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Building Tips and technical articles. => Building techniques => Topic started by: Chris Belcher on April 30, 2017, 11:34:00 AM
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I coated the inside of my molded shell with 2coats of nitrate dope thinned 50/50 to apply carbon veil and it shrunk up.....width wise, like it "humped" up so the edges dont line up. I wonder if I coat the outside if it will go back to original shape? Or just make formers?
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I coated the inside of my molded shell with 2coats of nitrate dope thinned 50/50 to apply carbon veil and it shrunk up.....width wise, like it "humped" up so the edges dont line up. I wonder if I coat the outside if it will go back to original shape? Or just make formers?
Chris,
Got photos?
CB
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I coated the inside of my molded shell with 2coats of nitrate dope thinned 50/50 to apply carbon veil and it shrunk up.....width wise, like it "humped" up so the edges dont line up. I wonder if I coat the outside if it will go back to original shape? Or just make formers?
Chris;
You don't say what this is for? A leading edge or fuselage top? I wonder why the carbon veil on the inside? I haven't done much of this type of work, but I would think you want the carbon on the outside to create a stiff, monocoque structure.after you have sanded everything. Applying dope will have an effect, and if you really feel you need the carbon on the inside, I would have put a couple of coats on the outside at the same time to limit warping. Putting dope on one side is a common way of starting a sheet to curl or roll on purpose for making a rolled tube type fuselage. Give us more details.
Type at you later,
Dan McEntee
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Chris I do not think is a shrinking issue but a material stability issue. If you do not laminate two layers of balsa you will allays fight this tendency. Most subscribe to the Windy 3/32 single layer balsa which like to flatten back over time. If you watch his videos he makes a holder to maintain the shell shape after he molds the shells. Two laminated layers (1/16 balsa) will stay stable over time and you can sand it down a bit to 3/32 size if you wish to do so. I never had any sagging wavy issues on fuselage shells with this technique and the weight is about the same.
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I coated the inside of my molded shell with 2coats of nitrate dope thinned 50/50 to apply carbon veil and it shrunk up.....width wise, like it "humped" up so the edges dont line up. I wonder if I coat the outside if it will go back to original shape? Or just make formers?
Yes, that is exactly what happened to the turtledeck on my airplane- except it was assembled at the time. It caused severe "starved horse" effects. The solution (suggested by Ted Fancher) was to mix up some more nitrate but add plasticizer. Within 10 minutes, the problem got a lot better and it has stayed better since then. Unfortunately in my case, it also had negative effects on the adhesion of the paint, which led to some other problems later.
Note that Brodak sells two kinds of nitrate, tautening and non-tautening. Use non-tautening, of course.
If you are going to put something on the inside of sheeting or molded parts, use thinned epoxy and remove most of it by blotting or rolling with toilet paper to soak up the excess. That's a trick from the good old days - the epoxy fills the pores a bit, so the pores are more difficult to compress when the finish goes on the outside, reducing the possibility of it causing starved horse or other shrinkage issues.
Brett