Hi Mike,
Have you removed and measured how much fuel was actually
in the tanks? What did your fuel gages say at the time? What is your
tank capacity? Each wing on my plane holds 33 gal, so getting down to 5
gal with very little dihedral in the wings, means I am pretty low on fuel.
1/8 tank in fact. The way I calibrated my gage was to drain the tank dry,
add one gallon, calibrated this to be Zero, then added 4 gal and calibrated this
to be 1/8, and then each 4 gal was another eighth, etc. I think it would
be very easy to unport my tanks with only 5 gal in them. With the plane
sitting level on the ground, it will drain the tanks dry. When the engine
quits from fuel starvation, you can not get a drop of fuel out of the
sumps. There are two of them on each wing and they are both dry when the
engine quits sitting on level ground.
I think in flight would be a different matter
tho’. I think there should be some “unusable” in flight but I don’t
have any plans at present to try and find out. When I get to ¼ tank, I
plan to “get er down”.
Assuming any kind of reserve, how much flying time did
you feel you had when you were down to 5 gal in each tank? Reading this
last question, it sounds like I am being critical but it couldn’t be further
from the intent. :>)
If you had 5 gal in the tank, what angle of bank would
it take to unport the fuel on the ground? You could jack up one wing to
try it. If it is a low angle, very little turbulence would be
required even if you were coordinated. I think my dihedral is 3
degrees, so 4 degrees would run everything to the outboard side. Hardly
any movement of the plane and you can hear fuel sloshing around in
there.
Bill B
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mike Wills
Sent: Saturday, March 13, 2010 11:29
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: fuel supply
problem?
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.
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.
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