Monday, January 09, 2006

Back to School: Night 2

This was the first real night of class - the full four hours. The FAA, understandably, has to assume that you may have never seen a hand tool before, so we had to go through the four major categories: holding, cutting, turning, and pounding.

You would think this would be pretty dull, but you'd be surprised to learn that you have probably been using at least one tool incorrectly for your entire life.

Interspersed with the lecture discussion were trips to various shops and to the hangar to look at examples of various tools and airplane features. Finally, we were ready to actually pick up some tools and do a little lab work. Tonight we worked on center punching aluminum and drilling straight holes through it with a pneumatic drill. The center punch is intended to put enough of a dimple in the aluminum to keep the drill bit from "walking" as you start to drill the hole. For the most part my holes were nice and straight, but one was pretty embarassing: I could still see the mark from the center punch! That's a pretty bad miss!

We talked a little bit about riveting, in the context of oversize holes leading to very bad riveting. As a pilot, the instructor thought it interesting to point out that most airplane wings are only flush riveted on the first 1/3 back from the leading edge. This is where the air over the wing is still laminar, or "attached" to the wing skin. Flush riveting here reduces drag. Further back on the wing where the air has separated, most manufacturers will not use flush rivets because it is more expensive and time consuming, and offers no benefit in return.

Interestingly, the wings on the RV are flush riveted all the way back to the trailing edge, as is the fuselage. There's no aerodynamic benefit to this that I know of, but it sure looks good!

As part of the hole drilling exercise, I asked the instructor about deburring the holes and the edges of the piece of scrap aluminum I was working with. I wanted to try this out since I will be doing a lot of this when I fabricate the new instrument panel. I had also hoped to try out a fly-cutter on a drill press, but that's a later lesson. The fly-cutter is a somewhat intimidating bit that I'll have to use to drill the 3 3/4" holes for the round instruments. I'd also like to practice a little with tin snips since I will need to cut rectangular holes for the radios, GPSs, and VM1000. Hopefully that will come in a later class as well. And I did confirm that we will be learning to rivet, too. This just gets better and better!

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