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Well-Known Member
Jan 13, 2004
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I ran into a problem with my TTW application recently.
I had some glue build up on the motor mount centering rings. It made it impossible to get a tight flush fit. I ended up with some gaps between the motor mount ring and the top edge of fin that is supposed to butt to the underside of the centering ring.
My qustion is...
The fin is still through the wall, but not butted tight to the centering ring. How bad is this gap going to effect the strength? It is intended to be a mid power rocket.
Do the fins go all the way to the motor tube? If so, you should be fine as long as you have some nice fillets on all the exposed joints.

If you can remove the aft centering ring, you can add some more epoxy fillets internally.

If you drill some holes in the aft centering rings, you can pour some expanding foam in the area between the fins and tubes. Be careful when you do this... if you put to much foam in, it may deform you rocket. I had this happen with my Big Daddy :(.
Yes, They do. The foam idea is pretty good though! I like it. I think I may be ok as you said. Only one way to find out... LET HER RIP! (or R.I.P. which ever the case may be) It's a learning experience either way.
you can trim the corners off the fin tab ,so they don't interfere with the fillets,
I just had to do what Stymye recommended on my Fat Boy build. The centering ring / engine tube fillets were interfering with the fins. I sliced off small 45 degree corners off the fin tabs. I'll post a pic shortly.