It's actually the density of the fuel that varies with temp, not the volume. Usually roughly around the 0.800kg/m3 (0.8 of a kilo to each metre cubed gross volume) at 15 degrees Celcius. You could for example pump 100 gallons (379 litres) of liquid into the tanks one morning and then do the same the next morning. Both mornings, you would add a volume of 100 gallons into the tanks, but dependant on ambiant temperatures, may have a denser volume of liquid (if the ambiant temp was cooler than the previous morning), thus increasing the overall ramp/operating weight of the aircraft in relation to the uplifted volume of liquid. In short, two equal volumes of fuel may have a varying mass.
Commercially speaking, lbs tend to be used these days only with older Boeing (or other US manufacturer's older airframes) aircraft, which of course, the B-52 is one of. Most modern commercial and military aircraft universally use Kilograms now, even when airframe is of American origin. Load and Trim sheets are all produced in a Kg format, along with the direct effect an increase of kgs would have on the aircraft's Mean Aerodynamic Chord. Whilst some combined lbs/kgs calclations are required (the Boeing 747-400F was the most recent airframe and last type that I encountered this on...and bloody annoying it is too!), it's much safer for the Load Masters and Load Controllers of such aircraft to be able to stick to one universal weight format.
There was an incident some years ago where an Air Transat Airbus ran out of fuel midflight (luckily, the driver was something of an old hand and managed to GLIDE it for 20 mins off his NAT Track and into his ETOP routing alternate on the Azures). The reason it ran out of fuel was because the planner had completed the aircraft's Loadsheet in kgs, but had calculated the fuel in lbs. Working out that the aircraft would have a fuel uplift of a certain number of kgs, somewhere along the line, the same figure was used for transferring the fuel to the tanks...except that the number used was actually lbs, not kgs...meaning that didn't even have half of the fuel uplift the pilot's thought they had in tanks.
We'll keep the Red Flag flying high,
Cos Man United will never die!
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normadamous
13 years ago
OUICH !!
the metric/fractional issue always crops up, doesn't it? NASA crashed an experiment in to the backside of Mars a few years back for the same reason.
Some day hopefully the US will switch over to SI units. (i quite often convert all my values to M-K-S units to do calculations then convert them back at the end -- slugs? really?!)
(of course, you're right about the density being the variable w/temp -- i was thinking of a fixed quanitity of fuel that then expanded or contracted w/temp.)
I guess kg/lbs does make more sense, then than liters/gallons since density changes with the temperature -- now I know...
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Talking monkey, yeah, yeah. Came here from the future, ugly sucker, only says "ficus"
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