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----- Original Message -----
Sent: Thursday, May 27, 2004 9:09
AM
Subject: [FlyRotary] Re: Fuel Pump
Design
The
attached drawing is my idea of a simple fuel system for the 9a that I am
building, with Aux fuel tanks akin to Berne Kerr’s Project. I would like some feed back as to what
problems this arrangement might pose, and what the remedy would be for such
problems. The plan is to use
large diameter pipe between the main fuel tanks so as to allow the fuel to
equalize
Bob Perkinson.
Fuel system design hasn't come up in quite a
while. But since a large portion of accidents are fuel related, I
thought this would be worthy of discussion.
I have experienced a
failure mode during ground runs on my Lancair ES with 20B that seems to be a
problem with other types of installations as well. I recently read a
first flight report by a professional test pilot, David Allen, that almost
had to set a Lancair ES, N711RG, down on I-70 due to the inability to
restart the engine after running a tank dry. (See www.geocities.com/daveandjj for the full
story.) This was a certified fuel-injected engine installation.
Also, the Subaru guys (I have been lurking on the Eggenfelder Subie site
today) had a similar situation, resulting in some glider time and a
dead-stick landing.
The problem is that after exhausting the
fuel in one tank an airlock forms between the fuel pump(s) and the fuel
pressure regulator that the efi pump cannot overcome due to lack of fuel in
the supply line. This is what I have experienced with my installation
on ground runs. I can't get the efi pumps to re-prime unless I
momentarily break a line loose between the pump outlet and the pressure
regulator. As soon as I do that the pump will re-prime and all is
well.
For the record, I have two of Tracy's efi pumps, with
two efi filters, hooked in parallel. They are mounted low on the fire
wall. Upstream is a gascolator and an Andair 6-port selector
valve. Downstream of the pumps/filters is a map sensing pressure
regulator. There is a -6AN going to the fuel rail, and a -4 return
line back to the Andair valve/tank.
I was curious if anyone else has
had this happen and what they did to resolve the issue. I have come up
with two possible solutions.
1. Tee off the pump output
and put an electric solenoid valve in the line and tee the outlet of the
solenoid to the fuel return line, past the regulator. Push-button
switch on panel would activate the solenoid. If needed, a second or
two of activation should relieve the air-lock and allow the pumps to
re-prime.
2. Install a bleed line around the pressure regulator
with a small metering orifice (.020-.030") that would bleed off any air that
might get trapped. (This appears to be the solution the Subaru group
is focusing on). This would be a full time bypass. This seems to
be the simpler solution.
3. Install a low pressure, high volume
fuel pump in one, or both, of the wing tanks. Procedure would be to
always keep reserve fuel in this tank.
Any comments from
seasoned flyers would be welcomed.
Mark S.
Hi, Mark.....looking at the drawing, I noted that there are two spring
loaded ball check valves after the two fuel pumps. In order to possibly
simplify the installation, might I suggest using fuel pumps such as the MSD
high pressure fuel pumps, as they already have a built-in check valve inside
each pump. I am unfamiliar with Tracy's pumps, so I don't know if his has the
check valve built into it as well? Paul Conner
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