Fuel Caps

[Scouter]

Jerry:

Can you explain why the fuel tank caps on Citabrias are not vented? I understand how the underwing vent works. I had a sucking sound the other day on the right tank when it was gassed, and found a plugged vent cross over tube. If the left tank had run dry, I wondered if any gas would come from the tank that had the vacuum. I thought maybe vented caps would prevent this, but have never seen any of these planes with vented caps. How come? The inverted work of Decathalons make sense to me to be unvented caps.

Jim

 

[jerrymjr]

Vented caps only work if its ram air vent. Which then leads to moisture in the tank.

The placement of the filler neck on the 4412 wing for the airplane is such that localized pressure is always quite a but under ambiant pressure and will thus always make a vacuum....sucking gas out of the tank and into the sky.

With the current ram air vent, you greatly reduce the vent flowing gas out of it instead of into it. The extra pressure from the ram air isn't really needed in a high wing, but it cant hurt.

Odds are you would still get your gas from the other tank. It would not have the static head pressure of the tank that went dry, but should have been plenty to feed the engine. Its not an option most people like to test though :lol: