John Kahrs

Bending the first skin
I'm pretty much done float sanding both sides of the elevator. I think it's been a couple weeks now. Not every night, but I've spent some real time on it. It seems to be one of those things you can never be completely satisfied with. I spent a couple hours knocking together a mandrel to bend the leading edge skins over. It's just a long stick holding a row of leading edge ribs made of scrap wood. The bending involves a lot of wrestling, clamping, wet plywood and sometimes steam, and I'd rather do it this way than bend the skin over the actual elevator. I figured I've beat on the poor thing enough as it is by breaking ribs off and knocking it into the walls as I carry it around the shop. Last night I bent the first skin around the mandrel and it's drying now. I'm hoping it will dry very close to the final shape of the elevator, leaving only the tiniest gaps, eliminating any shortcomings with clamping pressure when the gluing begins.

I bought a wood moisture meter and thermometer/hygrometer that now sits on the garage wall. The values go up and down from day to day, although I don't know if there's much that I'll do about it. I suppose skinning when it's not too dry is all I can manage without buying a humidifier.

If there's one lesson I've learned with the float sanding, it's that I shouldn't expect it to make up for subpar construction (such as misaligned ribs, or ribs that are slightly too small) just as I shouldn't expect the fillers in the plywood skins to make up for subpar float sanding. Each layer covers the sins underneath, but those sins just emerge later as many more hours of work. If there is a greater precision in the framing of the skeleton, the sanding will be far easier.

Meanwhile, I tried building a scarfing jig with a router - the first version of which tore the plywood to smithereens. I'm considering trying a laminate trimmer instead, or a sanding drum.

The spar arrives, and so does a setback
Friday the wing spars arrived at my office. I commisioned the help of the only fella I know with a lumber rack, Manuel (who was the foreman on our house renovation). It's strange seeing something that big maneuver through a quiet residential neighborhood. They looked good, and as I hung them from the rafters, I felt a little humbled knowing that this was all taking far longer than expected, that I probably wouIdn't be taking them down until a year from now. And today I probably added three months to that schedule.

I opened up the garage door today and all hell broke loose. I had hung the tail group spars from the rafters, up out of the way, bolted together in an inverted T. The door would clunk against them when it raised to the end of its travel, and I always took note of that, always opening the door only halfway. It was stupid and lazy, really, not to move them to a better location. Today I just opened that door without thinking. The spars snapped from the loops of twine holding them, came crashing down on the work table below, and crushed the elevator, which just happened to be resting on the table beneath. I was actually preparing to put the second leading edge skin on it - the piece was perhaps 90% complete.

The spars were fine, but the elevator is beyond hope. A third of the ribs are gone, the leading and trailing edges were snapped off. I was stunned, knowing that trying to rebuild it was a little silly. That all thay work was out the window in an instant. Sipping a double martini, I considered that I may not be cut out for this project- I am far too careless. But I also considered that I now had a chance to build the damn thing properly. As the elevator progressed, the number of things I didn't like about it kept piling up. Several weeks of work were lost, but several weeks of learning how to do it properly were gained, and I wasn't doing it properly.

Tonight I simply cleaned up. I will make the ribs and tip bows myself this time, and use the other spar I bought from Stan Weiss. It will be better than the first one.

The Stabilizer
I decided to teach myself a lesson and make the elevator from scratch the second time. First I made new ribs. For a bunch of little wooden triangles, it took a long time and I thew several away before I got them right. They were all pretty much junk until I brought home a planer. It seemed an extravagance as I carted it through the Home Depot parking lot, but now I can't believe I lived without one for all this time.

When the spruce stock for the elevator spar showed up, I decided to backburner the whole thing and move on, doing the trailing edge ribs for the rudder, then the tedious tapered triangular trailing edge strips for the stab. I kept going with the stab, flipping it over, leveling it and gluing on ribs. Up until last night I had been using heavy duty monofilament fishing line to jig the framing of stuff. I was sick of not being able to see it so I switched to black thread. Sounds like a boring detail, but it was like turning on the accuracy lights. Suddenly I could see everything and I could align all the ribs centerlines with much greater precision. When the errors diminish to one fifth the size they were before, it's very gratifying.

With the forward stabilizer spar now in place, the emergent framing of the thing is already rather beefy. (The elevator now seems like a wisp of a thing by comparison: a delicate model airplane part trailing behind the plane.) The Falco is becoming greater than the sum of its parts. Aside from the obvious strength of the spars, you can't really point to one structural element that keeps it together. It is the whole plane that keeps itself together- the aggregate of all the little joints and skeletal parts glued to other parts, skinned with other parts that collectively becomes something very very strong. It's heartening to see that strength revealing itself this early in the game, especially considering it's something I'll trust my life, and the lives of others in.

Since I wrecked the elevator, I've taken a more careful approach. I've slowed down. Last night I glanced at the clock after an exciting, tour de force round of sanding rib ends- 1:30am, and considered gluing on a couple more ribs. I thought better of it. Though I like to sleep while the Aerolite cures instead of waiting around, too many times I've pulled off clamps the next morning and furrowed my brow over subtly misaligned parts. There's not much you can do about it at that point. Of course you can fix anything, but in any case it's easier to simply do it right the first time, and when I'm tired, I'm sloppy.


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