Ran a tank out of gas

Weekend Warrior

Weekend Warrior

Pre-takeoff checklist
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Mr Madman
So the thread on "Engine out practice" got me thinking about how I've always wanted to run a tank dry (obviously with gas in another tank), so I tried it this morning. I know some people, in an attempt to maximize range, do this regularly. My warrior holds more gas for much more flight time than I'm willing to sit in the plane at one time, so I have never felt a need to do this for range. But, I still wanted to try it.
The results were not what I expected:
I've heard that when the tank reaches empty/starts sucking air, the fuel pressure gauge gets erratic then the engine quits. All true, but a bit of an over simplification. In my warrior, I have two tanks (L/R) a fuel pressure gauge, a JPI fuel monitor, and both mechanical and electric fuel pumps. So today at a very high altitude, I let one tank run dry, with just the mechanical fuel pump working, and the electric pump off. Of side note, my JPI seems to work very well. I had run on the left tank for 1.5 gallons just to be sure all was well in that tank, before switching to the right and running it dry. The JPI indicated 18.9 gallons (Warriors have about 1 gallon unusable) on the 18 gallon tank when I noticed the pressure gauge drop, to about half of its normal reading.
At the first sign of the pressure drop, I watched the gauges but left everything alone. The plane flew on, making normal power for about 30-45 more seconds, before it slowly started to lose power over about 20 seconds. While this was going on, my JPI fuel monitor went nuts, indicating 30+ gph fuel burn, setting off the low fuel warning (mine is set to warn if there is less than an hour of fuel). I assume it read this high because there was air in the line instead of fuel.
As the engine lost about 50% power, I turned on the electric fuel pump, and the engine went back to normal power for another 10 seconds or so, before finally dropping to idle. When it dropped this second time, it was nearly immediate. Leaving the electric pump on, I then switched over to the nearly full tank, and the engine fired back up, also nearly immediately. I've heard that normally it takes some time for the gas in the other tank to reach the engine, so I was expecting some glide time, but it went back to normal power/normal fuel pressure in 2, maybe 3, seconds.
When I got back on the ground and to the hangar, I tried switching back to the empty tank, but the engine died somewhat quickly. I then tried draining the "empty tank" with the quick drain. About a quarter gallon was still able to come out the quick drain (this makes sense and is what I would expect, as I would think the quick drain needs to be lower than the fuel pickup tube for water/sediment reasons).
 
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Is there legally any reason you couldn't run a tank out of gas? I actually wanted to do this while wearing a heart rate monitor and see how I react physically.

I will admit over the summer I inadvertently ran out of gas because I miscalculated my fuel burn and it was a solid 10 seconds before I had my wits about me and that surprised me.

I want to go up and do it intentionally but I don't know if that is frowned upon or in some way not legal
 
SixPapaCharlie said:
Is there legally any reason you couldn't run a tank out of gas? I actually wanted to do this while wearing a heart rate monitor and see how I react physically.

I will admit over the summer I inadvertently ran out of gas because I miscalculated my fuel burn and it was a solid 10 seconds before I had my wits about me and that surprised me.

I want to go up and do it intentionally but I don't know if that is frowned upon or in some way not legal
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It's legal.
 
SixPapaCharlie said:
Is there legally any reason you couldn't run a tank out of gas? I actually wanted to do this while wearing a heart rate monitor and see how I react physically.

I will admit over the summer I inadvertently ran out of gas because I miscalculated my fuel burn and it was a solid 10 seconds before I had my wits about me and that surprised me.

I want to go up and do it intentionally but I don't know if that is frowned upon or in some way not legal
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It’s the only legal way to fly with an inoperative fuel gauge.
 
On those unfortunate trips when fuel reserves are getting tight, many folks like to run the tanks dry before switching to the final tank used for approach and landing. They want to make sure every bit of available gas is in the tank used for those approach maneuvers at low agl.
 
