exoskeletal-glove-provides-precision-control-super-strong-robot-arm

http://www.popsci.com/technology/article/2012-04/video-3-d-printed-exoskeletal-glove-provides-precision-control-super-strong-robot-arm



This system allows the robot to accurately mimic the controller using a series of sensors that maps

the‎ controller’s‎ position,‎ and‎ by‎ monitoring‎ the‎ sensors‎ located‎ in‎ the‎ glove‎ the‎ user‎ can‎

command the robot to pick up and use an object remotely. This type of system would allow the

robot to perform the operations required on the patient as needed with very little operator training

being given to the medic as the robot is simply mimicking the movements that the medic would

actually do if they were there. This type of robot would work on the ground, however in the air,

turbulence could cause the robot to unintentionally/uncontrollably collide with the patient and

possibly cause more damage than good.

Therefore to counteract this problem a linear robot arm control was considered; if all of the parts

were controlled using threaded rods then the robot arm would be very stable and therefore almost

immune to the turbulence that could occur during flight. Although this type of robot arm is

limited to where the arm can actually reach on the patient the control and stability offered is

significantly better than most other types of robotic arm devices. For this reason this type of robot

arm was chosen to be the basis of the treatment system.

42.2 Robotic Arm Sensors

To carry out the treatments that the robot is intended for, the robot needs several sensors to

identify what is going on. The robot needs to be able to provide a close up colour video feed of

what the robot is looking at, a 3D view of what is below the robot and a method of telling if there

is severe blood loss.

There are several different sensors that can produce a 3D scan of what is going on underneath the

robot arm and lots of small colour cameras that could be used. However the Microsoft Kinect has

both a colour camera and Depth Sensing system. The Depth sensing system works by projecting a

pattern of infrared dots across the viewing area, the shape of the dots on the object can be

processed to determine the orientation of an object in the viewing area and the distance between

the dots showing the distance the object is from the sensor. This is shown in Figure 74.



Figure 74: Kinect View of a Person (http://blog.jozilla.net/2012/03/29/getting-up-and-

running-with-the-kinect-in-ubuntu-12-04/)

Once the image in Figure 74 is processed an accurate image of the object can be generated

containing both depth and orientation information, which can then be used to accurately control

where the robots tools need to go to treat the patient.

To detect if there is blood loss a thermal imaging camera could be used as this would clearly show

which areas of the patient were at a different temperature to the rest of patient and if there were

pools of blood on the stretcher. One such thermal imaging camera that could be used is a FLIR

Quark Thermal Imaging Camera, which allows for interchangeable lenses to make sure that he

camera can see as much as possible from each possible location. This camera is shown in Figure

75.

Figure 75: FLIR Quark

(http://www.flir.com/cvs/cores/view/?id=51266&collectionid=549&col=51267)

With the 13mm lens fitted to this camera at the furthest point from the patient (0.4m) the swath

width would be about 0.33m, which would be sufficient to see the whole width of the patient

without needing to move.

42.3 Layout

In order to give the operator the best possible view of where the tools on the robot are pointing the

Kinect Sensor and Thermal Imaging Camera are arranged either side of the connecting fitting for

the tool. This enables each of the cameras to have an unobstructed view of the patient even when

the tools are attached. A basic design is shown in Figure 76.

http://blog.jozilla.net/2012/03/29/getting-up-and-running-with-the-kinect-in-ubuntu-12-04/

http://blog.jozilla.net/2012/03/29/getting-up-and-running-with-the-kinect-in-ubuntu-12-04/

http://www.flir.com/cvs/cores/view/?id=51266&collectionid=549&col=51267



Figure 76: Robotic Head showing Thermal Imaging Camera and Kinect Sensor Locations

The tools that attach to this robot are detailed in Section ‎43.The Kinect Sensor is mounted on a

swivel bracket enabling the sensor to be tilted and scan the patient without the robot moving. This

allows the operator at the ground station to generate a three dimensional image of the patient to

identify where the patient is in the cabin in relation to the robotic arm. By having the cameras on

the robotic arm the ground controller can move the robotic arm over the patient to have a closer

look at areas on the patient to help diagnose injuries better than the overhead camera mounted in

the cabin can, allowing the ground controller to diagnose the patient better.

To move the robotic arm a stepper motor is used to turn a threaded rod to precisely move the parts

of the robot to the desired position. To ensure that the robotic arm remains rigid there also needs

to be a smooth rod to stabilise the horizontal parts of the robotic arm, this is shown in Figure 77.

Figure 77: Robotic Tool to Aid Treatment

Stepper motors are used for this robot as the speed, direction and position can be accurately

controlled compared to a standard DC motor. Although the stepper motor is slower than the DC

motor, because the stepper can be moved an exact distance the accuracy of the robot positioning is

significantly higher than if using DC motors. To stop the motors burning out and trying to move

the robot off the ends of the rods, micro-switches are needed that would detect when the parts

reach the end of the rod and stop the motor from turning anymore.

Due to the simplicity of this design the movement of the robotic arm can be controlled by a

simple microcontroller. This means that the whole of the robotic arm weighs no more than 40kg

Thermal Imaging Camera Kinect Sensor

Tool Attachment Fitting



with a majority of the weight being made up of the stepper motors. A breakdown of the

components is shown in Table 16.

Table 16: Robotic Arm Component Masses

This is therefore a small amount of mass to add to the aircraft to ensure that the operator can treat

the patient correctly and treat the most common medical problems that could kill the patient

before the aircraft lands.

43 Robotic tools

It was decided that the robotic arm should have interchangeable heads to allow for the use of

different treatments. A simple design for the robotic arm head and is attachment point on the tools

was chosen. The head of the arm was designed in a way that it could slide into the attachment

point and that once inserted fully if rotated 90 degrees it would lock into place and would not be

able to slide out again unless rotated back to the original position. The arm head and insertion

point can be seen in Figure 78. This design allows for the robotic arm to have interchangeable

tools which it can switch between easily.

Component Individual Mass (Kg) Quantity Total Mass (Kg)

Stepper Motor - NEMA 34 5 6 30

Kinect Sensor 0.2 1 0.2

Thermal Imaging Camera - FLIR Quark 0.023 1 0.023

Structure 5 1 5

Total Mass 35.223



Figure 78

The first tool required was one that allowed for the application of celox powder to any open

wounds. The design that was chosen can be seen in Figure 79, it has an opening for the head of

the robot arm to attach too as well as an attachment point for the tube carrying the celox. There is

a rigid tube attached to the bottom of the tool as well which will allow for more precise

application of celox powder, which will help application to penetrating injuries such as that

caused by bullets and shrapnel.

Figure 79



The second tool was one that allowed for a pressure to be applied to a wound to ensure a seal was

formed by the celox powder, which might be required for the more severe injuries. The CAD

model of it can be seen in Figure 80. The design is simple and basic but it meets our requirements,

it is essentially a solid block which provides an attachment area for the robot arm and it has a

softer padding at the base which can conform to the area where the pressure is being applied.

Figure 80

The third tool required was one that allowed for needle decompression to be carried out if

required. The inner part of the tool can be seen in Figure 81, it would have an outer covering

normally. The main part of the tool is the needle attached to a spring which is being compressed

and prevented from moving by a second part. The part holding the spring back is hinged at the

middle with a solid bar attached to it which extends below the level of the needle. When the tool

is pressed against the skin that solid bar is forced upwards and applies a moment to the part

holding the spring back causing it to become parallel to the vertical bar. This means the spring

loaded needle is no longer held back and therefore extends, puncturing the skin and allowing for

needle decompression to occur. It is only capable of being used once within the MedEvac but it

was thought it would be‎better‎as‎a‎consumable‎item‎which‎has‎to‎be‎restocked‎as‎it’s‎an‎invasive‎

medical device, which means the risk of infection, is high. With a consumable device it can be

made sterile and therefore less of a risk.



Figure 81

Another tool required was a tool which could be used to grip things and move them about, the

main use being to move clothing out of the way to allow for other treatments if it is inhibiting

their application. The final design was a standard two pronged gripping tool with motors

controlling the position of the arms; it was attached to a base which had the attachment site for it

to connect to the robotic arm. A basic CAD model can be seen in Figure 82.

Figure 82



44 Program Costs

The costs incurred by the research, development, materials procurement, manufacture, quality

control and flight testing make up the program cost of the UAV. In the preliminary design phase

these costs are difficult to estimate with any degree of accuracy, and therefore it is normal for cost

models to be employed at this stage based on knowledge gained from previous aircraft

development programs. One example of a cost model is the DAPCA IV model (Raymer, 1992, p.

507) which uses cost estimating relationships (CERs) to estimate the costs of the various program

elements from the simple inputs of the aircraft cruise speed, its empty weight, the quantity to be

produced, the number of aircraft required for flight testing, and the number of engines required.

The number of UAVs to be produced in this project was decided to be 50 units with 2 flight test

aircraft, a cruise speed of 55m/s (107kts), an empty weight of 950kg (2090lb), and 2 engines on

each UAV. For the following program elements, first the number of man hours required for that

component are estimated, which are then multiplied by the hourly wrap rate to get the component

cost. The hourly wrap rate includes the direct salary costs as well as the indirect costs involved

with the work including benefits and manager overheads. These average wrap rates are typically

three times the individual salary, which for the case of engineering was taken as £40k giving an

hourly rate of £20 and therefore an hourly wrap rate of £60. This was also used for the hourly rate

of the tooling hours, but £50 and £55 were used as the hourly wrap rates for manufacturing and

quality control respectively, as slightly reduced rates for these areas are suggested in the DAPCA

IV model.

( )

The remaining program element costs below are calculated in 1986 dollars, and therefore they

also need to be converted to firstly 2012 dollars and then to 2012 pounds. The conversion of 1986

dollars to 2012 dollars is at the rate of 2.09 (Manuel, 2012) and then the current exchange rate of

0.62 is used to convert this to 2012 pounds.

Finally the costs of the engines is determined from similar engines as the unit price of the TM333

engine was not available, this cost was found to be $900,000 (£562,000); the avionics costs are

not estimated by the DAPCA IV model, however due to their complex nature in this project, they

are estimated as 25% of the flyaway costs here, which is the upper limit of the 5-25% suggested

by (Raymer, 1992, p. 510).



