Dale:

With a BOTH function and such a low gravity head, the tanks may not feed
equally, or worse, the engine quits while there is still fuel in one of
the tanks, the same problem that Jim S. has described having with his
Velocity sump.
If you have an EFI pump in each tank and both pumps are providing fuel
to the EFI fuel rail at the same time, that would not be the same
situation, there is no gravity feed from separate tanks to a common
point in that design.

I'm doubtful that this BOTH function was the cause of Paul's accident,
but I still think you want to avoid a BOTH function in a LEZ or other
low-wing fuel system.

Perry

Bill,

   Thank you for that clarification. When I read Perry's
comments, I was wondering "why?" - because the system I'm
building has the functions: Left, Right, Both, None.

   Now I'm not so worried, because each high pressure fuel
pump draws from it's own tank and the only point of inter-
connection is where the lines join at the fuel rail(s).

   I borrowed the basis of my setup from Marc and Nadine
Parmalee's COZY:

http://www.marcnadine.com/fuelvalve.html

Dale R.

 > From: "BillDube@killacycle.com" <billdube@killacycle.com>
 > Date: 2005/05/29 Sun AM 02:03:31 EDT
 > To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
 > Subject: [FlyRotary] Re: Paul's Fuel System Error
 >
 > About a year ago I did a little "Google" research on the John
 > Denver fatal crash. The bottom line appeared to be that one tank was
empty,
 > and the fuel selector was not fully turned to the other tank. (It was
in a
 > very awkward position to reach, and this may have also caused the
pilot to
 > auger in while attempting to reach it.) Thus, it was in the
equivalent of a
 > "both" position. This caused air to be drawn in to the fuel supply line
 > from the dry tank. This, in turn, caused the pump to lose its prime and
 > stop pumping fuel to the engine.
 >
 > As Perry mentions in his post, only a gravity feed fuel system can
 > have a "both" type fuel selector. Low-wing aircraft that have negative
 > pressure in the fuel lines from the tanks must NOT have a "both"
position
 > on the fuel selector, otherwise the pump (or the sump) will suck air
if one
 > tank runs dry (or if there is a leak in a fuel line.)
 >
 > This kind of makes you want to put a pump in each tank.
 >
 >

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