Ye Olde Rocket Forum

Ye Olde Rocket Forum (http://www.oldrocketforum.com/index.php)
-   Ask the Doctor (http://www.oldrocketforum.com/forumdisplay.php?f=22)
-   -   Busted fins (http://www.oldrocketforum.com/showthread.php?t=17935)

UlteriorModem 05-29-2019 05:37 PM

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?

ghrocketman 05-29-2019 06:32 PM

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.

mycrofte 05-30-2019 05:58 AM

All I use is 5-Minute Epoxy for fillets. It cures rubbery and has some "give" to it.
__________________________________________________ _______

ghrocketman 05-30-2019 10:02 AM

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".

UlteriorModem 05-30-2019 04:43 PM

Never is a long time as my Father would say :D

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 :o

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 :chuckle:

Chas Russell 05-30-2019 06:18 PM

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

UlteriorModem 05-30-2019 08:10 PM

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.


All times are GMT -5. The time now is 12:37 PM.

Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.