Time to restart after running tank dry

[Andres Darvasi]

I would appreciate having your opinions on the time that takes the engine to restart after running a tank dry, after switching tanks and turning the electrical pump on

On my Caribbean trip next December, I want to maximize the useable fuel in the aux tanks, but as I will most of the time be flying over water I don't want either my wife or myself to faint during the procedure

I must confess that I am not convinced that I will have the gust to do it!

[kenhill]

after you switch tanks, about 3 seconds. Pull throttle back then switch tanks so you do not over rev.

[Andres Darvasi]

Thank you very much Ken

[Kristin Winter]

I have run tanks dry, deliberately, many dozens, maybe over 100 times in 35 years. With a single engine, fuel injected, 5-10 seconds. However, I advise against it with your wife, unless she is utterly unflappable. This is especially true if it is your first time running the tanks dry. You will be nervous and she will read that. It is not worth the risk of turning her off from flying with you.

If you have a fuel totalizer, like a Shadin or a JPI, you can get very close to the bottom by noting the fuel left each time you switch tanks. You can get almost as close with timing.

If you are going to go to the ends of endurance, then I recommend that you find out exactly how much fuel each tank holds by running it dry and then filling it up. You may be surprised at how much the tank holds, or not. Don't trust the book numbers. Remember, the mains need to be filled all the way to the very top of the collar or they are not full.

[Andres Darvasi]

Thank you very much for your excellent advice Kristin.

I do have a fuel totalizer and I keep close tab of my consumption at every tank switch, even made a little form for this purpose, that gives me the exact amount left in each tank. Also, at the recent annual I had the fuel level sensors overhauled and the gauge is working accurately.

My wife flies with me because she likes de idea of travelling together, she does NOT enjoy flying in small aircraft, so you are right that I should not try anything "strange" with her on board, when i had the T210 we had a couple of times vapor lock issues which made the engine cought for a few seconds, and she REALLY noticed it.

Moreover, I got with the aircraft a perfectly calibrated measuring stick that I use in every pre flight.

The mains are always filled to the collar.

I will follow your advice and measure the real capacity of each tank.

Again, many thanks for your help.

[JIMICS2452]

Andres, in my experience it usually only takes a few seconds to get a restart, but I have waited as long as 30+seconds. When the engine is quiet that is a very long time. As Kristin suggested, do a few trial runs with the aux tanks and get a feel for how close you can go to dry with the fuel totalizer.

I know you have a few long legs planned on your trip. When is your group heading east and could you give a route?

[N3322G]

Andres,

On the Twin the Shadin fuel flow shows rapid and dramatic variability in fuel flow before any engine sound of fuel starvation is heard or felt. So, I enlist whoever is flying right seat to monitor during last 2 gallons by keeping their finger on the edge of the gauge. Like Kristin, I have run the tanks dry hundreds of times - catching the fuel flow variability has allowed many no-engine-sound change tank changes while running tanks dry and it takes away the scary surprise of engine noise change.

That being said, I would go to perhaps 0.5 gallons and change so your wife can ride in comfort - perhaps she would monitor the totalizator for you -just a thought.

Hope this helps.

[Andres Darvasi]

[Andres Darvasi]

Pat, the fuel flow tip is a great one, many thanks

I will enlist my wife's help in several tasks during this trip so hopefully familiarity will help her relax and enjoy the flights!

[Kristin Winter]

I would caution that Pat's trick might not work in a single because the transducer is closer to the engine in a single than in the twin. In my airplane, I can't reliably catch it with Shadin fluctuation so I would test that out alone before relying on it.

[Andres Darvasi]

Thank you Kristin, I will rely on other calculations and try to avoid the "thrill"

[Hank Spellman]

Andres,

An additional tip: when filling the tanks, first pull the nose down to collapse the nose strut as much as possible. The more level attitude allows more fuel in the tank because it makes the air bubble at the top of the tank smaller. The late Bill Creech, a past president of ICS, even made a device to jack up the tail when refueling to achieve the same result. His experience was that the additional capacity was as much as a gallon per tank. My experience matches his.

On the aircraft with carburetors, the very first indication of a dry tank is the fuel pressure gauge going nuts. It gives at least 15 seconds warning of the coming silence. I don't know if this applies to fuel injected engines.

Hank
Henry A. Spellman

[kenhill]

I remember reading where somone installed an warning light to indicate the fuel pressure dropped downstream of the engine fuel pump. This would allow you to change tanks before the fuel bowl runs dry. Perhaps they will chime in.

[Kristin Winter]

Fuel injected engines do not have the carburetor bowl to give you a cushion of time like a carburetor does. With a carbureted engine, it is easy to look for the drop in pressure and then switch tank and you are likely to have no hiccup at all. The fuel injection system will quit very shortly after you see a change in flow or pressure.

[MULEFLY]

I agree with Kristin here... regarding twins: I realize that Pat has had a lot of experience interpreting the drop on her JPI, and switching before loss of power. I've tried it about 6 times... each time knowing that it was going to happen... I think I am 2 for 6 for not having it go "silent"...

After about a 4 hour leg on an 8 hour day... in the single... we lost power due to fuel starvation -- after the "what the heck?" moment... I quickly switched and it was back on line within less than 10 seconds... my wife still claims it was closer to 30 minutes, ... but the truth is probably somewhere in between.

I think that there is a spec for a certificated airplane that it must start withing "X" seconds after loosing power due to fuel starvation and when a tank has been switched. Perhaps someone knows that number.

Jim Covington