Use a borescope
to look into your tanks Mike, a lot easyer, I found a cheap one with a 1/4" fib.
optic wand, slips up into the drain hole even with the stiff wire taped to it
bent into a 90 deg. curve, someone at the airport or EAA chapter should have one
or your friendly local auto-tech might loan you one. David R.
Cook RV6A Rotary.
----- Original Message -----
From: "Mike Wills"
<rv-4mike@cox.net>
To: "Rotary motors in aircraft"
<flyrotary@lancaironline.net>
Sent: Saturday, March 13, 2010 11:03:42
PM GMT -05:00 US/Canada Eastern
Subject: [FlyRotary] Re: fuel supply
problem?
Tracy,
I do have filters between tanks and pumps. I had
an issue early on with junk in the filters but never enough to cause any
issue. This was just a little construction debris and remnants of some
automotive sealant I initially used to install the access plates (since
reinstalled with Proseal). I just did my first condition inspection and
checked the filters about a month ago and they were clean. But I will check
them again.
Never have had a problem previously with pressure drop
across the filter. The problem happened at about the 1.3 hour point
in the flight. At the time I was motoring around at 8500' and at a pretty
low power setting - EFISM said fuel flow was about 7.8 GPH. I did run it up to
full power on the ground and couldn’t duplicate.
My pickups have a screen and have the Vans required
anti-rotation tab riveted to the access cover plate. But I suppose if I cant
attribute it to anything else I should probably pull the tank and make sure the
pickup hasn’t moved. Man that sounds like a lot of work.
Mike
Sent: Saturday, March 13, 2010 10:35 AM
Subject: [FlyRotary] Re: fuel supply problem?
I had a similar thing happen but the engine would recover when I
reduced throttle. Problem was clogged filter between tank and pump.
At low flow rate all was OK but pressure drop across filter at high flow rate
caused pump to cavitate and fuel pressure to drop. Did you try high
throttle on ground test later?
But you didn't mention a filter between
tank & pump. That has potential problems as well since it doesn't take
much trash to foul up an EFI pump & might have cleared up after it
passed. Do you have only the slots in Van's suggested tank pickup between
tank & pump? Problem might have been trash going through
pump.
I guess Ed already mentioned the loose tank pickup problem he
had.
Tracy
On Sat, Mar 13, 2010 at 11:29 AM, Mike Wills
<rv-4mike@cox.net> wrote:
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.
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