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Carbon veil covering

Old 03-05-2019, 10:11 AM
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jester_s1
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Default Carbon veil covering

I'm building a Tiporare pattern plane and want to do a painted finish. I've glassed a plane before with looking results. I'm thinking of going with .2 oz carbon veil applied with nitrate dope on this one though to save some weight. If I do the wings in carbon, do I still need to glass the center section? If so, should I glass it after applying the carbon? I'm also curious if carbon will go around the compound curves of the fuselage or wingtips?
Old 03-05-2019, 11:42 AM
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speedracerntrixie
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Jester, I did a set of pattern wings with Carbon veil once and it will be my last time. What I found was that it was much more difficult to apply as it would not conform to the leading edge or tips very well. Trying to form it to the compound curve would get tears easily. It required more bonding agent ( in my case Klass Kote clear ) and then it required more filler prior to primer. I figure it took me twice as long to do the job and I don't think I saved any weight. IMO the best system is going to be .75oz cloth applied with Klass Kote clear, light sand, mix up some Klass Kote primer with some micro balloons for a runny paste and smear all over the wing, allow to dry and hit it with some 320 grit. After that spray a coat of Klass Kote primer.

When it comes to glassing the center section, I like to overlap the 3/4oz cloth about 8", then apply a 6" strip of 3oz and 4" strip of 3oz. This will allow you to easily feather the center section. Do not apply the thinner strip first, this leaves a ridge at the edge of the thin strip and while feather sanding you will burn through the wider strip making the wider peice useless.
Old 03-05-2019, 04:59 PM
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jester_s1
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What did you use to adhere it? There is an old thread on here about using dope, which supposedly loosens up the fibers a bit to help it conform. Obviously, I haven't done it before though.
Old 03-05-2019, 07:56 PM
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I used Klass Kote clear. I suppose it is possible that dope may make it a bit more workable but I doubt it. I didnít have issues with the binder not loosening up just that CF is not as pliable.
Old 03-13-2019, 05:09 AM
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kenh3497
 
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There is a thread in the pattern section about using silkspan and dope. Probably not as strong as glass cloth but the claim is it is lighter. I would think lacquer would work as well as dope. I would have to think there was some type of structure (carbon strips, balsa spars etc) under the wing to add some strength to the wing. I think that is pretty much SOP for pattern wings.

Ken
Old 03-27-2019, 09:29 AM
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I did a fuselage just as you are proposing to do on your wing. Carbon veil and nitrate dope. I was very pleased with the results. The veil seems to "loosen up" a little bit in the presence of the dope, allowing it to conform fairly well. Also, the nitrate dope is more sticky than something like an epoxy resin. Between the more sticky consistency and the shorter drying time, it seemed to me that the nitrate dope was pretty easy to handle.

There are a couple of other factors favoring the dope rather than a resin . First, the nitrate dope penetrates nicely into the balsa substrate, giving a fairly tough finish that is more resistant to handling dings. Think of the nitrate & balsa as a composite in its own right. The classic glass cloth and resin finish always seemed to me to be like an egg shell: hard on the outside, but easily broken through with an impact. The nitrate & carbon finish seems tougher.

The nitrate dope also seems to make for a lighter finish. If you allow resin to soak into the balsa, you will have a heavier finish. With dope, most of the weight is in the solvent, and that part evaporates away.
Old 03-28-2019, 06:03 PM
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jester_s1
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Thanks for sharing your experience, otrcman. If you don't mind going over it, what was your procedure for covering with the veil? I've never used dope before for anything. Does the procedure for silk work well,3 coats of 50% thinned dope and then a coat to adhere the veil and then fill?
Old 03-28-2019, 07:28 PM
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It's been long enough since I did a dope & veil job that I don't remember the precise sequence. But I have been doing dope/silk & dope/paper for more years than I care to think about and I don't use any strict procedure. You might say that I "read" the balsa surface and proceed accordingly. But roughly speaking I usually apply three or four coats of nitrate before putting the cloth or veil down. I'll start with a pretty thin coat of dope. Maybe as thin as 30-70 to ensure that the dope sinks well down into the balsa. What I'm trying to do is use the dope as a binder in the same way that we use epoxy resin as a binder for fiberglass cloth. Stiffening and stabilizing the fibers is the goal.

Depending on how dense the balsa is, I might go with a couple of coats of 30% dope and 70% reducer for good penetration. And then maybe a coat of 50-50. If the balsa looks like it's beginning to fill up, I'll apply one more coat of perhaps 50-50 to make a bit of a surface shine overall.

Then I'll lay the veil down with some 50-50. Let that dry well, and start filling it with more 50-50 until the shine begins to show up again. Then a few coats of dope/talc to give a sandable surface. Once the surface is sanded and looks good, maybe another coat of thin nitrate to bind it all together and harden the surface. Then another light sanding. If all looks good, a couple coats of butyrate color for the final finish.

Note in all this that I am judging how much reducer to use not only on the density of the balsa, but also on the thickness of the nitrate as it comes out of the can. Some nitrate comes out of the can like molasses, but other batches are already fairly thin when you buy them.

Dick

This pictue shows the dope/veil surface ready to coat with dope/talc for a sandable surface. The blue tint color is because I had purchased some tinted Randolph nitrate for full scale use. I had several gallons unused and was using it up.


Fuselage after applying & sanding dope/talc. Ready for color butyrate.


Finished product.

Finished product.
Old 03-28-2019, 10:09 PM
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My experience is that the blue tint was put in "non-tautening nitrate". This was done so that when you opened the can there would be no confusion about the material. Randolph Aircraft Finishes does offer clear, and tinted tautening, and non-tautening nitrate dope.Dick made a very important point about the particular sources of your paint. Places like aircraft supply companies sell dope that is a lot higher in solids, so for our purposes it's a better deal, but usually requires more thinning. I've done a lot of dope and silk, and dope and tissue over the years,(using nitrate), and then clear, or color over it. Lately I've been using a lot of KlassKote, but it IS a little pricey! Another pitfall if you want a clear, or opaque finish is to try to avoid blushing, which is caused by high humidity. It is caused by moisture being trapped in the paint when it dries too fast. Usually it can be prevented by using retarder, or low grade thinners. The only carbon veil I ever did was about 25 years ago, and I definitely don't remember what I did.I get my dope from Wicks, or Aircraft Spruce.
Old 03-30-2019, 08:49 AM
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Art ARRO
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For more info using carbon veil for finishing, just use the RCU Search function. Most results will be in the Classic Pattern segment of the RC Pattern sub-forum. There are some excellent tips by MattK and Portland Flyer on the application of carbon veil as a finishing technique. MattK's technique utilizes Esaki (Japanese tissue) as a finishing surface. Thinned nitrate dope is the preferred adhesive for the veil and tissue.
I've also used carbon veil as an layer between foam wing cores and the balsa sheeting with finishing epoxy resin as the adhesive. . This makes for a very stiff and light weight wing suitable for pylon racers and turbine jets.The veil is available from ACP Composites and Bob Violett Modes.
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Art ARRO
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