H ANDS ON HINTS FOR HOMEBUILDERS
Homemade Hybrid Blind Rivets BY RICK GIRARD, EAA 597933
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.
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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. Now I had a new problem. The mandrel of a standard 1/8- to 1/4-inch grip blind rivet
PHOTOGRAPHY BY RICK GIRARD
is too short to use with the extended nose. The jaws of the rivet puller couldn’t reach it. The last thing to do was make a hybrid rivet to accommodate the longer nose. McMaster-Carr carries 3/16-inch stainless steel rivets in grip lengths up to an inch. At 75 cents each with shipping, this trick was getting expensive real quick. Fortunately, I only needed 14 of them, and the long grip rivets come in boxes of 10 so the expense was tolerable. I took the mandrel from the 1.00-inch grip rivet and the 1/8- to 1/4-inch grip rivet and put the long mandrel in the short body. By the time it was all said and done, each hybrid rivet cost about $1.10, but combined with the extended nose on my air-powered riveter, I could get right up next to the flange, square up the rivet, and “pop.” It worked; the rivets are nice and tight, the right and left stabilizer are flying together, and the elevators travel up and down without a hitch. The extended nose on my air-powered riveter allowed me to get right up next to the flange and square up on the rivet.
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