Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > The Doctor is In! > Ask the Doctor
User Name
Password
Auctions Register FAQ Members List Calendar Today's Posts Search Mark Forums Read


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 05-29-2019, 05:37 PM
UlteriorModem UlteriorModem is offline
Intermediate Rocketeer
 
Join Date: Sep 2015
Posts: 97
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?
Reply With Quote
  #2  
Old 05-29-2019, 06:32 PM
ghrocketman's Avatar
ghrocketman ghrocketman is offline
President, MAYHEM AGITATORS, Inc.
 
Join Date: Jul 2005
Location: Michigan
Posts: 9,414
Default

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.
__________________
When in doubt, WHACK the GAS and DITCH the brake !!!
No Harm=NO Foul advocate

If you are NOT FLYING LOW in the left lane, you need to GET THE #$&@ OUT of it !

Yes, there is such a thing as NORMAL
, if you have to ask, you probably aren't
!
Reply With Quote
  #3  
Old 05-30-2019, 05:58 AM
mycrofte's Avatar
mycrofte mycrofte is offline
Trust me, it'll work!
 
Join Date: Mar 2009
Location: Illinois
Posts: 1,706
Default

All I use is 5-Minute Epoxy for fillets. It cures rubbery and has some "give" to it.
__________________________________________________ _______
Reply With Quote
  #4  
Old 05-30-2019, 10:02 AM
ghrocketman's Avatar
ghrocketman ghrocketman is offline
President, MAYHEM AGITATORS, Inc.
 
Join Date: Jul 2005
Location: Michigan
Posts: 9,414
Default

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".
__________________
When in doubt, WHACK the GAS and DITCH the brake !!!
No Harm=NO Foul advocate

If you are NOT FLYING LOW in the left lane, you need to GET THE #$&@ OUT of it !

Yes, there is such a thing as NORMAL
, if you have to ask, you probably aren't
!
Reply With Quote
  #5  
Old 05-30-2019, 04:43 PM
UlteriorModem UlteriorModem is offline
Intermediate Rocketeer
 
Join Date: Sep 2015
Posts: 97
Default

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
Reply With Quote
  #6  
Old 05-30-2019, 06:18 PM
Chas Russell's Avatar
Chas Russell Chas Russell is offline
Retired Missile Technician
 
Join Date: Mar 2005
Location: Fort Worth, TX
Posts: 901
Default

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
__________________
Charles Russell, MSgt,USAF (ret.)
NAR 9790, Lvl 1
SAM "Balls Three"
Reply With Quote
  #7  
Old 05-30-2019, 08:10 PM
UlteriorModem UlteriorModem is offline
Intermediate Rocketeer
 
Join Date: Sep 2015
Posts: 97
Default

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.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump



All times are GMT -5. The time now is 07:59 AM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe 1998-2019