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Old Jul 18, 2015, 04:00 PM
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Mini-HowTo
Repairing a broken boom on a glider

Here's my venerable beater, the Typhoon. I snapped the boom recently and decided to fix it myself using ideas gleaned from my local Orange County slopers.
Things I needed to do the job:
Two 2x4s about a foot long, a horizontal level and a vertical level
C clamps and/or 3" drywall screws and electric drill
6 oz fiber glass
About 8' of carbon tow
Epoxy finishing resin
Thin CA and kicker
Wax paper and vinyl electricians tape.
3M 77 spray
Hot air gun
Disposable paint brush or roller.
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Last edited by Slopedaddy; Jul 18, 2015 at 04:50 PM.
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Old Jul 18, 2015, 04:05 PM
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First step: layout the fuse plus wings on a wooden table and level the wings and stabilize them so they don't move. I made a jig to stabilize the boom out of the wood and screwed one down and clamped the other.
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Old Jul 18, 2015, 04:16 PM
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Now I'm cutting a piece of fiberglass to fit a 5 inch length of the boom and will go around the boom exactly, plus a quarter inch extra for overlap. Spray a little 3M 77 on the end of one long side. Stick that down and wrap the glass around the fuse, fairly tight. Cover it with wax paper and line everything up in your jig. Make sure the wings are level and tail is straight as you clamp it all down. Saturate the glass with CA and don't be shy. It will naturally run down all through the glass. Hit it with kicker and tighten up the wax paper that surrounds it, a bit.
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Old Jul 18, 2015, 04:22 PM
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Let it sit in the gig a while to set up, maybe ten minutes. Then remove from the Jig and peel off the wax paper.
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Old Jul 18, 2015, 04:35 PM
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Now you don't need the jig anymore, nor do you need the wings so put all of that away.
The fuse should be strong enough to work on for the finishing steps.
Spray a little 3M77 on the end of carbon tow to hold it in place and start wrapping the fuse about 1/2 inch before the glass patch to 1/2 after. I 3M77ed that end down as well so it wouldn't unravel. Wrap the tow fairly tightly and make sure the repair is totally covered.
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Last edited by Slopedaddy; Jul 18, 2015 at 04:54 PM.
Old Jul 18, 2015, 04:44 PM
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Next, I mixed about an ounce of epoxy and brushed it on thick using a heat gun on low to make sure it saturates the tow. I'm not worried about too much epoxy so make sure it's all shiney looking and wetted down. I got this finishing epoxy at a local surf shop in San Clemente and it's of very high quality, yet much
cheaper than other products I've bought at hobby stores and marine stores.
Now for some fun:
Wrap the repair with wax paper and completely wrap over that with the vinyl tape. Make it fairly tight with consistent pressure. Use alchohol to clean up the excess that's going to run out of there.
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Last edited by Slopedaddy; Jul 18, 2015 at 04:58 PM.
Old Jul 18, 2015, 04:46 PM
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I'm letting it cure overnight and will unwrap it tomorrow. Stay tuned for the result:
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Old Jul 18, 2015, 07:16 PM
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Wrapping w carbon tow, the way you did, and soaking with epoxy will just add a bunch of weight and not offer very much strength in the way you need it on a boom. Your wrap only gives "hoop" strength which is good for pipes that need to hold or withstand pressure but does nothing to add longitudinal strength (what you need for a stiff bending moment) which is what you really want for a fuse boom.
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Old Jul 18, 2015, 09:44 PM
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What's your alternative?
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Old Jul 18, 2015, 10:12 PM
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Quote:
Originally Posted by Slopedaddy View Post
What's your alternative?
Hmmm,....

....on a clean break (thru n thru) I actually like to make a fiberglass/carbon fiber tubular insert and epoxy it in place, one side at a time.

With your fiberglass material rolled on the bias and carbon fiber tow or weave added in 0-90 configuration, you're adding strength to your fuselage boom
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Old Jul 18, 2015, 10:24 PM
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I snapped the fuse of my Mini Blade a while back. We simply ran a carbon sock over it, soaked it with epoxy, slid a tube of shrink tubing over it, heated it up, waited for the epoxy to set, cut the shrink off, sanded to blend and painted to match.

Took less time to do it than talk about it.

mw
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Old Jul 18, 2015, 10:30 PM
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On many occasions I have used an internal bladder (one of those long balloons) to do a completely internal repair using just carbon fiber cloth. I bond the fuse together first and sometimes use temporary external splints similar to your 2x4's. I then roll up a few layers of wetted out cloth around a lightly inflated balloon and insert into the fuse (this is tricky and may take several tries but once you get the technique you'll come to really appreciate it). After insertion you then inflate the balloon. The rolled up cloth will expand with the balloon and you will get a vacuum bag like squeeze out and solid bond all around (many weak repairs are a result of having way too much resin to cloth ratio).

You can put in some tow in your "roll up" but you will want it going lengthwise (parallel to the fuse axis).
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Old Jul 18, 2015, 10:56 PM
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Quote:
Originally Posted by Mark Wood View Post
I snapped the fuse of my Mini Blade a while back. We simply ran a carbon sock over it, soaked it with epoxy, slid a tube of shrink tubing over it, heated it up, waited for the epoxy to set, cut the shrink off, sanded to blend and painted to match.

Took less time to do it than talk about it.

mw
Yeah, I've used carbon sock to beef up a cracked fuse and it works well. With all my linkages intact, I went this way since there's no way to pull on the sock over this boom
without taking it all apart. The tow wrap,
like the sock, is also very strong and only took 45 minutes.
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Old Jul 18, 2015, 11:03 PM
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Quote:
Originally Posted by Douwe View Post
Wrapping w carbon tow, the way you did, and soaking with epoxy will just add a bunch of weight and not offer very much strength in the way you need it on a boom. Your wrap only gives "hoop" strength which is good for pipes that need to hold or withstand pressure but does nothing to add longitudinal strength (what you need for a stiff bending moment) which is what you really want for a fuse boom.
It needs to be super strong for DSing and after squeezing out quite a bit of excess
resin, the weight, though a factor, won't be a problem. Your idea of fixing it from the inside sounds interesting.
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Last edited by Slopedaddy; Jul 19, 2015 at 12:59 AM.
Old Jul 18, 2015, 11:04 PM
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Now you can fly it like you stole it, good job
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