Trammel the wing to ensure compression struts are perfectly perpendicular to the spars. Trammelling means that you measure the diagonals that the drag wires form in each wing bay. In other words, you'll measure the "X" s made by the drag wires and adjust the wires until both arms of the "X" are the same.
The wires in each bay are adjusted to the same length. But then the trammel bar is reset for the next bay and the wires in that bay are adjusted independently. One bay at a time.
Before you start, while the wires are loose, wrap each wire with about 1 inch of vinyl electrical tape where the wires cross. This will reduce the chafeing of the wires and cut any noise they would produce rubbing together. Don"t tape the wires together as you want them independently able to move when you rig in the wing wash out later. Photo 1.
I suppose you could trammel the wings with a tape measure, but the actual length of the drag wires is unimportant...what you want is just for the lengths to be the same. A trammel bar a quick, handy way to do it. If you can, barrow one for a few hours. Otherwise, it's easy to make your own out of scrap steel and a bolt. Mine is a 6 foot length of 3/8 steel rod, with a one inch length of 3/8 ID tube slipped over and a AN3 bolt and nut make the adjuster. I used some scrap 1/8 inch rod to make the pointers and welded it together. Photo 3.
Start at the root end of the wing and work toward the wingtip. Adjust the wires in one bay until the trammel bar says they are identical length, then move on to the next bay and do the same. After you've trammelled the entire wing, go back and double check...you'll probably have to do some minor adjustment. Photo 2
When you get done the wires should all have approximately the same tension and give a nice TWANG when you pluck them. Use a very short wrench to keep from getting the wires too tight. I made my own out of a 1/2 by 1/8 by 3 inch long piece of steel. I simply hack sawed a slot in the end. Photo 4
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