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Building Tips and technical articles. => Building techniques => Topic started by: Allen Eshleman on May 22, 2019, 08:41:05 PM
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I have a several times repaired Shark 402. With the last repair, the inside wing hangs down in the back, causing the outside wing to hang down in flight.
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What is it covered with? Try using a monokote heat gun or iron, give the wing a slight twist in the direction you need to go, then shrink the wrinkles out. This will work with iron on coverings the best, but will also work with silk span and dope to a certain extent. You can also try the old standby, steaming it out.
Type at you later,
Dan McEntee
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I have a several times repaired Shark 402. With the last repair, the inside wing hangs down in the back, causing the outside wing to hang down in flight.
As Dan notes, it depends on what it is covered with. Heat-shrink, twist it past straight, then hit it with a heat gun until the wrinkles are gone. Keep adjusting until straight. Don't expect it to stay for long, at least the first time you do it.
Doped or painted, steam in extremely large quantities might work, but for something really sturdy like a silkspan d-tube, wrap it with a bath towel, boil up a big pot of water, then while you twist, get someone to pour the boiling water on the towel. You will almost immediately feel it release and move, leave it for a 10 seconds or so after that, then have your helper unwrap it and let it cool down, so it stiffens back up. This is pretty much the only thing that will fix full-sheeted or D-tube wings with dope or other paint. This method is reasonably stable on built-up structures, even fuselages.
BTW, while I know it doesn't apply here, none of this will work at all on sheeted foam wings. But of course, once you sheet them, they aren't prone to warping with time, no matter what you put on them. If it is built warped, "fixing it" is a relative term, and any reliable method requires extreme measures involving large Exacto knife cuts and epoxy. Or another core and some more wood.
Brett
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A hot towel always works. I put a wet towel in the microwave until it is steamy. Wrap that around the wing panel and pile weights in the direction you want to warp the wing. Leave this for a couple hours.
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I haven't got to this yet. It is covered with monokote or else Brodak Kote. I don't remember.
So do I heat it with the gun first and then twist.
Which side of the wing? The side I want to twist toward of the opposite side or both?
If I can't expect it to stay for long as was suggested. Should I do it again and overbend it?
With the hot towel work with monokote or film coverings?
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Hold the fuselage with your left hand. Hold the affected wingtip with your right hand, and twist it past straight. Now, with your remaining hand, pick up the heat gun and shrink both the top & bottom of the wing. Let it cool, recheck for warps.
You may wish to hold the fuselage between your knees, or on your bench with sandbags -- this is easier than growing a third hand.
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No hands required with the hot towel method. You need some floor space, and some heavy books (or cans of fruit or tomatoes from the pantry) to coax the wing to twist in the right direction. When this is set up, go away and open a bottle of your favorite beer.
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I haven't got to this yet. It is covered with monokote or else Brodak Kote. I don't remember.
So do I heat it with the gun first and then twist.
Which side of the wing? The side I want to twist toward of the opposite side or both?
If I can't expect it to stay for long as was suggested. Should I do it again and overbend it?
Twist the wing that is warped past the point it is straight, then heat it on both sides until the wrinkles go away. Monokote doesn't need to be too far past, China-kote from Brodak, probaby pretty far, but you may not ever get it right, because the film is both thin and soft. Don't get it hot around the edges where it is stuck down.
With the hot towel work with monokote or film coverings?
No, or at least it won't accomplish much.
Brett
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I have used MonoKote since it first came out. I currently have it on three of my practice ships. All had some minor warps and I used the same method Brett put forward with a slight twist. On one I have not had to do it a second time. On the other I had to do it three times till it held. Balsa molds easily, that is the reason the hot towel works even on a "D" tube. Once the balsa has relaxed in it's new position it usually stays that way. Try and keep the heat away from the LE and TE and I have found useful on non cap-stripped wings is to use an iron over the ribs while it is twisted to soften the glue and let the whole area reposition. I have also found that the initial removal of the wrinkles works best if you do the side of the wing where the monokote needs to pull (ie: LE is Low - do the top first tightening from the back forward.). It should pull out the warp by tightening only one side. Then use just enough heat to take the wrinkles out of the other side AFTER the 1st side cools.
Another "trick" I have used years ago on a seriously warped I-Beam was to cut the monokote off of 1-2 ribs on the bottom of the wing then use the hot towels to bump up the moisture content in the wood. Steam would work too. Re-monokote, twist and tighten before the balsa dries out. If you keep it in position till the balsa dries out it will stay that way.
Ken