I am working with a university bunch of other university students on building a very large amateur rocket. Our objective with this rocket is just to go very high, with no significant payload or flight ceiling to consider. We obviously must recover the rocket within the range.

Conventional logic would indicate that launching straight up would be the optimal strategy to achieve our desired apogee, but due to range safety, there must be a minimum launch angle off of the launch rail. Our vehicle will feature fins and spin tabs for stability.

What I am trying to do is analyze the flight dynamics of our Rocket and make sure it won't kill us, will stay within the range, and attain its design altitude.

This image by NASA is what I am basing much of my intuition on, along with some intuition on gyroscopic procession/vectors for the spinning. NASA Rocket stability

In my mind, as long as the cp is a couple of rocket body diameters below the cg, the rocket will try to restore itself to a 0deg alpha very aggressively. Add in a spin, and there should be an appreciable measure of stability while in motion. Because of this, I believe it should be accurate enough to state the rocket will follow its velocity vector once at appreciable velocity. If I am wrong, what do I need to do to analyze stability during this phase?

The trickier part for me is analyzing stability off of the rail, at ""Low"" velocities, since the stability off of the rail will largely determine how successful we are at staying on range, and achieving altitude. What analysis is necessary to determine stability here? I know potential sources of torques (external plumbing, launch lugs, fins), but I am unsure of if these are useful and how to proceed.

Thanks, any help would be greatly appreciated.

  • 3
    $\begingroup$ The most important thing to consider is that aerodynamically stabilized rockets lean into the wind (the wind pushes the fins more than the body tube). It's also surprisingly hard to build a rocket that doesn't spin and even fast spinning ones don't seem much more stable. At big heights even a small lift-off angle results in huge horizontal speeds at the apogee so make sure to use a drogue and deploy the main chute at ~100m above ground. Use OpenRocket to simulate your rocket. TBH Finding a big enough launch area and getting a launch permit are the hardest parts. $\endgroup$ – Christoph Mar 13 '19 at 7:49
  • $\begingroup$ We are well aware of the need for a drogue chute. 100m is far too low, as the dry mass of our rocket is currently projected to be around 250 lbs. Loaded, the sucker should be about 700 lbs. To my knowledge, we should be granted a extended range at spaceport America for the competition. Is it possible to get a launch into the wind granted to minimize the amount of deflection weather cocking will cause or is that too dangerous? $\endgroup$ – WhisperingShiba Mar 14 '19 at 0:25

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