Building the Super Baby Great Lakes: Drag Wires

What gives the wings their strength and rigidity are three things: the spars, the compression tubes, and the drag wires that pull that structure tight. A similar structure is built up on a different level between the upper and lower wings: the wings are like the spars, the interplane struts and the fuselage are like the compression tubes, and, like each wing, you also have wires going between the upper and lower wings to pull everything together.

The drag wires are made from 3/16" 2024-T3 aluminum rod. The wing metals kit calls for 6-foot-long pieces, but I would order them a couple inches longer. I think you'd have less waste that way, but maybe there's a way to cut them to reduce the waste. I then measured out each piece and chopped them off on the band saw. Although the throat of my little band saw isn't big enough to fit these wire lengths in (each drag wire is around 24"), I simply made the cut at an angle, then used the grinder to square off the ends, with a little chamfer for ease of starting the threading (the oscillating belt sander would probably be better, so you don't clog up the grinder wheels with aluminum). You could easily cut these to length with a hack saw, too, if you don't have a band saw.

EDIT: I just discovered that Aircraft Spruce sent me 6061-T6 aluminum instead of 2024-T3 aluminum for the drag wires, so I will have to make all of them again. Ugh! 2024-T3 has a tensile strength of about 60,000 PSI while 6061-T6 has a tensile strength of only about 45,000 PSI. Of course the load on the drag wires is tensile. Glad I made this discovery now instead of after the wings were assembled and covered!!!

Next, you simply use a 10-32 die to create threads on each end, one inch on one end and one-and-a-half inches on the other. Frankly, I don't know why the instructions say to put one inch worth of thread on one end, because they then tell you to put two nuts on that end (locked against each other) with about three threads showing at the end. You probably really need only a half inch of threads on that end. Use padded jaws in your vise so as not to mar the wire, or just throw a couple blocks of wood in there, as I did.

I used AlumTap when cutting the threads. It's quite popular and, in my limited threading experience, seems to work well. I really enjoyed doing the threading. Of course I primed the drag wires with zinc phosphate primer. I think I might cover up the threads if I had to do it over, as it kind of gunked things up when I screwed the nuts on later. I'd be interested to hear what an expert has to say on the matter.