Tuesday, August 3, 2010

Back from Oshkosh

It was a long week, but it flew by (so to speak). My annual shopping spree netted four cases of Phillips 20w-50 oil and a Dynon D-6 for the RV-6, and a set of stubby wrenches for the RV-12. Darned if I didn't forget to get a set of nut drivers, though. Shamefully negligent, that. There were a handful of RV-12s there and I looked at each of them. Other than paint, they all look pretty much alike which is, of course, to be expected. I have to confess that I did look at the belly skins of a couple them to see how the edge breaking looked, something I swore that I wouldn't do.

With hundreds and hundreds and hundreds of airplanes there, I also spent some time just walking around looking at paint jobs. I'm still leaning towards a vintage air racer look - I really like that era. I'm sure it was a lot like early auto racing where fatal accidents were more common in any given race than not, which would make them very difficult and painful to watch, so it's lucky for me that my interest in them has the benefit of being viewed through the lens of nostalgia. From eighty years away, it looks like a glamorous, liberated era of pre-meddlesome government flying. The design of the planes is crude by today's standards, but is attractive and artful in the way a classic painting is. Face it, if the Mona Lisa were painted today, she'd have to be soaking in a jar of urine to be considered art. Back then the artistic flare was more subtle and evidenced in small details rather than in grand, swooping forms and gestures.

That level of artistic craftsmanship is by no means dead in certain areas. Where it thrives today is in one of the last bastions of aviation freedom, the Experimental category. While you won't see a lot of innovation and flare in the RV-12 world, a world in which we straddle the divide between regulatory rigidity and unfettered freedom to build what we want, you will still see in in the rest of the Experimental fleet. You will see it in spades in airplanes like this one, the 2010 Grand Champion kit built:

You can get a feel for the astonishing effort that goes into crafting an aircraft like that by viewing it from a distance, but it is the close-up details that really tell the story. There are hundreds of examples, some as seemingly mundane as the custom fuel caps. Every single part of that airplane was built or modified to be the best it could be. In my opinion, the very definition of art is beautiful artifacts created by supremely talented and dedicated people.

So, there I go, off on a tangent. Back to the paint schemes. Here are a few pictures that fit with the general look I will be going for, absent in all but one case the required distinctive logo somewhere on the side of the fuselage.

None of that will ever come to fruition if I don't get back into the business of building an airplane, so to that end I spent the last couple of evenings on finishing the fuel system. Tonight I put the final line into place. The last line to go in was the long length of 1/4" tube that runs from the firewall shelf back to the bulkhead fitting. Once installed, this line completed the fuel return line. I learned a little bit about the Rotax 912 up at Oshkosh and now know why a return line is necessary.

The Rotax is a low displacement engine relative to the normal Lycoming and Continental type engines found in most planes, my RV-6 included. More horsepower can be gained in two ways: increase the displacement of the engine, or increase the RPM of the engine. Or both, if you're made of money. The older engines have higher displacement but turn at lower RPMs. They turn relatively slowly because if they turned any faster, the tips of the propellors would approach the speed of sound and there is a whole lot of drag at those speeds.

The Rotax takes a different approach. It is a smaller, lighter engine with lower displacement and it makes up for the loss of horsepower by increasing the RPM. A lot. But what about the prop going too fast? Well, the Rotax has a gearbox called a PSRU: Prop Speed Reduction Unit. (I might be making that up - you can never tell with me) The engine runs fast (5,000 RPM), but because of the gearbox, the prop turns at a more sedate speed and avoids the high speed drag.

Running the engine that fast creates a lot of heat. If you shut the engine down and all of that residual heat causes the fuel in the fuel lines to boil, you get vapor lock. Good luck starting that engine, Bub. So what Rotax does is let the fuel in the lines vent itself back to the fuel tank through the return line.

Or so I understand. It doesn't really matter; the return line is in the plans, so I put it in.

Speaking of the plans, the directions for this particular line left me in a haze of what-duh-heck-are-they-saying?? The drawing was no help either; it seemed to show a complex pair of bends where the directions said there was a simple 90 degree bend. Well, a picture may be worth 1000 words, but I'm not sure even that many words could have described what was going on here. I finally just decided if the words say "make a 90 degree bend," well, that's what I'd do.  It worked out fine. So here's how it went.

First, remove the rudder pedals. They're just in the way. I took them out and set them back in the finished-but-not-yet-attached pile.

I cut a length of line a few inches longer than specified so as not to come up short. The plans suggest marking a line 14-ish inches to mark the start of a 90 degree bend. That's not the way my tube bender works, so that line would be useless, save for decorative value; I just made a bend that left me 14 inches of tubing to go up through the firewall shelf. That leaves about five or six feet of tube that has to be fed through the bushings and back out through the inspection port in the belly. Luckily, the tube bends easily.

I wrapped the flaperon mixer (I know the magic behind that thing now, having seen a completed one at Oshkosh. I'll share that with you some day) with duct tape to keep it from scratching, dinging, or gouging the fuel tube.

It took a few trips from the front of the plane to the bottom in order to get the tube to come out through the inspection port.

With the full length of the tube installed, I measured, eyeballed, guestimated, and SWAGed my way through cutting the excess length on each end to fit, flaring the ends, and installing the nuts to the various fittings. I installed the clamp that holds it into place on the firewall, a job that would have gone more smoothly if I had chosen the correct size screw out of bag 2727. For future reference, it's a stubby, fat little guy with a big head.

Insert favorite Napoleon joke here.

That's it for the fuel system. The longerons get bent next. I talked to a few people at Oshkosh about how it's best done but got no consistent answers. It's just something I'll have to work through.

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