The original wing design for the Bede BD-4 used a one-piece flap, about seven feet long. The new metal wing on my Bede BD-4C airplane uses a two-piece flap, with each half being about 3.5 feet wide. The ribs at the ends of each half are tied together with a pair of 1/4 inch steel pins and there is a piece of rib material filling the 3/8 inch gap. Here are photos of the two sets, one assembled and one disassembled so you can see how it works. (Click on this photo, or any other, to see a larger version.)
I have been doing metalwork to construct most of the rest of the plane. Making this mid-flap assembly gave me a chance to do some woodwork, a nice change. Here is a shot of the finished assembly. You can see the bracket between the two ribs. The bracket will get riveted to the rear spar of the wing.
I used my circular hole cutter to make the brackets (pictured below) and to cut out the end of each spacer to clear the brackets.
I sanded the spacers to exactly match the shape of the flap ribs. And then, with all three pieces held together with a jig, I drilled holes for the pins with a 0.25 inch drill bit through the whole stack.
Finally, I then went through the holes in one rib and the spacer with a 0.2510 reamer, enlarging the holes by 0.001 inches. The result is a “press fit” for the pins in one rib, which will hold the pins securely, and a “slip fit” for the pins in the other two pieces, which will allow everything to be easily assembled.
