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Apr 04, 2016, 10:39 AM
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Help!

Carbon fiber for wing repair


Unfortunatly I crashed my Gabby last Saturday and have a "crack" on the top and bottom of one fo the wings. I want to do a reapir with carbon cloth and epoxy but don't have a clue what to use. Any advise would be appreciated.

What type of carbon fiber? It will be on a compound curve as I want to wrap from the top of the wing to the bottom.

What type of epoxy?

Do you only use one layer or multiple?
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Apr 04, 2016, 11:08 AM
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exf3bguy's Avatar
How much of a hurry are you to do this? I will be at the Sunset Beach event later this month and would be happy to take a look at it. I've done these types of repairs on many giant scale composite airplanes as well as sailplanes. I also do composites for a living.

That being said, the most common carbon fabric available and least costly is 5.7 oz plain weave. That may be overkill for what you are doing and in fact you may not need to use CF at all. As far as epoxies go, everyone has their favorites. I have found that Tap Plastic's Marine grade epoxy works really well for our applications and its local to you. If you can wait, I would be more then happy to bring some different materials,make a look at the wing and in general give you some tips on how I would proceed.
Apr 06, 2016, 12:54 PM
AMA 353531
rdeis's Avatar
Big Gabby or little Gabby?
Apr 07, 2016, 09:58 AM
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Thread OP
2M GAbby E from NSP.
Apr 07, 2016, 10:35 AM
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mlachow's Avatar
A picture of what you need to repair would help.
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Apr 07, 2016, 11:58 AM
Pompano Hill Flyers
jwmercado's Avatar
FYI,
If you need small amounts of carbon fiber check out Graves Hobbies, they stock from light to heavy, I purchased some fabric not to long ago for a boom repair.
Apr 07, 2016, 04:57 PM
Registered User
I would recommend severeal layers of light fiberglass in different orientation with a little overlap (first pach is mall, next just a little bigger, etc..), for compound curves you ideally want "twill" weave or similar suitable for two-direction curves but it does not always come in "light".

If I was to use carbon fiber other than simple tow reinforcements (like on a wing skin), I would use light (<93g/m2) standard twill weave or similar if I had some. I guess it all depends on whats there already in the wing..
Apr 07, 2016, 05:18 PM
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Thread OP
There "was" a crack in the top and bottom of the wing on both sides of it all the way back to the spar and the spar was detached from the underside of the wing. I have cut out the damaged part and am using a piece of foam to infill it.

I ordered a few different kinds of CF from AFC as they are local to where I live. This will be my first repair and it was a little nerve racking making the initial cut into the wing I guess we all have to start somewhere.

We had a bunch of different foam laying around at work so I tested it with ca/epoxy and an using the lightest and strongest one I could find.

I'll post pics as I go.
Apr 07, 2016, 05:59 PM
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mlachow's Avatar
Quote:
Originally Posted by jwmercado
FYI,
If you need small amounts of carbon fiber check out Graves Hobbies, they stock from light to heavy, I purchased some fabric not to long ago for a boom repair.
Gravesrc.com sells a patch of spreadtow carbon for repairs. The west systems repair pack is also handy if you have no thin epoxy. The repair kit is thin enough. Works great for an overnight repair. They stock both.
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Apr 08, 2016, 12:09 PM
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Thread OP
Here's the progress so far.

I cut the foam for it last night and epoxied it in. I'll sand/form it later today and get it ready for the cf.

The picture does not show the damage very well but the LE was split and both the top abd bottom were cracked.
Apr 08, 2016, 04:52 PM
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exf3bguy's Avatar
That peice you cut out could have been easily repaired. Personally I would not bother with the foam, I would use the other side of the wing to make a quick mold and then mold a new peice.

That's the fun with composites, no clear cut way to go but in the end many methods will get the sailplane back in the air.
Apr 11, 2016, 05:45 PM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
yup...instead of a 1" crack, there is now 6" of fully severed wing skin with sharp corners for stress risers.
It'll take a whole lot more material and likely look much uglier, with potentially less strength...but enough of being negative! Forget the past! Forge ahead!
Apr 12, 2016, 09:06 AM
Registered User
Agree - too radical to cut that much off for a small ding but there is an easy solution that I found works best better then foam infill. Cut 1mm balsa into strips, say 5mm. CA sections of these strips on the INSIDE of the wing skin - I gap them apart so as to reduce weight a little. What this does is two fold - re-aligns the bent bits a provides a ledge to place the cut out skin back on. Bridge the hole with straight strips then with a split upper and lower skin mount onto these balsa 'boards'. After that you can then infill the joins/breaks with very small strips of glass or carbon - the balsa acts as a backing board. Minimal refinishing is needed as you are recycling most of the skin. This method often only needs one side of the skin to be cut out - preferably the lower- and you can work from inside.

These skins have a strong carbon outside layer and incredibly light layer of foam and glass inside (the composite of the three is what gives it the rigidity) the balsa would be over and above the strength required hence produces a stronger section then before. The foam itself is often CA'able hence the bulk repair can be done in one evening.


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Apr 12, 2016, 11:33 PM
Registered User
I've found light unidirectional carbon to be good for repairing cracks. It's not like you need much strength along the crack, mostly just across it. If you use the right kind of epoxy, and wait enough time, carbon sands quite nicely. However, it might be best to repair with the same materials. Is the l.e. carbon? Glass is pretty flexible compared to carbon. If you do use carbon to repair glass, you may want to taper the edge somehow. That's a good idea even if you're repairing glass with glass.
Apr 13, 2016, 09:17 AM
Registered User
Also with the crack or cut - sand it first down to the foam to create a hollow, say sand paper round a dowel. Then push the edges of the skin down into the foam - that way the carbon or glass will lap over the skin to make the join while able to sand and make level.


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