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Old Mar 10, 2012, 01:05 AM
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United States, CA, Los Altos
Joined Feb 2012
228 Posts
Skinning the wings

I really debated on whether to go the 3M Spray 77 or the epoxy route. Both are techniques I used back in the day, although I used Spray 77 far more of the time than epoxy because I made a lot more gliders than power ships and always felt 77 ended up lighter. However, I was also concerned about the strength of the wings. Sure, these things were designed to go screaming around at 150 mph or so for the QM versions and even faster for the .40 size, but these original wings do not even have spars. And the wing is so thin at the tip (only 3/8" sheeted) that it really gave me pause for thought. Especially when it's so easy to find old stories on the Web about how this plane or that had its wing fold.

After considering various ideas, I finally decided to go with something not even available back in the day -- carbon fiber -- after spotting plain/unimpregnated fiber at the local hobby shop. This also dictated going with epoxy.

I don't have pictures, but I first coated a thin, even coat of 45-minute epoxy on each wing skin. I was concerned about weight, too, and first tried a fairly hard push while scraping the epoxy (I used a 4 inch or so section of 1/16th balsa stick as a scraper). This actually removed so much glue that it left the surface with no gloss and a fairly dry appearance. So I went back and used just enough pressure on the scraper to leave a gloss finish... any more pressure and I would lose the gloss... so I think this is about the minimum required for an excellent bond.

I then laid in the carbon fiber tape (only .004" think and about a half inch wide -- no problem in potentially creating any bump in the upper surface) down where I had previously marked as the eventual high point of the airfoil at root and tip, then pressed hard with the scraper right on the carbon strip to get epoxy to seep up from underneath. I drizzled on a bit extra and worked it in throughly on each strip, again ending up with just enough to leave a gloss. Finally, I weighed each wing skin to make sure I was putting the same amount of epoxy on each and again made them the same to within 1g.

Here are the results.
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