My Wooden Airplane
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12/29/2013 - 1/18/2013

Fuel Tank, Part 1

I decided to mount my fuel tank behind the seats and to make it out of aluminum. My friend Andy made a similar auxiliary tank for his RV-12, so I decided to copy his technique.
Although I used .040 6061 T6, I would have been completely comfortable using .032.

There are a few interesting features to this tank. First, because of the elevator bellcrank located just behind the seats, I had to make a "tunnel" to accomodate it (as well as the elevator cables). This means that when the fuel level gets below about 1/4 tank, the fuel is split between two sections. That means I needed two pickup points. (You can see one of them near the middle of the tank. It looks like a finger screen, attached with 6 screws. The other one is on the other side of the "tunnel".) There is a large, 4-inch diameter hole in each of the two middle bulkheads that will allow fuel to transfer both "sides" of the tank. The next two bulkheads out from those have the corners cut out to allow fuel to reach the outer "chambers" without too much sloshing. There also two fuel drains (one for each side) near the outer-most bulkheads and towards the rear of the tank. (The tank will rest on the baggage compartment floor, which slopes downward slightly, front-to-back.) Near the middle of the picture is a fuel-level sender mounted to the top of the tank. This is a 240-33 ohm "Datcon" sender. Finally, just visible in the upper-right corner is the filler neck. It is welded at a 60-degree angle, and will connect to a remote filler neck that will be mounted to the passenger side of the fuselage (under the rear window). The total capacity is estimated to be just over 20 gallons.

Here, you can see the fittings a little bit better. The round aluminum fittings that the fuel drains and finger screens are threaded into are meant to be welded on, but I decided to drill and tap them for 10-32 machine screws. The filler neck will be riveted on. The fuel drains are 1/8 inch. I may regret that I didn't choose the next larger size later on.

Oh, and let me just say for the record that deburring almost 600 holes is a big pain in the butt!!! Counting the inside and outside faces of both pieces of metal for each hole yields almost 2400 deburring operations. Ouch! My fingers STILL hurt!

Total Time: 51.0 hrs.