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AKPilot

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. . . doing it this way?

Primarily, the family and I launch LPRs. I've searched the forum and haven't seen anyone do this as a primary method, but does anyone else just use gap filling CA for fillets? It's quick to use and cure.

It's just an old habit from building R/C airplanes, but I've never had a fin break off using this method. I'm not building for competition and the finished product, covered in paint, looks fine to me. Plus, I'm being lazy, I just can't be bothered to mix up any 5-minute epoxy and spread it.

Any thoughts?
 

wwattles

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I've used it as a work-around when I've over-sanded the root edge once or twice, but generally it's not considered to be the "best" method of fin mounting. While it does indeed produce a nice strong bond, that bond is also more brittle and will have a greater tendency to snap. Yellow/white glues/adhesives are typically more forgiving since they do have a little more "give" in them. There are quite few I've seen who will tack the fin in place with CA at the ends, then hit it with a full glue joint and fillet.

Just my observations...

WW
 

sandman

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A lot of us keep our models for a long time...well, we WANT to anyway.

CA doesn't really last that long. It gets brittle over a few years.

Elmer's...that seems to hold up better to age.
 

AKPilot

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Interesting thoughts . . . with both of you saying agreeing that CA is more brittle. I've never thought of it from that perspective.

Generally, when building R/C aircraft there's points where we use CA and points where we use epoxy, because of a large surface area or desire extra strength.

I guess, for the most part, there is probably more stress and force on a rocket versus an aircraft. I haven't had the opportunity to have my Zero or Corsair go vertical at 100+mph. Then again, unfortunately, I have had landings similar to rocket recovery.
 

gpoehlein

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I've always been told that CA has its good and bad points - it is super strong when holding a joint on-axis (remember the commercials with the guy super-gluing his hard hat to an I beam?), but it has lousy shear strength. In other words, using CA on fins puts it's weakest axis in the direction of the thrust.

I've had really good luck with the epoxy putty that Apogee sells - it smooths out well with a bit of alcohol and it is really tough.

Greg
 

Zack Lau

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I use it all the time.

I don't recall any problems with fins snapping off--but it could
be that I often use through the wall fins or reinforce the joint
with tissue or paper whenever I think it might be a problem.

I use pistons a lot--I worry more about fin flutter, since I
try to make the fins as thin and light as possible.
 

North Star

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This is one of those questions that I can't give a definitive answer to; but I do it my own way and it seems to work!

I use CA all the time for low/mid power fin attachment. I've just checked my records and models built from '94-'95 on, have been 'all CA' and there is no difference in failure rates from the earlier 'white glue' types. In both types I have had damage where the fin becomes detached along with some surface body tube and I've had fins break above the joint. neither is the fault of the adhesive.

I personally find the length of time needed for CA to grab is such a big plus-point that it's won me over.

I just wonder about the choice akpilot is faced with, epoxy is so much heavier than CA or white glues/aliphatics that I wouldn't consider it on anything other than HPR or the bigger mid power types. (Oh and I once tried putty with G10 fins on a Rugged Rockets Spitfire - all the fins came loose :eek: )
 

brianc

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Originally posted by akpilot
Interesting thoughts . . . with both of you saying agreeing that CA is more brittle. I've never thought of it from that perspective.
Yeah, but in Alaska it's so cold, doesn't everything gets brittle after time??? :)
 

Stymye

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cya has very low shear strength,compared to most "rocketry" glues ,and It does dry out over time.
still every one has their preferences. no harm in that
I always have it close by
 

AKPilot

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I'm becoming more intrigued by the standard glue method, and may start giving it a shot. On the positive side, CA is fairly quick and convenient. I've had R/C planes for years and haven't had a failure yet. BUT, on the other side, I am getting tired of the CA fumes.

Brianc . . . actually, in Anchorage, the weather really doesn't get as cold as you may think. Often in the winter we're warmer than most of the northeast. And in the dead of winter, if it's cold enough to freeze my nose hairs - I don't fly.

North Star . . . where in Yorkshire are at? My wife is from Leicester and we got engaged in York.
 

DynaSoar

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Originally posted by akpilot
. . . doing it this way?

Primarily, the family and I launch LPRs. I've searched the forum and haven't seen anyone do this as a primary method, but does anyone else just use gap filling CA for fillets? It's quick to use and cure.

It's just an old habit from building R/C airplanes, but I've never had a fin break off using this method. I'm not building for competition and the finished product, covered in paint, looks fine to me. Plus, I'm being lazy, I just can't be bothered to mix up any 5-minute epoxy and spread it.

Any thoughts?
Done it, and it works fine, but I put the epoxy for making thicker fillets. More aerodynamic. Now I used epoxy clay since you can woprk it to get the shape just so.
 

Zack Lau

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If I want a LPR rocket to look nice, I'll often use wood glue to attach the fins accurately in place and add fillets made out of CA for aerodynamics/appearance.

Sometimes, I'll use Red Devil Spackling to make really large fillets--it is extremely light (glass microballons?) But the stuff doesn't sand well, so I typically cover it with Fill n Finish and sand that smooth.

I used Apogee's two part epoxy on my 3" BSD Diablo--worked great, but I haven't built anything else this big and heavy.
 

North Star

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Originally posted by akpilot

North Star . . . where in Yorkshire are at? My wife is from Leicester and we got engaged in York.
Between Leeds and York ... Wife Judy is from York :)
 
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