Fuel Management Inquiry

bnt83

bnt83

Final Approach
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Brian
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I've seen this more than once in several different owner's manuals but how many of you folks run a tank dry (engine dies) then switch tanks and restart the engine?

Any concerns over engine driven fuel pump damage, assuming the engine is injected?

Any other posibilities this is just a dumb practice?
 
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No restart procedure required. The prop will still be spinning, just add fuel and everything is good.

The problems include shock cooling (if you're worried about that) and possible sucking up gunk from the bottom of the tank. Plus your passengers may not like it.

Personally, I try to switch before the fans go quiet.
 
Ted DuPuis said:
No restart procedure required. The prop will still be spinning, just add fuel and everything is good.
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This is true but many of these manuals state the boost pump may be required to get the restart and its recomended to check boost pump operation prior to "flame out"...
 
Watching the pressure gauge like a hawk can let you dry tank with out the engine stopping, if you have one.
 
bnt83 said:
This is true but many of these manuals state the boost pump may be required to get the restart and its recomended to check boost pump operation prior to "flame out"...
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If it is a low wing you gotta get the fuel back up to the engine driven pump
 
Skylane81E said:
Watching the pressure gauge like a hawk can let you dry tank with out the engine stopping, if you have one.
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Now it would be a good trick if you could watch the fuel totalizer and predict within 2 minutes of the flame out.
 
I'm too much a coward to deliberately run a tank dry while flying. I don't see any upside to doing so.
 
Remmeber your procedure for engine failure: typically it includes fuel pump on, mixture rich, switch tanks. You should know if the pump works when you start the plane.

I've never noticed a significant difference, though. The Aztec always recovered quickly when I ran a tank dry in it.
 
Ted DuPuis said:
The problems include <snip> possible sucking up gunk from the bottom of the tank.
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Since 90% of "gunk" is heavier than avgas aren't you always "sucking up gunk from the bottom of the tank?"

Ted DuPuis said:
Personally, I try to switch before the fans go quiet.
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bnt83 said:
Now it would be a good trick if you could watch the fuel totalizer and predict within 2 minutes of the flame out.
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That's exactly what I do. The fuel flow will "wag out" for quite some time before the engine sputters because the gascolator and carb bowl are on the secondary side of the fuel flow "pick-up" and that reserve allows the engine to run even though fuel is no long flowing steadily from the tank.

I regularly dry tank on long XC flights to increase my safety margin because I can pick up 5 gallons (0+27) of usable in level flight that's considered unusable in my tanks.

Also, I always dry tank the left tank for two reasons. First, if I'm flying solo it helps to balance the craft. Second since most patterns are LH that puts the fuel in the high wing when flying the pattern.

Also, I'll switch back to the dry tank occasionally (about every 15 minutes) after it's dry to make sure it stayed dry. It typically does but...
 
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Tim, put a little dirt in the bottom of a bucket with a plugged hole in the bottom, pour in some water, pull the plug and watch when the dirt really starts coming out, it will be as the bucket empties.
 
I'll try that, Dunc!

Do I get to slosh the bucket around like a tank gets "sloshed" by turbulence and changes in attitude?
 
If you like. What you will see is for most of the draining the dirt will not move much if at all, then at the end of the flow it will start to go.
 
Skylane81E said:
Tim, put a little dirt in the bottom of a bucket with a plugged hole in the bottom, pour in some water, pull the plug and watch when the dirt really starts coming out, it will be as the bucket empties.
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#1, The pickup is in the side of the tank, about .5 inches off the tank floor not the bottom of the tank. So sucking up gunk is very unlikely

#2 Water has different properties than fuel. Fuel will not hold as many particles in suspension as water can.
 
It's easier than that in some Cessnas. My 210 would quit when the center of the needle was aligned directly over the dot on the gage. I suggest watching carefully a couple of times to see if you can peg the exact location for your plane.

bnt83 said:
Now it would be a good trick if you could watch the fuel totalizer and predict within 2 minutes of the flame out.
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bnt83 said:
#1, The pickup is in the side of the tank, about .5 inches off the tank floor not the bottom of the tank. So sucking up gunk is very unlikely

#2 Water has different properties than fuel. Fuel will not hold as many particles in suspension as water can.
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We aren't looking for suspension just what gets swept along, you can exchange the water for fuel, the result will be unchanged.

But I agree it is unlikely, but it is less unlikely as the tank empties
 
bnt83 said:
I've seen this more than once in several different owner's manuals but how many of you folks run a tank dry (engine dies) then switch tanks and restart the engine?
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Not me (a.t least, not intentionally). Only way I'd do this intentionally is if things went really sour and I needed every last drop of fuel in the airplane because I'd run out of other options -- which has happened only once in my 40-year flying career, and I vowed then never to let it happen again.
 
Skylane81E said:
We aren't looking for suspension just what gets swept along, you can exchange the water for fuel, the result will be unchanged.

But I agree it is unlikely, but it is less unlikely as the tank empties
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I was actually surprised how far off the bottom of the tank the pickup was on a Cessna 177B I inspected a while back. It seemed very high like an inch or so.
 
I run the right tank dry regularly. No problem, the engine restarts in less than 2 seconds. Only in cruise flight, above 3500AGL are my rules. YMMV.