( )

The total program cost is then found by summing these elements to give £132million which

between the 50 operational UAVs gives a unit cost of £2.6million.

A sensitivity study was also carried out to determine how the program cost and unit cost varied

with the production quantity. It was found that program cost followed a near linear relationship as

shown in Figure 83 with production quantity and therefore in terms of program cost there are no

optimal production quantities.

Figure 83: Variation of Program Cost with Production Quantity

However the unit cost was found to follow an inverse power relationship with production

quantity, and therefore the unit cost falls sharply as production quantity increases from 10 to 50,

but then the unit cost reduction with increasing production quantity begins to reduce as shown in

Figure 84. Therefore this shows that whilst the optimal unit cost solution would be to make as

many units as possible, that by producing 50 units most of the mass production costs saving

benefits are achieved.



Figure 84: Variation of Unit Cost with Production Quantity

45 Overall CAD Technical Drawing

The technical drawings shown below provide an overview of the UAVs key dimensions, and also

the relative layout of the main components; however for clarity purposes the structural elements

are not shown, nor are the internal cabin equipment on the front and top views. An overview of

the structural elements layout is given in Figure 28 for reference. The UAV is shown to have

principal dimensions of a 2.91m x 7.59m footprint, with a height of 2.03m.


Author: Group 45-131

1:50

1:50

1:50

1:50

7587

2500

1045

1016

480

2029

R24

6.5

2500

O 2040O

2348O

2909

735 1500

1168

2909

389

O 600



46 Specification

The following specification points have been developed using the research presented in this report

and the inception report, and any quantitative specifications have been chosen based on typical

values of competitors and similar aircraft as well as research.‎ Note‎ that‎ ‘must’‎ means‎ the‎

requirement must be met; ‘should’‎means‎the‎requirement‎is‎a‎desirable‎feature‎and‎therefore‎does‎

not have to be met.

46.1 Performance

1. The UAV must have a mission radius of at least 100km and should be maximised.

2. The UAV maximum take-off weight (MTOW) must be less than 2000kg and should be

minimised.

3. The UAV must be capable of carrying a casualty payload of up to 150kg including

apparel.

4. The UAV must have a service ceiling of at least 5000m and should be maximised.

5. The UAV must have a cruise speed of at least 200km/h, and should be maximised.

6. The UAV lift to drag ratio should be maximised.

46.2 Control and Stability

1. The UAV must be capable of vertical take-off and landing (VTOL)

2. The UAV must be capable of maintaining stable flight in cross winds and/or turbulent

conditions in all flight modes.

3. The disturbances to the UAV flight path from cross winds and/or turbulent conditions

must be minimised.

4. The UAV must be inherently stable or have appropriate control algorithms for stability.

46.3 Operation

1. The UAV footprint must be less than 3.7m in width (the standard width of a single lane

road), and should be minimised as much as possible.

2. The UAV must have sufficient interior volume for a casualty, avionics, fuel, and medical

equipment.

3. The UAV must be capable of operating in the outside air temperatures (OAT) expected

within its possible deployment zones, approximately between -30°C and 60°C.

4. The UAV must have de-icing capabilities.

5. The UAV must be capable of landing and take-off in constricted spaces either by the use

of automatic sensing, or through ground control station piloting.

6. The UAV must where possible utilise contra-rotating blades/fans to reduce continual

stressing of the airframe through neutralising the torque created by the blades/fans.

7. The UAV electronics must be protected from adverse atmospheric conditions if required.

8. The UAV must utilise existing systems as much as possible to reduce training and

development overheads.



9. The loading mechanism for the casualty must be ergonomically designed for ease and

speed of use.

10. The UAV must be capable of automatically determining its altitude, heading, airspeed,

pitch, yaw and roll.

11. Background acoustic noise levels inside the casualty cabin should be less than 70 dB in

the‎ vicinity‎ of‎ the‎ casualty’s head and the location of any voice communication

equipment.

46.4 Powerplant

1. Due to the UAV entering service in 5 year, the powerplant must be selected from existing

designs with a proven performance.

2. The UAV powerplant must be capable of providing sufficient thrust/power.

3. The UAV powerplant must be capable of safe operation within the specified flight

conditions.

4. The UAV powerplant fuel burn should be minimised.

5. The UAV and its powerplant must be able to operate in adverse weather conditions such

as rain, hail and snow.

6. The UAV electronics and powerplants must have sufficient protection against fire.

7. Acoustic noise emitted from the UAV and associated powerplants must be minimised.

46.5 Aircraft Systems

1. All of the UAV systems must be capable of being operated and monitored remotely.

2. The UAV payload doors must be operated manually via a button on the outside of the

aircraft.

46.6 Flight Controls

1. The UAV must have remote throttle control.

2. The UAV must have remote navigation control.

46.7 Sensing

1. The UAV must be capable of accurately determining its current position anywhere on the

planet.

2. The UAV must be able to accurately determine its current heading at all times.

3. The UAV must be able to accurately determine its altitude.

4. The UAV must be able to avoid obstacles in its path.

5. The UAV must be able to operate in low light conditions.

6. The UAV should be able to return to base automatically.

7. The UAV should be able to fly to a user entered waypoint automatically.

8. The UAV should be able to identify a suitable landing site automatically.



46.8 Communication

1. The UAV must have a communication link suitable for sending control commands to the

aircraft, for flight operations, from a remote location.

2. The UAV must have a communication link suitable for sending information from the

aircraft to the ground station pertaining to the location, heading and health of the aircraft.

3. The UAV must have a communication link to relay live information from the sensors on

the aircraft to the ground station.

4. The UAV must have a communication system that can be encrypted to stop unauthorised

control of the aircraft.

5. The UAV should be capable of automatically returning to base if the communication link

to the aircraft is lost.

6. The UAV must be immune to communication jamming equipment.

7. The UAV must be able to send and receive information / data when operating at low

altitude or between obstacles.

46.9 Remote Control

1. The UAV should be capable of being flown accurately and safely with minimal training.

2. It should be possible for manual control of the UAV to override automatic control when

desired.

46.10 Casualty Loading

1. The casualty loading system must be capable of being operated, by a maximum of, one

person.

2. The casualty loading stretcher should allow treatment to be performed, if required, on the

casualty’s‎back.‎‎

3. The casualty loading stretcher must be easily integrated with current military casualty

transport.

4. The casualty loading system must be capable of carrying a casualty payload of up to

150kg including apparel plus any medical equipment it should carry.

5. The casualty loading system should provide support for the worst case casualty.

46.11 Medical

46.11.1 Operation

1. The UAV must be able to reach the patient from the point of deployment within 40

minutes.

2. All medical equipment on the UAV must be able to be operated remotely or

automatically.

3. The UAV should provide relevant medical diagnosis information to the field hospital to

allow for uninterrupted care.

4. The UAV should be able to store any amputated body parts.



5. The UAV must have enough suitable storage space for any medication or disposable

equipment‎required‎for‎the‎casualty’s‎treatment.

6. The UAV interior should be easily and quickly cleaned and sterilised to enable a short

turnaround time.

7. Any medication and disposable equipment used in the UAV should be easily and quickly

replaced if necessary.

8. The UAV should have a method by which the casualty and a medic at the ground station

may communicate.

46.11.2 Diagnosis

1. The UAV should provide the necessary equipment to enable the medic at the scene to

remove‎a‎casualty’s‎clothing.

2. The UAV must be able to identify critical injuries to the casualty.

46.11.3 Treatment

1. The UAV must be able to continue or begin CPR effectively during transit according to

Advanced Life Support (ALS).

2. The UAV must be able to treat the upper extremities, lower extremities and chest wounds.

3. The UAV must be able to treat open wounds, fractures, contusions and collapsed lungs.

4. The UAV must be able to treat haemorrhaging of the casualty, including from amputation

of a limb.

5. The UAV must be able to treat severe burns.

6. The UAV must be able to provide ventilation and airway support to a casualty suffering

from impaired breathing.

7. The‎ UAV‎must‎ be‎ able‎ to‎ provide‎ defibrillation‎ for‎ casualty’s‎ suffering‎ from‎ cardiac‎

arrest.

8. The UAV should provide adequate support and stabilisation for the casualty’s‎neck‎and‎

spine.

9. The UAV must be able to provide fluid resuscitation quickly and efficiently to any

casualty requiring it.

46.12 Regulatory/Safety

5. The UAV must adhere to MOD regulations as defined in UK MOD Defence Standard

00970 – Part 9.

6. The UAV should meet the CAA regulations as defined in CAP 722 Unmanned Aerial

Vehicle Operations in UK Airspace – Guidance, to allow training operations to be carried

out in the UK.



46.13 Assumptions

1. It is assumed that a person other than the casualty is present at the scene to assist with the

loading of the casualty to the UAV, initial medical diagnosis and treatment; including

removing any clothing in the injured areas as appropriate.

47 Medical Treatment

A table was produced, Table 18, to identify the most likely injuries that would be seen on the

battlefield, the treatments and diagnostics they require and whether the MedEvac should be

equipped to treat these. To assist in the selection of procedures to offer on board the MedEvac, a

severity and likelihood scoring was used, as detailed in Table 17. Issues associated with the

medical procedures were also identified.

Table 17: The Severity and Likelihood Scoring System

Severity Likelihood

1. minor 1. <10%

2.

moderate 2. 11-20%

3. serious 3. 21-30%

4. severe 4. 31-40%

5. critical 5. 41-50%

6. maximal 6. >51%



Table 18: Medical Treatment Evaluation

Injury Considerations Diagnostics Treatment Equipment needed Likelihood Severity Treat? Issues

Haemostasis Camera Iv Drips, Stopping blood loss IV/IO, Haemostatic agents Y

Infections N/A Debridment, Antibiotics, Removal of foreign bodies IV/IO, Antibiotics Y

Shock Blood Pressure IV drips, Blood Transfusion, Anti-shock garment IV/IO, Blood Y

Pain Relief Camera / Audio Morphine IV, Painkil lers IV/IO, Painkil lers Y

Immobilisation X-ray Apply splint Splints Y Could be difficult to detect

Shock Blood Pressure IV drips, Blood Transfusion, Anti-shock garment IV/IO, Blood Y

Nerve Injuries N/A N No real method of treatment, only possible to control

Pain Relief Camera / Audio Morphine IV, Bandages IV/IO Y

Shock Blood Pressure IV drips, Blood Transfusion, Anti-shock garment IV/IO, Blood Y Difficult to determine presence of open wound

Obstruction of Airway Camera Endotrachial tube, Jaw thrust Endotracheal tube N Tube may be inserted prior by medic

Nerve Injuries N/A N No real method of treatment, only possible to control

Pain Relief Camera / Audio Morphine IV IV/IO Y

Sucking chest woundsCamera / Audio / X-ray /

Blood Pressure / Heart RateAsherman seal Asherman seal Y unable to insert endotracheal tube as invasive procedure

Removal of fluid X-ray Chest drain Chest tube ?

