MODEL OF CHARGE CARRIER ROCKET LOUNCHER ON RESEARCH MEASURING PRESSURE, TEMPERATURE, AND HUMIDITY

International Conference on Engineering of Tarumanagara (ICET2013)

Faculty of Engineering, TarumanagaraUniversity, Jakarta-Indonesia,October,2-3,2013

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MODEL OF CHARGE CARRIER ROCKET LOUNCHER ON RESEARCHMEASURING PRESSURE, TEMPERATURE, AND HUMIDITY

Mochammad Ilham Attharik1), Ahmad Hidayat Furqon1), Pirnardi2),Eko1)

1)Mechanical Engineering, Pancasila University, Jl. Srengseng Sawah,Jagakarsa, Jakarta Selatan 12640, Indonesia.2)LAPAN, Rumpin, Bogor, West Java, Indonesia

e-mail: [email protected], [email protected],[email protected],

Abstract (10pt)

Rocket is flying vehicle that can be used for research measuringpressure, temperature and humidity at a certain height. So that therocket can glide, need a launcher, this paper discusses the creation andtesting of two kinds of launchers, the pneumatic system and the fuelsystem (butane). The test results of the model rocket launcher with atotal weight of 1.5 kg can fly as high as up to 7 meters from the runway..

Keywords: launcher, pneumatic system, the fuel system.

INTRODUCTION Rocket is one of the aerospace vehicle that has a specific

function. This vehicle can be used to carry out the mission ofpeace and defense, such as Rocket Launchers Satellites (RPS),weather detection rocket, guided missile, rocket ballisticsurface-to-ground, ground-to-air and air-to-air. In otherwords, the rocket could also serve as tools to safeguard thesovereignty of the State and nation, whether on land, sea andin the air to the space. Indonesia as the country's large andextensive it is fitting to achieve sustainable independence incontrol of rocket technology. Therefore, continuous efforts areneeded to achieve this independence. One of them grow anddevelop the business through a love of technology throughtechnological mastery aerospace rocketry since early incollege.

This technology is expected to develop in the students inthe design rocketry technology, both in terms of the rocket and

mailto:[email protected]





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its payload ranging from stage design, create, test to testfly. Through understanding the behavior of rocket launcher thatis applied to the operational requirements of the rocketpayload, the students will be able to understand the technologyof rocketry, which in its development, payload design studentoutcomes can be a forerunner to the birth of rocketry inIndonesia.

In this paper, we discuss one of the supporting of rocketlaunchers models using butane, using potato gun. Fromexperiments we made this launcher, the launcher turns the modelis able to fly a rocket weighing 1.5 kg.

MATERIALS AND METHOD MATERIALSHere's a list of parts we bought for our gun:- 13" of 4" PVC, 48" of 2" PVC, PVC Cement (the glue),Increaser 3 " to 4 ",- 3" to 2" Bushing, 4" Threaded Adapter, 3" Threaded Adapter,4x4x3" PVC T-Pipe (the handle)

- 4" Threaded Plug, 3" Threaded Plug- Electric BBQ (igniter)

METHOD Barrel Size:

: The combustion of the fuel in the firing chamber willcreate a set pressure that has to escape through thebarrel of the spud gun accelerating the potato out at aspecific velocity. The size of spud gun barrels usuallyrange from 1.5 to 2.0 inches in diameter with 1.5 inchesbeing the standard. The larger the diameter the less theacceleration of the spud projectile. This is due toNewton’s 2nd law F=ma which can be written as a=F/m orm=F/a. If the diameter of the barrel is increased theforce acting on the spud is dispersed over a largersurface area and therefore it will have a sloweracceleration and intern a lower muzzle velocity. Also withthe larger diameter there is a larger projectile whichwill have a larger mass. This larger mass will reduce the



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acceleration of the spud as well. The length of the barrelis entirely up to you but remember the longer the barrelthe more friction has to be overcome. It is safe to saythat to an extent a longer barrel is more accurate than ashort one. The typical range of barrel length is betweentwo feet and four feet..

Rifling: The inside surface of a barrel can be riffled or unrifled.Riffling is essentially several spirals cut into theinside of the barrel to cause the projectile to spin inthe barrel. When the projectile leaves the barrel itspirals down range much like a football. When theprojectile spins on only one axis, the one parallel to theaxis of the barrel, it reduces the drag on the projectile.The less the drag is the farther the spud will travel andwith the reduction of cross forces, due to the wobbling ofthe spud, a higher accuracy can be achieved. The unrifledbarrel does not provide this balancing to the flight ofthe projectile and it therefore is unstable and lessaccurate as a result. However due to the difficulty ofmachining riffling on the inside of a 1.5 inch PVC pipethe unrifled barrel is the most common in use..

