CFI Pop Quiz #321 - Dry

[Chris Burgess]

Running a fuel tank dry before switching tanks is not a good practice because

A) any foreign matter in the tank will be pumped into the fuel system.
B) the engine-driven fuel pump is lubricated by fuel and operating on a dry tank may cause pump failure.
C) the engine-driven fuel pump or electric fuel boost pump draw air into the fuel system and cause vapor lock.

[Paul_Zurawski]

C sounds good, but I know B is right....(B)

[B8MFlorida]

Bravo..................
As for "A" foriegn matter does not always settle on the bottom of the tank(s)
As for "C" Vapor lock is defined as gas boiling/bubbling in the lines thus preventing free flowing fuel.
This is how I deduced my answer and I'm sticking to it!

[mceagle]

"a".............

[EI-GYRO]

All of the above, with varying degrees of likelyhood. ??

Also, if the engine stops, can anyone recommend a good in-flight
hand-propping procedure. ??

Furthermore, the absence of a second fuel tank on most gyros should
act to discourage the practice. Yeah, I know, I'm just tired and cranky
tonight.

[Chris Burgess]

There is a "most correct answer"

[Timchick]

B..............

[mceagle]

Can't be "B" because an engine driven pump won't keep operating with a dry tank.
Can't be "C" because you don't get vopour lock from drawing air into the system.

[Chris Burgess]

Most correct, "C". Running a fuel tank dry before switching tanks is not a good practice because (C) the engine-driven fuel pump or electric fuel boost pump draw air into the fuel system and cause vapor lock. Reference FAA-H-8083-25

A) any foreign matter in the tank will be pumped into the fuel system, wrong. Foreign matter will be filtered out by the fuel filter.
B) the engine-driven fuel pump is lubricated by fuel and operating on a dry tank may cause pump failure, wrong. Engine failure will result before damage can be done to the fuel pump.

These are text book explanations from a commercially available study guide.

[Aussie_Paul]

Most correct, "C". Running a fuel tank dry before switching tanks is not a good practice because (C) the engine-driven fuel pump or electric fuel boost pump draw air into the fuel system and cause vapor lock. Reference FAA-H-8083-25

A) any foreign matter in the tank will be pumped into the fuel system, wrong. Foreign matter will be filtered out by the fuel filter.The book is a little incorreect. The foreign matter in the tank will be pumped into the fuel system BUT then filtered by the fuel filter!:D !
B) the engine-driven fuel pump is lubricated by fuel and operating on a dry tank may cause pump failure, wrong. Engine failure will result before damage can be done to the fuel pump.

These are text book explanations from a commercially available study guide.

Oops, sorry, I got a bit carried away!! Back into my "reformed stirrer and trouble maker box!!!!"

One must retain ones sense of humour to survive the "so called experts in the gyroplane field.:rolleyes:

Aussie Paul.:)

[Chris Burgess]

Aussie Paul, some tanks have a strainer of sorts mounted inside the tank to stop the "foreign matter" from entering the fuel lines. Then also, many tanks have unusable fuel in them, and/or a low spot in the tank. The junk (foreign matter) lies on the bottom of that "low spot". I vacuum the bottom of my tank when ever I see "junk" laying there. ooHH, ooHH, don't use a match to look!!!

OK, I agree, this one could be argued, but "most correct" rules.

[B8MFlorida]

Whoo-whoo-Tell 'em what they won Johnny!

[mceagle]

Paul = "any foreign matter in the tank will be pumped into the fuel system, wrong. Foreign matter will be filtered out by the fuel filter" Paul, the fuel filter is part of the fuel system.

Please note - my opinion only - a dry tank does not cause vapor lock, it simply causes air in the lines that is purged when the tank is switched over.

Vapor lock is caused when atmospheric pressure is reduced enough for the fuel to vaporize into a gas. It is dependant on two main factors, the lift head for the pump, (the greater the head, the lower the pressure) and the fuel temperature, (the higher the temperature, the more readily the fuel will vaporize). Thus the time most likley to get vapor lock would be with a large decrease in pressure (from high head or restriction) and on a hot day.
The main problem with vapor lock is that it will not go away unless one of the requirements is changed, unlike air due to a dry tank, which will go away as soon as you switch tanks.

[Aussie_Paul]

Paul = "any foreign matter in the tank will be pumped into the fuel system, wrong. Foreign matter will be filtered out by the fuel filter" Paul, the fuel filter is part of the fuel system.

Please note - my opinion only - a dry tank does not cause vapor lock, it simply causes air in the lines that is purged when the tank is switched over.

Vapor lock is caused when atmospheric pressure is reduced enough for the fuel to vaporize into a gas. It is dependant on two main factors, the lift head for the pump, (the greater the head, the lower the pressure) and the fuel temperature, (the higher the temperature, the more readily the fuel will vaporize). Thus the time most likley to get vapor lock would be with a large decrease in pressure (from high head or restriction) and on a hot day.
The main problem with vapor lock is that it will not go away unless one of the requirements is changed, unlike air due to a dry tank, which will go away as soon as you switch tanks.

Agreed Tim.

I hate this most correct answer "poo" There should be one correct answer and some almost correct and 1 way of the beam.

Aussie Paul.:)

[Chris Burgess]

Story time. "Once upon a time", I ran a tank dry. The engine quit so I switched tanks, set the throttle, and went for the restart. No go. Checked all the settings and switches. Tried again, no go. Now it's time to complete the autorotation to the ground rather than botch it trying for the restart. Soon as I got on the ground and stopped, the engine was restarted without any trouble. I think the carburetor was empty, the pump dry and it took that amount of time for everything to reprime, fill, and fire. "And they lived happily ever after" :o

[birdy]

No time is a good time for me to switch tanks, coz me other tank is on the ground.