Skinning Jig


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Last Update:

May 12, 2011



My wings are built on a flat table, so when moving the wing skeleton to the skinning jig I had to establish a plane for the wing to hang in. After placing the skeleton in the jig, I first clamped the main spar at the root and the tip ends. The root end was fixed and the tip end was adjusted to achieve a level condition. I used a water level (about 20 feet of clear poly tubing filled with food coloring dyed water) to establish level. I shimmed the tip of the main spar with aluminum shims until the spar webs were level, then clamped it tight.

At this point the ends of the main spar are level with each other and the two top corners of the wing skeleton are clamped tight.


The next step was to bring the rear spar in line with the main spar. I used a plumb bob dropped from the center of the main spar attach hole to point to the center of the rear spar attach hole. After sliding the rear spar to the proper alignment, it was clamped tight to the jig brace.

Now the rear spar is exactly in line with the front spar at the root end. I am now assured that the wing is square at the root end.

Now the third corner of the wing is clamped tight.

The next step is to remove any twist or washout from the wing. To do this I dropped a plumb bob from the bottom side of the main spar past the bottom side of the rear spar near both the root and tip ends. Shown is the tip end plumb bob.


By carefully measuring the distance from the rear spar to the plumb line at the tip and the root ends I can see which way I need to move the tip end of the rear spar to remove any twist.

Measure both and then move the tip end of the rear spar a little and then reclamp. Keep doing this until both measurements are the same.


Once both measurements are the same clamp the last corner securely. The wing now has no twist and is secure at all four corners.

The last bit of business is to reestablish the straightness of the spars. To do this I abandoned gravity and used a laser line tool. I set the laser up on a tripod and adjusted it until it was in line with the main spar web at both ends. I then used two screw type bottle jacks with 2x4s at two points in the middle of the wing to move the middle of the main spar up or down until the laser line was tracking the spar web for the length of the wing.

I ran a line through the nose rib jig holes to double check for straightness there just to be sure. Looked great.

The wing is now straight, square and has no twist. Ready to skin!

I’ll leave all the plumb bobs on during skinning to be sure nothing moves.


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