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Building Tips and technical articles. => Building techniques => Topic started by: Tim Wescott on April 09, 2015, 10:09:06 AM
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Just how stout do horn pockets need to be in flaps and elevators? This is an area where I'm tempted to aim for something that's maximally beefy, yet it seems that one can get away with some pretty light construction (as, drill a hole in a 3/16" flap and bung in a 3/32" wire).
I'm not pleased with the stoutness of the flap horn receivers supplied with my Brodak Legacy kit, but I'm wondering if the various solutions bouncing around inside my head are all over-engineered.
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I've always done flaps and elevators like you're talking about. Back in the olden days. Also using hinge material wrapped around the surface and smeared Ambroid over them. Never had a problem.
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3/16" flaps?? Too thin for that wing area, they most likely won't be rigid enough. I have plans, and I know it says 1/4" but, make them thicker. I make a box (AKA "lucky box) with 1/64 top and bottom plywood sandwiched around 3/32 lite ply. CF plate is even better. Make it nice and square and glue it to the end of the flap. Fill as needed to fair it into the rest of the material. When you install it, don't glue it. I'll be in Portland, if I can remember I'll show you mine.
That's one reason I don't build many kits. When I do the plans are mostly for dimensions.
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Just how stout do horn pockets need to be in flaps and elevators? This is an area where I'm tempted to aim for something that's maximally beefy, yet it seems that one can get away with some pretty light construction (as, drill a hole in a 3/16" flap and bung in a 3/32" wire).
I'm not pleased with the stoutness of the flap horn receivers supplied with my Brodak Legacy kit, but I'm wondering if the various solutions bouncing around inside my head are all over-engineered.
That's fine for flight loads. If it loosens up, drill a small hole in the bottom right over the wire, and dribble in some thin Hot Stuff.
It's not very good when you go to tweak it, however, particularly when you use music wire horns. I used basswood blocks on the current airplane and they swelled up a lot when they got wet. I switched to plywood saturated with thin hot stuff on the new airplane, and left the side open so I can get paint on it to water- and oil-proof it.
Brett
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3/16" flaps?? Too thin for that wing area, they most likely won't be rigid enough. I have plans, and I know it says 1/4" but, make them thicker.
The quote was from my Twister. The Legacy supplies 1/4" thick flaps, and I'm using 1/8" wire. I was kind of planning on lucky boxes similar to what you're describing.
I'm trying to stick close to the plans on this one (well, mostly), but I might put more than one layer of CF veil on the flaps. Or I'll get something more substantial and see if my flying buddy's vacuum bagging stuff still works from back in the day when real glider pilots still made their own.
I hear you on the kit-built stuff: I think the next plane is going to be scratch-built.
That's fine for flight loads. <snip>
It's not very good when you go to tweak it, however, particularly when you use music wire horns. <snip more>
I'm making Paul-style tweakable flaps that adjust with the turn of a hex driver, so it only has to stand up to flight loads.
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Sorry Tim, I sucked into the assume syndrome. Get screwed every time. I still don't like making a permanent attachment to the horn with the flaps.