Gentlemen, since the demise of the Chartruese Martian Butterfly Q-ship,,, I am in process of getting another P-40 ready to fly,, I commented that I would be adding dihedral and asked if pictures and a post would be appropriate, so following is a step by step of the process I went through. I take NO credit for the method, just the pictures as the designer Pat Johnston told me how to do it.

pictures
Start off with a towel or something on the bench to protect the covering and place the wing upside down on the bench, yeah the same one with the towel on it,,

Using a yardstick mark in from each tip 25 inchs, then take a straight pin and begin to gently poke the sheeting inside the mark you made, find the rib, you can feel when you poke it. mine was about 1/4 inch inside the 25 inch mark


with a sharpie or whatever, gently mark outside the pin about 3/4 to one inch, depending on how controled you are with fiberglass and cloth application, neat and tidy,, go out less distance, if you like to "make sure you get 'er down" and possibly expand the area as you go, well remove the monokote accordingly. I cut the film in two places right where I intended the splice to be so that if I happened to cut the skin it wouldnt compromise the strength. then I slipped several layers of strong paper under the outside covering and cut the excess back towards the tip. this keeps you from hurting the balsa skin where you arent going to repair.

 I used a xacto saw and carefully cut along the line at 25 inchs which with the pin I had verified was outside the first two ribs in the wing. NOTE, YOU ARE CUTTING THE SKIN OUTSIDE THE FIRST TWO RIBS, IF YOU CUT INSIDE YOU WILL COMPROMISE THE BELLCRANK MOUNT and ,, the wing wont bend anyway so its bad news all around.

Cut the majority of the way through the leading edge and trailing edge as well, see picts.

find a block mine was about a half inch thick and as long as the chord of the wing. I wrapped a handtowel neatly around it and placed it under the center of the wing, it needs to be around 3 inchs wide, in other words narrower than the cut you made, and you also have to clear the pushrod coming through the top of the wing. Hm I forgot to take a picture of this but,, with the block centered under the wing, wing placed bottom up with the cuts showing, begin to gently stack magazines on each tip, I put them on in increments of about 5 per tip, keep it even, the wing will begin to bend, and may even make some nasty cracking noises, ( hey you would too if you were bent against your wishes) . When the tips settle onto the desktop you should have about 3/4 inch dihedral. The two gaps that opened should be really similar in size.

Begin by making shims to fill in the gap, the gap at the bottom spar should be somewhwere around a shy 1/8 inch wide and taper towards the leading and trailing edges. work your way each direction making shims, sanding a taper to make them fit, dont
force them in as it will localize stress in the skin and perhaps cause all kinds of nasty stuff!  As you make each shim wick thin CA along both sides of the shim. Please pay attention to the level of the skin especially on the outboard side. It can want to position itself lower than it should be, you can wiggle the shim up and down to get the skin to relocate itself correctly.

After all the shims are shaped and glued in place, I   sanded them all flush, note the tape on each side to keep from sanding trenchs into the skin and creating weak spots.

I used several layers of fine cloth and finishing resin to reinforce the joint. the first strips were about an inch wide and directly over the joint, the others were wide enough to cover both joints.

Now remove the magazines and read them as you wait for the epoxy to cure, or go to bed, heck you cant do anymore till tomorrow anyway!

All in all, I spent about 90 minutes doing the complete operation, not bad considering the huge improvement it will make in trimming your plane correctly.

Thanks Mark: That looks easy enough and a very neat job.