Name: Fuel system A-D010.jpg Views: 2951 Size: 59.5 KB

Attached is a drawing of a internal fuel tank using gravity fuel feed. Drwg 'A' is acording to the plans. Should work fine as long as the vent doesn't get clogged.
Dwg 'B' is a tail dragger setting at rest. Notice the fuel level is full and covers the vent. Fuel runs out.
Dwg 'C' shows the vent line routed to the rear. Fuel runs out only easier.
Dwg 'D' has the vent moved to the front. No fuel spill?

OK, I'm getting there.

Dwg B: you just stopped for fuel. The FBO filled it all the way up with cold fuel on a hot day. No problem, right....WRONG. At least I think there could be wrong. Fuel expands, fills the vent line, you start and Ram air holds the fuel in the line (like a finger over a straw). Is there enough Ram air to lift the fuel back to the tank??

Dwg C: Same basic senerio. Just easier to happen. Like when the fuel sloshes back at full throttle.

Dwg D:Seems like a better location, till the fuel expands.

My question: Is there a problem?? Will prop wash and air stream lift fuel 36" to clear a vent line? If it will, then why do we have fuel pumps on wing tanks? Why not just use Ram air to lift the fuel to the header tank. I know of two times where the engine quit on takeoff after the plane was just filled with fuel. Would it be worth adding a second Ram vent. A boost pump won't clear a mud dauber or bug. Maybe a check valve to let the vent air in. The best I've found is no Ram, vent is straight down. But, I've seen several tubes bent into the air stream.
Seems like there should be a more fail safe fuel delivery system just in case gravity fails.

Thanks,


Bob