Monday, November 23, 2009

Just like a butterfly

Or more fittingly, I suppose, a schmetterling.

Right before your eyes and without the privacy afforded a caterpillar by a cocoon, the Horizontal Stab box is transmogrifying into the Horizontal Stab skeleton.

Well, it will.


But first, I had to fabricate the inner pieces of the hinges that the stab will pivot on. And by "fabricate," an overly lofty sounding word, I mean "make." And by "make," which in this case is also overly aggrandizing considering the nature of the actual work involved, I mean cut a little tube of aluminum into smaller tubes of aluminum. 21/32" long tubes, in fact. With a tolerance in size of plus 1/32" and minus 0. Zero. None. Nada. (As is "nada smidgen shorter." Oh, you thought I knew Spanish? Nope.)

You'd think my first step would be to find a ruler graduated in 1/32" increments. And, well, you'd be right. But I haven't got one. So my second step was to pull out my precision calipers. Which quite naturally led to the third step: go back upstairs and get a calculator to find the decimal equivalent of 21/32. Which, as I'm sure most of you already knew, is .65625 inches. My calipers are only useful down to .656, though.

It would have to do.

Cutting the tube with a hacksaw was easy enough, but doing it well was a completely different story. The saw leaves a rough edge that has to be deburred, and the deburring is not easy. In one case, I deburred a piece to below the minus zero tolerance. You can pick it out easily enough:

You can also see that the remaining pieces will still need to be cleaned up a bit. I'm letting them sit over night while I think of a way to get them nice and flush in the ends without chasing them down to below the allowable size. I'm thinking it's going to be something not involving the Scotch-Brite wheel. The great thing about the wheel is that it removes a lot of metal quickly. Of course, the bad thing about the wheel is that it removes a lot of metal quickly. It's a lot like working with fiberglass that way.

With that part back-burnered, it was time to move onto something more gratifying. Something like a little helicopter flying:

Unable to put it off any longer, I started attaching the parts that would hold the ribs that in turn would support the skin of the stabilator. This is another of those situations where Van's made sure that the parts could only (correctly) go in one way:

If you tried to install them incorrectly, the holes in the flange wouldn't match up with the holes in the spar box. That's what drills are made for if you're the type to insist on having things your own way, but I found it easier to just turn the part over so it would fit:

Those little parts will have the ribs aft of the spar box riveted to them. Eventually. Not tonight. For tonight, I was concentrating on the stuff forward of the spar box. That involved the preparation of eight ribs. The preparation included the normal deburring, plus some fluting to straighten them out and some grinding away of material on their noses. Just as with the vertical stab, the noses of the ribs are going to have to nestle into the bend at the leading edge of the skin. To allow for that, some of the material that got pushed forward of the leading edge of the rib when the flanges were bent needed to be ground away.

This is a before and after picture:

Grinding that much material off of eight ribs takes a toll on the relatively spendy Scotch-Brite wheel. After enough time watching the wheel shrink, I started to feel like it was billing me by the minute! Here's the spar box, half way to becoming the horizontal spar skeleton:

I hope to get to the back half tomorrow, but I'm on vacation. It seems like that would be a great time to get airplane work done, but my time seems to be getting soaked up honoring all of the "I'll do it when I'm on vacation" commitments that I've been piling up for three or four months. Plus there's RV-6 cowl work to do, although that's going to be on hold while I wait for a few little bags of appropriately sized rivets to arrive from Van's.

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