Manual ventilation Breathing rate Tracheal intubation Manual ventilator Y Assuming tube has been entered by Medic

Decompression X-ray Needle thoracentesis Needle thoracentesis kit ?

Shock Blood Pressure IV drips, blood transfusion, anti-shock garment IV/IO, Blood Y Depending on the extent of burns, could inhibit other treatment

Fluid resuscitation Blood Pressure IV drip IV/IO, Blood, Colloid and Crystalloid solution Y

Burn dressings Camera Cover in a special bandage Special Bandage Y

Blocked airways Camera Endotrachial tube, jaw thrust Endotracheal tube N Tube may be inserted prior by medic

Dislocations Immobilise Pre-identified Apply splint Splints 1 1-2 Y To be applied prior to take off by Medic

Sprains and strains Immobilise Pre-identified Apply splint Splints 1 1 Y To be applied prior to take off by Medic

3-51

1-61

5 1-5

2 2-4

1 1-6

Open wound

Fractures

Contusion

Tension

Pneumothorax

Burns



Injury Considerations Diagnostics Treatment Equipment needed Likelihood Severity Treat? Issues

Haemostasis Camera Iv Drips, Stopping blood loss IV/IO, Haemostatic agents Y

Shock Blood Pressure IV drips, blood transfusion, anti-shock garment IV/IO, Blood Y

Storing Limb Medic Freezer blocks Freezer/ice box N Likely to be too much damage to tissue to reattach limb

Immobilisation Medic Apply splint Splints Y To be applied prior to take off by Medic

Pain Relief Camera / Audio Morphine IV, bandages IV/IO Y

Infections N/A Debridment, Antibiotics, Removal of foreign bodies IV/IO, Antibiotics Y

Blocked airway Camera Endotrachial tube, jaw thrust Endotracheal tube N Unless medic could put tube in

Chest Compressions Heart rate ECG Y

Defibril lation Heart rate ECG Defibril lator Y Placement of chestpads

Ventil lation Breathing rate Ventil lator Y

Heart Monitoring ECG Y

Chemical burns Camera / Pre-information Wash burn Water Y

Vomiting Camera Stomach drainage / Medication IV/IO, Medication Y

Infections N/A Debridment, antibiotics, removal of foreign bodies IV/IO, Antibiotics Y

Healing process slowed down N/A Monitor Process ? Can impair healing and other treatment

Pain Relief Camera / Fang Marks Apply bandage- cravat over affected limb to constrain ?

Vomiting Camera Immobilise l imb leave limb below heart level Splint Y To be applied prior to take off by Medic

Shock Blood Pressure Clean wound with soap and water Water Y

Hyperventilation Breathing Rate, Camera Controlling the effect of toxins using medication Medication Y

Convulsions ?

Control Bleeding Y

Blood Pressure Blood Pressure Patch Y

Breathing rate Ventil lator Y

Oxygen saturation level Pulse Oximeter Y

4-52

4-61

N/AN/A

1-6

4 -51

Resuscitation

Radiation

General

Amputations

Bites and stings



48 Medical Training

The MedEvac introduces‎many‎new‎procedures‎and‎treatments‎that‎aren’t‎practiced‎in‎the‎military‎

at present; this means that training personnel in how to use the MedEvac to its fullest capability

will be required.

The majority of the training required will be focused on those personnel who will be controlling

the medical procedures of the MedEvac. The MedEvac requires most of the procedures to go

through a medic at the base station, these procedures range from confirming or altering the actions

decided by the MedEvac such as the required fluids for fluid resuscitation or procedures which

require direct control such as the application of the haemostatic powder celox.

The medics chosen for this role will either already have medical training or will require it before

they can start training in the use of the MedEvac’s systems. The medics will require training in

controlling the medical systems remotely; this includes altering and setting medical procedures as

well as controlling the method of delivery. An example being using the medication delivery

system to inject lactated ringers solution alongside morphine but with an alternating delivery.

They will also require training in the control and use of the robotic arm and the tools that can be

used by it; which would include changing the tools, moving them to the correct area and using

them correctly. The diagnostics and sensors would also have to be covered to ensure they can

quickly diagnose patients. This would most likely involve placing medics on a training course

covering a few weeks to ensure familiarity with the system; virtual training programs could be

created and used to help in this regard.

Training would also be needed for troops on the ground so that they can correctly load and secure

a patient in the MedEvac without any problems or delays which could have a negative impact on a

patient’s‎ health‎ and‎ their‎ chances‎ of‎ recovery.‎ The‎ training‎ required‎ would‎ involve‎ how‎ to‎

correctly load a patient as well as set up the various treatments that are required beforehand. This

would include how to set up an intraosseous injection, remove clothing covering wounds and treat

fractures as well as other treatments. They would also have to cover the situations in which the

MedEvac would‎ be‎ used‎ and‎ any‎ situations‎ it‎ wouldn’t‎ be‎ able‎ to‎ deal‎ with‎ as‎ well‎ as‎ the‎

information that should be provided to the ground medic or when calling in the MedEvac. This

training‎wouldn’t‎be‎as‎detailed‎as‎that‎ required‎for‎ the‎medics‎controlling‎ the medical systems

and could be incorporated into the basic military first aid training that all personnel undergo,

however this would require training sessions for all current personnel to be up to date with new

personnel. This could take up considerable resources, an alternative is to provide this training to

combat medical technicians who undergo a 27 week training course where it could be fit in. 1 in 4

ground personnel are medical technicians, which would have a lower resource requirement for

their training however we would have to assume that they would be the personnel loading any

injured patients into the MedEvac.‎ This‎ isn’t‎ a‎ bad‎ assumption‎ considering‎ the‎MedEvac will



have to be called in and in most cases it will be the medical technician who has done this after

providing immediate care.

49 Mass, Size and Power Estimation

To get the best possible estimation of the mass of the UAV, the individual masses of each of the

identified constituent components have been aggregated. As some components are custom and

full details are not available some of the component masses themselves have been estimated

(highlighted in yellow).

Table 19: Mass and Size Budget for MedEvac UAV

Subsystem Item Individual Mass Quantity Total Mass

Kg Kg

Propulsion

Engine 156.50 2 313.00

Transmission 100.00 1 100.00

Fuel 251.00 1 251.00

Structural

All Structural Elements 319.00 1 319.00

Electrical

Battery 10.00 3 30.00

Power Supply - Fuel Cell 2.60 1 2.60

Electrical Harness 66.00 1 66.00

Communicaion

SatCom Router 1.49 1 1.49

SatCom HPA/LNA 2.72 1 2.72

SatCom SBU 2.27 1 2.27

SatCom Antenna 2.32 1 2.32

Navigation

GPS Tansciever 0.53 1 0.53

Inertial Mesurement Unit 0.58 1 0.58

LIDAR 2.00 1 2.00

Radio Altimeter 2.09 1 2.09

On Board Computer

Computer 1.50 3 4.50

Mass Memory Unit 1.00 1 1.00

Medical

Robotic Arm 40.00 1 40.00

NATO stretcher 7.60 1 7.60

Equipment

Defibrillator (ECG) 2.90 1 2.90

CPR- D -Padz negligible 1

Ventillator 6.30 1 6.30

Splints for limbs 2.50 2 5.00

Neck brace 0.50 1 0.50

Refrigerator for blood 9.00 1 9.00

FAST1 0.50 1 0.50

BIG 0.50 1 0.50

Bag valve mask 0.50 1 0.50

Autopulse 2.25 1 2.25

Portable suction device 4.00 1 4.00

Spare first aid IFEK 0.23 1 0.23

Oxitone wireless Pulse oximeter 0.01 1 0.01

Supplies

Oxygen tanks 9.10 1 9.10

IV drugs 6.34 1 6.34

Blood 4.00 1 4.00

Casualty

Casualty and Apparel 150.00 1 150.00

Estimated mass TOTAL 1349.83



The total mass, shown in Table 19, can then be used to inform selection of engines that are

sufficient to power the aircraft and to ensure that the structure designed is sufficient to support the

entire mass of the aircraft. The support structure and design is described in section ‎8.

The electrical power requirement for the aircraft is shown in Table 20. As not all of the equipment

needs to be powered at all times, the continuous power draw is different to the maximum power

draw required if all systems are powered at the same time.

Table 20: Power Budget for MedEvac UAV

Table 20 shows the navigation sensors, particularly the IGI Litemapper and IGI DigiCam use a

significant amount of power, indeed some 44% between them of the total power requirement.

