Aircraft fuel: POUNDS vs. GALLONS

I'm Brodie Brazil, Commercial Pilot & Certified Flight Instructor.
On this channel, I'll share the best tips & tricks for learning how to become a better pilot.
IN THIS VIDEO: Why do some aircraft measure fuel in pounds, while others stick to gallons?
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** I am a licensed FAA Flight Instructor, but in this video, not acting as YOUR flight instructor. None of the content presented here should supersede your ACTUAL flight training. **
#aviation #flying #airplane

[@BigDougJeeps]

Found the answer to a question I had. Thanks. Been watching you with the Sharks for years. Who knew you were a pilot too. I fly at KLVK. See ya!

[@fivestringslinger]

I have to present a correction. The vent tube under the wing is actually what prevents a vacuum from developing in the tank. That's why it's critical to check the vent tube for blockage during your preflight, or you could end up in a fuel starvation situation. That's why it's also common in gravity fed aircraft like the high-wing Cessna family for the left tank to draw faster than the right even with the selector on "BOTH". It's common for fuel to leak from the vent tube when it expands, but that's not the purpose.
I can also speak from the line tech side of things back before I moved into the shop as an A&P apprentice. Most crews were pretty good about placing their fuel order in gallons for us and doing the calculations themselves. But I've had to explain to several pilots that I can't (per policy) do the calculation for them and that we could only accept their order in gallons, unless they requested a full top-off. The only exception is if the aircraft had a fuel panel where you could set a target fuel weight, begin pumping and the valves would stop flow when you hit the target.
For sports team charters when we would have to go and fuel a 737 tended to involve a lot of math. Inside the single point panel is a control panel with an open/close switch and a display for each wing tank and the belly tank. It displays in pounds (or sometimes kilograms), and we would get a sheet with their fuel request. It was up to us to divide the load 25% to each wing and 50% to the belly tank, and pay close attention during the fueling process and close the valves accordingly.

[@BrodieAviation]

good info on fueling, I appreciate that firsthand perspective of it!.
going back to the vent/vacuum thing... it's always been my understanding on Cessna & pipers that the fuel CAP itself had a discrete vent so that air could enter and replace the displaced fuel inside the tank. is that not accurate? would make more sense on the upper camber of the wing. the vent on the bottom is definitely partially for excess drainage, you wouldn't want that leaking out the top side of a wing.
thanks for being here on the channel!

[@fivestringslinger]

@@BrodieAviation Of course! My flight experience (and the bulk of my growing systems knowledge) is primarily with Cessna aircraft so I can't speak with authority on Piper. But I do know that the vent tube on high wing Cessna aircraft behind the left wing strut is the primary tank vent. They provide a positive pressure within the tank, and the two tanks are connected by a crossover that runs over the windscreen. The vented caps are a failsafe (as an example see AD 79-10-14 R1) in case the vent tube or valve becomes obstructed.

[@TheJdiggety]

5:10 - Water is denser than fuel. Did you mean “if” there is water in the tanks, the water would sink and not the fuel?
Because when (preflight) sumping, you would find possible water at to the bottom of the tank, making it easier to sump the water out of the tanks.