FAA certification standards:

FAR 23.955(e) Multiple fuel tanks. For reciprocating engines that are supplied with fuel from more than one tank, if engine power loss becomes apparent due to fuel depletion from the tank selected, it must be possible after switching to any full tank, in level flight, to obtain 75 percent maximum continuous power on that engine in not more than -
(1) 10 seconds for naturally aspirated single engine airplanes;
(2) 20 seconds for turbocharged single engine airplanes, provided that 75 percent maximum continuous naturally aspirated power is regained within 10 seconds; or
(3) 20 seconds for multiengine airplanes.​

FAR 25.951(a) Each fuel system must be constructed and arranged to ensure a flow of fuel at a rate and pressure established for proper engine and auxiliary power unit functioning under each likely operating condition, including any maneuver for which certification is requested and during which the engine or auxiliary power unit is permitted to be in operation.
(b) Each fuel system must be arranged so that any air which is introduced into the system will not result in -
(1) Power interruption for more than 20 seconds for reciprocating engines; or
(2) Flameout for turbine engines.​

The earlier CAR 3.4221(d) had an even stronger requirement for single-engine airplanes:
If an engine can be supplied with fuel from more than one tank, it shall be possible to regain the full power and fuel pressure of that engine in not more than 10 seconds (for single-engine airplanes) or 20 seconds (for multiengine airplanes) after switching to any full tank after engine malfunction becomes apparent due to the depletion of the fuel supply in any tank from which the engine can be fed. Compliance with this provision shall be demonstrated in level flight.​
 
I’ve always wondered if you make a mess of sucking whatever junk is in the very bottoms of the tanks up.
 
James331 said:
I’ve always wondered if you make a mess of sucking whatever junk is in the very bottoms of the tanks up.
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If it was at the bottom, it’d get sucked up first, or nearly first. Now if it was floating on top, then it could get to the motor when running dry.
 
I ran one tank almost dry in an Archer. I knew from the clock that the tank was almost dry so I was watching the fuel pressure closely. When the pressure began to drop significantly, I switched tanks and turned on the electric fuel pump. The engine didn't miss a beat. -Skip
 
Skip Miller said:
I ran one tank almost dry in an Archer. I knew from the clock that the tank was almost dry so I was watching the fuel pressure closely. When the pressure began to drop I switched tanks and turned on the electric fuel pump. The engine didn't miss a beat. -Skip
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Now that I’ve tried it, I could see it could have some usefulness. I’m now pretty sure I could switch tanks without my passengers even knowing a tank was run dry.
 
Weekend Warrior said:
If it was at the bottom, it’d get sucked up first, or nearly first. Now if it was floating on top, then it could get to the motor when running dry.
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Stuff sitting on the bottom is more likely to get sloshed around when there is very little fuel left.

But, in any case, what happens when the tank runs dry depends on the airplane / tank. With my original tanks, I had, like, purd near zero unusable fuel - when a tank went dry, it was like flicking a switch. With the new tanks (more flat bottom area), it gets into running lean / rough as some, but not enough, fuel makes it through.
 
James331 said:
I’ve always wondered if you make a mess of sucking whatever junk is in the very bottoms of the tanks up.
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If the tank has schmutz in it, that schmutz is going to find its way into the intake tube regardless of how much fuel is left.
 
Next time you try running one dry, wait till it quits, then put the plane in a hard slip to get the unusuable fuel closer to the intake tube and see if the engine comes back. If it does, see how long it'll keep running. I know someone who ran a supercub out of fuel about 15 miles from the airport. He got the engine running again by putting the plane into a hard slip. He flew it back to the airport that way.
 
Juliet Hotel said:
Next time you try running one dry, wait till it quits, then put the plane in a hard slip to get the unusuable fuel closer to the intake tube and see if the engine comes back. If it does, see how long it'll keep running. I know someone who ran a supercub out of fuel about 15 miles from the airport. He got the engine running again by putting the plane into a hard slip. He flew it back to the airport that way.
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Dang, wish I had thought of this. I would of liked to see if it would run awhile like that. I guess its an experiment for another time.
 
