stringfellow
Active Member
My question is more related to high-wing aircraft than RVs, but it may be germane to both, and I expect some learned folks here who may have thought of this at some point.
I'm designing a fuel system layout to support the SDS/FlyEFII system where the wing tanks have ports both fore and aft. An additional bung has been added for a return fuel line. An EFII system runs fuel in a continuous loop through the rail at high pressure, and to prevent vapor lock, recirculates the fuel to keep it cool. There are two ways of doing this, though they are not mutually exclusive: 1) Fuel is routed back through a duplex valve into either the L or R tank, or 2) a header tank is used.
In this case, only a duplex valve is being used and fuel is being run back to the fuel tank.
My question is how best to deal with the potential for "unporting" either of the fuel tank ports/pickups when fuel level in the tank is low. As you can imagine, in a high pressure system, this could suck air into the line and some bad stuff could happen. For STOL aircraft that often experience high AOA, this could be a real potential issue.
One solution I've had suggested is to only use the aft port, and just use the forward port for the return line. That sounds okay, but what if pitch-low scenario causes the same issue?
Would the addition of a very small header tank help? Once air is sucked in, even if the tank pickup is re-primed, the air is in there. Could one use a header tank like the opposite of a gascolator? I don't see any way to separate and vent air though safely.
Set aside the concept of EFII for a moment-- how does any fuel system that uses a boost pump deal with this issue? Is it just one of the perils of low fuel management?
I'm designing a fuel system layout to support the SDS/FlyEFII system where the wing tanks have ports both fore and aft. An additional bung has been added for a return fuel line. An EFII system runs fuel in a continuous loop through the rail at high pressure, and to prevent vapor lock, recirculates the fuel to keep it cool. There are two ways of doing this, though they are not mutually exclusive: 1) Fuel is routed back through a duplex valve into either the L or R tank, or 2) a header tank is used.
In this case, only a duplex valve is being used and fuel is being run back to the fuel tank.
My question is how best to deal with the potential for "unporting" either of the fuel tank ports/pickups when fuel level in the tank is low. As you can imagine, in a high pressure system, this could suck air into the line and some bad stuff could happen. For STOL aircraft that often experience high AOA, this could be a real potential issue.
One solution I've had suggested is to only use the aft port, and just use the forward port for the return line. That sounds okay, but what if pitch-low scenario causes the same issue?
Would the addition of a very small header tank help? Once air is sucked in, even if the tank pickup is re-primed, the air is in there. Could one use a header tank like the opposite of a gascolator? I don't see any way to separate and vent air though safely.
Set aside the concept of EFII for a moment-- how does any fuel system that uses a boost pump deal with this issue? Is it just one of the perils of low fuel management?