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Building Tips and technical articles. => Paint and finishing => Topic started by: Allen Eshleman on May 06, 2015, 09:46:26 PM
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We are currently working on an ARC Vector. We did one side of the wing in Ultra Cote Blue. It worked marvelously and really tightened up and smoothed out with the heat gun.
Then we attempted some yellow on another piece that had ribs. The yellow did not stretch with the heat gun and sagged as it cooled.
Any ideas?
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It's difficult without pics, but is the part that sagged over an open bay without support on the other side? When i cover a wing, or part that can warp easily, i do not use anything at all to shrink it until after the job is complete. Also, i do not use a heat gun. Only for difficult stretching areas like curvy wing tips. If you could put up a pic, i think i can help a little better 😄
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I recently had a similar problem over the open bays of a wing. The cause was the wing was sealed by the covering and when I shrunk the covering it pressurized the wing with hot air puffing the covering up. When the air in the wing cooled the covering was loose and sagging. I poked a few pin holes in the wing tip to relieve the pressure and re-shrunk the covering. Worked like a charm, nice and tight. Fortunately this was for a biplane and there is a small area on each wing tip that isn't covered so it was easy to poke the holes there. Not sure if this is what you're experiencing, but maybe worth looking into?
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Shouldn't happen on a mono-winged plane, since the air can pass through the leadout guides.
Whether it's the problem or not, Dane is right about covering the whole wing before shrinking it. I only use an iron too, with no sock.
I alternate shrinking bays on opposite sides, and top and bottom, starting at the root, and work toward the tips. Every color acts different, but they all turn a dark shade right when they reach shrinking temperature. Don't stick it to the rib edges any more than you can help until the whole wing is shrunk. Then stick each rib. A gun indiscriminately cooks everything in it's path and can cause ribs, and thus the rest of the framework to twist and turn.
Ultracote will loosen in the sun a lot worse than Monokote, especially the dark colors. Monokote can be forced into shape with the iron a lot more than Ultra. It takes high heat, and the glue adhesion temp overlaps the shrinking temp. You have to get the hang of each one in its own way, knowing the temperatures to work with. Monokote takes more finesse with the heat, but you can really do some beautiful work with it.
The only time I use the gun with either brand is to adjust a twist.
Rusty