First a quick bio ... I’ve built two kits in the past, both a “few” years ago (close to twenty).

I’ve recently gotten back into building and now I’m putting together a Midwest Citabria. After building the vertical and horizontal stabilizers as well as the rudder and elevator, without problem or incident, I started on the wing. Everything’s been going great with no problems or issues and I’m really enjoying building again. Until yesterday, that is.

About ten inches of the wing is sheeted with 1/16 balsa in the center section of each wing half after joining, the kit supplies 10” pieces of 1/16 balsa sheeting for this purpose, so about 20 inches of the full wing center section is sheeted both top and bottom, (ten inches on the left and ten on the right - I would have preferred 20" pieces, but that's another story.). The top of the wing had been sheeted last week ... actually the right side is sheeted prior to joining the wing, then the left top is sheeted after joining the two halves. All was fine with the wing up to this point. Oh... and I also sheeted the bottom leading edge (about three inches - from the leading edge to the main spar). The top had been done earlier. I would supply pictures, it would probably be easier then trying to describe his, unfortunately my digital camera just decided to stop working ... As a side note, the plans call for about 2 deg of dihedral. Instead, I built the wing flat.

So... my problem is that after sheeting the bottom of the wing ... in an unrestrained condition ... the wing now has about 1 deg 'negative' dihedral. I used medium CA and simply held each piece in place for a minute while it set. There was a total of four pieces and two small strips total.

My big question is; Why did it move? It was fine, setting flat on my workbench, I walked away, grabbed some lunch and now it’s raised up about half an inch!

My second question is; Now what? I figure that I have a couple of different ways to fix it, I hope ...?...

John

Balsa has a grain. You added glue to one side - grain stretches as the cells soak up the glue and/or the glue soaks into the pores. Part bends because of uneven internal pressures. As the glue dries it "sucks up" and tends to pull itself into itself - contracting the piece. If you are lucky the pushes equal the pulls. CA's tend to pull more as it dries very rapidly. With white and yellow glues that contain a lot of moisture the wood absorbs it on the wet side and the glue grabs as the moisture evaporates and/or is absorbed down into the cells and pores. They tend to push more.

By pinning and weighing the pieces flat and forcing them in place to cement them the pieces tend to dry into the shape they are held at. You may be able to spritz the wing with water from some kind of mister/atomizer, or even a damp cloth, and work it straight. Heat sometimes helps. Work slow and be patient. When balsa/cement lets go it does it all at once with a "SNAP!"

When I glue a wing I put LOTS of weight on it.

You can also stretch rubber bands between pins stuck into the worksurface to squeese the spars (and later the sheeting) down.

I would buy a new wing kit, and build it to the mfg specs. The other options are to cut the wing apart and fix it with the correct angles, or try to fly it as is, which I think would be a bit difficult.

Windex works wonders .
Spray windex on both side of your wing, at center where it is joined together so it stays damp. block up both wing tips and weight down the center and let dry.

I haven't tried the windex method but I believe Windex has ammonia in it. I've fixed a badly constructed/warped wing similar to RC Outlaw's windex method with straight ammonia and water mixed at about 50/50 sprayed on and then weighted with sandbags. Sometimes it take several applications.

I have used RC Outlaw's method and it works great. Spray liberally until dripping on both sides from center out about 10", weight it down and go eat supper and come back in the morning. All will be well. 4 or 5 magazines on each side should do the trick. Wish I had some of those old Sears or Montgomery catalogs.

Thanks guys! All of this is GREAT information. I've used the "Windex" method before with success on a wing panel that had a hump in the trailing edge and it worked great ... the 50/50 mix of water and ammonia may be a better alternative ... it would avoid the blue discoloration of the balsa.

I'm actually quite happy with the wing as it is ... except for the slight negative dihedral in the rear of the wing (the issue I brought up here). If the "Windex" method doesn't work, I'll try slitting the trailing edge, straightening it and then re-epoxying (while restrained!) ... I still have the "formed" trailing edge to install behind this sheeted area. (a piece of 2" x 1/2" trailing edge material to fill the center trailing edge of the wing) once I slit the sheeted area and then epoxy the "formed" trailing edge in place, (while restrained!) any minor deformity should be eliminated. Removing the sheeting and redoing it is another option ... worse case, I'll just build a new wing.

Thanks again for all of your help.

John

Charlie P, that rubber band trick is genius.

I'll take credit for it, but I don't remember if I thought it up or read about it in the past. ;-) It was certainly "pre-Internet" in either case.

Cheapness is the muther of invention.

Here are two more "invaluable" rubberband tricks.

Strung between pencils or chopsticks they make perfect fuselage clamps. Can be a test of dexterity (hint, do the lower ends first)

If you look close at the horizontal stabilizer you'll see a chopstick under with rubber band over. Use a pair of each to hold the control surfaces in straight alignment when zeroing control rods and servos and for setting 0º or 0" on alighment gauges.

I have been known to use the RBs for A lot of things but CharlieP just showed me something new. Holding spars??? Why haven't I come up with that one. Today I was out of ammonia so I just shot down the 1/32 ply with water then bent with RBs to shape. I let it set up then tomorrow I will glue and epoxy the sheeting down. This is just pre shaping to make life easier. Thanks for that tip Charlie!!!!!!!

OOps, wrong photos.

For preshaping the sheeting, I prefer to use masking tape. I don't like the RB holding because it tends to leave dents in the balsa. Masking tape is much quicker and easier to control.

Brad

Charlie P.

Are you going to round off the LE and TE of the short stubby wing in your first photo before you attach the ailerons?

I just wonder how he is gonna fly that squigly plane in first post third picture. Anyone know what model that is??