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Running one tank dry. How?

Somewhere else I just read about running one wing tank dry. Now I’m wondering how people might be doing that?

Is is as simple as waiting for the engine to stumble and then quickly switch with the electrical fuel pump on? I can imagine that one must switch quite quickly to avoid the engine to stop.

Not that I’m eager to try this for real but it sparked my interest and so I wanted to bring it up.

Frequent travels around Europe

Stephan_Schwab wrote:

s is as simple as waiting for the engine to stumble and then quickly switch with the electrical fuel pump on? I can imagine that one must switch quite quickly to avoid the engine to stop.

Yes. The engine cannot stop because the propeller keeps turning. All you need is fuel and sparks.

The reason low wing aircraft cannot have a BOTH selector like high wing aircraft is that when one tank runs try, the engine would be sucking air because that has less resistance than the fuel in the other tank.

I personally wouldn’t undertake flights where my fuel calculation is so tight that I have to run a tank dry in order to establish the exact quantity.

It’s not really a problem. The engine won’t stop even if you don’t respond quickly.
If I’m quick, I’ll get it when the pressure starts to drop.
At worst there’s 4-5 seconds of rough running, so best to forewarn passengers as they might otherwise get a bit jumpy.

If you do aerobatics in a carburated aircraft, you get used to the fuel system re-sorting itself and there’s no real drama.

KHWD- Hayward California; EGTN Enstone Oxfordshire, United States

There is an article by John Deakin where he writes about this. I never did it, though.

EDFM (Mannheim), Germany

I don’t profess any knowledge or expertise here, so I’ve no idea how typical my experience is to other aircraft.

But for what it’s worth, when I intentionally ran a tank dry, the engine started to mildly surge. Not great big surging that would make you jump up, but a slight note change from my constant rpm prop. I could see it also on the fuel pressure gauge. This was within 2 minutes of my predicted dry tanks time.

After about 20 second of the mild surging, waiting on the engine to stop, I lost the nerve and switched thanks

But that in itself taught me an interesting lesson. If I saw those signs again, I think I’d recognise them quickly.

Whether this is typical behaviour or not, I’ve no idea.

Colm

EIKH Kilrush

I have a feeling that a fuel injected IO540 engine suddenly starved of fuel might do something more “interesting” than surge for a bit…

John Deakin is of course right that certification-wise this should be safe, in that the engine on a SEP is required to restart within X seconds (longer for a MEP, BTW) but certification-wise the KFC225 autopilot….

I don’t think I would do it over water…

I can speak only for the TB20GT and that has accurate fuel gauges and a LOW FUEL light which comes on at 8 USG in that tank (which I have experimentally verified pretty well), so if you are burning 8 USG/hr you have 1 hour left at that point. What I have done, on specially long flights, is waited for the low fuel light and then timed 1/2 of the remaining time and that is (a) safe and (b) should leave me say 30 mins’ fuel in that tank should I have a genuine emergency which involves tank switching.

The reason for running a tank dry, or very low, is to make full use of the fuel being carried. This becomes a big issue with more complex fuel systems with say four tanks, where you really do want to run say the tip tanks dry.

Administrator
Shoreham EGKA, United Kingdom

I’ve had one problem in running a tank dry that might be of interest. It probably wouldn’t apply with a pressurized system but with an otherwise reliable gravity feed fuel system and a Stromberg (old) carb, I believe the in-rush of fuel when feeding a full tank to an empty carb knocked the float closed so hard that it stuck closed. That is not a good thing, because the engine then stops again shortly after restarting. Vigorous pitch control may knock it loose. In my case I also inspected the float valve and didn’t find much. Its something I now bear in mind as a possibility when running tanks dry. Unexpected things can happen.

I have a feeling that a fuel injected IO540 engine suddenly starved of fuel might do something more “interesting” than surge for a bit…

Your feeling might not be correct. This was a fuel injected IO360. So nothing radically different from yours. At least I know what happens with my engine…you’re guessing

But as I said, I’ve no way of knowing if this is typical or not….just a single data point.

EIKH Kilrush

The left tip tank fuel gauge on the 235 is in-op so I ran the tank dry to see exactly what I would get out of it as I was planning a long trip in her. Even though I was expecting the engine to become unhappy with life, I did not enjoy making it unhappy and was very happy when she roared back to full chat when I switched to good tank. Interesting I was out by I think 5 minutes with the time I calculated the donkey would protest and when it actually coughed……………..

Always looking for adventure
Shoreham

I’ve run tanks dry when there was a reason. During long ferry flights, where you like to be confident about fuel quantity, running tanks dry progressively lets you know what you have remaining. I’ve never had a problem doing this, having done it in many types I have ferried. One caution is that flight manuals sometimes state that the mixture should be selected to “rich” when restoring power changing from a dry tank. If you were at altitude, and leaned, select a little more rich, but not full rich, or the engine will stumble, simply because of that!

I used to fly a C 310 long distances. It had six tanks, and a rather complex fuel system, in that the aux tanks would return excess unused fuel to the main tanks. But this worked very well once you understood it, as you could run four tanks dry, and know exactly what you had left. I disliked the C 303 for the opposite of this feature, a left and right tank only. It’s un nerving watching the fuel quantity indicators bouncing lower than one quarter, and not seeing Iceland yet! My Teal has four tanks, and I have on occasion run three completely dry for enroute fuel planning….

Home runway, in central Ontario, Canada
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