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Author Topic: How to Glass/CF  (Read 2624 times)

Offline Motorman

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How to Glass/CF
« on: August 09, 2014, 09:22:02 AM »
I want to apply CF or glass to strengthen the center section of my wing which has 6 Lb. balsa sheeting. Want to get maximum strength from it to combat the vibrations coming through the fuselage. Thinking of multiple layers of CF veil or maybe 1 Oz. glass cloth.

Would epoxy paint (original K&B Superpoxy) provide enough adhesion or should I spread out a thin layer of regular epoxy? Do I fill the wood first with dope and talc. What do you do after it's glued on? The wing box is only 3" wide so the whole thing will be covered. Need suggestions on how to get monokote to stick to the reinforcement.

Thanks,
MM
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Online Gerald Arana

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Re: How to Glass/CF
« Reply #1 on: August 09, 2014, 07:27:27 PM »
Monocoat sticks good to FG if it has lots of resin on it.

First cut your 1oz. cloth on the bias (45 degrees) and then spread out 30 minute epoxy with an acid brush (60 minute gives more working time) on one side and place cloth on it. Wrap it all the around the other side. Add as much resin as it takes to fill both sides completely smoothing out the bumps as you go. Then with out hesitation, use toilet paper two or three layers thick and blot off as much resin as is necessary to make it look like a nylon stocking on a freshly shaven leg...........Yeah, we all know what that looks like! y1

Trim off any excess FG when the resin is green (use a No. 11 exacto blade) because if you wait until its cured completely you'll have a much harder job. (and have to use a dremel) Then you can either fill it with another coat of thinned resin or primer, etc.

To remove FG use a heat gun and a No. 10 (I think it is) exacto blade to start the peel off. Then heat the remaining residue and scrape it off with a single edge razor blade held vertically.

Good luck and let us know how it came out for you.

Jerry

PS: I hope this is clearer than mud!
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Offline Motorman

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Re: How to Glass/CF
« Reply #2 on: August 09, 2014, 09:43:21 PM »
How do you thin 30 minute epoxy, with acetone?


Thanks,
MM
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Offline Steve Helmick

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Re: How to Glass/CF
« Reply #3 on: August 09, 2014, 10:29:49 PM »
Acetone and dope thinner usually makes epoxy brittle, so probably not best. Denatured alcohol is the approved stuff (by the FAI FF guys, from way back when they used .6 oz fiberglass/epoxy over the entire plane). No, not "rubbing alcohol", that's got water in it.

The way to use the TP is to leave it on the roll and roll it across the resin, in the direction which leaves it on the roll! When the paper is soaked, peel it off and put it in the wastebasket in a plastic bag. Keep rolling until the fiberglass is saturated but "dry" looking, and the TP doesn't pickup anymore epoxy.  H^^ Steve

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Online Gerald Arana

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Re: How to Glass/CF
« Reply #4 on: August 10, 2014, 08:49:30 AM »
That will probably work fine Steve. I usually press the TP down and rub it with my fingers.....
Your description of "dry looking" is better than mine......... y1

When removing the TP pull it back against itself so it doesn't lift the FG off your wing.
Good luck, Jerry
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Offline John Craig

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Re: How to Glass/CF
« Reply #5 on: August 11, 2014, 07:44:58 AM »
Just used the above techniques to sandwich FG in between balsa fuselage & ply doublers.  My only deviation was: I used a finishing epoxy resin which gave me a much longer working time. The technique has always worked well & kept the weight gain to an absolute minimum.

I have tried the CA route but never been really happy with the end result.
« Last Edit: August 11, 2014, 08:11:11 AM by John Craig »
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Offline L0U CRANE

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Re: How to Glass/CF
« Reply #6 on: August 15, 2014, 09:21:24 PM »
When I stopped flying RC gliders, those folks were using vacuum bagging with Mylar faced 'pressure surfaces' for an instant -well, curing time plus stripping time - high, smooth finish. Release 'stuff' was a water soluble poly vinyl alcohol (?), and it worked.

Squeegee on and off as much bonding resin as possible, the toliet paper rolling technique is good, and cheap, too, before bagging and vac-pumping.

It IS an art, but results in a very slick finish surface. Stress areas, like across the wing center section. can be layered up with 'darts' of CF or glas fabric. The negative-gauge pressure presses any edges down to 'faired' perfectly.

This was used for winch launched 2 meter and larger gliders, where you could see the wings bend drastically, or snap, from launching loads. Good enough for us, most likely.
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