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I was to design my own rocket.

  1. Apr 17, 2008 #1
    I was to design my own rocket and build it eventually. I am a Computer engineering student and want to go for the other side of engineering. I want to learn all the math and everything. So how an I go about this? Is there some good books? just a general introduction would be great.
  2. jcsd
  3. Apr 17, 2008 #2
    ......No. Just no.
  4. Apr 18, 2008 #3
    Why not start with model rockets?
  5. Apr 18, 2008 #4
    how high are your ambitions ? do you just want it to rise some 100 feet into the sky and then come down on a parachute ? in this case a model rocket would be fine. or higher ?

    do you want it to carry a payload (please dont say "a warhead" :eek:) ? perhaps some device to record the acceleration or air pressure ?

    do you want it to rise more or less straight up into the sky or do you want it to have some sort of attitude control ?
  6. Apr 18, 2008 #5
    start with model rockets first
  7. Apr 18, 2008 #6
    Q1. How much do you already know?

    Q2. How big do you plan on going?
  8. Apr 18, 2008 #7
    The basic ideas are very simple. Simply create a streamlined body and add a source of propulsion to the back of it. A small rocket can be constructed using material available from the Estes Rockets Company, which sells kits for model rockets. To be able to predeterimine the rocket motion will require a bit more. The rocket equation requires a basic understanding of physics and a year or two of calculus. To include air resistance you can either get into the very difficult task of attempting to calculate it from basic aerodynamics principles or you can simply place it in a wind tunnel and measure the resistance. The later is much easier and will allow you to start working with it earlier. After you get the hang of the simple stuff and you learn more math and physics then you can start thinking about guidance systems. You can also start working with high power model rockets. To actually design and build liquid rocket engines will require some advanced knowledge of materials and thermodynamics.

  9. Apr 20, 2008 #8
    I'm not an expert, but here is some ideas:

    If you neglect both gravity and air resistance then the final speed of the rocket will be determined by formula:


    where v0 is the speed of exahaust gases, M is the starting mass and m is the final mass of the rocket. This formula follows from conservation of momentum.
    The assumption was that the difference between masses M-m equals the mass of the fuel (single stage rocket).
    You want to maximize v0 and the quotient M/m to get the greatest speed.
    ***I'm not sure if propulsion for model rockets needs air to work. In this case the calculation of the final speed is a bit different, since the mass of the exhaust gas is not equal to the change of rocket mass.

    If the rocket is accelerating in Earth's gravity (but still no air resistance), then it is best to burn all fuel as fast as possible, because the energy efficiency of a rocket is best at higher speeds: burning a small fuel mass dm only determines the change of momentum(speed) of a rocket dp(dv), so the rocket will gain more kinetic energy if the fuel is spent at greater speed. Slow acceleration upwards is not a good thing. In this aproximation the maximum hight you can achieve is v^2/2g=v0^2*Exp(2*M/m)/2g. This solution corresponds to instantaneous burning of all fuel.

    Air resistance has the reverse effect: if the rocket accelerates to a high speed very quickly, the drag force will increase. So you must find the correct balance between fast acceleration (to maximize efficiency) and slow speed (to reduce air resistance). The differential equation for vertical flight should look like:

    dm/dt=-mf(t) (mf=mass flow)

    I think this equation should be solved numericaly: for each mf(t) you get the maximum h at the moment when v(t)=0. k should be estimated with a test flight. Then you try to distribute the mass flow mf(t) over time to get maximum hight.
    Last edited: Apr 20, 2008
  10. Apr 20, 2008 #9
    Isnt the formula v=v0*ln(M/m) ?

    and I dont think model rockets need air to work. in fact I think the only kind of rockets that need air are some advanced designs like scram-jets. the "classical" rocket does not need oxygen, it has its own oxydizer.
  11. Apr 20, 2008 #10


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    Staff: Mentor

    You are correct - it wouldn't be possible for air to get into the combustion chamber to make a model rocket engine work. So it has oxidizer in it already.
  12. Apr 21, 2008 #11
    Sorry for the mistake: of course the formula for the speed of the rocket is

  13. Apr 22, 2008 #12
    Just want to start slow and work my way up. As for math and Physics Ive taken Engineering Physics 1-3 and math from calc1-calc 3, Linear algebra and differntial equations.
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