All GA planes built since about 1946 have to be shown to restart in the air after switching tanks when one is run dry.
 
When I first started flying I would routinely run a tank dry on the Arrow or the 180D because that was what I was taught. Knowing just a bit more now than then I am not so inclined to do that, unless as Ron stated, things were going sour quickly.

I do remember that when running a tank dry I was always monitoring things quite intensely and all the engine did was slow a bit as if you had leaned a bit too much. The fire lighted very quickly and it was really a non event.
 
Tim, Duncan is correct. Same thing occurs in cars, and we've seen it happen and cause clogging in carbs and injector servos.

If your tanks are clean, it's a non-issue.
 
2 reasons to run a tank dry.

1. This is the only 100% proven way to know exactly how much useable fuel your tanks really hold. Alternating which tank is run dry and then filling it first you will see exactly how much useable gas you really have.

2. As mentioned prior an extra ~3-5 gallons per tank all in the last tank can equal a lot of extra margin for reserves (especially in a 4 tank bird).
 
I drained mine on the ground and "measured" (watched carefully as the fuel truck filled) the amount needed to top off the tanks. It was closer to book than I expected it to be.

Ted DuPuis said:
If your tanks are clean, it's a non-issue.
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Define "clean". My tanks are "clean" but I still end up with little flakes of sealant in the samples sometimes....
 
wsuffa said:
Define "clean". My tanks are "clean" but I still end up with little flakes of sealant in the samples sometimes....
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Lacking that sealant that you sometimes see. :)
 
The only sage advice my CFI gave me on a Cherokee checkout was if you run one tank dry, try not to run the other tank dry.
 
I was flying the family to Colorado Springs in Charlene, my former 421B, and while switching tanks I inadvertently went to the OFF position on one side. :mad2: The good news is, I got my wife's undivided attention!:nono: It restart almost instantly. :yes:
 
Bob Noel said:
I'm too much a coward to deliberately run a tank dry while flying. I don't see any upside to doing so.
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The upside in running a tank dry is you don't have to worry about anything being left in that tank. Run it out, switch,... if the next tank runs out switch again to the next or land. :lol:
 
I have a couple of times (on different flights, obviously), for very specific reasons:

1 - Its my plane, and the gauges work. I wanted to see how the fuel indication on the gauge related to remaining usable fuel (how empty is 'empty'?)
2 - I wanted to determine how long it took from first indication of fuel pressure decrease to exhaustion (about 5 minutes).
3 - I wanted to determine the exact amount of usable fuel in the tanks.

A couple of things to think about:

1 - Make sure you switch tanks at least once before exhausting a tank. You don't want to find out there's a problem with the valve or the other tank after you've run one tank dry.
2 - Do it solo the first time.

Now on long XCs, I'll alternate until the right tank is down to two hours, run the left tank down until the fuel pressure starts to drop, then to the right tank for the remainder of the flight. All my running fuel and 1hr reserve is in one tank.
 
There's no question that fuel mismangement has caused accidents. I'm guessing somewhere in the past there's an accident that can be attributed to running a tank dry and not switching to a tank with fuel. I don't know if there is a documented case of running a tank dry, then switching to a tank with fuel and having it not prime or deliver fuel. I know I've never heard of it, and I know that the CAR regs from way back in the day require each tank to draw fuel as long as the engine is spinning. That's one of the primary reasons that carbs are on the bottom of engines from the get-go, so that they can gravity feed in most cases.

So, if you fear running a tank dry in cruise flight it's basically unfounded. Unless someone knows of or wants to search the NTSB DB for a case where a tank with fuel in it wouldn't draw fuel(for reasons other than damage).
 
"WARNING
Airflow Performance and Bendix/Precision fuel injection systems are non-returning systems. In the event that a tank is run dry in flight, an air lock will be formed on the out let of the pumps. It is possible that the boost pump will not pick up fuel, as the boost pump cannot create enough air pressure to over come the flow divider opening pressure, thus displacing the air and resume pumping fuel. It is not recommended to run a fuel tank dry in flight without adequate testing and proper documentation of the procedure for this operation."

So, no I don't run mine dry. I have a fuel totalizer and run each tank no lower than 5 gallons.
 
N747JB said:
I was flying the family to Colorado Springs in Charlene, my former 421B, and while switching tanks I inadvertently went to the OFF position on one side. :mad2: The good news is, I got my wife's undivided attention!:nono: It restart almost instantly. :yes:
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I was planning on running a tank dry one day and planned to tell SWMBO about it a couple of minutes before it happened. I got the timing wrong by a minute or two, so the engine died without her being briefed to expect it.

Based on the grief I received, I'll tell her an hour in advance from here on out...
 
I've found that pax aren't thrilled about a tank running dry. Did it once with 3 non-pilots in the plane. We were chatting, I got distracted. Woke everyone up. Fortunately, these were adventurous folks who also trusted me, so when I explained what happened and why it was fine, they were fine as well.

I have let tanks run dry to drive home the point of fuel management to students who are having issues. These students usually have 500+ hours. It does a good job. One almost shut down the engine, and wouldve found himself with a double engine failure 2 minutes later.
 
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