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Building Tips and technical articles. => Building techniques => Topic started by: steve pagano on May 05, 2007, 02:51:13 PM
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Hi Guys;
Any one know how to get a warp out of a flap thats already been painted?
Check out the pics, i was hoping to Finnish this plane by next week but........
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Hi Steve,
It looks like it has enough hinges that when you put hinges in the flap and then bend it straight to put the hinge in the wing, the wing will hold it straight. Do a dry run by installing all the hinges (no glue) in the flap and then install it into the wing (no glue) and then sight down it and see if it still looks bad????
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Personally, I don't use dope, but if I did and had a warp, this is what I'd do. I'd twist it back straight and then a bit more. Tie it down in that stressed attitude and spray it with some retarder, both sides, to soften the already applied finish. Retarded is a powerful thinner. Left over night your problem may very well go away as a result of this treatment.
Al
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When I have a warped flap I fix it the way Al says to do it. Except I use clear dope and I put the flap in a jig.
The jig is just several balsa blocks glued to the table. I use dowels on the end blocks and rubber bands to hold the ends of the flaps.
This works best if you leave the whole thing alone overnight.
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If it's doped, pour boiling water on it while twisting it opposite the warp. If it has plastic covering, iron it while twisting it opposite the warp. You can iron a doped flap if you're careful.
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Obviously, use low shrink "non-taunting" dope. I had to build 4 sets of flaps for the USA-1 a couple of years ago because the first three would just not stay straight. I've never had much luck straightening them and making them stay (though I'm told other's have). When I see a warp, the thing just goes in the can in favor of a new and hopefully straight unit.
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Steve,
You said painted, but not with what...
If it was doped, it is possible - easy actually - to straighten that kind of bend with a hot air gun, like used for shrinking $Kote. Be careful NOT to heat the surfaces so much the dope blisters... Heat one side, bend it against the curl. If possible, wipe down the heated side with a damp cloth. (I haven't tried this with non-doped pieces, like epoxy-coated, etc.)
Do the same on the other side.
Check how straight that got it. Repeat as necessary. (Check again a few hours later...)
Each pass is a matter of (5 to 20) seconds, so this is quick. Repeat as necessary to get both 'force-cooled' sides straight. A-a-and if you need to do it again, sometime later, you bin thare, dun that...