Fin bent

[askrob]

I launched my Wildman Gizmo a couple of weeks ago. I was using an Aerotech K535. Well, the ejection charge went way early, which I think was a faulty motor, but not sure. This caused my chute to ripped off. The rocket came down hard on one of the fins and bent it. How can I straighten the fin?

 

[Tractionengines]

Here's what I would try... CAREFULLY.

HEAT. Use a heat gun to soften the epoxy. When you hit the right temperature you can flex it back. Then hold in place as it cools back down. It wouldn't be as strong as original, but should be passable.

At that point if you want more security, then cut out the external fillets and redo them. (I wouldn't unless cracked. Which it looks like at least part of yours is.)

 

[askrob]

Here's what I would try... CAREFULLY.

HEAT. Use a heat gun to soften the epoxy. When you hit the right temperature you can flex it back. Then hold in place as it cools back down. It wouldn't be as strong as original, but should be passable.

At that point if you want more security, then cut out the external fillets and redo them. (I wouldn't unless cracked. Which it looks like at least part of yours is.)

Thanks. I'll try that. I think some of the internal fillets are cracked as well, so planning on injecting some epoxy.

 

[David Schwantz]

Is the fin bent or is the epoxy being out of place just holding it that way. I agree with heat, but I would soften the epoxy, scrape it off and redo.

 

[askrob]

Is the fin bent or is the epoxy being out of place just holding it that way. I agree with heat, but I would soften the epoxy, scrape it off and redo.

It looks bent but could be the epoxy.

 

[Handeman]

Fiberglass fins don't really "bend" permanently, they crack or break. If it's "bent" it's because the inner and outer fillets are broken.

I would remove the outer fillets, pull the fin out and use a Dremal to clean up the MMT and fin. Then re-epoxy to the MMT and new external fillets.

 

[mrwalsh85]

I think it's broken inside the airframe. Whether the fin itself is broken, or the epoxy joint below the body tube.

Can you wiggle it side to side? If it was able to "relocate" itself, I suspect you should be able to "flap" the wing, for lack of a better word. If so, you need to extract the fin. Hopefully it's just the epoxy joints, and you can get it out and do some cleanup and throw in some new epoxy and go for it. But if the fin is broken, a little more surgery is required.

 

[BigMacDaddy]

Would you guys ever use a temporary (or permanent) pin through the airframe against the fin / inside the fillet to make sure that fin stays straight?

 

[askrob]

I think it's broken inside the airframe. Whether the fin itself is broken, or the epoxy joint below the body tube.

Can you wiggle it side to side? If it was able to "relocate" itself, I suspect you should be able to "flap" the wing, for lack of a better word. If so, you need to extract the fin. Hopefully it's just the epoxy joints, and you can get it out and do some cleanup and throw in some new epoxy and go for it. But if the fin is broken, a little more surgery is required.

It does not wiggle. It's firmly in place. I'm going to drill a hole next to the fin so I can look inside and inject some epoxy. At least that's my thought. I'll get the outer fillets off first.

 

[David Schwantz]

I have never used a pin, but, I have made fin slots in MD rockets so the fin goes in the slot, but not into motor.

 

[cichlidgoob]

It does not wiggle. It's firmly in place.

I recently had a similar failure on a 4 inch fiberglass rocket due to a CATO. Two fins broke free from the epoxy bonds on the motor and body tubes but both fins moved only about 1/8 of an inch. The paint was chipped and that is the only reason I knew something was wrong. The crazy part is that the fins were still solidly in place and could not be moved by hand. They were so tight that I bet it could have flown. After wrestling it for a few minutes I ended up putting the fins in a vice and beating the body tube off of them with a rubber mallet to get them out. There was some minor damage to the ends of the fin slots but the fins were in good shape. It’s all repaired now waiting for the next flight, which will hopefully be Saturday.

Unfortunately, I broke the first rule of TRF…I did not take pictures. I will do better next time.

 

[askrob]

The epoxy was holding the fin. I was able to remove the fin with heat and an X-Acto. Now to sand everything down and reattach.