Articulated Wing Framework

Step 5 Shoulder hinges (upper and lower)

The shoulder hinges are made from the strapping bent around the pieces of the wing base tube (the pack's inner frame that you cut up in step 2). Cut an appropriate length of strapping for each hinge - for me it was 8 holes' worth for the upper and 6 for the lower hinge. I also had to drill out holes on some of the ends, as the holes were of 2 sizes and my screws did not fit through the smaller ones. Bend the pieces into the shapes as shown in the pictures. The upper hinge straps have extra bends so the balsa bone will fit between the sides when they are held together.

Fit the pieces of strapping over the wing base tube so that the centers are 9-3/4 inches apart. With the nuts & bolts (E), screw the straps tight around the tube.

Assemble the upper shoulder hinge using one balsa bone X, two nylon washers (N), and one short binding post (K). The binding post should go through the strap, one washer, the balsa bone, the other washer, and the other side of the strap. Then screw the second half of the binding post in until the hinge is closed. Verify that the bone rotates sufficiently, you may have to trim the edges down.

Cut the dowel into 4 pieces, 2 of 8-3/4 inches and two of 18-7/8. (Many of these photos show a metal dowel instead of a wooden one. The metal turned out to be too heavy for the balsa, which in retrospect was not a surprise. I had to swap them out but didn't bother to re-take all the pictures.)

Assemble the lower shoulder hinge using one shaft collar (F), one 1/2" machine screw (H), one of the 8-3/4 inch dowel sections, and as many nylon washers (N) as needed. Fit the dowel section through the shaft collar (take out the tiny screw that comes with it). Put the screw through the lower strap (both pieces) from the front of the wing towards the back, and screw it into the shaft collar thread until the dowel is held in place. If there is extra space along the length of the screw, add some of the small nylon washers (P).