Friday, June 17, 2011

What's all the flap about?

The autopilot servos that I ordered from Van's last week arrived while I was out in Vegas, as did the replacement system block tops that I had ordered as a ploy to trick the ones that I had lost into revealing themselves. That reminded me that the tops had not yet been installed, so I decided to knock that task off of the list today. It seemed like it would be a pretty straightforward deal to install them since it is simply a matter of putting them in place and tightening a nut onto each of the two studs. Having not worked on the airplane all week, I thought a quick and easy job would be a good way to get back into the game.

I had forgotten about the curse that these studs have one them. As I recall, the installation of them was one of the very last things to do when building up the bottom center section of the fuselage. "Just one more quick job and I'm finally done with this seemingly interminable section," I remember thinking. It didn't work out that way. Try as I might, I couldn't get the nuts to screw down onto the svrews that were to act as the studs that would support the nylon blocks. If I remember correctly, I only managed to get one fully installed before ruining the other five screws by rounding out the heads with the screwdriver. I had to order an entire set of new nuts and screws from Van's. The new ones installed very easily, as it turns out.

Still, bygones are bygones and I approached today's job just brimming with high confidence and good cheer. Which is to say, a solid quart of coffee in my belly. In any event, I started out optimistic and for the most part that's how I stayed. It wasn't to last. It all fell apart on the sixth (of six) screws. As luck would have it, that was the only one that I had been able to get installed on the first effort way back when. And as bad luck would have it, it was also the only one that I didn't get tight enough so that it wouldn't just turn and turn and turn in its hole when I tried to install the top lock nut onto it. I was going to need someone to stand on the other side of the belly skin and hold a screwdriver on the offending screw. Luckily for me, Cadillac Pete was on his way to help. We made quick work of the job once he arrived and thus finished the final page in the wiring section.

Next up was the flap handle. This airplane has manual flaps. That's as opposed to the electric flaps in the RV-6 that extend and retract at the touch of a switch. These flaps will require me to pull on a lever between the seats to lower the flaps. Today's job was the installation of that lever.

The lever pivots inside of two plastic blocks that also act as its support mounts. Those blocks get bolted into some nut plates installed in the belly of the fuselage. It was a fairly tight squeeze trying to get the flap handle and the support blocks positioned into the narrow confines of the tunnel, but I eventually forced the entire mass into place only to find that the pivot tube of the flap handle was rubbing against the fuel lines. Pretty much the last thing you want to do when building an airplane is to install a moving part in such a way that it rubs against a soft aluminum tube that is carrying a highly flammable liquid under pressure, so I figured that I was going to have to do something about it.

I remembered reading that one of the Van's employees that built an RV-12 had encountered the same problem. He fixed it by crafting a piece of slotted wood that could be used to press down on the fuel lines in order to bend them down out of the way. I tried that, but found that I didn't have the proper tools on hand to craft the bending tool. While I was thinking about an alternative means, it struck me that the cheapy tube bender that I bought at AutoZone before breaking down and spending more money on a good one might be just the thing I needed.

All I had to do was remove the "roller" part of it and use it to push against the fuel line. Because of the grooves in the roller, I wouldn't run the risk of flattening or creasing the fuel lines.

It worked like a champ, although I did need to push on it harder than I could by hand. I just put a block of wood against it and tapped on it with a one pound dead fall mallet. After bending the tubes sufficiently out of the way, I was able to install the flap handle and verify suitable clearance with a very appropriate business card.

The flap handle works by way of a pushrod that gets attached to the mysterious flaperon mixer box. There is a bolt that goes through a washer, the top arm of the mysterious flaperon mixer, a bearing in a strangely shaped piece of metal, a bearing in the push rod, another bearing in a strangely shaped piece of metal, a washer, and into the bottom arm of the mysterious flaperon mixer. This is quite a trick! Holding all of those parts in place without dropping anything requires a level of finesse and Zen-like calm that I doubt that I will ever achieve, especially with a solid quart of coffee working its magic on my fingers. By which I mean making them quiver like a palsied Eskimo taking a cold shower.

The biggest challenge was sure to be that second washer; there was just no way to hold it in place while juggling all of those other parts.

Well, I suppose there was one way. When all other options have been exhausted, when failure is no longer an option because it has graduated to being an inevitability, when all is surely lost, there is only one answer: duct tape.

That worked astonishingly well! Let's hear it for duct tape, the scrim-backed pressure sensitive adherent of the gods!!

The two oddly shaped pieces of metal were actually parts that had been fabricated a couple of weeks ago. I don't think I ever mentioned them. They're very critical parts, though. Here's a closer look at them.

These plates will somehow assist in transferring control stick roll commands out to the flaperons, I think. It's still something of a mystery at this point. What I do know is that I have to fabricate a couple of pushrods that will attach the control sticks to these plates, and the first step of that fabrication is to cut two lengths of aluminum pipe and tap them with a 1/4"x28 tap. The tapping step itself has a preliminary step, which is to drill the tubes with a #3 bit.

I didn't have a 1/4"x28 tap on hand, so that was the last job of the day.

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