A wing building jig can be a useful tool to aid in building a straight and well aligned “built-up” balsa wing. The common method of building directly on top of the wing plan works well, and is simple in the case of a flat-bottomed wing profile. However, in the case of a semi-symmetrical wing, i.e., one in which both the top and the bottom surfaces are curved, that method is complicated by the need to somehow keep all the wing ribs uniformly aligned at the proper angle to the plane of the building surface instead of rocking on their curved bottom surfaces.
The Great Planes Super Decathlon I’ve been working on has such a semi-symmetrical wing profile. The plans and instructions detail a method of propping up the trailing edge of each wing half on an included balsa “jig stick”. They also mention, without detailing, the alternate option of purchasing and using a Wing Jig Kit, which is nothing more than a pair of 1/4 inch rods held in an aluminum frame. Each of the wing ribs in the kit were already drilled with two evenly spaced 1/4 inch holes, ready to slide onto the jig.
This looked like a convenient system, and one I hadn’t tried before, but I didn’t want to pay for the commercial jig. Instead I made my own out of some steel rods and scraps of 1×2 hardwood I had lying around. It probably took less than twenty minutes to put together, and worked out very nicely. It is possible to move the jigged up assembly around if needed, or even take it outside for sanding without disturbing the alignment of the parts. The finished wing halves turned out straight and true, so the jig did its job.
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