From: "Walter Klatt" <walter.klatt@shaw.ca>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, June 29, 2003 8:08 PM
Subject: Fuel Flow Problem?
Hi Walter,I had a little situation yesterday that I believe I
know the cause of, but thought I would run it by the
group to see if anyone else has encountered this, and
would be interested in your opinions.
My engine cut out after a rough water take off. I was
about 100 AGL when it happened, and had just started a
steep climb after gaining speed and lowering flaps. I
quickly lowered the nose and was setting up to land,
pulled back the throttle, when the engine started up
again. I pushed in power again, and the same thing
happened. So I pulled back the throttle a bit, and
managed to retain enough power to maintain a slow climb
to about 1500 feet. There, I tried full power again,
but with same result. It seemed like it couldn't get
enough fuel. Anyway, after a couple more tries, I flew
back and landed at my cottage.
My first thoughts were plugged vents, so I checked
them, but they were OK. I checked the gascolator and
fuel drains for water or dirt, but everything was good.
Couldn't see anything wrong under the cowls, but did
not pull them off since I was sitting on the water.
I had extra fuel at the cottage and added 2 cans to
bring my fuel up 30 US gallons. I then flew it again
this morning, and absolutely no problems. I then flew
it back to my hangar at Langley, and started checking
everything out.
I have a fuel flow transducer after the gascolator on
mine, and did fuel flow tests at the line going into
the carb. I thought perhaps I might have a problem with
the transducer, but the fuel flow was fine on both
tanks. To be sure I drained one, and checked the intake
screens, but it was clean as could be. Even if that was
a problem, I couldn't see how both would plug at
exactly the same time.
My fuel at the time of the incident was about 14 US
gallons (7 each tank) and was using regular mogas. It
was very hot, though, about 31C (90F+), and had been
flying about 2 hours earlier. The plane was sitting in
the sun, and it was pretty hot. However, it started
fine, and the run-up, etc, was all normal right up to
take-off.
I have taken off with this low fuel before and have run
it down a lot more than that in flight many times with
no problems. I use mogas most of the time, and the hot
day was not unusual either.
However, it was a very rough water take-off, and with
my low fuel (although again not the first time with
this combination), I am thinking with the bouncing off
the waves that air got into my fuel intake lines
resulting in reduced pressure with the gravity feed
thus reducing fuel flow. My fuel flow transducer does
use .5 PSI, so I know I am a little more susceptible to
this than if I didn't have one.
I know air does take a little while to purge itself
from the lines, and while in flight probably longer. I
have found this out on the ground some time ago, after
adding a little fuel to empty tanks, and trying to
start it up after just opening up the tank valves. It
would run for a minute and then quit. The solution was
to let it sit for 1/2 an hour with the tank valves
open, and then no problem.
Anyway, since I couldn't find anything else wrong, my
theory is the air in the lines at take-off. I am
planning a few long trips this summer, and some over
hostile mountain terrain, so sure hope I am right about
this.
My engine is an 0320 150 hp on a Rebel with 1800
amphibs, and no fuel pumps.
Any opinions and thoughts welcome.
I had a very similar problem, took off with about half tanks, but on ONE
tank only. Lost power but didn't quit. Throttled back and it pulled OK for
a slow climb. Got back and checked it out. Here's my conclusion:
an air bubble in the line will not move up or down unless there is a
considerable slope or hi flow. It will however let flow pass by it. Enough
to do a runup, and to run a small engine,(912?) so no problems appeared
until we started with the big Lycs. (Mine is an O320 150 hp also). I did
the testing on a mockup using plastic hose and water so I could see what was
going on. I was amazed to see the fluid flowing pretty well with this huge
bubble in the line!!! The numbers fit with the experience.
So what to do? First, always have both tanks on. Lets a bubble get back to
a tank easier. Second, make sure your lines NEAR THE TANK are big, and
slope down as much as possible. I have an oversize screen and fitting to
install there,( but haven't done it yet.) Third, always keep the tanks
full!!! (yeh.)
During the early days of Rebel flying, some problems started to appear when
ARRIVING, (easiest time to get air in the tanks) and resulted in no power
for an engine clearance or go-around. Scary isn't it?
To get my confidence back I duplicated the event on the ground. I tipped
the plane (one wheel in the ditch) and with one tank off, I drained fuel
from the gasacolator the ensure I had a bubble in the line. Then I
relevelled, and started the engine. Ran fine for a long time. When I
opened to full throttle it gave about 40 secs full, then lost power for
several seconds, and then cleared itself. DUPLICATING THE ACTUAL SITUATION.
(Only problem is that I burned my speed cowl. Maybe I should trash it
anyway according to Wayneand Bob)
Note that I knew of a problem during construction and we all tried our
fixes. I added a reservoir ABOVE the gascolator, vented back to the tanks,
and this gave me several seconds running time while this littel tank
swallowed the air bubble.
Hope this helps tou get a fix and confidence.
Phil. R302 and 5 years but not many hours.
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