Trimmed Trailing Edge of Ribs

 The ailerons use a folded ">" shaped piece of steel for the trailing edge.  Today you can buy a similar, aluminum, trailing edge material from most aircraft supply houses.  During WWI some of the aircraft, like the SPADs used a wire trailing edge.  That's how it's done on the NINE wings.

They use a length of 1/6" music (piano) wire for the trailing edge.  To hold it to each rib the wire is soldered to a strip of thin (0.020") copper, the width of the rib capstrips (3/8" for most ribs) and, about 3 1/2" long.  The copper is folded around the trailing edge of the rib and nailed to the upper and lower capstrips.  The noticeable thing about this method is that the tension on the fabric causes the wire to sag between each rib giving the trailing edge a scalloped look.  The wire sags in the shape of a Catenary Curve, like the cables on a suspension bridge (Golden Gate or Mackinaw).

To support the wire the ends of the ribs need to be square, not pointy, so there is a surface for the wire to bear against.

I had planned to make a fixture for the table saw, like I did for the Lead Edge wood on the nose ribs.  I forgot to do that and built the first 2 wings with pointy ribs.

I decided to make a fixture which would work for the ribs for these next 2 wings, but could also be used to go back and trim the ribs on the first 2 wings

After much rechecking dimensions the cut needs to be 20 3/8" from the rear face of the aft spar

For my fixture I used a piece of 3/4" plywood.  I need to cut out some holes in it to clear some diagonal braces on the wings so I needed it thick enough that it shouldn't break once I make those cut-outs.

There are 3 reference points to assure the fixture is in the correct position on the rib.  The 1st is the forward end of the fixture which rests against the rear face of the spar.  The 2nd, right behind it, is a block which holds the fixture in the correct vertical location.  The 3rd is forward of the trailing edge.  The rib sets down in the pocket resting on the 3rd stop.

I made a pocket, with another piece of 3/4" plywood,  just to get better control of the cut-off saw location and angle.  I wanted a nice square cut.

I used the square on these ribs to simulate the spar.

Once the rib was in the fixture correctly I clamped it in place at 2 of the vertical sticks.

A few gentile strokes with the X-acto Saw and the job is done, next rib.

A nice square end to each rib.

Look like I need to build wings.