This table also shows that on average, only 180.46 Watts\Hour is needed, however on some

occasions, if all the components are active, then the power system needs to be able to supply some

217.81 Watts. The power system designed to supply this amount of power is shown in Section ‎20.

Subsystem Item Active Power Draw Time On Power Draw

Watts % Watts\Hour

Propulsion

Transmission 5.00 10% 0.50

Fuel Sensor 0.10 100% 0.10

Front Fan Optical Tachometer 0.50 100% 0.50

Rear Fan Optical Tachometer 0.50 100% 0.50

Communicaion

Antenna + Radome 5.00 100% 5.00

X-Band Transciever 30.00 100% 30.00

Communcations Computer - Xilinx Artix 7 2.00 100% 2.00

Navigation

LiDAR - Velodyne HDL-32E 24.00 100% 24.00

LiDAR - IGI LiteMapper 6800 40.00 100% 40.00

Imaging System - IGI DigiCAM 40.00 100% 40.00

Inertial Measurement Unit - MOOG Crossbow 9.00 100% 9.00

Altitude Sensor - Pressure Transducer 0.01 100% 0.01

Flight Computer - Xilinx Artix 7 2.00 100% 2.00

Mass Memory Unit 5.00 100% 5.00

Medical

Medical Computer - Xilinx Artix 7 2.00 100% 2.00

Robotic Arm 5.00 10% 0.50

Ventilator 10.00 50% 5.00

Defibrilator 10.00 5% 0.50

Blood Pressure Patch 0.10 50% 0.05

Blood Oximeter 0.10 50% 0.05

IV Pumps 5.00 50% 2.50

Auto Pulse (CPR) 20.00 50% 10.00

Monitor 1.00 50% 0.50

Cabin Camera 0.50 50% 0.25

Robot Camera 0.50 50% 0.25

Thermal Imaging Camera 0.50 50% 0.25

Total 217.81 180.46



50 Financial Analysis

50.1 Development Program Costs

To calculate the program cost for this particular aircraft there are three main sections that need to

be examined, these are:

Airframe, Structure and Engines

Electronics

Medical Equipment

Table 21: Airframe Development Cost

The amount of inflation that needed to be applied was generated using the online inflation

calculator hosted at http://www.davemanuel.com/inflation-calculator.php. The electronic

development cost for this UAV has been calculated using (Wertz & Larson, 1999). This cost

estimation has been used as this Aircraft has a lot of similarities with a satellite, in terms of the

payload needed and the remote operation of the device. By using the mass estimations in Table 19

and the equations in Section Electronics Development Cost Estimate, the results in Table 22 were

produced. The development cost and the cost of installing each UAV with the necessary

electrical equipment is shown separately.

Table 22: Electronics Development Cost

Most of the medical development costs will be the costs incurred by modifying the existing

equipment; the modifications are needed to enable the data generated by the equipment to be sent

to a processor on board the UAV. The cost of these modifications is therefore likely to be

Hours Rate (£/hr) Cost (£)

Engineering Hours 227248.51 60 £13,634,910.31

Tooling Hours 164290.34 60 £9,857,420.52

Manufacturing Hours 457782.09 50 £22,889,104.32

Quality Control Hours 60885.02 55 £3,348,675.96

Total £49,730,111.12

(FY00) (FY12)

Communications System 15.50 $2,170,000.00 $2,886,100.00

Electrical Power System 15.20 $893,232.84 $1,187,999.67

Attitude Determination and Control System 14.60 $2,352,717.53 $3,129,114.32

Integration, Assemble and Test 44.51 $462,904.00 $615,662.32

Total $7,818,876.31

(FY00) (FY12)

Hardware Component Cost £206,608.00

Integration, Assemble and Test 44.51 £287,000.48 £381,710.64

Total £588,318.64

Development Cost Component Parameter

RDT&E Costs

Individual Aircraft Cost Component Parameter

RDT&E Costs

http://www.davemanuel.com/inflation-calculator.php



significantly less than the development costs for the airframe and the electronic systems, and

should not drastically affect the program development cost. The individual section costs then need

to be combined with the other costs, such as the flight test costs to produce a total program cost.

The conversion rate of 1 USD = 0.62 GPB (On 27/12/12) was used to calculate the values detailed

in Table 23.

Table 23: Program Cost

This program cost however does not include the software development cost, needed to program

each of the processors on the UAV and the ground control stations. The software development

cost is likely to increase the total program cost significantly, due to the number of processors that

are needed on this UAV and the complexity of the ground control stations. This development cost

is likely to increase during the development program as the operation of the UAV is fine-tuned

and new features are added. As this is a prototype program, the entire program cost is not needed

at the start of the project. Therefore the cost of the program can be spread out over the entire five

year development time. To estimate the amount of money that is needed each year an analytical

spreading function can be used. The spreading function was developed by Wynholds and Skratt in

1977 using experience gathered from actual research and development programs. For this type of

research and development program most of the costs occur before the middle of the time scale of

the project as this is when most of the research and development is being done, for this estimation

60% of the total cost of the program will happen before the midpoint of two and a half years (30

months)

Program Cost

Airframe £49,730,111.12

Electronics £4,847,703.32

1986 ($) 2012 ($) 2012 (£)

Development Support Cost $2,429,702.14 $5,078,077.46 £3,148,408.03

Flight Test Cost $929,723.01 $1,943,121.09 £1,204,735.07

Manufacturing Materials Cost $5,202,529.51 $10,873,286.68 £6,741,437.74

Engine Production Cost (each) - - £561,870.00

Electronics Cost Per Aircraft - - £588,318.64

Medical Equipment Cost per Aircraft - - £7,978.93

Program Cost £155,114,348.84

Acquisition cost per aircraft £2,982,968.25



Figure 85: Yearly Expenditure needed for Program

Figure 85 shows that initially this project would only need a small amount of investment to start

the project off, to test the feasibility of the idea. However after the first couple of months the level

of investment needs to rapidly increase to ensure that the project is finished by the deadline.

As this project is a United Kingdom Ministry of Defence Project it is not necessary to produce a

plan to generate the capital to fund this project, as all funds would be supplied by the Ministry of

Defence.

50.2 Operational Costs

The main operation costs for this UAV are the initial cost for the aircraft and then the cost to

replace all of the consumables on the aircraft. A breakdown of the cost of the UAV is shown in

Table 24.

£0.00

£2,000.00

£4,000.00

£6,000.00

£8,000.00

£10,000.00

£12,000.00

£14,000.00

£16,000.00

3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60

Ye

arky

Exp

en

dit

ure

(£

K)

Time Since Start of Project (Months)

Yearly Expenditure



Table 24: UAV Cost Breakdown Estimate

Table 24 shows an estimate of the total cost to purchase all of the equipment needed to build the

MedEvac UAV is about £1.5 Million (Component Cost Total), whereas the Aircraft Cost Total

includes an estimate of the cost of assembling the aircraft ready for flight, and an equal proportion

of the program cost, is about £3 Million. This cost is similar to that of a civilian Air Ambulance

Subsystem Item Quantity Individual Cost Total

Structure

Manufacturing Materials Cost 1 89,889.99£ 89,889.99£

Propulsion

Turbofan Engine - Turbomecha TM333 2 561,870.00£ 1,123,740.00£

Communication

Antenna + Radome 1 1,000.00£ 1,000.00£

X-Band Transciever 1 50,000.00£ 50,000.00£

Communcations Computer - Xilinx Artix 7 2 210.00£ 420.00£

Medical Robot

Robot Motors - NEMA 34 6 250.00£ 1,500.00£

Kinect Sensor 1 100.00£ 100.00£

Thermal Imaging Camera - FLIR Quark 1 15,000.00£ 15,000.00£

Structure 1 500.00£ 500.00£

Navigation

LiDAR - Velodyne HDL-32E 1 25,000.00£ 25,000.00£

LiDAR - IGI LiteMapper 6800 1 75,000.00£ 75,000.00£

Imaging System - IGI DigiCAM 1 5,000.00£ 5,000.00£

Inertial Measurement Unit - MOOG Crossbow 2 12,000.00£ 24,000.00£

Altitude Sensor - Pressure Transducer 2 50.00£ 100.00£

Flight Computer - Xilinx Artix 7 2 210.00£ 420.00£

Electrical

Tachometer - LaserTach - ICP Laser Tachometer 2 150.00£ 300.00£

Internal Cabin Camera 1 200.00£ 200.00£

Enviromental Sensors - SENSIRION - SHT15 4 17.00£ 68.00£

Hydrogen Fuel Cell 2 4,000.00£ 8,000.00£

Medical

Medical Computer - Xilinx Artix 7 2 210.00£ 420.00£

Flight 60 Ventilator 1 15.60£ 15.60£

Combat life saver bag 1 126.00£ 126.00£

Auto- External Defibrillator 1 3,180.00£ 3,180.00£

CPR- D-Padz 1 79.00£ 79.00£

Evac -U -Splint set 1 364.00£ 364.00£

Maimi J collar Advanced 1 87.00£ 87.00£

Head immobilizer 1 44.33£ 44.33£

Autopulse 1 2,690.00£ 2,690.00£

Pulse oximeter 1 154.00£ 154.00£

Suction unit 1 819.00£ 819.00£

1,428,216.92£

Development

Engineering Cost 1 272,698.21£ 272,698.21£

Tooling Cost 1 197,148.41£ 197,148.41£

Manufacturing Cost 1 457,782.09£ 457,782.09£

Quality Control Cost 1 66,973.52£ 66,973.52£

Develepment Support Cost 1 63,354.09£ 63,354.09£

Flight Test Cost 1 24,242.38£ 24,242.38£

Electronics Devlopment Cost 1 96,954.07£ 96,954.07£

Electronics IAT 1 381,710.00£ 381,710.00£

2,989,079.68£

Component Cost Total

Aircraft Cost Total

Cost of UAV



such as the Eurocopter EC10, costing around £2.6 Million. However this is not the only cost

associated with this aircraft, there are also numerous consumables that are needed for each flight

to enable the aircraft to perform all of the necessary functions.

If all of the fuel on board the aircraft was consumed for each flight then the cost of the fuel for

each flight can be calculated, firstly the total amount of fuel that can be held in the aircraft needs

to be calculated as shown in Table 25.

Table 25: UAV Fuel Costing

This amount of fuel can then be added to all of the other consumables that the UAV needs for

each flight to produce a cost estimate of how much each flight would cost the operator.

Table 26: UAV Consumables Costing

Table 26 shows that the total cost of each flight is about £1,500. If the aircraft was to carry out ten

missions a month, then the total cost of the aircraft to purchase and then run for a year can be

calculated. This value is shown in Table 27.

