Wing Trammel Points and Starrett Trammel Points

 To square up the wings we adjust the length of the diagonal Drag and Anti-Drag wires.  The turnbuckles are used to both tighten the wires and to adjust their length.

The idea is that if you adjust the wires at each bay so they are the same length the wing will be square.  You can't easily measure the length of the wires.  Instead we mark points on the bottom of the spars and measure between them to square up the wing.

 We don't actually take a measurement with a tape measure, but you could I suppose.  Instead we use some Points, like on an awl, attached a small beam.  Mine were made by Starrett.  They clamp onto a stick, in this case spruce.  The one is fixed, you clamp it where you want it.  The other has a thumb screw which adjusts to position of the point to increase or decrease the distance between the tips of the points.

To measure the diagonal distance between the points marked on the spars at each bay, you set the fixed point at one mark, then adjust the movable point to align with the mark on the other spar.  Then you use this length to measure the opposite diagonal length and adjust the turnbuckles to lengthen or short the wires.  As you adjust the length of the wires, and re-tighten them, you needed to readjust this length between the trammel points until the 2 wires are exactly the same.

 I used the optical center punch to make a light punch mark at each trammel point, on the bottom of the spars.  The punch mark makes it so much easier to do this by your self.  Now that that I've worked out the locations for the points I'll mark the spars for the other wings before I start assembling them.

On the lower wing the points are located at these distances from the root end of each spar.
Root 2"
Light Compression Rib 46 13/16"
Heavy Compression Rib - Inner Bay 91 3/4"
Heavy Compression Rib - Outer Bay 93 1/4"
Tip Compression Rib  139 5/8"

 On the Upper Wing the points are located at these distances from the root end of each spar.
Root 2 1/4"
Light Compression Rib 55 9/16"
Heavy Compression Rib - Inner Bay 108 11/16"
Heavy Compression Rib - Outer Bay 110 3/4"
Tip Compression Rib  156 5/8"

Now I can start adding part to the wings.