Hello everyone,
I have a wing with both leading and trailing edge sheeting which has a slight amount of warp. I have read that using a covering with a lot of shrinkage (such as monokote) can get the warp out, but does this tend to hold up over the long term? If not, any ideas? Thanks in advance.

John

it may be normal, what kit? are you sure it's a warp and not washout? does the warp go from root to wing tip? slight amounts of warp/twist in a wing may be designed in. if it is warped the covering trick works.....it will tend to move back over time. best thing to do is remove the warp now building the wing stright before covering, you'll probably have to remove the sheeting and start over.

John

I have had similar problems with warp on my Tiger 60. After covering the wing I found that I had induced different warp than it had bare bones. If twist is your problem then using the heat gun on the covering, and twisting the wing in the opposite direction of the warp you will find the warp will dissapear. Don't overdo it and check as you go. My wing is now warp free, although I haven't checked up on it lately (one year later).

This was advice I got one day from the guys at the field.

Good Luck!!!

Had another Idea - Spray structure with 50/50 amonia - water mixture. Fix it to you building board and hold it in place with what ever means until it dries - 1 day or so. This may remove the warp.

The wing is SUPPOSED to be straight...hehehe. Can shear webs (rectangles of balsa between the top and bottom main middle spars) help? I haven't added those yet. Taking off the sheeting will be a real problem.

Don't know how far along your wing is, but looks like you already have the sheeting done. One thing you could try is re-enforcing the wing with some of that carbon fiber wing reinforcement tape that you CA to the surface of the sheeting, then sand smooth. If you can get the wing held down perfectly flat with some weights or something then apply your CF to the sheeting over where the spars are located, then that should help. Here is one technique I found that I will be using on my wing for a bipe I am building.

Over the top and bottom of wing, inline with the spar location, take a 1/2 or 1" wide sanding block, depending on how wide your CF strip is, and lay a long drywall ruler over the wing as a guide. Then sand a very slight channel along the length of the wing where the CF will lay, thus allowing it to lay flush with the sheeting. Then lay your strip in place, and thin CA the whole thing down through the CF itself, since it is usually pourous. For super strength, you can also apply a VERY thin layer of epoxy to the channel first, instead of using CA, then lay the CF into the channel, and squeegie out as much epoxy as you can to make it flush with the sheeting and minimize weight. I will be using epoxy myself, I love epoxy. It doesn't add much weight if done right. That CF strip is only about .007" thick, and needs just a tiny bit of epoxy to do the job. Then spend some real quality time and sand smooth carefully.
Once it all sets up, the Carbon Fiber strip should help to straighten it out. It may not be perfect, but you will have one strong wing when complete.

Patriot

This is just a tip to prevent these warps in the first place.

When you put covering on the wing, don't shrink it until the entire wing is covered. Just iron the covering around the perimeter. Don't iron it to any ribs or shrink it.

Now take your heat gun and shrink it one rib bay at a time doing the top then the bottom. Work your way across the wing like this and most of these warps won't happen. I can't say it entirely prevents them but any warps the covering does induce are much more easily removed.

When you are done shrinking the covering, go back and iron it down to the ribs.

Apparently, from your last post, the wing is not finished yet. Jig it up so that it is flat and finish the wings. How big is this wing?

You should be able to remove some warp after the wing is done by shrinking the covering. You may have to do it more than once. Normally, to remove a warp, or add washout, you have to warp the wing in the opposite direction more than the amount of the warp. Be sure to heat both sides of the wing when trying to remove the warp with the covering. One side will shrink and the other will stretch when the heat is applied. A second set of hands is helpful.

Once the warp is out, let it set a day or two and check it again. It might take more than one attempt before it sets in the position you want.

The post that suggested ammonia will work too, if the wing has a bad warp. Just be sure to jig it and not induce a bow or some other unwanted twist. If you use this method, be sure to let it completely dry before removing it from the board.

Well, I finally just accepted the inevitable and resheeted the wing. It's now flat to within 1/32", as far as I can tell. Thanks to everyone who helped me out.