GoNavy

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I'm looking for suggestions to solve a problem with split flap construction on a Midwest AT 6, which is an all wood kit.

The wing surface above the split flaps has curved upward because the top sheeting, 3/32 balsa, shrunk. This has moved the trailing edge about 1/16 inch out of position. The good news is the trailing edge remained straight; It did not raise just between the ribs.

I believe I can restore the area to its original shape by wetting the sheeting and clamping a straight edge (pine board), but the problem with reoccur as the balsa sheeting again dries out.

The rib ends in the area are about 1/4 inch deep at the front of the split flap and taper to nothing at the trailing edge. They are not strong enough to overcome the pull of the shrinking sheeting.

I suppose one fix would be to cut off the existing rib and sheeting and replace it with solid balsa with the proper cross section. Short of that, I wonder if any of these might work:

1. Moisten the sheeting, realign it, and glue carbon fiber strip to the underside of the sheeting.

2. Moisten and realign, and epoxy medium weight fiberglass cloth to the underside.

3. Cut the top sheeting and, if necessary part of the ribs beneath, to allow realignment of the surface, and fill the cut with epoxy with micro balloons.

I would appreciate comments and suggestions. Thanks!

Tall Paul

On my DynaFlite PT-19, I did it this way...

paladin

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Go Navy!
I have an old flop tite Hollywood Zero (built some time around 1991, 240 flights) with this problem. I have a Pica Focke Wulf (built 1983, 210flights)with splitt flaps and no problems. The FW has 1/64 ply under the sheeting the full length of the flaps, and from the TE to two inches ahead of theflap hinge point. This plane has no internal suports (not needed). The Zero is built to plans with a 1/2 inch width of 1/64 the full length of the flap. the TE on the Zero looks like a lezonia noodle.

Joe

GoNavy

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Paladin:

Thanks for the info.
I doubled the rib thickness in the area of the split flaps, and then added 1/64 ply gussets. Maybe if I had used the ply throughout I wouldn't have had the problem.

I guess so much depends on the grain of the sheeting. In some areas my construction was fine.

I think next time I will either use solid tapered stock or add the same thickness balsa sheeting underneath the overhang.

Were both kits, the Zero and the FW, designed for split flaps, or did you kit bash?

paladin

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GoNavy!
Both were kitted for split flaps.

The zero was built for moch combat with my son so it was built stockand monokoted to allow for easy repairs. In the first season of combat this plane showed it needed strengthening in meny areas to handle the stress. At some point the center section needed replacement so I band sawed it apart and put a new crossection with the 1/64 ply like on the FW and the centersection has held up very well. But the outboard flap sections still look like lezonia.

I've included some pic's that kinda show the warp.

GoNavy

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Not hard to spot!