My experience running a tank dry.

[Vac]

Hi Ron,

You won't know until you flight test. You have two options: design a flight test with appropriate risk mitigation considerations after you consult with the AFP engineer(s) or never run a tank dry because flight test data is unavailable. If a system failure occurs and you haven't tested, well you are definitely a test pilot at that point and have no choice but to finish the experiment!

FAR 23 certification criteria do require the ability to run a tank dry and restart, but those criteria do not apply to EAB types. While it is best if the fuel system is plumbed strictly in accordance with the designer's instructions, there are simply too many variables to to make any assumption, thus the requirement to properly test your airplane.

Unfortunately, every RV is unique, and while there are excellent lessons that apply (our community is an outstanding "brain trust"), each airplane has to be tested. Such is the nature of EAB aviation.

You might consider engaging with an EAA Flight Advisor or test pilot to help meet your objective. Drop a PM or email if there is anything I can do to help you out.

Cheers,

Vac

[Ron77]

Originally Posted by Vac

Hi Ron,

You won't know until you flight test. You have two options: design a flight test with appropriate risk mitigation considerations after you consult with the AFP engineer(s) or never run a tank dry because flight test data is unavailable. If a system failure occurs and you haven't tested, well you are definitely a test pilot at that point and have no choice but to finish the experiment!

FAR 23 certification criteria do require the ability to run a tank dry and restart, but those criteria do not apply to EAB types. While it is best if the fuel system is plumbed strictly in accordance with the designer's instructions, there are simply too many variables to to make any assumption, thus the requirement to properly test your airplane.

Unfortunately, every RV is unique, and while there are excellent lessons that apply (our community is an outstanding "brain trust"), each airplane has to be tested. Such is the nature of EAB aviation.

You might consider engaging with an EAA Flight Advisor or test pilot to help meet your objective. Drop a PM or email if there is anything I can do to help you out.

Cheers,

Vac

Thanks for the great response Vac. AFP also recommends testing, however since my fuel system (including the AFP pump) is built per plans, perhaps someone on this forum has already tested this scenario and can share their experience? Nonetheless, I will test on my plane as you suggest.

Thanks again, Ron B.

[rbibb]

I find my bladder endurance is much less than my fuel capacity so this is rarely an issue. But I've run a tank dry before. Never quite planned on it but was squeezing the last drop o a long leg. Had plenty in the other tank. Engine coughed and when I switched tanks was purring again before I could even hit the boost pump. Not FI which may have helped.

[Bevan]

For those of you that want to run one tank dry (for whatever reason), you may want to take a look at this low fuel sensor. Ive just discovered this and got me thinking that if it was put into the tank at the very bottom or in the fuel line via a tee fitting (perhaps in the wing root area), it would give you advance notice that the "big bubble" is coming and that it is time to switch tanks, before that big bubble makes its way past the fuel selector. Just a thought.

http://www.aircraftextras.com/LowFuelSensor.htm

Bevan

[lr172]

Originally Posted by MConner

It cannot be good for a motor to go from cruise power to off to cruise power again.

If this were true, just imagine the abuse you put on your car's engine - Idle at the light until it turns green. Hit the gas and rev up to 4000 RPM. Push in the clutch, back to idle, shift gears/release clutch and back to 4000 RPM again - repeat, repeat... I won't belabor this, but most cars do this millions of times in their 150,000 mile life. Same goes for starting and stopping the engine withing a few seconds. The oil pressure doesn't even drop more than 10-20 PSI.

Larry

[myrv6180]

I took off one cold morning after a hard rain the night before and ran one tank nearly dry then switched to the other tank which showed plenty on my gauge. After switching tanks and about 15 seconds, ca-chug. She quit, yawing hard because I was in a climb. I immediately lowered the nose and switched to the previous tank and turned on the aux pump and after a long while the engine caught back up and I made it back to the airport. Don't ever run a tank dry!!!! If I had run mine dry I would have had to crash land in the mountains. Always have an out if you want to live to fly 52 years as I have. Turns out my fuel cap had leaked water into the tank the night before and then froze before morning blocking the fuel pickup.

[odens_14]

Originally Posted by myrv6180

I took off one cold morning after a hard rain the night before and ran one tank nearly dry then switched to the other tank which showed plenty on my gauge. After switching tanks and about 15 seconds, ca-chug. She quit, yawing hard because I was in a climb. I immediately lowered the nose and switched to the previous tank and turned on the aux pump and after a long while the engine caught back up and I made it back to the airport. Don't ever run a tank dry!!!! If I had run mine dry I would have had to crash land in the mountains. Always have an out if you want to live to fly 52 years as I have. Turns out my fuel cap had leaked water into the tank the night before and then froze before morning blocking the fuel pickup.

Yes running one tank to empty without using the other is dangerous, as in your situation you can't be sure the other side is useable. However, even a simple balancing of fuel mitigates this risk.

My typical fuel management is burn from the right tank until it reads 11 gal, switch to left until 5 remaining (if I need max endurance this is where I'd run to 0), then back to right tank to land which still has about 90 min at cruise.

[Canadian_JOY]

An alternative to the sensor suggested by Bevan:
http://www.pillarpointelectronics.com/kits.html

These sensors are used fairly widely in the Glasair Glastar/Sportsman fleet. If you think there is lots of gnashing of teeth and hand wringing over fuel management here in the RV world, with only two tanks to choose from, you'd go nuts with a Glastar (with long range fuel) or Sportsman with its 4 fuel tanks and 2 header tanks! :-)

For those who are curious... The low fuel sensor is often installed between the Aux and Main fuel tanks in each wing. Aux holds 10 gallons, main holds 15, so 25 gallons in each wing. The only way fuel gets from the Aux to the Main is by actuating an electric transfer pump. Since many of the Aux tank installations have no fuel quantity gauge one has to rely on timing the run-time of the transfer pumps. Fly on a main tank for an hour or so, then pump from the Aux tank to the Main tank and monitor the main tank fuel gauge to ensure fuel is transferring. Pretty simple. The optical fuel sensor is used to automatically turn off the transfer pump so it doesn't burn out by pumping air instead of fuel.

Header tanks are installed below each wing root to ensure unporting a tank, especially in a prolonged, steep descent, is a non-event. Fuel pickups are in the aft end of the main tanks so a prolonged nose-low condition could cause unporting if there is very little fuel in the tanks. The half gallon or so in the header tank ensures the engine keeps running.

[tomww]

Originally Posted by myrv6180

I took off one cold morning after a hard rain the night before and ran one tank nearly dry then switched to the other tank which showed plenty on my gauge. After switching tanks and about 15 seconds, ca-chug. She quit, yawing hard because I was in a climb. I immediately lowered the nose and switched to the previous tank and turned on the aux pump and after a long while the engine caught back up and I made it back to the airport. Don't ever run a tank dry!!!! If I had run mine dry I would have had to crash land in the mountains. Always have an out if you want to live to fly 52 years as I have. Turns out my fuel cap had leaked water into the tank the night before and then froze before morning blocking the fuel pickup.

Maybe if you wish to continue your run past 52 years you could invest in a fuel tester cup. Then you can check for water in the tank. This might even be an obvious thing to do when it hasn't been raining a lot. The other thing that might extend your life expectancy would be to check both tanks on the ground.

[rv8ch]

Originally Posted by tomww

...The other thing that might extend your life expectancy would be to check both tanks on the ground.

I may be interpreting what was written, but it sounds like the water froze in the tank, so testing the fuel might not have picked this up. I could be wrong of course. It's something that I don't believe I've ever experienced, but will keep an eye out for.