Sunday, June 27, 2010

Just Fueling Around

As with many things, it all has to start with a trip to Lowe's. In this case, it was step one that called for a small amount of pipe thread seal. "Small amount" indicates some arbitrary value greater than zero, and zero is precisely what I had on hand.

It was to be used when installing AN fittings in a couple of the fuel system's mechanical devices. First up was the fuel pump. Nothing fancy about this - I suspect they have them at Walmart.

The mount for the fuel pump was installed in Section 21. While the fuel system is presented as Section 28, I think it ought to be Section 24, coming right after the addition of the nose chin and lower firewall. I chose to do it this way so that I wouldn't have to work around and over the side skins, but it would also have been a little easier to install the pump if it had been done the same time as the mount. I would have bolted the pump to the mount, then riveted the mount to the belly skin. That would have saved me a couple of lacerations caused by rubbing my hands against the edge of the tunnel while reaching down in with a wrench. Another thing that would have helped that would have been to buy the nut drivers I went to Harbor Freight to get. I'm not sure how I managed to forget to do that.

There it is, ready to be the first station on the fuel's journey to the engine.

Aircraft fuel systems always have a valve for stopping the flow of fuel to the engine. The next piece of hardware was this type of on/off valve. In most airplanes, this valve would also act as the selector between two or more fuel tanks. This is the case because most airplanes carry their fuel in the wings. The valve selects which wing tank is to be used, in addition to providing the normal on/off selection. In the RV-12, there is only one fuel tank located back in the baggage area. Having only one tank simplifies the fuel system and also makes it much easier to have removable wings. Not only is fuel heavy, which would make the wings much harder to remove, store, and reinstall, but the added complexity in building a fuel system that could be easily connected and disconnected would be prohibitive.

With that in mind, behold the simplicity of the RV-12 fuel shutoff valve.

The first step is to remove the red plastic sleeve on the handle of the valve and drill a #30 hole in the handle.

The red knob comes with its own instructions, but they are confusingly written. They say to start by drilling a #16 hole and then drill the hole wider to #11. I'm not sure what the #11 hole would be intended for. Drilling it that large would make it much larger than the screw provided to hold the knob on the handle. I drilled the #16 and called it quits.

A couple more AN fittings get screwed in. I used a couple of wrenches to get them in nice and tight. It was blind luck (or good design) that they tightened up right when they were oriented correctly.

With both fittings in, a little box is built around the valve to hold it. 

If you look under the two clecos, you will see a little plate slid under the side wall of the box. That's the way that it fit in the easiest. But...

Darn. The drawing has it on the other side. It would have to be moved. On the correct side, though, the fit was much tighter and it was harder to get the rivet holes completely aligned. Now I've been known to grab a drill and use it to remind some holes just what it means to wear the #30 on this team, but I was reluctant to do that in this case. It took some pushing and prodding, but I finally got it assembled.

The actual installation in the plane was a piece of cake.

A piece of cake which, it would appear, has a cherry on top!

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