Saturday, July 2, 2011

Candle Making

One of the things Van's (surprisingly) doesn't tell us to do as part of the RV-12 build is to leak test the fuel lines before covering them up with a bunch of airplane. I'm not the first person to figure out that it makes a lot more sense to test the lines now, when all of the irritating obstructions are still sitting on the shelf, rather than later when the fuel lines are not only blocked but also inconveniently populated with fuel. Because Van's (surprisingly) doesn't advocate this kind of testing, they provide no mechanism for doing so. The kind of people that are attracted to the idea of building their own airplanes are (not surprisingly) somewhat industrious in nature, so (not surprisingly) there have been a number of testing methods developed by those that have gone before me.

The most popular way seems to be to employ a user-fabricated stand pipe made out of leftover fuel line, a brass T-fitting, a Schrader valve, a rubber hose to act as a proxy for the pressure-sensitive fuel tank, and last but by no means least, the diligence required to gather all of that stuff up. I was lacking in every single one of those things. Fortunately, RV-12 building compatriot Torsten is not only far more energetic than I am, but also far more generous. He kindly sent me his test kit to use. He didn't actually send the faux fuel tank rubber hose - I purloined that from the local mechanic at the airport.

The fuel that will be pushed through the fuel lines will only exceed 5 PSI through some kind of miraculous pump failure mode in which it actually works harder than normal as it dies, but I still decided to test at a hefty 20 PSI.

Here's the faux fuel tank closing the fuel system:

And here is the fuel leak that I detected by brushing on some of the bubble-blowing liquid that kids know and love:

The leak was (not surprisingly) in the second worst possible place for it. Actually, that ranking could be argued - the only potentially worse place would be where the return line passes through the firewall shelf. That would be hard to get too, of course, but the leak at the bottom of the fuel shutoff valve actually required the entire valve to be removed in order to tighten the fitting. And by "removed," I mean "the rivets that hold it in drilled out."

Here it is after the fix and 20 new PSIs stuffed in to replace the previous twenty that escaped when I loosened the fittings in order to remove the valve. No more bubbles!

That all took a few hours of sporadic effort; the remainder of the time was spent making some yard long candles.

Well, no, they aren't actually candles. Those are the pushrods that will be attached to the oddly shaped assembly of metal that rocks left and right as the control sticks are moved. These rods will convert that lef/right action to forward/aft motion in order to transfer it further back in the fuselage. They will attach to a couple of rotating columns that will transfer torque forces out to the flaperons. Or, in easier to elucidate terms, these control rods will help the airplane remain right side up, and turn it on demand from the pilot or autopilot.

The fabrication of the two pushrods was a matter of cutting one long aluminum tube into two equal length shorter tubes and a third very short tube that ended up in the scrap box. Being that the two shorter (but not shortest) tubes are almost a yard long, the first cut had to be done with my old friend, the hacksaw. The throat of the band saw is nowhere near big enough to swallow that much tube.

Once cut, each tube end had four holes drilled through the both the tube wall and a brass(?) threaded fitting, with the intention of providing holes to allow the riveting of said threaded fitting into the control rod ends.

It was humid today and that, combined with the fact that I put three coats of paint on the control rods all at once, means that the rods need a good 24 hours to dry. In the meantime, we prepared the torque tubes that will convert the forward/aft motion of the control rods into, well, torque. By "prepare" I mean "remembered that powder-coated parts need to have the bolt holes drilled to final size before expending great effort getting them into the tight and confined place that they need to go, only to find that they need to be removed to drill out the bolt holes."

That didn't take long, mostly because I beat the long odds and managed to not lose anything.

While I was doing that, Cadillac Pete was gathering up the parts for the next thing to do. These are the parts that will complete the flap handle. The tube will get the silver knob-looking thing attached to it to give the pilot a place to press with his thumb. The spring will go into the flap handle tube before the new tube and force the tube back after the pilot releases the thumb pressy-on-thingy. The idea behind this pressing and releasing is to move a clevis pin in and out of the teeth on the part that has the three notches that look as if they were sized specifically to the correct width required to absorb a clevis pin.

Where is the clevis pin?


Remember when I ordered all of those cotter pins to replace those lost when bag 2791 flew the coop? There's something I didn't tell you about that. You see, there was a clevis pin in that bag too and I failed to order it. I thought for sure that the act of ordering the cotter pins would be enough to convince the misbehaving bag 2791 to come out from hiding. As it turns out, fate will not be fooled by such transparent shenanigans.

I ordered the clevis pin this afternoon when I got back from the hangar.

I know when I'm beaten.

Having crapped out on assembling the inner guts of the flap handle, we pressed on with installing the torque tubes. That turned out to be another of those three-handed acts. One hand holding the bolt, the other handing holding the washer wrench, and the third hand (i.e. my teeth) holding the inspection mirror while trying to get the washer lined up with the bolt hole.

What can I say? I'm good with my teeth.

Compared to the control rods, the torque tubes were a piece of cake to install.

Hmmmm, cake. And I'm hungry. And there is a pristine cake sitting out in the kitchen.

That gives me an idea....


Rick Lee said...

The longer I read this blog, the scarier this enterprise seems.

Rick's Bro-in-Law's wife Gail said...

What does a pristine cake taste like - mountain air? Does it look like air too?

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