Ryanb said:
So is it true that the engine will lose power if there’s no fuel in the tanks?
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Ask CNN:

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I ran one of mine dry today also. I usually switch as soon as the jpi shows a drop in fuel pressure, I can time it to within a minute. But I got distracted and let it run all the way dry. Threw the switch and didn’t even lose any altitude. Non event. I don’t want to have to be switching tanks if I get into a situation where I’m running low, because the only way that will happen is if things are already going very badly.
 
Juliet Hotel said:
If the tank has schmutz in it, that schmutz is going to find its way into the intake tube regardless of how much fuel is left.
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Yup. If a pilot is properly sumping before flight, the schmutz won't be there at all.

There's a coarse finger screen on the outlet to prevent larger debris from entering the system. There's a fine screen in the fuel strainer, and an even finer screen in the carb or fuel injection servo inlet. They're all there to stop crud, and they should all be checked at annual or whatever hourly period the OEM recommends. And yet, it was not unusual to find fuel strainers seized shut becaue they hadn't been opened in 20 years.
 
Juliet Hotel said:
If the tank has schmutz in it, that schmutz is going to find its way into the intake tube regardless of how much fuel is left.
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I think its like playing the odds and percentages. Hypothetically, lets say there is an ounce of schmutz floating around in your fuel tank. With 30 gals of fuel, there is a .00026% chance of sucking up the schmutz. When the tank is run dry, there is a 100% chance that you sucked up the schmutz.
 
Do it all the time on long X-Country including trips to Puerto Rico. I carry 120 gallons in 6 tanks on my single engine airplane. I can fly 7 hours nonstop at 165 kts true air speed.
Once you know a tank is empty then u ain’t going back to it.

I watch my JPI and when my gph drops, I switch and wait for the sputter, maybe 5 seconds of engine reduction and then she is good to go.

I gonna try the slip when I have no other options..... until then, I will switch to a tank with fuel.
 
lsaway said:
I think its like playing the odds and percentages. Hypothetically, lets say there is an ounce of schmutz floating around in your fuel tank. With 30 gals of fuel, there is a .00026% chance of sucking up the schmutz. When the tank is run dry, there is a 100% chance that you sucked up the schmutz.
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That depends on how much unusable fuel you have. Varies from plane to plane. If you have a higher unusable amount then you may not be sucking as much schmutz, because most schmutz doesn’t float.
 
lsaway said:
I think its like playing the odds and percentages. Hypothetically, lets say there is an ounce of schmutz floating around in your fuel tank. With 30 gals of fuel, there is a .00026% chance of sucking up the schmutz. When the tank is run dry, there is a 100% chance that you sucked up the schmutz.
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A .00026% chance on that particular tank of fuel. What about the next tank? And the tank after that? And the tank after that?

Once something ends up inside the tank, its going to come out. Either through the sump drains or through the intake pickup. Well ok to be fair, if you drop a screw driver or your car keys in there, that will probably stay until you pull it back out the fill port, but I think you get what I mean. If something is mixed in with the fuel in the tank, its going to come out with the fuel. If its specific gravity is heavier, it will likely come out the sump drain. If not, its going down the pipe. At that point the choices are stops in the filter or goes through a cylinder.

The notion that because you're now sucking the last usable ounces means you're more likely to get dirty fuel is just silly. I tell all my truck drivers to add a bottle of fuel treatment (prevents gelling) every time they put diesel in the truck during the winter. But truck driver's are like deaf dogs in that you can tell them something, but not much. And I know this because some of them continue to add fuel treatment only every other time they fuel and then they gell up and wonder why. Its because the sh*t you dumped in the fuel tank time before last came out when you burned that fuel tank you dipsh*t. That's what happens. You put something in the fuel cappy end and it comes out the fuel liney end. It doesn't magically stay in there not getting to the engine because you wished it would so you wouldn't have to add more treatment next time you fueled. It works that way with fuel. It works that way with fuel treatment. It works that way with fuel contaminants. If they're ending up in with the fuel, they're going out with the fuel. Pretty simple that way.
 
