Why is aircraft fuel measured in pounds rather than in gallons?

 

Isn't it because they have so many Weight related things to consider and using weight co-oincides with everything else.

Could you image the mixup if the volume was short ?

EDIT:

I found this because I too want to know

http://www.aviationtoday.com/sia/20010401.htm

 

Aircraft are carefully balanced before and during flight, and relaying the amount of fuel in pounds rather than gallons makes it easier to relate it to other cargo. Not all aircraft use weight, actually the old Cessna I flew in flight school had a regular old guage, just E-F.
Scott

 

Well, a pound weighs a pound no matter what.

But a gallon of fuel (Jet-A for example) can weigh anywhere from 6.3 to 7.0 pounds, depending upon the fuel density. And when you're fueling up with 9,000 gallons of fuel, that can mean a huge difference in the actual weight the plane is carrying. There are times when passengers have to be bumped because the fuel requirement is so great, it can't carry both.

The standard weight for a gallon of Jet-A is 6.7 pounds per gallon.

 

I think you got it. A pound is a pound no matter what. Won't temperature affect the density the most? Like the density is more in a cold area like Alaska than say somewhere warm like Florida?

 

For small aircraft, it's still measured in gallons. Same car style of pump that counts out the dollars and the gallons. Balance is everything when flying even in a little Cessna. It is amazing to feel the difference when you load the plane. You want a smoother landing? Load the weight towards the rear and you may not have to correct the trim wheel.

Too much weight in the back and the aircraft may not have enough control surface to correct for the nose high attitude - resulting in a stall that may not be recoverable, i.e, you crash in uncontrolled flight.

Controlled flight is Good!

Aircraft are limited by their control surfaces, think of them as the traction your tire provides to your truck. Too little is a bad thing as can be too much.

For an airplane that is loaded to max load, everything must be right. A little thing like frost on the wing can spoil enough lift that the plane cannot get airborne. Remember the Concord crash? They crashed in part because they could not raise the landing gear and so could not keep accelerating to a flyable speed. The fire did not help either. But if they could've raised the gear, they could've kept flying.

 

Right-
When your center of gravity is forward, the plane is less stable(by stable I mean flies in a straighter pattern automatically), yet more controllable(more reactive to your controls), but when your center of gravity is rear, the plane is more stable, but less reactive. A forward COG also allows slightly faster airspeeds in small aircraft.
Scott

 

FWIW, you can calculate the weight of a gallon of fluid by first finding out the specific gravity of the fluid. You can find the specific gravity listed on product spec sheets, MSDS, Bill of Lading etc... or use a hydrometer. Multiply the specific gravity by 8.34 (the weight of a gallon of water) to calculate the weight of the fluid.

Example: Using the example for Jet A above, the specific gravity of Jet A would be .803. Multiply by 8.34 and the rounded up weight of Jet A is 6.7 pounds per gallon.

Water is assigned the specific gravity of 1.0.

 

First off your car/truck does'nt measue in gallons, only the gas station pump does, your car measures the volume of the fuel in the tank F 1/2 E.
They(Large aircraft) measure in pounds for proper indication in flight. The only reason a gallon of fuels weight varies is that it expands and contracts with temp, so one gallon of fuel pumped on a 90 deg day is lighter than a gallon of fuel pumped on a colder day. (Example) Fill up a small gas can half way and weigh it on a cool morning set it out in the hot sun by the afternoon it expands and you have more in the can now, but its the same weight!
Now on a large aircraft mulitply that expansion amount by 10,000, (average fill for an international flight) and if you measured the fuel tanks by volume the tank would read full on the ground get up to altituide of 20,000ft and its -60f and it apperars a 1/4 of you fuel is gone, get back on the ground were it is warmer and it comes back not good way measure the fuel quanity.
A certain weight of fuel 10lbs has a set amount of energy in it weather that 10lbs is expanded or contracted. So you can fill your car up in the morning and drive to work and in the afternoon your fuel will expand in your tank and you will have a full tank again however the fuel is less dense thus you will burn more of it on the way home and when it contracts overnight your fuel gauge reads the decreased volume. So if you buy cold fuel you get more "bang for the buck"(no pun intended)
Hope that explains it. Sorry for the lengthy response. BTW I'm not a Pilot Just the guy that repairs the Aircraft.