Leaning fin?

[Kevin OslerParticipant]

OK, question for you aerodynamic wizards. Son in law is building his first HPR rocket. Its a PML Calisto with a 38mm motor mount and will fly, according to PML, to 7k on a J330.

Well, as he was epoxying one of the fins in place last night, it must have been hit by the cat or something while it was drying and one of the three fins is now leaning to one side by about 15 degrees. Its a through frame construction rocket and he used 30 minute epoxy. I am afraid of cracking the Quantum tubing, breaking the fiberglass fin or at least tearing up the motor mount if we try to correct it.

Here is my question, what affect will this have on rocket stability? I know in smaller rockets there doesn’t seem to be much affect, but how about larger, faster ones like this? I would be more concerned if it wasn’t straight as I know this would seriously affect it, but what about leaning?

[MikeSModerator]

I have two cats. Sometimes it’s impossable to work without cat help.

I found this. Covers it pretty well.

http://www.apogeerockets.com/downloads/Newsletter42.pdf

Does not say what will happen but it will not be 100% stable.

My guesssssss. The J will make the rocket haul &%#. But the
G10 fins are thin. If the CP/CG is correct it will probably be OK.

I have seen worse fly well.

I would make a maiden flight on a much smaller motor to
see what may be any issues, at a much slower speed.

[edwardModerator]

You’ll get a rocket that has some nice coning action. I had a rocket like that once also. Fin was leaning. About 5 seconds into a 8 second burn the rocket was coning in about 5 foot diameter circles. I thought it had lost a fin. I had to replace that fin.

http://www.info-central.org/?article=124

Edward

[Kevin OslerParticipant]

Great articles!

Well, we remeasured and its more like 10 degrees off I guess. He was planning to cert with the I540 (to take advantage of the Cessaroni deal), but I think instead he will cert off of the smallest H Joe brings to see how bad the coning is.

He is reinforcing right now with fillets but should be ready for Saturday.

[Jeremy Long]

Thanks for all the input guys. After running RockSim and doing some heavy duty fillets I am hoping she will have a decent maiden flight on Saturday!

[James Russell]

You could fix the problem if you have not done fillets. If you have just tacked the fin in place by putting epoxy on the root edge of fin and pushed it though the airframe to the motor tube. You might pull a little paper off the motor mount but it really is not that hard to break the fin loose again if you need to. Once you have added fillets inside, out side or both it is to late. As they have said, it should fly fine with maybe some coning or will not have a straight flight. Let us know how the flight went.

[Kevin OslerParticipant]

His rocket flew pretty good. A slight wobble can be seen from the smoke but not much. http://www.youtube.com/watch?v=X84gufeiOmw&feature=youtu.be

5,261ft on a H175.

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