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  #1  
Old 05-29-2019, 04:37 PM
UlteriorModem UlteriorModem is offline
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Default Busted fins

A couple of weeks ago I launched my Goblin and when it came down one of the fins busted loose. It actually tore off the paper tube and was not broke.

So I repaired it with some Titebond figuring that would fix it. About a week later I flew it again on a C6 3 and the same fin busted off again! Although one of the two streamers came off in descent. But still the same fin?

Also the same day I launched a quite old Baby Bertha. It had been in 'storage' for about 4 years. When it came down two of the fins broke. The glue joint held but the fins broke along the grain. Was that because it is old and the balsa is dry and brittle?

Anyhow, some tips on this kind of repair?

Would epoxy be a better choice?
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  #2  
Old 05-29-2019, 05:32 PM
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ghrocketman ghrocketman is offline
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When in doubt, use Epoxy... I always say.
Do NOT use "5 minute" epoxy... 15, 30, or 60 min work time epoxy will soak into both the wood and cardboard actually strengthening it.
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Old 05-30-2019, 04:58 AM
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mycrofte mycrofte is offline
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All I use is 5-Minute Epoxy for fillets. It cures rubbery and has some "give" to it.
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Old 05-30-2019, 09:02 AM
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ghrocketman ghrocketman is offline
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That's the problem with 5 minute epoxy.
It IS rubbery and almost never fully cures, unlike other types.
I do the opposite with fillets, using the longest cure time...30 min pot life epoxy.
It dries extremely smooth and hard. Soaks into both the wood and cardboard.
Impact would destroy the rocket before the joint.
Probably why I NEVER have "Busted Fins".
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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL
, if you have to ask what is "NORMAL" , you probably aren't !

Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, and HAVOC !
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  #5  
Old 05-30-2019, 03:43 PM
UlteriorModem UlteriorModem is offline
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Never is a long time as my Father would say

I use this stuff for fillets. Works well. Also for attaching the fins I used the 'double glue joint' method.

https://www.landmsupply.com/departm...=All%20Products

Like I said on the Baby Bertha the fins broke along the grain line. I think they were old and dry and brittle. Also I put the fins on wrong so the grain was running the wrong way

The Goblin the glue joint did not really fail, it ripped off the glassine and some cardboard with it.

On bigger models I do use epoxy and have learned to use JB Weld on the engine mounts. Had an old Big Bertha, thing probably had 2 dozen flights on it. One day I hit the ignition switch and the engine mount shot out of the centering rings, up the tube, popped off the nose cone and went flying in circles
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Old 05-30-2019, 05:18 PM
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Chas Russell Chas Russell is offline
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I cut or scrape away the glassine coating on paper tubes to get to the rougher paper to aid in the adhesive soaking in. I score the glassine slightly wider than the fin and the fillet covers the bare area. Another technique is the in method. Use a pin, drill bit, or knife blade to put small holes along the fin mounting line. I also carefully poke holes or score the balsa fins for adhesive absorption. On plywood fins I use a razor saw to cut lines in the root area to increase the area to glue.

Chas
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  #7  
Old 05-30-2019, 07:10 PM
UlteriorModem UlteriorModem is offline
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Quote:
Originally Posted by Chas Russell
I cut or scrape away the glassine coating on paper tubes to get to the rougher paper to aid in the adhesive soaking in. I score the glassine slightly wider than the fin and the fillet covers the bare area. Another technique is the in method. Use a pin, drill bit, or knife blade to put small holes along the fin mounting line. I also carefully poke holes or score the balsa fins for adhesive absorption. On plywood fins I use a razor saw to cut lines in the root area to increase the area to glue.

Chas


Thanks Chas, Yea I only recently learned about the glassine coating and tricks to mitigate it. But you offer even more great ideas. My thanks.
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