EAA Sport Aviation

Homemade
Hybrid Blind Rivets

THERE WERE THREE PROBLEMS with the horizontal stabilizer brackets on the Kolb Mk III Xtra I’m working on. The first was that the brackets were mounted a bit more than 3/8-inch off each other, causing about a one-degree difference in angle of incidence between the left and right stabilizers. This particular airplane has been known to have a built-in turn from the reports of previous owners, and this mis-mounting surely was not helping things. So right off the

They say that to a man with a hammer, all
the world’s problems are a nail. The same
idea holds true when you have a lathe,
except the problems can be turned away.

bat, one bracket would have to be remounted to get them evened out.

Second, it is a Mk III Classic to Xtra conversion. When this is done, both the wing and horizontal stabilizer incidence must be lowered to keep the fuselage pod from flying at a negative angle in cruise flight, which makes for a squirrelly handling, draggy airplane. The airplane is also of pod-and-boom design so when the wider X brackets are mounted further toward the center of the boom tube, it spreads the front of the stabilizers such that the elevator hinges bind so much that you can feel them pop over center as they travel up and down. Surely, not a way to prolong the life of the elevator hinges or make the airplane easy to trim. Both brackets would have to come off and be narrowed to relieve the bound hinges.

Third, the builder drilled the mounting holes so close to the flanges of the brackets that it was impossible to get the rivet square with the bracket even after I solved problem two by cutting down the flanges of the brackets and moving the top hole inboard 3/8 inch.

I needed an extended nose for my air riveter. They say that to a man with a hammer, all the world’s problems are a nail. The same idea holds true when you have a lathe, except the problems can be turned away. I won’t bore you with the details, but it could just as easily be done one of two ways. The simplest would be to use a piece of 3/8-inch by 0.125 tubing (yes, Aircraft Spruce has that size) cut 3/4 of an inch long. You could just hold it in place on the air riveter. A more involved solution is getting an extra nose piece and using some J-B Weld to stick it on. I elected to do it the hard way, although I did cheat and use a loose 3/8-26 thread to approximate a 10-mm by 1.0 metric thread (.393-25.4 inches) as cutting metric threads on my lathe is just a booger involving gears, belts, and a bit of voodoo.