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Simple Model Rocket Project

  1. Aug 31, 2009 #1
    We need to design a model rocket from scratch that is resistant to crosswinds and keep its trajectory withing a target zone.

    Does anyone know any methods to keep a model rocket stable in windy conditions?

    My idea was to make the rocket rather heavy, to resist the force of the wind. Would this work? Any other suggestions? Thanks
     
  2. jcsd
  3. Aug 31, 2009 #2

    berkeman

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    Staff: Mentor

    Gyro? Sun tracker?
     
  4. Aug 31, 2009 #3
    As you probably know, for a rocket to be stable the center of gravity (cg) must be closer to the nose than the center of pressure (cp). This is why the fins are at the tail of the rocket instead of the nose.

    http://exploration.grc.nasa.gov/education/rocket/rktcp.html

    The fact that the cp is closer to the tail than the cg means that in a wind the rocket will tend to weathervane into the wind. To prevent that, the cp must be at the same location as the cg but this will make the rocket unstable.

    To stabilize the rocket the easiest solution is, as berkeman suggests, a gyro.
     
  5. Aug 31, 2009 #4

    turbo

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    Gold Member

    How complex and expensive can this rocket be (assuming that you're going to build and test it)? The OP doesn't give parameters like weight, budget, etc.

    For example: If you have a very tight budget, and small solid-fuel motors, you may want to try spin-stabilization. Just attach the tail fins at an angle to make the rocket spin as it ascends. Very simple and low-budget.
     
  6. Aug 31, 2009 #5
    Combining the two ideas, I wonder if instead of using a gyro, if the angled fins were moved up so that the center of pressure was at about the same location as the center of gravity, whether the spinning rocket would be enough to stabilize its flight. Perhaps the cp could be slightly below the cg, enough to keep the rocket stable and yet minimize the weathervaning.
     
  7. Aug 31, 2009 #6
    It's a freshman Aero E project. We're supposed to build the rocket from scratch on a budget not exceeding $40. My original idea was to construct a heavy rocket, with angled fins. Instead of a gyro, would a spinning rocket be stable in window conditions?
     
  8. Aug 31, 2009 #7
    Oops, ok sorry. Didn't see all the posts. Thanks, Turbo.
     
  9. Sep 1, 2009 #8
    I'm not sure if a heavy rocket will be any better than a light rocket. Spinning the rocket will make it into a kind of gyro. The major effect you're going to experience is weathervaning, however.
     
  10. Sep 1, 2009 #9
    Wind resistant model rocket

    I have a new idea for this project I posted a few days ago.

    This is supposed to be a freshman Aero E project: fly a model rocket (built from scratch) in high winds to stay within a target area (10 degrees on either side of a straight line)

    My new idea is to reduce the size of the rocket to minimize the area the wind has to act on, and also increase the mass by adding weights inside the body to resist the force of the wind with it's momentum.

    Does anyone have any other suggestions to keep a rocket in stable flight in high winds?

    Or can anyone tell me if my idea is appropriate for this situation?

    Thank you all for your help,

    Abraham
     
  11. Sep 2, 2009 #10

    berkeman

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    Staff: Mentor

    Multiple threads merged into this original thread. Please do not multiple-post here again, Abraham.
     
  12. Sep 2, 2009 #11
    Sorry everyone. I hadn't realized that wasn't allowed.
     
  13. Sep 2, 2009 #12
    Re: Wind resistant model rocket

    What is your idea of how the wind will affect the rocket's flight? Do you expect the wind will blow the rocket downwind?
     
  14. Sep 2, 2009 #13
    Re: Wind resistant model rocket

    No, I meant to say a cross wind, which will travel perpendicular to the rocket's flight. The goal is to get the rocket to stay on a straight course. I'm thinking that if I reduce the area of the rocket normal to the air flow, there's less acting force on the side of the rocket?
     
    Last edited: Sep 2, 2009
  15. Sep 2, 2009 #14
    I presumed the rocket's path is vertical so the wind would always be perpendicular, or isn't the rocket's path vertical? Again, how do you think the wind will affect the rocket's path?
     
  16. Sep 2, 2009 #15
    Ah, right, I forgot to mention.

    We're allowed to angle the launch rod up to 30 degrees from vertical, which would send the rocket forward. The rocket should not veer more than 10 degrees outside a straight line drawn on the ground.

    I understand the effect of weathervaning, and the proper locations of the CG and CP. I am assuming that if I can reduce the area exposed to crosswind, that the rocket will not experience as much force on it from the wind. Is this assumption correct?
     
  17. Sep 2, 2009 #16
    I think that assumption is correct. Are you planning to minimize the size of the fins.

    I was thinking if you move the fins up so the cp is just slightly behind the cg and angled so they spin the rocket, the rocket will still be stable, the wind will have only a slight weathervaning effect and what effect it does have will tend to counter it being blown downwind.
     
  18. Sep 2, 2009 #17
    Excellent. Thanks for your help skeptic2, much appreciated
     
  19. May 29, 2010 #18
    I know that this is bit late for this thread but...
    Why don't you compensate for the wind by measuring its speed an firing the rocket at an angle into the wind. This would be similar to a sniper compensating for the wind affecting the bullet. you would need to measure the wind effect on your rocket for different wind speeds but it would be an inexpensive approach on your very limited budget.
    Or is the direction of launch not a parameter that you have any control over.
    Either way, I expect that you have done your launch by now. Let all us know how it went.
     
  20. May 30, 2010 #19
    yeah, we've since launched and I almost forgot about this whole thing!

    Eventually, I couldn't convince the rest of the team to make a spinning rocket by angling the fins. Everyone was concerned with the probability of a fin not being just right and the rocket veering off course.

    The final design was less than just over 8in in length and razor thin stub wings. We were trying to make it fly as fast as possible. Launches went well, we even got extra credit

    In the end, I think I was over-designing rocket (spin stabilization, haha). Clearly I overestimated the expectations for a freshman project... but it worked just fine anyways....
     
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