Sure I over simplified it and was misunderstood, so I apologize for that. There are many other factors involved that change the odds, including specific gravity, strainers, pickup location, resistance, etc.... There are some contaminants and organisms that stay suspended in fuel, especially when the fuel gets agitated. Not to say that it isn't possible to get sucked up in the first minute of flight, but the odds that it will be ingested go up as the fuel quantity goes down.

I believe there are other factors as well. I have seen sediment at the bottom of fuel tanks (not specifically aviation) that seemed to be stuck to the bottom. As long as it stayed wet and compacted from the fuel weight, it adhered to the bottom. After the tank was run dry, the sediment dried and became loose. There is also the notion that as the tank level gets very low, the sloshing and splashing effect of the fuel can dislodge sediment that has been stuck to the bottom. There will be more agitation from maneuvers in a tank low on fuel compared to a full tank.
 
Don’t run your first tank dry while your mate is asleep next to you.


Sent from my iPad using Tapatalk Pro
 
Be ready once u refill those tanks that you ran empty as u will get a surprise sputter in the air. Those lines are still dry from the tank to the engine.
 
lsaway said:
There is also the notion that as the tank level gets very low, the sloshing and splashing effect of the fuel can dislodge sediment that has been stuck to the bottom. There will be more agitation from maneuvers in a tank low on fuel compared to a full tank.
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And that is just what you said it is, a notion and nothing more. Its your own guess as to what might happen. Here is what I know. I used to do very long flights in a plane with 4 tanks and I ran tanks dry during those flights many many times. Never once had an issue with fuel contamination doing it. Not once. Never once had the engine not restart within 2 seconds of switching tanks. Not once.
 
PiperW said:
Be ready once u refill those tanks that you ran empty as u will get a surprise sputter in the air. Those lines are still dry from the tank to the engine.
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Again, depends on the airplane, but that issue is one of the big reasons I rarely run my aux tanks dry in the Beech 18. The surging when trying to go back to those tanks after refueling is worse/more startling to pax than the initial running it dry.

My Waco and T6 in the other hand have never had that issue. I run those dry every cross country flight and have never had an issue with surging/air in the line after refueling.
 
lsaway said:
Sure I over simplified it and was misunderstood, so I apologize for that. There are many other factors involved that change the odds, including specific gravity, strainers, pickup location, resistance, etc.... There are some contaminants and organisms that stay suspended in fuel, especially when the fuel gets agitated. Not to say that it isn't possible to get sucked up in the first minute of flight, but the odds that it will be ingested go up as the fuel quantity goes down.

I believe there are other factors as well. I have seen sediment at the bottom of fuel tanks (not specifically aviation) that seemed to be stuck to the bottom. As long as it stayed wet and compacted from the fuel weight, it adhered to the bottom. After the tank was run dry, the sediment dried and became loose. There is also the notion that as the tank level gets very low, the sloshing and splashing effect of the fuel can dislodge sediment that has been stuck to the bottom. There will be more agitation from maneuvers in a tank low on fuel compared to a full tank.
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Have you ever done maintenance on aircraft fuel tanks and delivery systems?
 
Dan Thomas said:
Have you ever done maintenance on aircraft fuel tanks and delivery systems?
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I just took the tanks out of my RV10 after 1200 hours as part of my effort to add a bit of tankage. Interestingly I could barely find a thing. No sludge, no debris, the only stuff that looked like bit of debris contamination turned out to be bits of tank sealant that remained adhered to the tank skin.

I clean a fuel filter every year and only find a few specks of stuff. Seems like if I never cleaned it, it would still be passing fuel without a problem.

No experience or opinion here, just a share.


Sent from my iPad using Tapatalk Pro
 
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