Projectile Motion:: If physics has taught man anything other than that gravityworks it would be that a projectile follows a parabolicpath when launched. This is because the force of gravityis independent to the force of the combustion in thefiring chamber acting on the projectile. Using physics itis possible to calculate the distance that the projectilewill follow one fired. If a pressure gage is inserted intothe firing chamber so that it can take a reading of themax pressure build up before the spud is propelled out ofthe barrel several equations can be applied and ultimatelythe distance traveled by the spud can be found. It isimportant to place the pressure gage in a fitting orthicker part of the firing chamber so that it will not beblown out of the chamber as a projectile. The preferred



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type of gage to be used is one that pushes a peg to thehighest pressure and then stays requiring that it be resetafter each use. Otherwise you would have to estimate themax pressure by inspection of the dial during firing. Oncethis max pressure is obtained you can use it to calculatethe force on the spud in thebarrel. .

F = p*c(1)

Where F is the force in Newton’s on the spud in thebarrel, p is the max pressure in the firing chamber inPascal’s, and c is the cross sectional area of the spud inthe barrel. To convert psi into Pascal’s multiply by6.895E3. Remember that the cross sectional area of thespud is the cross sectional area of the barrel. This isfound by using

c = p * r2

(2)

Where c is the cross sectional area of the barrel, and ris the radius of the barrel in meters used. Once the forceon the spud projectile has been found Newton’ second lawcan be applied

F= m * a(3)

Where force F in Newton’s, is equal to mass m in kg, timesacceleration a in m/s2. The mass of the potato can easilybe found by finding the mass of the whole potato beforebeing cut in the barrel and then taking the mass of thatpotato after being cut and to find the mass of the potatobeing shot out of the barrel. Set m*a equal to the aboveequation p*c after making the substitution for c and solvefor a. This gives

m * a = p * p * r2



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(4) a = (p*p*r2)/m (5)

After taking the mass of the projectile potato, m in kg,you will have the pressure in the chamber, p in Pascal’s,prior to firing the spud, the radius of the barrel, r inmeters, and the mass of the potato shot. From all of theabove equations it is possible to find the acceleration ofthe potato down the length of the barrel given by equation(4). This is of course assuming a frictionless barrel. Inorder to calculate the friction of the spud in the barrelit is suggested that a spud projectile of average size anddensity be pulled out of the barrel by use of a hookthrough the spud and attached to a fish weighing scale.This will give the kilogram force needed to overcomefiction in the barrel but it must then be converted toNewton’s by multiplying the value times g..

W*g=N (6)

W is the weight read from the scale in kg, g is thegravity constant =9.81m/s2, and N is the force of thekinetic friction of the potato in the barrel in Newton’s.So from the previous calculation of the kinetic fiction Nof an average spud projectile it is possible to find thetrue acceleration of the spud as it passes down the barrelfrom this equation.

m * a = ( p * p * r2) – N(7) a=[(p * p * r2) - (W*g)] / m(8)

Where a in m/s2 is the acceleration of the spud in thebarrel, p is the max pressure in the firing chamber givenin Pascal’s, p is the constant » 3.14, r is the radius ofthe barrel in meters, W is the weight given by forcing anaverage potato out of the barrel with a scale inkilograms, and m is the mass of the potato projectile.



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Where not quite done yet! We still have to find thevelocity of the potato now as it leaves the barrel. Thiscommonly referred to as muzzle velocity. This can be foundfrom the equation::

V2 = Vo2+2*a*x(9)

Where V is the muzzle velocity, Vo is the initial velocitybefore firing or 0, a is the acceleration found above, andx is the length traveled by the spud or the barrel length.This yields the following equation..

V2 = 2 * a * x(10)

After substituting in a from equation (8) in to equation(10) You get

V2 = 2 * x * {[(p*p*r2)+(W*g)]/m}(11)

From this muzzle velocity V can be found by taking thesquare route of both sides

V= sqrt [ (2*x*{[(p*p*r2)+(W*g)]/m})](12)

Once the muzzle velocity V in m/s2 is accuratelycalculated being careful to have the correct unitconversions the following formula can be applied to findthe distance that the spud could travel if there is no airresistance or drag. .

