Finishing Up the Wing Brackets

Each upper wing has three compression tubes which, along with the drag wires (and spars, of course), give the wing its strength and rigidity. On the ends of each compression tube where it butts into the spars, there is a bracket with a little aluminum "button," or "compression tube locators." Each of these is held to its bracket with a small countersunk screw. The smooth part of each screw should fit nicely into the reamed hole, although by the time you're done countersinking the bracket, there's not much of a hole left. I was about to countersink all the way through, when I realized that something was wrong. The head of the screw wasn't fitting the countersink correctly, so I took some photos and measured some angles in Photoshop. Upon perusing the plans later, I discovered that they actually tell you to use a 100° countersink, while the one I had been using was 85°. There's a lot to keep straight, so I'm not surprised I missed it. Thankfully, I figured it out before I ruined any (or all!) of the brackets.

This is a countersink I already had on hand. I had used it in woodworking before. It's included angle is about 85°.

No wonder the screw didn't fit the hole properly! Their angles are totally different! So, I ordered the correct countersink (from MSC, I think) and the screws fit the countersunk holes perfectly, albeit with very little contact area left between the screw grip (the smooth part of the shank) and the hole. It was a great fit, though.

Getting ready to paint some brackets with zinc phosphate primer. That's the stuff that all interior metal gets coated with to help prevent corrosion.

Primed brackets. This primer doesn't seem very durable to me, so be careful with your primed brackets.

These are the compression tube locators, or "alignment buttons" as I like to call them. I made them on my new lathe, a Grizzly G0752. Check out my YouTube videos on the process.

This countersunk hole is to make some clearance for the grip (smooth part of the shank) in the screw so the button can get screwed down tight to the fitting. The countersunk hole I had some difficulty with is on the underside of that fitting.

This is an example of one of the brackets onto which the compression tube locator will be screwed. The bracket will be facing the other direction, though, of course. The screw head will be against the spar and the locator, or "button," will be facing outward toward the other spar to hold the compression tube in place between the spars.

Make sure to check out my aviation channel, Aviation Fanatic, to see some videos of me making the compression tube locators.