As I’ve mentioned previously, the spars are flexible with no skins attached, and Vans do stipulate that they should be clamped to a work bench, shimming as required. They don’t actually say to make sure the spar is straight etc, but do warn against the clamps causing twisting/bowing. 

Anyway, I decided that what they didn’t mention was probably equally important, so I took some time to clamp and shim the spar to ensure it was as straight as possible, and also not twisted. Clecoing the skins to an already true structure must be good! I used my laser level to adjust/cut shims accordingly.

Clamping at the root end is easy, but needs thought at the tip. So I screwed the shims to some timber, and clamped that to the bench.

I then found some small screws to screw the spar to the shims. This was required since the spar had a natural twist at the tip, and keeping it firmly down on the shims sorted the problem. I put some plastic under the screws to avoid damage to the rib holes.

Checking for Twist

Since the ribs are attached to the spar web, I decided to check for twist by ensuring the digital level was aligned with the web, hence the block of wood.

Next job is to cleco on the skins! : )