Initial Selection of T/W and W/S for Design Layout

Aircraft Design – T/W and W/S

Anup Ghosh

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Outline

1 Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W

Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S

Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat

and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W Thrust to Weight ratio during sea-level static,standard-day conditions at design takeoffweight and maximum throttle setting.

W/S Ratio of the weight of the aircraft during takeoffand the area of the reference wing (not theexposed wing area)

Other condi-tions of interest

Combat and Partial Power

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Outline

1 Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing.

No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.

High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing.

Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank.

Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).

Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.

Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W).

Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Landing Gear and Fuel Tank Problem

Very low W/S implies large wing. No trouble for landing gear andfuel tank.High W/S implies small wing. Problem for landing gear and fueltank. Could be put in fuselage resulting increased wetted area andassociated drag.

Short Takeoff Distance

Large wing (low W/S) with a relatively small engine (low T/W).Slow acceleration, moderate time to lift off.Small Wing (high W/S) with large engine (high T/W). Aircraftmust reach high speed to takeoff.

Stall speed during the approach for landing is a critical requirementfor wing loading and it is independent of engine size.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Outline

1 Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

T/W related performance parameters

For a high T/W

accelerate quickly

climb more rapidly

reach a higher max speed

sustain higher turn rate

consume more fuel throughout the mission

increase of takeoff gross weight.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Variation of T/W

For a high T/W

Variation of aircraft weight during flight (fuel consumption)

Variation of engine thrust due to altitude effect.

As a statistical approach T/W is our first guess

Typical values of T/W are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Variation of T/W

For a high T/W

Variation of aircraft weight during flight (fuel consumption)

Variation of engine thrust due to altitude effect.

As a statistical approach T/W is our first guess

Typical values of T/W are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Variation of T/W

For a high T/W

Variation of aircraft weight during flight (fuel consumption)

Variation of engine thrust due to altitude effect.

As a statistical approach T/W is our first guess

Typical values of T/W are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

For propeller-powered aircraft, the equivalent term is powerloading expressed as W/hp

Equivalent T/W for propeller aircraft is as follows

T

W=

(550ηp

V

)(hp

W

)(1)

Some typical values of horsepower-to-weight ratio are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

For propeller-powered aircraft, the equivalent term is powerloading expressed as W/hpEquivalent T/W for propeller aircraft is as follows

T

W=

(550ηp

V

)(hp

W

)(1)

Some typical values of horsepower-to-weight ratio are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

For propeller-powered aircraft, the equivalent term is powerloading expressed as W/hpEquivalent T/W for propeller aircraft is as follows

T

W=

(550ηp

V

)(hp

W

)(1)

Some typical values of horsepower-to-weight ratio are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

For propeller-powered aircraft, the equivalent term is powerloading expressed as W/hpEquivalent T/W for propeller aircraft is as follows

T

W=

(550ηp

V

)(hp

W

)(1)

Some typical values of horsepower-to-weight ratio are

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

First estimation of T/W and hp/W from Max. Speed

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching - a better initial estimate

In a level unaccelerating flight

Thrust available during cruise = Drag, or, T = D

Weight must equal to lift, or, W = L

(T

W

)cruise

=1(

LD

)cruise

(2)

– no wing loading is considered

– recheck after wing loading selection

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching - a better initial estimate

In a level unaccelerating flight

Thrust available during cruise = Drag, or, T = D

Weight must equal to lift, or, W = L

(T

W

)cruise

=1(

LD

)cruise

(2)

– no wing loading is considered

– recheck after wing loading selection

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching - a better initial estimate

In a level unaccelerating flight

Thrust available during cruise = Drag, or, T = D

Weight must equal to lift, or, W = L

(T

W

)cruise

=1(

LD

)cruise

(2)

– no wing loading is considered

– recheck after wing loading selection

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching - a better initial estimate

In a level unaccelerating flight

Thrust available during cruise = Drag, or, T = D

Weight must equal to lift, or, W = L

(T

W

)cruise

=1(

LD

)cruise

(2)

– no wing loading is considered

– recheck after wing loading selection

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching – Variation of Thrust

Cruise Thrust

High bypass ratio turbofan = 20–25 % of takeoff thrust

Low bypass ratio turbofan = 40–70 % of takeoff thrust

Piston powered with super charger = 75 % of takeoff thrust

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching – Variation of Thrust

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Thrust Matching

(T

W

)takeoff

=

(T

W

)cruise

(Wcruise

Wtakeoff

)(Ttakeoff

Tcruise

)(3)

or, (hp

W

)takeoff

=

(Vcruise

550ηp

)(T

W

)cruise

(Wcruise

Wtakeoff

)(hptakeoff

hpcruise

)(4)

where(

WcruiseWtakeoff

)= 0.970 × 0.987 = 0.956 and

(TtakeoffTcruise

)or(

hptakeoffhpcruise

)are to be determined from Appendix A.4 or from data

available in open literature.For first phase estimation of T/W, consider the higher of eitherstatistical value or the value obtained from thrust matching.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Outline

1 Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Parameters affected by Wing Loading

Stall speed

Climb rate

Takeoff and landing distance

Turn performance

Cruise

Loiter

Glide

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Representative wing loading

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Stall Speed

It is directly determined from W/S and CLmax .