Table 27: Cost to Purchase UAV and Operate for One Year

Density of Fuel 804 kg/m^3

Cost Per Litre 0.54£ £/litre inc. VAT

Fuel Tank Capacity 251 kg

Fuel Required 312.19 litres

Fuel Costing

Item Quantity Individual Cost Total

ATF K-50 Fuel (Jet A1) 312.19 0.54£ 169.56£

Lactated ringers souton 3 25.87£ 77.61£

Blood units 4 125.00£ 500.00£

Oxygen canister 1 217.63£ 217.63£

Recplacement First Aid Kit (IFAK) 1 164.76£ 164.76£

Big IO 1 106.00£ 106.00£

Fast IO 1 40.00£ 40.00£

Celox 3 17.50£ 52.50£

Morphine 1 157.00£ 157.00£

Tranexamic acid 1 6.74£ 6.74£

Pulse Oximeter 1 154.00£ 154.00£

Cost Per Flight Total 1,491.80£

Cost Per Flight

Cost of UAV 2,988,925.68£

Cost Per Flight 1,491.80£

Number of Flights per Month 10

Total Number of Flights in a Year 120

Number of Operational Years 20

Total 6,569,236.37£

Total Cost Of UAV and One Years Operating



Table 27 shows that the total cost to purchase and operate this MedEvac UAV (Excluding

maintenance charges) over a lifetime of 20 years is £6.6 Million, which is significantly less than

the £13.2 Million needed just to purchase the Sikorsky HH-60M (Blackhawk).

51 Project Management

Due to the wide array of disciplines needed to design the UAV, the project has been broken down

into‎smaller‎ sections‎ relevant‎ to‎ the‎ individual‎group‎member’s‎disciplines.‎Each‎ task‎was‎ then‎

assigned to a specific member of the team who could ask other group members for assistance if

needed.

Using the Gantt chart outlined in (Wood, et al., 2012), the progress of each of the tasks has been

monitored and recorded using the original Gantt chart as the Project Baseline. A copy of this

Gantt chart is shown in Figure 86.

The Gantt chart shows that during the project the initial time estimates have changed. The biggest

slippage was for the medical treatment and diagnosis, as it took longer than predicted to identify

which treatments and what equipment is needed to treat the injuries that could be faced by the

UAV. The delay caused by the medical treatment, caused a one week delay in starting work on

the financial analysis of the project. The project has still been completed on schedule as several of

the tasks in the project have been completed ahead of schedule enabling the time lost to be

absorbed by the other tasks.



Figure 86: Gantt Chart



52 Conclusion

The purpose of this project was to investigate and design a potential solution for a MedEvac UAV

which will operate in a physically constrained urban environment. Our solution to the project

brief is the integration of: Aerospace, Mechanical, Biomedical and electrical engineering

principles to solve the problems and issues that will be encountered if such an air ambulance

vehicle was to be designed. The design of such an aircraft was problematic as the footprint of the

aircraft had to be kept low, the aircraft had to be capable of VTOL and manoeuvre well between

buildings. A double ducted fan design with minimal footprint was investigated as a potential

solution. Furthermore redundant engines were used to be able to land safely in case of engine

failure. The UAV is capable of operating up to 5000m altitude with a 100km mission radius and a

maximum cruise speed of 71m/s (256km/h).

Two LiDAR units can be used in conjunction with each other to map possible landing sites from

altitude and detect obstacles around the UAV when operating in confined spaces. The aircraft is

designed to fly completely autonomously using an automatic flight control system, which is fed

by a variety of sensors including GPS and gyroscopes to accurately determine the position and

attitude of the aircraft. The autonomous operation was selected to minimise the amount of

interaction needed to operate the UAV, enabling the aircraft to fly in constrained locations

without worrying about the delay in commands, introduced by the communication system.

The MedEvac is designed to transport a casualty and provide the necessary treatment and

intervention to increase the possibility of survival without risking the life of other personnel. The

MedEvac has internal systems which are designed to operate with minimal human interaction and

can be remotely controlled by a medic at the ground station, thereby providing all of the necessary

medical treatment that conventional air ambulances are capable of. The MedEvac assumes there

is one trained medical soldier on the ground with the casualty to assist in initial medical

assessment, treatment and casualty loading.

Due to the hazardous environment that the MedEvac will be operating in several defence

countermeasures have been implemented to protect the casualty and the UAV, such as the

Crosshairs sense and avoid systems, flare and chaffs and E/O jammers.

The operation of the MedEvac can be easily integrated with current military operations, and the

program cost of manufacturing 50 MedEvac UAV’s‎ is‎ £155‎million‎ the‎ initial‎ funding‎ of‎ this‎

project will come from the MOD.


54-150

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333-2m2-24.html


Safran Turbomeca, 2010. TM 333 2B2. [Online]


333-2b2-23.html


Sandia National Laboratories, 2005. MiniSAR Radar, Albuquerque: Sandia National Laboratories.

Scaffolding Direct, 2011. Scaffolding Fittings - Pressed Steel Double Coupler. [Online]

Available at: http://www.scaffolding-direct.co.uk/scaffolding-fittings-pressed-steel-double-

coupler-25-.aspx


Shelley, K. H. et al., 2005. The Effect of Venous Pulsation on the Forehead Pulse Oximeter Wave

Form as a Possible Source of Error in Spo2 Calculation. Anesthesia Analg, Volume 100, pp. 743-

747.

society, P. s. A., 2004. A quick derivation relating altitude to air pressure. [Online]

Available at: http://psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf

[Accessed 09 11 2012].

Stokes, A., 1970. High Performance Gear Design. Sussex, UK: The Machinary Publishing Co.,

Ltd..

The Engineering Toolboox, n.d. Torsion of Shafts. [Online]

Available at: http://www.engineeringtoolbox.com/torsion-shafts-d_947.html


TSS International BV, 2012. Avoid the danger of fire and explosion with TSS Protected Fuel

Tanks, Barendrecht: TSS International BV.


54-158

Turbomeca, n.d. Turbomeca - TM333 2B2. [Online]


333-2b2-23.html


United States Air Force (USAF), 1973. Baffle and Inerting Material, Aircraft Fuel Tank, s.l.:

United States Air Force (USAF).

US Army, 2000. Emergency War Surgery. s.l.:s.n.

Velodyne, 2012. High Definition LiDAR HDL-32E, San Jose: Velodyne Lidar Inc.

Wayne, M. A., 2009. Adult Intraosseous Vascualr Access in Emergency Medicine. European

Critical Care and Emergency Medicine, p. 4.

Wendelken, S. M., 2004. Using a Forehead Reflectance Pulse Oximeter to Detect Changes in

Systempathetic Tone, New Hampshire, USA: Thayer School of Engineering.

Wertz, J. R. & Larson, W. J., 1999. Space Mission Analysis and Design. 3rd ed. El Segundo:

Microcosm Press and Kluwer Academic Publishers.

Wikipedia, 2012. Arterial blood gas. [Online]

Available at: http://en.wikipedia.org/wiki/Arterial_blood_gas

[Accessed 11 11 2012].

Wikipedia, n.d. Differential. [Online]

Available at: http://en.wikipedia.org/wiki/Differential_(mechanical_device)


Wood, M. et al., 2012. Design of a MedEvac UAV for Operation in Physically Constrained

Environments - Inception Report, Surrey: University of Surrey.

ZOLL Medical Corporation, 2011. AED Pro Operators Guide. In: s.l.:ZOLL Medical

Corporation.



Appendix A – Current Aircraft Data

Table 28: Data for Helicopters and Selected Aircraft (Filippone, 2000), *added separately

Aircraft Type D (m) u (km/h) rpm MTOW

Disk Loading

(N/m2)

Bell 406/OH-58D Helicopter 10.7 232 395 2500 274

Bell 407 Helicopter 10.7 237 413 2270 249

Bell 427 Helicopter 11.3 250 395 2835 278

MD-500E Helicopter 8.1 248 492 1360 262

Enstrom 480 Helicopter 9.8 204 334 1300 170

Aerospatiale 550 Helicopter 10.7 248 394 2250 246

Eurocopter BO 105 Helicopter 9.8 240 424 2500 322

Eurocopter EC 120B Helicopter 10.0 228 415 1700 212

AVERAGE OF HELICOPTERS 10.1 236 408 2089 252

Bell/Boeing V-22 Tilt Rotor 11.6 185 333 27440 1271

Bell X-22A* Ducted Fan 2.1 - 2590 8000 5506

Doak VZ-4* Ducted Fan 1.2 - 4800 1451 6293

Urban Aero Airmule* Ducted Fan 1.8 - - 1406 2710



Appendix B

Figure 87: Vertical response to vestical gust for a range of aircrafts

Table 29: Preliminary estimate for performance calculations

g 9.81

MTOW 2000 kg 19620 N

altitude, z 0 m

Flight Speed, V 200 km/hr 55.55556 m/s

Mission radius 100 km 100000 m

density, ρ 1.225 kg/m3 sea level

area (body

drag) 3 m2 12.81748

Power (hp) 1200 894839.8464 watts

Blade radius, r 1.25

Equation 69- Aerodynamic lift

Equation 70

Where, A = area of lift surface

V‎=‎Flight‎Speed;‎ρ‎=‎air‎density‎and CL = Coefficient of lift



Table 30: Calculations to obtain wingspan required

α CL

S = (b*c)

m2

Wing span,

b chord, c

S = (b*c)

m2

Wing span,

b α CL CL/CD

wing loading

(W/S) Flight Speed

0

-1.15E-

11 -9.016E+11 -4.508E+11 2 42.406 21.203 0 0.244744 20.11 47.16 108.89

1 0.203546 50.989 25.494

28.717 14.358 1 0.361413 30.03 69.65 89.60

2 0.410942 25.256 12.628

23.080 11.540 2 0.449677 35.34 86.65 80.33

3 0.48022 21.612 10.806

19.315 9.658 3 0.537322 38.57 103.54 73.49

4 0.538661 19.267 9.634

16.554 8.277 4 0.626958 40.96 120.82 68.03

5 0.602125 17.237 8.618

14.441 7.221 5 0.718688 42.67 138.49 63.54

6 0.674122 15.396 7.698

12.781 6.391 6 0.812014 43.56 156.48 59.78

7 0.752276 13.796 6.898 11.465 5.733 7 0.905224 43.73 174.44 56.62

8 0.823253 12.607 6.303

10.397 5.198 8 0.998264 43.20 192.37 53.91

symmetrical airfoil

9.521 4.760 9 1.090118 42.37 210.07 51.59

8.808 4.404 10 1.178328 41.68 227.07 49.62

8.265 4.132 11 1.255761 41.18 241.99 48.07

Variation of CL with α was obtained from XLR5 airfoil 7.857 3.928 12 1.32095 40.83 254.55 46.87

http://www.xflr5.com/xflr5.htm 7.609 3.804 13 1.363996 39.37 262.85 46.12

7.616 3.808 14 1.362771 34.25 262.61 46.14

Cambered airfoil 27.06

19.59



14.78

Drag, Fuselage lift and high lift devices haven’t been

considered

Disc Loading

(W/AR)

Rotor Area

(Pi*r2)

407.4366543 4.909

Tilt rotor

Effective Wing Span 8.23 metres

Power loading 91147.64

Fixed wing aircraft Effective Wing Span 5.73 metres

Thrust Loading 0.25

Lift 22780.45



Figure 88: NACA23012 – cambered aerofoil profile

Figure 89: Technical Specification of TROPHY Family(RAFAEL Defense System Ltd.,

2010)



Figure 90: Span wise distributions of inflow and thrust on a

rotor blade for different linear twist rates(Leishman, 2006)

Figure 91 - Thrust variation with RPM and tip gap



Figure 92: Effect of blades’ number on airflow

Table 31: fan Parameters

mass 1300kg 1275N R eff.

