Diagonal Rib Bracing For Trailing Edge Wire

The trailing edge of the wing is made with a piece of piano wire attached to the trailing end of each rib.  The fabric pulling on the wire causes the trailing edge to scallop, like on a WWI SPAD.

 The fabric pulling on the wire puts a significant tension in the wire.  For the upper wing the ends of the trailing edge wire are attached to the root rib and the rib at the aileron cut out.  The aft portion of both of these ribs are made with a 1/4" thick spruce rib web and with 1/4" x 3/4" spruce cap strips.  To support each of these ribs, so they can take the wire load, there is a diagonal brace, 1/2" x 1/2" spruce, running from the tip of the rib to the lower flange of the rear spar.

 The wing drawing shows the end of the stick 3 1/8" from the trailing edge of the rib.  I made a small block of spruce to fill between the cap strips to that point.

 I cut the brace stick so it bears on the block and a little on the rib web.

The top and bottom had to be sanded down to fit snugly in this pocket.

 I used the flange of the spar to layout the cut lines on on the forward end of the stick.  There is a piece of 1/2" plywood that the end of the stick pushes against, so the cuts are like on the other end.  The cut against the block was made so it fully pushes on the block.

  

 Before gluing the brace I clamped a straight edge to the rib to make sure I didn't move the end of the rib out of line.  My biggest concern was to move it inboard, which would cause the ribs to interfere when the wing panels are assembled together.

I found it almost impossible to get the nails through the 9 ply birch plywood.  Instead I used the pin nailer to hold it in position and a clamp for glue pressure.  This was one of those operations where T-88 was a better glue to use than Resorcinol.

 The rib at the aileron cut out is about the same process.  I used a square to hold the rib in position.

 The 1/2" square corner block was easier to hold in place with clamps then nails.  The block with the big clamp is pushing the rib and corner block together.

The little block at he tip of the rib started sliding out so the clamp is just holding it in.