Fuse repair...

[soholingo]

I am a big miffed at myself. I called myself repairing a fuse and as soon as I do a nose in the fuse breaks at all the repair spots. Some notes on the fuse and the repair.

Its an f5b fuse, pretty much a fiberglass cylinder with a tail.
I repaired cleanly broken off nose with kevlar anc carbon tows. Which seemed to do the job.
The problem is this: the repairs to the cracks didn't take.

I am against better judgement going to rerepair this fuse. What I need are answers to the following questions...

1. I am going to reepoxy the repair. The fiber glass will be better matted to the kevlar inside the fuse. Should i put on a thinlayer of Glass on the outside to hold the fuse together?

2. How should I reattach the tail? It came apart just behind the wing mount. I was thinking of taking two strips of ply wood and mounting that to the inside of the fuse. Then I would wrap the outside glass and epoxy.

3. How do I get the tail lined up so that it isn't twisted when I reattach it?

Thanks,

Jay

Any suggestions are welcomed.

[davidfee]

Very often repairs to composite parts will fail. Sometimes the reason is that the reinforcements are weaker than the original material but it can also be that the bonds fail. Did you scuff the inside of the fuse well and clean with acetone or alcohol? If not, subsequent repairs will likely fail as well. What type of epoxy did you use?

1. A thin layer (how thin?) will basically be useless. Any material you add should be strong enough to carry the loads by itself, since there is a discontinuity at the previous fracture point. That means that the stresses at the crack will be very high. You can use light glass to help fair in the repair area, but don't expect to gain any strength from it.

2. First scuff the inside of the broken area with coarse sandpaper, then clean the area with acetone or alcohol. There can be mold release, epoxy hardener residue, grease, etc. which will weaken any bonds you attempt to make.

3. Bolt the wing and tail to their respective fuselage parts. Carefully align the tailboom section with the nose by checking the stab against the wing. When satisfied, tack the boom in place with CA. Remove the wing and stab. Apply a strip of 4 or 6 oz fiberglass all around the inside of the fracture. Make the strip wide enough that it extends approximately an inch on either side of the break (probably about 2-2.5" wide). You can tack it in place with spray contact cement. Add a narrower second strip, centered on the first, so that the thickness of the repair increases as you get to the break, then tapers off again. Make this second strip maybe 1-1.5" wide. Wet out the glass with laminating epoxy. Find a party balloon (the kind clowns use to make animals) and inflate it inside the repaired area to force the glass up against the fuse sides.

4. Next time buy a Kevlar fuse. ;)

good luck,
-David

[soholingo]

Good stuff Dave, thanks...

I can't remember if I scuffed the inside or not, I am almost sure I cleaned the surfaces with acetone or denatured alcohol. I will post pictures...it is NOT going to be a pretty plane, but it should fly again...

[watnsee]

I would clean, sand thoroughly, clean repair the inside. After the inside cures clean the outside and sand the breaks back to the inside repair. so it kind of makes a channel. Fill this with new material. let cure then block sand smooth. This is like making a scarf joint. hope it helps

[checkenbach]

I'm in the process of repairing a few as well- a HillBilly, broken at the base of the tail, and a Filip, broken behind the wing saddle. I used a road (thin) tube instead of the ballon trick, on the HillBilly- it conformed well, but did stick and blew out the tube. Being ever resourcsefull (cheap), I cut the tube and tied each end of the tube, and used it again. It worked but leaked also, was easier to get into smaller spaces as well.
I have a carbon sleeve on the boom of the Filip and have an arrow shaft taped on the centerline of the fuse as a sighting device. That's as far as I've got.
Chris