Running a fuel tank dry in flight in the Rebel?
Posted: Fri Feb 17, 2012 9:21 pm
I have had a situation happen to me twice now, that has got me wondering
whether I could encounter a potential safety problem.
I was doing some weight and balance work after my float installation which
involved draining the fuel from my tanks. Later, I put back about 5 gallons
into one tank, and then tried to start the engine. I shoved in the mixture
and gave it the usual 5 primes for a cold engine. It fired up as usual but
would only run for a few seconds. I tried again and again, but it would only
run with the fuel primed into the cylinders. I checked fuel flow at my
gascolator drain and it was fine, so obviously it was feeding to there. I
then put some fuel into the other tank and then it started and ran fine
after that.
I can shut off either tank and it also runs fine. I have done this in flight
many times.
Then, just recently, I encountered a similar situation again. This time, I
drained only one tank dry. I had mogas in this one, and decided to drain it
and fill it with avgas. After it was dry, I selected my other tank which
still had 15 gallons of avgas in it, and was going to taxi over to the
airport fuel pumps for a fill-up. To my surprise again, the engine would not
start beyond the priming, same as last time.
Since I didn't want to put the mogas back into the drained tank, I proceeded
to drain some fuel out of the avgas tank, from the gascolator drain. I put
about 3 gallons into my plastic gas can, but before pouring it into the
empty tank, decided to try starting it one more time. This time, to my
surprise, it started and ran fine, with just the one tank.
I should mention at this time, that I have a fuel flow gauge instrument, so
have a fuel flow transducer that is mounted down line of the gascolator,
just before the fuel goes into the carb. It does take some pressure, about
.5 PSI, I believe. When I did my fuel flow tests prior to first flight, my
flows were right at the minimum (150% of max power) at low fuel and the
airplane set at maximum climb angle. When I tried it without the flow
sensor, the rate of flow was considerably higher (about double actually). So
as not to risk a fuel starvation in flight due to inadequate pressure, I
added ram air tubes to the tops of my gas caps with flared openings facing
into the windscreen.
Anyways, I have never had a problem in flight, and have tested it back when
I was on wheels at maximum power climbs on one tank, and never a burp from
my engine, even with one tank down to less than 5 gallons.
However, I have never actually run one tank dry in flight, and wondering if
what happened to me on the ground could be repeated in flight. On the
ground, I assumed air in my lines somehow caused a low fuel pressure problem
when starting a new tank. In flight, this shouldn't happen with my ram air
vents, but I am not overly anxious to try it now given my ground experience.
My Rebel has the fuel shut off valves up top at the tank outlets, so the
lines can fill with air if you shut off a tank and run the other dry. The
lines join at a tee just before going through the firewall to the
gascolator. If the valves were at the bottom, this air in the lines problem
shouldn't happen, at least that's my theory.
Anyway, I wanted to get some feedback from the group and those that are
flying to see if they have encountered this situation, and if anyone has run
one tank dry in flight.
From a safety perspective, I used to think that it would be a good idea to
switch to one tank, if you're caught in a low fuel situation, and then when
it is dry, switch to the other one and look for a place to land. Not sure
now, whether this is such a good idea.
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whether I could encounter a potential safety problem.
I was doing some weight and balance work after my float installation which
involved draining the fuel from my tanks. Later, I put back about 5 gallons
into one tank, and then tried to start the engine. I shoved in the mixture
and gave it the usual 5 primes for a cold engine. It fired up as usual but
would only run for a few seconds. I tried again and again, but it would only
run with the fuel primed into the cylinders. I checked fuel flow at my
gascolator drain and it was fine, so obviously it was feeding to there. I
then put some fuel into the other tank and then it started and ran fine
after that.
I can shut off either tank and it also runs fine. I have done this in flight
many times.
Then, just recently, I encountered a similar situation again. This time, I
drained only one tank dry. I had mogas in this one, and decided to drain it
and fill it with avgas. After it was dry, I selected my other tank which
still had 15 gallons of avgas in it, and was going to taxi over to the
airport fuel pumps for a fill-up. To my surprise again, the engine would not
start beyond the priming, same as last time.
Since I didn't want to put the mogas back into the drained tank, I proceeded
to drain some fuel out of the avgas tank, from the gascolator drain. I put
about 3 gallons into my plastic gas can, but before pouring it into the
empty tank, decided to try starting it one more time. This time, to my
surprise, it started and ran fine, with just the one tank.
I should mention at this time, that I have a fuel flow gauge instrument, so
have a fuel flow transducer that is mounted down line of the gascolator,
just before the fuel goes into the carb. It does take some pressure, about
.5 PSI, I believe. When I did my fuel flow tests prior to first flight, my
flows were right at the minimum (150% of max power) at low fuel and the
airplane set at maximum climb angle. When I tried it without the flow
sensor, the rate of flow was considerably higher (about double actually). So
as not to risk a fuel starvation in flight due to inadequate pressure, I
added ram air tubes to the tops of my gas caps with flared openings facing
into the windscreen.
Anyways, I have never had a problem in flight, and have tested it back when
I was on wheels at maximum power climbs on one tank, and never a burp from
my engine, even with one tank down to less than 5 gallons.
However, I have never actually run one tank dry in flight, and wondering if
what happened to me on the ground could be repeated in flight. On the
ground, I assumed air in my lines somehow caused a low fuel pressure problem
when starting a new tank. In flight, this shouldn't happen with my ram air
vents, but I am not overly anxious to try it now given my ground experience.
My Rebel has the fuel shut off valves up top at the tank outlets, so the
lines can fill with air if you shut off a tank and run the other dry. The
lines join at a tee just before going through the firewall to the
gascolator. If the valves were at the bottom, this air in the lines problem
shouldn't happen, at least that's my theory.
Anyway, I wanted to get some feedback from the group and those that are
flying to see if they have encountered this situation, and if anyone has run
one tank dry in flight.
From a safety perspective, I used to think that it would be a good idea to
switch to one tank, if you're caught in a low fuel situation, and then when
it is dry, switch to the other one and look for a place to land. Not sure
now, whether this is such a good idea.
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