R = [V2/g]*[sin (2q )](13)



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Where R is the range in meters, V is the muzzle velocityof the projectile, g is the gravity constant = 9.81 m/s2,and sin (2q) is the sin of 2 times the launch angle q .When (12) is substituted into (13) the following equationresults. .

R = {[ sqrt (2*x*{[(p*p *r2) +(W*g)]/m})]2/g}*{sin (2q )}(14)

Again to summarize:

V– Muzzle velocity (m/s), x– length of barrel in (m), p–Max firing chamber pressure in Pascal’s or (N/m2), p – »3.14, r– radius of barrel in (m), W– weight shown on scalewhen pulling spud out of barrel (kg), g– gravity constant= 9.81 (m/s2), m– mass of the spud projectile in (kg), R–is the range of the projectile in (m), q – is the launchangle (deg).

RESULTS AND DISCUSSION

ResultsWe did a bit of research on the ideal combustion chambervolume to barrel volume ratio. Information on this is hard tocome by but one source said 1.5:1 was ideal. we measured SpudLauncher I and it had a ratio of 2.1:1 and it was quitepowerful. If we followed a 1.5:1 ratio the gun would totallyloose the cool "canon" appearance so we decided to go with aratio of 1.8 : 1. How we built or potato cannon was simple. We tooktwo pieces of PVC piping, one piece had a twist off cap andthe larger chamber was connected to the smaller chamber. Ahole was drilled on the side of the PVC pipe in it we placeda grill igniter. For fuel we used hairspray, gas, butane etc,basically anything that would combust with a spark. So nowhow does the design help shoot the potato out see figure 1.



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Figure 1.part of our design potato gun with igniter

Figure2. susunan rancangan potato gun

We was planned to use 4" PVC, for the chamber and 2" PVC forthe barrel.= Pi*4^2*21 / Pi*2^2*47= 1.78 : 1 and dimension of our design see figure 3.

Figure 3. dimension of our design

Then do the testing of the design, field testing wasconducted in university engineering faculty Pancasila, theelevation angle of 90o on the ground, in the model rocketmass overload 1 and 1.5 kg (includes the components andhumadity pressure sensors, transmitters, etc). relative tothe reference engineering faculty building 3rd floor, betweenfloor height of 3.5 m.

http://4.bp.blogspot.com/-AzupmRjyefI/Tr3kZVm2siI/AAAAAAAAAC0/OhnnuO0pEt4/s1600/potato+cannon.jpg



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Used as the theodolite to measure the height of the rocket,for butane materials varies from 60%, 70%, 80%, 90% butane,the results obtained are table 1 and table 2:

Table 1 the results of tests for the launch of the load 1 kg

No Butanecomposition

High(m)

1 60% 52 70% 5.53 80% 7.54 90% 7.5

Table 2 the results of tests for the launch of the load 1.5kg

No Butanecomposition

High(m)

1 60% 52 70% 53 80% 6.54 90% 7

Analysis:The greater composition of butane, the greater the combustionchamber, and the resulting thrust will be greater, as well asthe resulting sound will be even greater.

The following 2 kinds of testing for the ignitor ignitornormal (A type) and large ignitor (ignitor is commonly usedin car cigarette / B type), with a composition of 80% butane,and 1.5 kg load as table 3.

No Ignitor type High(m)

1 A 6.75



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2 B 7.5

Analysis:The larger the resulting spike ignitor, then the greater the combustion chamber, and the resulting thrust will be greater,as well as the resulting sound will be even greater.

CONCLUSIONS

1. Of the design as a potato gun louncer for the modelrocket, able to function in accordance with thecalculation.

2. Butane composition in combustion chamber size, verydecisive thrust of the model rocket, the higher thecomposition, then the resulting distance further away,as well as the resulting sound.

3. Igniter is used to produce a spike in combustion chamberaffect, in this case the big spike of the Ignitergreater thrust.

4. Barrel size which is a variable length, must becalculated with certainty that the intended directionfor the better.

REFERENCES [1] Fishbane,. et.al, Physic for Scientist and Engineer 6th

edition, Pearson 2000.[2] Halliday, Resnick., Physic 5th edition, John Wiley and

Son’s. [3] Hibbler., Engineering Mechanics Dynamics 7th edition,

Pearson 2005.[4] Saad., Thermodynamics 2nd edition, Pearson 2006.

MODEL OF CHARGE CARRIER ROCKET LOUNCHER ON RESEARCH MEASURING PRESSURE, TEMPERATURE, AND HUMIDITY

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