My Wooden Airplane
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2/7/2013 - 3/13/2013

Fuel System

With the tank now properly sealed, I can move on to the rest of the fuel system. Since I have that tunnel in the middle of the tank, I have two fuel drains (one on each side of the tunnel), and each drain has its own associated fuel pump. The two pumps are connected in parallel (not series), so that if one drain becomes uncovered, I won't get any air sucked into the fuel lines. Here is the underside of the tank, with the fuel lines moving forward from each drain ("Forward" is "Up" in the picture.)

Here are the two fuel pumps installed under the floor, behind the pilot's seat.
(Again, "Forward" is "Up".)

I also installed a fuel shut-off valve in the floor near my left leg,
which is reachable in flight, if necessary.

I then installed a gascolator on the lower left portion of the firewall. Even though the gascolator is NOT the lowest part of the fuel system, it will still serve as a fuel filter. The drain is elevated above the bottom of the fuselage, so that if the landing gear gets sheared off, the drain won't scrape across the ground. By the way, you might notice something white around the fuel lines where they cross a fuselage bulkhead. This is heat-shrink tubing, and is there as a buffer to prevent chafing of the fuel lines.

I still have to test the fuel system for leaks, though. I figured I'd do that by putting some actual fuel in the tank and turning on the pumps. This actually might be a good place to mention something about the fuel lines being under pressure. A lot of people install the fuel pumps on the firewall, which means the fuel lines are under a slight vacuum, rather than being pressurized. One of the arguments against pressurized fuel lines is that if there is a leak, it could be sprayed all over the occupants if the fuel lines are pressurized. I thought carefully about this, and decided to put the pumps under the floor, back near the tank. One reason is because that's what the pump manufacturer recommends (near the tank, and slightly below it, presumably to keep them "wet" and primed). Another reason is that pressurized fuel lines are less prone to vapor lock. Finally, since my fuel lines are all run under the floor, I don't think there's much of a chance of the occupants getting sprayed with fuel, even if there is a leak.

Total Time: 18.5 hrs.