|
I'm pretty sure the turn was coordinated. Knowing
that both tanks were approaching (if not below) 5 gallons, it was the first
thing I thought of and I looked at the ball. It was centered. And I'm sure there
is going to turn out to be about 5 gallons left in the tank so its hard to
understand how this could have been an issue with the pickup uncovering. I just
don’t have a better explanation. If the pump failed I would expect it to stay
failed, not work fine on the ground.
I didn’t copy it, but my system I believe is the same
that Ian Beadle used. I have 1 pump for each tank. The outputs are T'eed
together - check valves built into the pumps prevents crossfeed. Both tanks have
return lines. The return line from the fuel rail goes through an industrial
grade electric valve.
I chose this design for a couple of
reasons:
1) Operational simplicity. I reasoned that most
fuel related problems in flight are due to stupid pilot tricks so wanted a
system that was as simple to operate as possible. In its original configuration
all that was required to switch tanks was to flip a single toggle switch on the
panel which would energize the appropriate pump and configure the return valve
to return fuel to the tank it came from. This has since been modified slightly
to have individual switches for each pump so both can be on at the same time if
needed.
2) I had previous experience (bad) with EFI in some
project cars before I built the airplane. I had a couple of fuel pump failures
and in researching found strong recommendations against putting the fuel pump
too far from the fuel tank. These pumps are designed to push fuel, not draw
fuel. A design where both pumps have access to both tanks requires the pumps to
be downstream of the fuel selector with several feet of fuel line ahead of the
pump. I wanted to avoid this type of design although it apparently is working
fine for Ed. My pumps are just inboard of the wing roots literally a couple of
inches from the pickups in the tanks.
Tracy's system is mechanically simple but has the
potential for pilot error resulting in pumping fuel overboard if the transfer
pump is forgotten and left on. Yes, I know there are ways to address that. And
clearly it works for him.
I think (thought?) I pretty well understand the pros
and cons in my setup. All things being equal I think before yesterday's
incident I would do it this way again. If it turns out that the issue was
due to uncovering the pickup (not real sure how to prove that) I'd consider
changing to include a header tank with a deep sump to prevent re-occurance. But
I don’t think I'd rely on suction to fill the header, think I'd use a low
pressure pump like the typical Facet pump.
One thing is for certain. Unlike a carbureted engine
which has a little cushion due to fuel in a float bowl, the instant fuel
pressure drops this engine quits. It's an attention getter. Particularly when
you are at the opposite corner of your test box from your home base. I ended up
flying back about 70 miles hopscotching from field to field.
Mike
Sent: Saturday, March 13, 2010 1:53 AM
Subject: [FlyRotary] Re: fuel supply problem?
There is certainly more
than one way to design a reliable fuel system – each with its pros and
cons. I too did not want a six way value for switching fuel between two
tanks and the engine with the ugh return line. Besides I had already
constructed my fuel system pretty much according to Van’s instructions. So
to preclude a return line I came up with my “almost returnless” system. It
uses a ½ pint capacity small header tank to return the injector fuel – the fuel
injected to the engine comes from this header tank thereby creating a “vacuum”
in the tank which pulls fresh fuel from the wing tanks. It has worked fine
for over 10 years.
Both fuel pumps draw
from this header tank and either tank can feed it and I have no return lines
going back to the tanks.
But, Tracy’s approach has shown
to work just fine – not knocking it by any means.
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bktrub@aol.com
Sent: Friday, March 12, 2010 11:43
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: fuel supply
problem?
I just copied
Tracy's setup-
all fuel is pumped from the right tank, and fuel is transferred from the left
into the right by a Facet pump. I didn't want to get into having a six port fuel
valve in order to get the fuel injection to return to the tank I was using at
the time.
It's really simple,
and hopefully that means reliable. We'll have to see, as this plane is looking
for it's airworthiness inspection in the next few months.
__________
Information from ESET NOD32 Antivirus, version of virus signature database 3267
(20080714) __________
The message was checked by ESET NOD32
Antivirus.
http://www.eset.com
|