How to add fillets to a rocket that needs them?

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Bill S

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I messed up and didn't put on fin fillets on my Estes Vesta Intruder. The directions didn't mention any sort of fillets (a significant omission on the part of Estes I think), and the fins seemed sturdy enough after being glued on. The fins actually survived the rocket's maiden flight (C11-5), but when I was prepping it for a second flight, noticed that the weight of the rocket lying down had actually broken off one of the fins. Naturally I couldn't fly it any more today, and I wrapped it in a pillowcase and put it in my car for the ride home. I then discovered that during the ride home, that a second fin had broken.

This is what I am talking about:
DSC02751.JPG


How am I to scrape away the paint to allow a good re-glue on and put in place proper fillets? Then somehow repaint the affected areas (3 fins worth) so it doesn't look awful? Thoughts?
 

Dawgbert

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I messed up and didn't put on fin fillets on my Estes Vesta Intruder. The directions didn't mention any sort of fillets (a significant omission on the part of Estes I think), and the fins seemed sturdy enough after being glued on. The fins actually survived the rocket's maiden flight (C11-5), but when I was prepping it for a second flight, noticed that the weight of the rocket lying down had actually broken off one of the fins. Naturally I couldn't fly it any more today, and I wrapped it in a pillowcase and put it in my car for the ride home. I then discovered that during the ride home, that a second fin had broken.

This is what I am talking about:
View attachment 487066

How am I to scrape away the paint to allow a good re-glue on and put in place proper fillets? Then somehow repaint the affected areas (3 fins worth) so it doesn't look awful? Thoughts?
Okay, here's what I'd do..
Tape off the fins except close to the root, tape off the body tube, anything you don't want damaged. Sand off paint down to cardboard and wood on all the fin joints and glue the broken fins back on. Let dry. Apply fillets, I like slow curing epoxy, let cure overnight.
Grind, sand and/or buff to desired finish and spray with primer, let dry.
This is when I re-tape around the repaired area a little further back and attempt to feather lines together with sanding.
Re-tape one last time, lightly sand, paint repaired area and remove tape while paint is wet. Paint will usually lay fairly flat if tape is removed while paint is wet.
I couldn't find photos after I finished this 4" Goblin, but it turned out better than I anticipated.
 

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kuririn

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This is a tough one.
I assume this is wood glue. I would remove all three fins with a knife (easier to sand the tube and fins with the fins off), then carefully scape/cut the glue off and sand the tube to bare paper. For the fins after removing the glue sand a strip following the root chord until bare wood shows. An emery stick is useful. Then tack glue, let dry, and fillet as usual. Tape and brush paint to finish. If the decals weren't there I would have said spray paint.

I recently cut off the three fins on my mini Fat Boy clone because the alignment was a little off. Sanded to bare cardboard and reattached. I got lazy and used thick CA, with small fillets applied and smoothed with an icepick.. It's 1/16" balsa. Did the wiggle test, seems solid. Next will be mask and brush paint.

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Bill S

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Kuririn, yes, I used carpenters wood glue. I think I'm going to decant some primer and spraypaint and brush paint them on, rather than spray painting. It won't look as good though. 99% my fault, though you'd think Estes would have had the builder fillet those fins. :(
 

jqavins

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I have only two things to add to the technique suggestions, and one more thing below that.

First, if the fins are hanging on by one side of the root (like a hinge) there is something to be said for leaving them attached, laying some wood glue into the rood joint, and rolling them on the hinge back into place. The two surfaces (fin root and tube) should fit back together nicely and give a good glue line. If they were well aligned in the first place then they still will be. You still need to sand off the paint around the joint, on both sides, and apply the new fillets. If the alignment wasn't so good to start, the just go ahead and remove them. Or just remove them anyway if you'd rather.

Also, sand and fillet around all of the fin roots, not just the ones that broke off. If you don't, the other two will break off eventually, and the damage may be worse.

Now the other thing. Just in case this learning experience hasn't taken root, the lesson is this: always fillet fin joints. Never mind what the instructions do or don't say. The glue joint that's only on the root edge of the fin should be considered tacked no matter what type of glue is used. The real strength of the joint is always in the fillets; never leave them out.
 

bjphoenix

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The rockets that I used to fly have required all kinds of repairs including forcing some glue into a joint and pulling the fin back into place and holding while the glue dried.
Assuming we are talking about LPR... Regarding adding fillets to a completed and painted rocket- in many of my rockets the paint is stuck to the cardboard tube better than the strength of the tube itself, so I just sanded the tube slightly and put on some epoxy. If you want to use wood glue fillets then you probably need to sand off the paint so you can glue directly to the balsa and cardboard. Granted I have some rockets where the paint has come off of the cardboard through handling and flying, those wouldn't be good for adding epoxy on top of the paint.
 
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