R 1.00 blade radius 0.70

Nb 5.00 No. of blades

θ 30.00 Pitch angle

RPM 2450.00 40.83333333

Ω 256.56 rad/s

Vinf 30.17 m/s

Table 32: Data used in calculation

Body Drag 4.00 m2

rhub 0.3 m

Adisk 2.86 m2

blade twist 1.50 degrees

Density, ρ 1.225 kg/m3

Chord, c 0.3 m

CD 0.35

a0 6.283185 rad-1

Power Available (single engine)

950.00 kw sea level

600.00 kw 5000 m



Table 33: Blade section data and linear twist

Propeller geometry data

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.95 1

Element radius, r 0.37 0.44 0.51 0.58 0.65 0.72 0.79 0.86 0.93 0.965 1

Chord (m) 0.28 0.2686567 0.2791667 0.3 0.275 0.2955 0.286154 0.2612903 0.2444 0.1841 0.18409

θ(deg) 30.00 28.50 27.00 25.50 24.00 22.50 21.00 19.50 18.00 16.50 15.00

(rad) 0.524 0.497 0.471 0.445 0.419 0.393 0.367 0.340 0.314 0.288 0.262



Table 34: calculation for each blade element

combined Blade Element Momentum Calculation

φ 0.30774736 0.2611742 0.2266323 0.200051368 0.179 0.1619 0.147779 0.1359045 0.1258 0.1213 0.11707 radians

σ 0.23873241 0.2387324 0.2387324 0.238732415 0.2387 0.2387 0.238732 0.2387324 0.2387 0.2387 0.23873

θ 0.524 0.497 0.471 0.445 0.419 0.393 0.367 0.340 0.314 0.288 0.262

α 0.2159 0.2362 0.2446 0.2450 0.2399 0.2308 0.2187 0.2044 0.1884 0.1667 0.1447

CL 1.35623444 1.4843691 1.5369087 1.539428096 1.5073 1.4501 1.374384 1.2845009 1.1836 1.0475 0.90939

CD 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02

ΔT 809.938065 1412.5697 2347.8073 3697.119827 4652.7 6518.1 7886.826 8668.5415 9437.1 7021.6 6778.55

ΣT 77.7877703 131.61319 211.57245 292.2444109 390.98 504.17 579.4379 633.6964 288.03 241.5 Trapezium Rule

ΔP 25692.1665 44931.235 75062.348 119012.7144 151043 213756 261795 291954.62 323481 245626 243404

ΣP 2471.81904 4199.7754 6792.6272 9451.947851 12768 16644 19381.24 21540.262 9959.4 8558

Single blade Thrust (T) 1609.77 N

single blade power 111767.33 W

total fan thrust 8048.85 N

total fan power 558836.64 W

total thrust 16097.69 N

total power 1117673.3 W

Table 35: Blade tip speed, thrust and power predictions at different altitudes

Vblade_Tip 198.97 m/s Single Fan

Both Fans

a Mblade_Tip Temperature (K) RPM

Altitude (m)

Density

(ρ) Thrust, T Thrust (N) Power Req

340.32 0.58 288.15 1900 0.00 1.23 8048.85 16097.69 558.57 kw

320.59 0.77 255.70 2350

5000.00 0.74 7103.68 14207.36 634.27 kw



Appendix C – Gear Terminology

The terminology of spur and bevel gears can be found below, respectively.

Figure 93: Spur Gear Terminology (Coord 3 Metrology, 2012)

Figure 94: Bevel Gear Terminology (RoyMech, 2011)


Author: Matthew Temple 169

Appendix D – Satellite Communication Equations

Azimuth, Elevation and Range Equations for Satellite Communications

These equations are taken from (Evans, 2012)

Table 36: Azimuth, Elevation and Range Equations

( ( )

( ))

(1)

( ( )

( ))

(2)

√( ( ( ))) (3)

Where

( ( ) ( )) (4)

( ) (5)

(6)

( )

( )

( )

( )

( )



Appendix E – Finance Equations

Electronics Development Cost Estimate

Taken from (Wertz & Larson, 1999), Page 796.

( )

( )

( )

( )

Analytical Spreading Function for Research and Development Projects

Taken from (Wertz & Larson, 1999), Page 806

( ) [ (( ) ) ( ) ( ) ( ) ]

Where:

( )

A B

80% 0.96 0.04

60% 0.32 0.68

50% 0 1

40% 0 0.68

20% 0 0.04

% Expenditure at

Schedule Midpoint

Coefficients



Appendix F - Flowcharts

Communications System

Communication System

Is there an Interupt

Was the Last Packet Data or

Video

Prepare Video Frame for

TransmissionVideo Frame

Telemetry

Prepare Attitude Telemetry Data

Video

Prepare Sensor Telemetry Data

Prepare System Status Telemetry

Data

Attitude Data

Sensor Data

System Status Data

Encrypt Data For Transmission

What was the Interupt

Prepare LiDAR DataLiDAR Sensor

Data

3D Scan Requested

Prepare Attitude Data

Attitude Data

UAV Under Fire

Prepare location engaged from Data

Direction of Fire

Prepare LiDAR Data

Obstacle Detected

Prepare Attitude Data

LiDAR Data

Attitude Data

Figure 95: Communication System Flowchart



Flight Operations

Flight Operations

Load Flight Path

Is UAV Currently Landed

Is UAV at Cruising Altitude

No

Vertical Take OffYes

Ascend to Cruising Altitude

No

Follow Flight Path

Yes

Has UAV Reached end of

Flight Path

No

Look for Beacon

Identify Landing Site near Beacon

Identify Landing Site

Beacon Found No Beacon Found

LiDAR Data

Is there a Suitable Landing

Site

No

Does Ground Station Approve

Landing Site

No

Fly to Directly Above Landing Site

Image Landing Site with Colour Camera

Yes

Yes

Colour Camera Data

Re-Image Landing Site

Is Landing Site still approved by Ground Station

No

Vertical Landing

Yes

Does Ground Station give

permission to open Door

Open Door

Wait for Permission to open Door

No

Yes

Is this a Patient Pick Up or Drop

Off Location

Wait for Patient to be Loaded

Wait for Patient to be Unloaded

Patient Pick Up Location Patient Drop Off Location

Has Patient been Loaded

No

Has Patient been Unloaded

No

Clean Aircraft

Has Aircraft been Cleaned

No

End

Load Flight Path to Nearest Medical

Location

Has Permission for Take Off

been Given by Ground Control

Wait for Permission to Take Off

No

Close Patient Cabin

Yes

Figure 96: Flight Operations Flowchart



Load Co-Ordinates of nearest Medical Treatment Centre

Generate Flight Path between

current location and new Co-Ordinates

Check for Danger Zones on Flight Path

Current Danger Zones

Does the Flight Path cross any Danger Zones

Relay Flight Path to Ground Control

Station

No

Does Control Station accept

Flight Path

Save Flight Path to Memory

Yes

End

Flight Path

Current Engagement Zone across Battlefiled

Current Flight Path

Generate New Flight Path avoiding

Danger ZonesYes

No

Nearest Medical

Treatment Centre

Location

Medical Treatment

Centres

What is the Destination

Medical Treatment Centre

Co-Ordinates of Patient / Landing Site

Transmitted by Ground Personel

Load Co-Ordinates of Patient / Landing

Site

Patient / Landing Site

Figure 97: Flight Path Creation Flowchart



Medical Operations

Figure 98: Pulse Oximeter Application Flow Chart



Figure 99: Blood Pressure Patch Application Flow Chart



Figure 100: Insertion of Intraosseous Cannula



Evac- U Splint, Pulse oximeter, Heamoclot, Manual ventilator, Portable suction machine

Procedure for dealing with fractures splintingA

sse

sm

en

t o

f A

irw

ay,

bre

ath

ing

an

d c

ircu

latio

nT

rea

tme

nt o

f F

ractu

res

Tra

nsp

ort

to

UA

V

Treatment fpr

fractures

(Immobilisation)

Locate patient and place on mobile

stretcher do not move limbs too far from

current postion

Transpot casualty to

Medevac UAV

No

Yes

No

Yes

NoAdminister CPRDoes the patient have pulse heart beat? (ECG/Pulse

Ox)

Carefully tilt the chin up to open the airway and open mounth with

jaw thrust

Is the patient breathingAdminister CPR

Is the airway blocked

Perform ABC Assesment (Check airway, breathing

and circulation)

Does the casualty

have a upper

extremity or lower

extremity injury

Does the

casualty have

an open or

closed

fracture

Does the

casualty have

an open or

closed fracture

Asses fracture site

for tenderness and

swelling

Asses for deformity

in limb and ask

patient if concious for

area of pain

Locate the

fracture site is the

fracture in the

knee, lower leg,

ankle, hip or

pelvis is there

partial

amputation?

Clontrol bleeding by

applying pressure and

dressing to the wound,

apply heamoclot

Does the

casualy have a

head/neck

injury

Apply a cervical

collar

Asses distal

pulse and

blood pressure

Closed

Asses for deformity

in limb and ask

patient if concious for

area of pain

Asses fracture site

for tenderness and

swelling

Locate the

fracture site

is the fracture

a shoulder or

wrist

fracture?

