rocksim really long rocket questions

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Well-Known Member
Jan 20, 2009
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At work (i work with composites for a living) we had a scrap part. The shop guys know never to dispose of scrap that 'looks like a rocket' but to give it to me.

I have a fiberglass tube 1.5 inches in diameter at the top, 2 inches in diameter at the bottom and 14 feet!!! long. Good and stiff, weighs around 4 lbs. I gotta launch that sucker!

does Rocksim handle something with this far out of an (70 to 1) aspect ratio? I'm a bit concerned about stability.
are you suggesting modeling it as a transition because of the taper or for stability?

I'm more concerned about the fidelity of the predicted CP and stability in this case.
I plugged the numbers into RockSim and gave it a nose cone. The CP prediction isn't too extreme, and even a set of small fins on the back would do well for a straight model of this size. Bring it out to NARAM-52 and enter it in F-SuperRoc Altitude!.
are you suggesting modeling it as a transition because of the taper or for stability?

Stability, so that it properly knows the shape, and can make a reasonable CP calculation.

Truth be told, because it doesn't flare much, you could model it as a tube the diameter of the top, with fins on it, and if it's stable that way, it'll be stable.

Would I fly it without any sort of fins? Nope -- it's basically a tube. Modeling it as a transition will likely allow you to reduce the fin size a little bit.

You hardly need a sim. An aspect ratio that high will make it stable almost whatever you do. As long as it's stiff enough, your only problems will be ones of handling.
I also found that a long and thin rocket of mine always broke its coupler. That one was rather bendy, though.
With Rocsim, can I put a single motor on one side? I have been thinking that I might try this one 'bottle rocket' style with the motor sitting on the top offset from the body tube. I was thinking of mounting a Skyripper k on the top. Have the chute come out on top. The launch setup would be a rod that would run 10 feet up the body tube (on the inside).

Cant think of any reason it wouldn't work, The stability would increase, the offset thrust can be minimized by slightly canting the motor mounts. There are some practical issues (long fill line for the hybrid, etc) Any way to model this in Rocsim?