Help Wanted : Repairing a cracked fillet.

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cmmeyers

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How do you go about repairing a cracked fillet?

On one fin on my Praetor I noticed that on either side there are some very fine cracks. They are not extremely noticeable, but if you flex the fin back and forth they become more visible. The fin has a dent on the leading edge so it is probably from the upper tube slapping back and hitting it. When building the rocket I poked small holes in the tube along the root edge of the fin in order to create glue "rivets". I used yellow wood glue for assembing the rocket.

What would be the best way to fix this? Would CA squirted into the crack do the trick?
 

powderburner

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Are you sure the fin itself is loose from the BT? (Does it move WRT the rest of the rocket?) Or is there just a crack in the glob of fin root material?

You can use CA, and it will wick into the joint quite readily. In my experience, however, CA is a fairly brittle adhesive. If the fin is really loose, I would be tempted to bend it enough to open up the crack enough to apply some thinned yellow wood glue (brushed along the crack with a small artist's brush). Or even thin epoxy, although it will be harder to work into the fin joint unless you take the fin completely off.

Just my opinion . .
 

limd21

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Personally, I would say, yes, some thin CA wicked into the cracks would be a fine fix. I've done it on my models and it seems to be a near ideal, not overly-engineered, solution to the problem. I keep a bottle of thin CA in my field box for just this purpose - keeps you flying even after an abnormally hard landing.
 

DynaSoar

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Originally posted by cmmeyers
How do you go about repairing a cracked fillet?

On one fin on my Praetor I noticed that on either side there are some very fine cracks. They are not extremely noticeable, but if you flex the fin back and forth they become more visible. The fin has a dent on the leading edge so it is probably from the upper tube slapping back and hitting it. When building the rocket I poked small holes in the tube along the root edge of the fin in order to create glue "rivets". I used yellow wood glue for assembing the rocket.

What would be the best way to fix this? Would CA squirted into the crack do the trick?
Probably. Put on a drop and wiggle it.

You might check out the epoxy putty that Apogee carries. It's 2 hour cure epoxy in putty form. You can make some excellent epoxy fillets or fillet patches with it.
 

cmmeyers

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Here are some pictures. (actually a 3 picture composite)

The crack only runs from the leading edge to maybe 1/3 of the way down. The fin itself does not seem loose from the rocket.
 

limd21

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Looks like a perfect candidate for thin CA. Wiggle the fin to open the crack a bit, add a drop or two of CA, hold it while it sets and simultaneously wipe up any excess CA that oozes out using a paper towel.
 

powderburner

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Can you get your finger (or a dowel) inside the rear of the BT, under the fin, so you can press the fin against the BT as the CA sets?
 
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