Hi Peter,PCH wrote: ↑Mon Mar 11, 2024 6:23 pmThe problem as I see it is this (and it affects both left and right fuel tanks): a climb out (say maximum performance take off) with 1/3 of a tank or less fuel unports the front fuel uptake. A climb (and perhaps a turn out) enhances the rear fuel line low point that occurs beneath the rear part of the door. On my 220C, fuel tank was pressurized by the forward facing air vent on top of the fuel cap. The pressurized air then rushes down the unported front fuel take-up blocking fuel from entering the line from the rear line. The air continues down the path of least resistance into the carburetor. The resulting engine stoppage is abrupt and sudden. Note that all this happened to me as I was on the left tank.
Safe flying to all!
Peter
I'm not an engineer, but I'm not sure this theory works. If the front pickup is un-ported, the fuel level in the front line should still be level with the rest of the fuel in the tank. And as far as the tank being pressurized, that pressure is also acting on the fuel that's remaining in the tank, meaning both pickup points have equal pressure on them, the front just has fuel further down inside the fuel line. The only time the engine would start sucking air is when the fuel level in the lines gets to the same level as the fuel valve.
Think of a closed, circular manometer with a T at the top and a restricted T at about the 4-5 o'clock position. If you fill it half way with a fluid, you can pressurize it from the top T and rotate it, and the fluid will remain level between the two tubes. But if you get the lower T above the fluid level, it will start blowing air.
Likewise, if you have one dry tank, the other has 10 gallons in it, and your fuel selector is on "both", will your engine suck air? I don't think so- the weight of the 10 gallons of gas is going to push the air back to the empty tank (assuming everything is flowing properly).
Your original post caught my attention because during the course of my rebuild, and getting ready to start my engine for the first time, I put 5 gallons in my left tank, but didn't get any fuel flow into the gascolator. I assumed the system would self prime from the weight of the fuel. It wouldn't flow until I opened up the bottom sump drain and "burped" the system, then suddenly the fuel rushed through the selector valve and filled the gascolator. I'm still not totally clear as to what's going on there.