Closed

Upper extremity

Attempt to straighten the limb

and apply traction Apply the

vacuum splint

Lower extremity

Do not, apply

traction, apply

vacuum splint

Yes

Is the fracture

in the mid

thigh reigon?

Yes

No

Manually

straighten the

limb

Apply the

vacuum splint to

the limb

Open Clontrol bleeding by

applying pressure and

dressing to the wound,

apply heamoclot

Open

No

Yes

Administer 50-100% oxygen,

continue to monitor patients

condition & transfer







No

Figure 101: Flowchart of treatment for fractures



Equipment: Autopulse, AED, Defib Pads

CPR, AED Autopulse device communication

Remove clothing on

Patient

Remove, oil

moisture from

patients chest

Apply defibrillation

electrode pads

CPR D-Pads and

plug into AED

Attach chest

compressions

straps

Power ON the

AED & Autopulse

Do not touch the

AED wait for AED

to finish analysis

on patient

Check rhythm

is shockable

After 30:2 compressions

stand clear allow AED to

monitor patient

Continue chest

compression 30:2

Autopulse

Wait for

defibrillator to

charge

Once charged and

tone sounds shock

button flashes

Press the shock

buttin/ initiate

shock/

Automatically from

base

Unit delivers

shock

Does the unit

resume ECG

analysis

Unit displays start

CPR

No

30:2 complete send message

Yes

base alert shock needed

Alert base on charges

Alert base after shock

Yes

No

Send message/ ECG trail & heart rate

Figure 102: CPR Flowchart



Treatment for casualty suffereing tension Pneumothorax

Attach diagnostic equipment

Remove clothing

Perform ABC Assesment (Check airway, breathing and

circulation)

Is the airway blocked

Is the patient breathing

No

Yes

Carefully tilt the chin up to open the airway and open mounth with jaw

thrust

No

Administer CPR

No

Does the patient have pulse heart beat? (ECG/Pulse

Ox)

Yes

Administer CPR No

Yes

Use portable suction device to

remove blood in the chest cavity/oral cavity/ trachea

Does the casualty have a noticable chest wound, does it make a sucking

sound?

Administer high concentration

oxygen 75-100%Yes

Apply Bolin chest seal

Continue to monitor the patients SPO2 level and breathing rate ( Pulse

ox)

No

Does the casualty have shortness of

(Difficulty breathing)

Check the SPO2 level on the pulse

oximeter is it < 60mm Hg, check

blood pressurer and pulse rate

Yes

Administer 75-100% oxygen

Continue to monitor the patients SPO2

level and breathing rate

Does the patient have equal chest

movement on both sides

No

No

Yes

Equipment

ECG monitor Pulse oximeter Bolin chest seal Ventilator Blood pressure

patch

Is the patient airway still blocked?

Yes

Figure 103: Tension Pneumothorax Flowchart



Appendix G - Communication Bus Diagram

Medical Control SystemFlight Control System Communications Subsystem

Anti Weapon System

Aircraft Counter Measures

Ventilator Unit Defibrillator Unit

IV / IO Unit

Robot

Blood Oximeter

Blood Pressure Meter

Automatic CPR Unit

Key

Intermediate Gain Antenna - IGA

HPA / LNA

Communications Processor

Flight Computer Medical Computer

Flight Redundant Computer

Light Detection and Ranging

Colour High Resolution CMOS

Camera

Inertial Measurement Unit

Global Positioning System Sensor - GPS

Anti Weapon System Computer

Radar Unit Acoustic Sensor

Flares

Chaff

Anti Aircraft Missile Jammer

Redundant Medical Computer

Mass Memory Unit

Fuel Level Sensor

Microcontroller

Microcontroller

Optical Tachometer 1

Optical Tachometer 2

Ventilator

Breathing Rate Sensor

Defibrilator

Electrocardiogram

Microcontroller

IV / IO Pump 1

IV / IO Pump ...

Microcontroller

Linear Motors X Axis

Linear Motors Y Axis

Linear Motors Z Axis

Microcontroller

Blood Oximeter

Microcontroller Blood Pressure Patch

Microcontroller

Autopulse

RF / Co-ax

UART

I2C

RS 232

Ethernet

Motor Driver

Thermal Imaging Camera

Microsoft Kinect Sensor

Figure 104: Communication Bus Diagram



Appendix H - Failure Mode Effect Analysis

Product Name:

Various

Developer: Michael Collison

Date: 28th December 2012

Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

TM333 Engine Propulsion Single engine

shutdown

Partial loss of

propulsive

power available

Malfunction Automatic

detection of

engine failure

from engine

control unit.

4 8 4 128 Attempt to

restart engine.

Stable flight

possible for

limited amount

of time –

truncate

mission if

necessary.

Cabin Pressure

Vessel

Structural Skin

Maintain cabin

pressurisation

Skin failure Cabin

depressurises

Material failure Periodic

inspection of

skin for defects.

3 6 2 36 Descend to an

altitude that is

safe with a de-

pressurised

cabin –

truncate

mission if

necessary.

Bullets Avoidance of

enemy fire

where possible.

5 6 2 60

Main Structural Maintain UAV Fracture Loss of UAV Fatigue cracking Periodic 3 10 4 120



Elements, e.g.

spars.

structural

integrity

structural

integrity –

catastrophic loss

of UAV likely.

or corrosion. inspection of

structural

elements for

cracks or

corrosion.

Landing Gear Maintain ground

clearance for

UAV body and

fans.

Failure to lower

from bay

Unstable

landing platform

Mechanical /

control system

failure

Control system

has multiple

redundancies,

and landing gear

will

automatically

lock in lowered

position under

its own weight.

3 8 2 48 If failure

occurs when

landing at

casualty site,

other means of

MedEvac will

be required and

mission will be

cancelled as it

won’t‎be‎

possible to

safely load the

casualty. If

failure occurs

when ending

mission,

casualty may

be unloaded

with other

means of UAV

stabilisation

utilised.

Allow ground

movement of

Tyre failure Ground

movement not

Puncture Post/pre-flight

checks will

4 4 2 16 Tyre

replacement



UAV possible until

tyre is replaced,

but no effect to

landings/take-

offs.

notice any tyre

failures.

between

missions, no

ground

movement of

UAV until tyre

is replaced.



