Paul's sump/header tank? (short, wide & narrow). Don't know
if it was a factor in the accident but another problem prone detail I
think.
----- Original Message -----
Sent: Monday, May 30, 2005 12:10 PM
Subject: [FlyRotary] Re: will EFI pumps
pump air was Re: Fuel Tank Selection
If that's the
definition of a sump system, then I do not have a sump system. I have a small
EFI tank with two internal EFI pumps, fuel return to this EFI tank. This EFI
tank is located where the gascolator is in the stock Long-EZ fuel system. I
have the complete stock Long-EZ fuel system otherwise with L-R-OFF selector
(no BOTH). I will not refer to my system as a sump system in the future, to
avoid misconception (and arguments).
You've said it yourself Jim in the
past, that you've had many problems with your sump system. Maybe sump systems
and BOTH selectors just don't belong on Rutan derivatives, as RAF itself has
said. As you saw, a Lycoming-powered EZ had an accident in 1995 just after
takeoff (sounds like Paul?) with such a system.
Jim S.
wrote:
A sump tank renders L-R(-B) selector redundant and
superfluous. L and R selectors allow the fuel pump to "suck" fuel from
the selected tank. When the tank is empty, you select the other
tank. If you have "Both" selected and one goes empty, the pump sucks air
through that line. Either way, the engine quits when one tank goes
dry. You get power back by selecting the tank that has fuel in it.
The main disadvantage with a "Both" position has to do with distraction and
delay - when the engine quits, you have to figure out which tank is dry and
which way to turn the knob to select the tank that has fuel. Takes time
and is a definite failure mode. Gravity feeding a sump through big
enough lines eliminates the need for valves. That's the main purpose of
a sump. Selectors are for when you don't have a sump. They have no
place on a system that does. The Rutan derivatives with a sump have no
selector; those with a selector have no sump. Paul's setup was
unique.
Just a theory ... Jim S.
rijakits wrote:
The only safe way to have a "Both"-selection for a low wing would be
(IMHO), to have a low pressure pump in each tank feed a fairly large sump ( 2
gallons +) with a system as described by Georges below:
EFI pump picking up at the bottom of the sump, with a return to the top
and baffels, not just separating the top from the bottom, but also side from
side, so when a tank pump starts to pump air into the sump, it can vent to the
top of the sump and out through the vent, which would have to go to both main
tanks.
With some additional cross-feed line from one tank to the other with a
manual valve, one could use one tank pump as the back-up for the other:
Open the crossfeed valve and slip the plane accordingly for a while. That
should push the fuel into the other tank, in case one of the pump fails.
One question remains: How would you prevent or equalize overflow from the
sump to the tanks?
Thomas J.
----- Original Message -----
Sent: Sunday, May 29, 2005 8:07 PM
Subject: [FlyRotary] Re: will EFI pumps pump air was Re: Fuel Tank
Selection
Group FWIW
Call it a sump or header tank, if its large enough say 3 liters oops! I
mean quarts with both pumps picking up fuel at the bottom 1/4 of the tank
with the fuel return pointing at the cover to avoid aerating the fuel in the
header (possibly a baffle below it & a vent pipe to each tank) Gravity
feed would work in a high wing , in a low wing I think you still need a low
pressure transfer pump to push fuel to the header tank from the mains. I
don't think it is safe to have "Both" position in the fuel selector except in
a gravity system with carburetors, not with EFI, the possibility of
"sucking air "is unavoidable without check valves ( more weight, more cost
& more possibility of problems).
Georges B. ( Not really stirring the pot, maybe just a little)
-------Original Message-------
Date: 05/29/05 17:42:01
Subject: [FlyRotary] Re: will EFI pumps pump air
was Re: Fuel Tank Selection
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).
This brings up a
question that I've had before, and I'm not sure this is exactly what anyone is
doing, so it's not meant that way.
Say you have two
tanks, with an EFI pump for each tank. You then connect the
output of each pump together, feeding into one line running to the fuel
rail. The question is: What happens when one tank runs
out of gas? Will the EFI pump move enough air through it to disturb the
fuel rail pressure that's being delivered from the other pump, or would it
just stop pumping at that point, and do no harm (other than maybe burning the
pump up eventually)?
Yep, still trying to figure out how to fix
my fuel transfer system.
Cheers,
Rusty
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