Improper estimation leads to failure to maintain flying speedand accidents.

Approach speed is also determined from stall speed.

Improper estimation also leads to post-touchdown accidents.

It is generally established from design specifications.

A stall speed of about 50 knots may be considered as theupper limit for a civilian trainer or othe aircrafts.

Apprach Speed

1.3 x Vstall for civil applications.

1.2 x Vstall for military applications.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

W/S from stall speed

In level flight and at CLmax

W = L = qstallSCLmax = 12ρV

2stallSCLmax

WS = 1

2ρV2stallCLmax

Anup Ghosh Aircraft Design – T/W and W/S

W/S from stall speed

In level flight and at CLmax

W = L = qstallSCLmax = 12ρV

2stallSCLmax

WS = 1

2ρV2stallCLmax

2013-09-11

Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design Layout

Wing Loading W/S

q = dynamic pressure = 12ρV

2,P0 = P∞ + 1

2ρV2

P∞ is Static pressure, P0 is Stagnation Pressure and an experimentally

measured value of this shows a pressure loss may be due to laminar region

near wall or due to stall induced flow separation in the trailing edge.

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Crude estimation of CLmax

CLmax∼= 0.9

{(Clmax )flapped

Sflapped

Sref+ (Clmax )unflapped

Sunflapped

Sref

}

or the previous figure maybe used for CLmax estimation.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Takeoff Distance Definitions

Ground Roll

Actual Ground Distance to takeoff(Minmum Vliftoff = 1.1 Vstal )

Obstacle Clearance Distance

50ft for Military35ft for Commercial50ft for Small Civil

Balanced Field Length or FAR Takeoff Field Length

Engine failure exactly at “Decision Speed”Same distance to Abort or Climb(Vliftoff = 1.1 Vstal to permit engine-out climb )

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Takeoff Distance Estimation

FindTOPfromtakeoffdis-tance.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

W/S from takeoff distance

Once the takeoff distance is obtained. Find the TOP from theprevious page figure.

Prop :W

S= TOP σCLTO

hp

W(5)

Jet :W

S= TOP σCLTO

T

W(6)

where, density ratio, σ = ρtakeoff alt.ρsea level

ρsea level = 0.00238 slugs/cft

CLTO=

CLmax1.1x1.1 , since takeoff speed is 10% more than the stall

speed.

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Wing Loading for Cruise

Maximum Prop Range

The speed of best L/D can be shown to result in parasitic drag equaling

the induced drag, (qSCD0 = qSC 2

L

πAe )

During cruise, W = L, so CL = W/Sq (wing loading divided by dynamic

pressure)

MaxPropRange :W

S= q

√πAeCD0 (7)

Maximum Jet Range

A jet aircraft flying a cruise-climb will obtain maximum range by flying at

wing loading such that the parasitic drag is three times the induced drag.

MaxJetRange :W

S= q

√πAeCD0/3 (8)

Anup Ghosh Aircraft Design – T/W and W/S

Wing Loading for Cruise

Maximum Prop Range

The speed of best L/D can be shown to result in parasitic drag equaling

the induced drag, (qSCD0 = qSC 2

L

πAe )

During cruise, W = L, so CL = W/Sq (wing loading divided by dynamic

pressure)

MaxPropRange :W

S= q

√πAeCD0 (7)

Maximum Jet Range

A jet aircraft flying a cruise-climb will obtain maximum range by flying at

wing loading such that the parasitic drag is three times the induced drag.

MaxJetRange :W

S= q

√πAeCD0/3 (8)

2013-09-11

Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design Layout

Wing Loading W/S

Wing Loading for Cruise

CD0 may be assumed as 0.015 for jet and 0.02 for a clean propeller

aircraft. e is the Oswald efficiency factor – a measure for the drag due to

lift, equals approx 0.6 for a fighter and 0.8 for other aircraft.

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Wing Loading for Loiter Endurance

For jet aircraft, the best loiter occurs at max. L/D (Eqn: 7)For propeller aircraft, loiter is optimized when the induced drag isthree times the paracitic drag. Wing loading for minmum powerrequirement.

MaxPropRange :W

S= q

√3πAeCD0 (9)

Anup Ghosh Aircraft Design – T/W and W/S

Initial Selection of T/W and W/S for Design LayoutCredible and judicious selection of T/W and W/SThrust to Weight Ratio (T/W)Wing Loading W/S

Selection of T/W and W/S

They are highly interconnected for Most RequirementsSelect T/W Statistically or by Thrust Matching then solve forW/S valuesConvert all to takeoff values for comparisionSelect lowest value for W/S, but ignore silly results.If required W/S is low, consider using better flaps to increase CL

Anup Ghosh Aircraft Design – T/W and W/S