Product Name: Various

Developer: Wasim Aslam

Date: 28th November 2012

Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

IV lines Deliver fluids

and medication

to patient

Developing air

bubbles

Introduces air

embolisms to

bloodstream

Introduction of

air into line

Ensure drip

chamber half

full and iv

placed above

patient

7 3 2 42 Not a serious

occurrence,

large amounts of

air would be

required for

severe injuries

which is

unlikely

IV lines Deliver fluids

and medication

to patient

Partially/fully

blocked lines

Prevents

medication to

patient, possibly

fatal effects

Sediment build

up within line

Perform regular

checks of line

and replace

regularly

2 9 2 36 Use of several

lines further

reduces risk

Ventilator Provide oxygen

and support

patient breathing

Malfunction of

ventilator

Lack of oxygen

to patient as

well as lack of

assisted

breathing

Perform regular

checks/

maintenance

1 9 2 18

Decompression

tool

To prevent

worsening of

pneomothorax

Failure of spring

mechanism

Pneumothorax

could worsen,

potentially fatal

Damage to

mechanism

Provide multiple

tools to reduce

risk

3 10 3 90



Product Name: Power System

Developer: Matthew Temple


Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Hydrogen Fuel

Cell

Provides

electrical power

to UAV

No Fuel No electrical

power supplied

to UAV

Fuel Leak Fuel Sensor

placed in tank

7 9 1 36

Hydrogen Fuel

Cell

Provides

electrical power

to UAV

No Fuel No electrical

power supplied

to UAV

All Fuel Used Back up

Hydrogen fuel

cell

7 9 1 63



Product Name: Communications System



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Antenna Send or Receive

data from

satellite

Loss of control Loss of

Communication

Motor Jam Motion sensors

in antenna used

to sense current

position

1 10 2 20 If the antenna

fails, the UAV

must fly back to

the home base

autonomously

Antenna Send or Receive

data from

satellite

Loss of control Loss of

Communication

Damage from

Projectiles

Motion sensors

in antenna used

to sense current

position

4 10 2 80 If the antenna is

damaged, the

UAV must fly

back to the

home base

autonomously

Communication

s Computer

Controls all of

the control

based

operations on

the UAV

System Crash Loss of

communication

Software crash Resetable by

flight computer

if no response

1 9 2 18



Product Name: Navigation System



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Obstacle LiDAR

Unit

Detects

obstacles

around the UAV

Mechanical

Failure

Loss of scan

capability,

resulting in

single point

measurement

Motor Jam 3 9 2 54 Flight computer

needs to

monitor power

consumption, as

motor jam

would increase

power draw

Obstacle LiDAR

Unit

Detects

obstacles

around the UAV

System Crash Loss of Obstacle

Detection

capability

Software Crash Resettable by

Flight Computer

1 9 2 18

Landing LiDAR

Unit

Detects suitable

landing sites for

the UAV

Mechanical

Failure

Loss of scan

capability,

resulting in

single point

measurement

Motor Jam 3 9 2 54 Flight computer

needs to

monitor power

consumption, as

motor jam

would increase

power draw

Landing LiDAR

Unit

Detects suitable

landing sites for

System Crash Loss of landing

site detection


Flight Computer

1 9 2 18



the UAV capability

Altitude Sensor Detects the

current altitude

of the UAV

Sensor Failure Cannot

calculate

altitude of UAV

Damage from

Projectile

4 9 2 72 Flight computer

needs to send

warning to

ground control

station, add

redundancy

Inertial

Measurement

Unit

Detects the

current

orientation of

the UAV

Sensor Failure Cannot

calculate

orientation of

UAV

Damage from

Projectile


needs to send

warning to

ground control

station, add

redundancy

Global

Positioning Unit

Detects the

current position

of the UAV

Sensor Failure Cannot detect

position of UAV

Damage from

Projectile


needs to send

warning to

ground control

station, add

redundancy

Landing Camera Images possible

landing sites for

the ground staff

System Crash Cannot image

landing sites for

ground control

staff


Flight Computer

1 9 2 18

Flight Computer Controls all of

the flight

operations on

the UAV

System Crash Loss of control

of the Aircraft

Software Crash Back up

computer to

take over if

needed

1 9 2 18



Product Name: Communications System



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Power Cable Provides power

to the

components on

the UAV

Cable Severed Loss of power to

component

Vibration /

Damage from

projectile

Multicore cable

used to

minimise risk

4 10 2 80

Power Cable Provides power

to the

components on

the UAV

Loose connector Loss /

intermittent

power supply

Vibration Screw type

connector used

3 10 2 60

Data Cable Sends data

between

components on

the UAV

Cable Severed Loss of

communication

Vibration /

Damage from

projectile

Multicore cable

used to

minimise risk

4 9 2 72

Data Cable Sends data

between

components on

the UAV

Loose connector Loss /

intermittent

communication

Vibration Screw type

connector used

3 10 2 60



Product Name: Transmission

Developer: Maria Wood


Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er Remarks/

Actions

Taken

Drive Shaft Transmit

rotational power

from engines to

fans

Torsion No transmission Overloading Ensure high

safety margin,

Regular

inspection of

cracks etc

4 10 6 240 Use strain

gauges to

monitor,

testing to

fatigue life

Drive Shaft Transmit

rotational power

from engines to

fans

Bending No transmission Overloading Ensure high

safety margin,

Regular

inspection of

cracks etc


gauges to

monitor,

testing to

fatigue life

Gears Transmit

rotational power

from engines to

fans

Gear teeth

shearing

No transmission Overloading Ensure high

safety margin,

Regular

inspection of

cracks etc


gauges to

monitor,

testing to

fatigue life



Product Name: Pulse Oximeter



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Pulse Oximeter Monitor

casualty blood-

oxygen level

No connection No

measurement of

blood-oxygen

level

Electrical

breakage

No connection

to computer; try

another device

4 4 2 32 Severity

dependent upon

casualty

condition


casualty blood-

oxygen level

Incorrect

positioning

No or inaccurate

measurement of

blood-oxygen

level

Soldier with

casualty

Training;

information

inside MedEvac;

support from

ground station

Medic

6 4 2 48 Severity

dependent upon

casualty

condition


casualty blood-

oxygen level

Faulty device No or inaccurate

measurement of

blood-oxygen

level

Manufacture of

Pulse Oximeter

No connection

to computer; try

another device

4 4 2 32 Severity

dependent upon

casualty

condition



Product Name: Blood Pressure Patch



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Blood Pressure

Patch

Monitor

casualty blood

pressure

No connection No

measurement of

blood pressure

Electrical

breakage

No connection

to computer; try

another device

4 4 2 32 Severity

dependent upon

casualty

condition

Blood Pressure

Patch

Monitor

casualty blood

pressure

Incorrect

positioning

No or inaccurate

measurement of

blood pressure

Soldier with

casualty

Training;

information

inside MedEvac;

support from

ground station

Medic

6 4 2 48 Severity

dependent upon

casualty

condition


casualty blood

pressure

Faulty device No or inaccurate

measurement of

blood pressure

Manufacture of

blood pressure

patch

No connection

to computer; try

another device

4 4 2 32 Severity

dependent upon

casualty

condition



Product Name: Intraosseous Insertion



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Intraosseous

Insertion

For the insertion

of fluids, drugs,

blood

Incorrect

insertion

Unable to insert

fluids; cause

additional injury

to casualty

Lack of training Training 6 10 5 300 Support from

ground medic

Intraosseous

Insertion

For the insertion

of fluids, drugs,

blood

Fracture in bone Unable to insert

fluids; cause

additional injury

to casualty

Injury Multiple

insertion sites

6 7 7 294 Support from

ground medic

Intraosseous

Insertion

For the insertion

of fluids, drugs,

blood

Needle breaks Unable to insert

fluids; cause

additional injury

to casualty

Faulty

equipment; lack

of training

Multiple

insertion sites

5 10 4 200 Support from

ground medic



Product Name: Blood Transfusion



Revision Number: 0

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Blood

Transfusion

To recover

blood loss

Reaction to

blood type used

Casualty

condition

worsens

Incompatibility

of blood

Stop blood

transfusion;

Require

immediate

attention; access

to casualty notes

3 9 10 270 Unless blood

type of

casualty is

known, type O

Rh-negative

blood will be

used. Will not

know there is

an

incompatibility

until reaction is

seen in

casualty

Blood

Transfusion

To recover

blood loss

Blood not kept

at correct

temperature

which leads to

bacteria growth

Casualty

condition

worsens

Insufficient

monitoring of

refrigeration

system

Stop blood

transfusion;

Require

immediate

attention

4 9 3 108 Alarms on

refrigeration

system/ power

loss



Product Name: Ducted Fans

Developer: Sarad Limbu Lawati

Date: 9th January 2013

Revision Number: 0

Sheet Number: 1 of 1

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Fans Propulsion/

Thrust.

Damage Low thrust

performance and

unstable flight

Bird strikes,

stuff entering

the duct while in

operation

Cover the duct

with a net made

of strong fibre.

1 7 1 7 Replace or

repair the

damaged fan or

fan blades.

Static Pressure

loss or

insufficient

airflow.

Fan blades stall Auto detection

from control

unit.

2 2 1 4 Control systems

auto adjust fan

RPM (and )or

descend to a

lower altitude.

Main Ducts Improve air

flow, thrust and

shield the fan

blades.

Material failure

due to stress

loads

Material Failure,

enemy fire

(bullets etc) and

cracking growth

due to cyclic

loading for long

periods.

Routine Checks

and Repairs.

Avoid enemy

attacks where

possible.

3 4 2 24 Repair /

Replace.

Second Duct Divert airflow

into the main

duct in order to

reduce flow

separation

problems.

Same as above.

Also, noise

increase and

power demand.

4 2 1 8 Critical to duct

performance in

forward flight.

So, Replace

/repair. And

since a 2nd

duct



is on each end

of UAV, it can

fly either ways

facing forward.

Stator Vanes Support

structure for

duct

components and

straightening the

flow as well as

noise control.

No/less support

for Fan. If all

fail then no

thrust. If only

one fails then

reduced

performance.

Routine Checks

and Repairs.

5 4 4 80 Continuous

checks.

Flow diverting

Flaps

Thrust

Vectoring

Failure due to its

structural

components.

Less control of

the UAV.

Components

such as screws

and bolts being

loose of

jammed.

Control

algorithms will

adjust the flight

.

7 2 1 14 Routine Checks,

maintenance and

Repairs

Duct Flaps Control for

rolling moments

7 2 1 14



Product Name: Medical systems

Developer: Dela Yohuno

Date: 28th November 2012

Revision Number: 0

Sheet Number: 1 of 1

Product,

Device, Process

or System

Name & No.

Function Possible

Failure Mode

Effect of

Failure

Cause of

Failure

Control

Procedure

Occ

urr

ence

Sev

erit

y

Det

ecti

on

Ris

k P

rio

rity

Nu

mb

er

Remarks/

Actions Taken

Chest

compressions

and ECG

analysis

Performing CPR

to a casualty

Chest

compressions

interfering with

ECG analysis

Unable to

monitor ECG

signal and shock

patient

Interference

between two

devices

Pause chest

compression

before ECG

monitoring

4 4 4 64 Enable the two

devices to

communicate,

pause chest

compressions

before ECG

analysis.

Rotary servo

motors

Provide a stable

platform for the

patient

Patient is too

heavy/ power

cut

Loose, unstable

platform, unable

to lock the angle

in a position

Power-loss/ high

torque applied

Servo motor

brake mounted

locks angle in

case of

powercut and

higher brake

torque

6 4 2 48

Oxygen cylinder

gas leak

Supplying

oxygen to

ventilator and

other necessary

equipment

Damage

resulting in

puncture of

cylinder

Potentially

dangerous

explosive

environment

because of

Cylinder

damage,

Oxygen sensors

to detect leak,

vales to bleed

oxygen out of

the cabin,

3 6 1 18



electronics and

possible spark

Medical

equipment

Provide medical

trestment

Movement of

Medevac

causing medical

equipment to be

hazardous to

patient

Dangerous for

patient

Equipment not

secured

Secure

equipment well

2 5 1 10

IV Lines Supply the

patient with

fluids

Electromagnetic

interference

Stops treatment

or malfunction

High energy

radio

frequencies

Locate away

from High

frequency

raioation

4 3 1 12



Estimate the Frequency of Occurrence of the Failure

1. 1 in 1500000

2. 1 in 150000

3. 1 in 15000

4. 1 in 2000

5. 1 in 400

6. 1 in 80

7. 1 in 20

8. 1 in 8

9. 1 in 3

10. 1 in 2

Estimate the Severity of Failure – Severity Rating

1. No effect

2. Defect noticed by discriminating customers. Defect product - rectified in process

3. Defect noticed by average customers. Defect products <100% - rectified in process

4. Defect noticed by most customers. Defect products 100% - rectified or sorted

5. Secondary functionality operable at reduced performance level. Defect products 100% -

rectified or sorted

6. Secondary functionality unavailable. Defect products 100% - scrapped

7. Primary functionality operable at reduced performance level. Defect products <100% -

scrapped

8. Primary functionality unavailable. Defect products 100% - scrapped

9. Failure would endanger customer, machine or operator with a warning

10. Failure would endanger customer, machine or operator without warning

Estimate the Detection of Failure – Detection Rating

1. Current controls certain to detect/prevent failure mode

2. Current controls almost certain to detect/prevent failure mode

3. Very high likelihood current controls detect/prevent failure mode

4. High likelihood current controls detect/prevent failure mode

5. Moderately high likelihood current controls detect/prevent failure mode

6. Low likelihood current controls detect/prevent failure mode

7. Very low likelihood current controls detect/prevent failure mode

8. Remote likelihood current controls detect/prevent failure mode

9. Very remote likelihood current controls detect/prevent failure mode

10. Current controls will not detect/prevent failure mode

Estimate the Risk Priority Number

Multiply together the ratings for occurrence, severity and detection.

Design of a MedEvac UAV for Operation in Physically ...

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