OT: Aircraft Fuel in Pounds Instead of Gallons?

A Kilogram is a unit of mass, not weight.

The international standard is kilograms. You'll have to look up who follows the standard and who doesn't.

For a good message posted on other newsgroups discussing the ICAO standards in various aspects of aviation, see Message-ID: which you can find at

snipped-for-privacy@posting.google.com&lr=&hl=en

Gene Nygaard

snipped-for-privacy@posting.google.com&lr=&hl=en

"International Standards" don't always hold up - as a former engine component designer, I can attest that specific fuel consumption for a jet engine is measuured (and designed for) in lbm/lbf/hour. In general, aircraft designers use British units, missile designers use Metric units. I can't say why, but that's generally how it is.

From the standpoint of operating the aircraft, as many have pointed out total gross weight is critical - especially in the case of a VTOL aircraft (like a Harrier) or any aircraft which may eject a payload (most combat aircraft can take off heavier than they can land)...anyway, for aircraft the only standard I've encountered in industry (or in a flight manual) is pounds, pounds/hour, pounds gross weight, etc.

Nope, one kilo of pure water is always one litre in volume regardless of the gravity field it is in, not so with a pound of water, that is going to vary in volume depending on the gravity field it is inso a pound of water on Earth is not going to weigh one pound on the moon, it will mass the same but not weigh the same.......one is mass, the other is weight.

Kilograms force units are Newt>

False. First, "kilo" is not an acceptable abbreviation for kilogram in the modern metric system, SI.

Second, the density of water depends greatly on temperature.

Third, that was true when the litre or liter was defined that way from 1901 (and not earlier, despite Lodder's claims) until 1964.

However, as the liter is now defined, water at its maximum density is

0.999972 kg/l, and it is less at any other temperature. It never crosses that 1.000000 kg/l line. Yes, it gets to 1.0000 kg/l if that's all the precision you use, for a limited range of temperatures.

You are correct that this density is pretty much independent of the strength of the local gravitational field. That doesn't, however, derive from the definition of a kilogram, nor does it prove the nonexistence of kilograms force.

Fools who want to use Fred Flintstone units ought to be required to first pass a proficiency test, showing that they understand them.

Didn't look up those official definitions of the pound I pointed you to, did you? I think these are both the same document, the current U.S. definition, which refers both to the earlier U.S. definition and also to the international agreement among the national standards laboratories of the U.S., Canada, the U.K., South Africa, Australia, and New Zealand. These avoirdupois pounds are exactly 0.45359237 kg by definition.

Since you didn't do that, you also proved the point that I directed you properly to this page. Turn up your speaker volume and go study it until you understand it: The maximum density of water is 62.4262 lb/ft³ at the North Pole, and it is 62.4262 lb/ft³ at sea level at the equator, and it is 62.4262 lb/ft³ atop Mt. Chimborazo, the highest mountain on Earth, and as long as you can keep it liquid it is 62.4262 lb/ft³ on the moon.

The amount of force that this much water exerts due to gravity varies with the strength of the local gravitational field. You can measure this force in pounds force, a recent spinoff from pounds. The pound force is so new that it is uniquely identified by that name--of all the hundreds of different pounds used at various times and places throughout history, only one of them has given rise to a force unit of the same name that has seen any significant use. The pound force was never a well defined unit before the 20th century, and even today it doesn't have an official definition.

That cubic foot of water at maximum density will exert a force of about 62.259 lbf at normal gravity at sea level at the equator (local anomalies will cause this to vary slightly at various places along the equator), and 62.589 lbf at sea level at the poles and about 62.13 or

62.14 lbf atop Mt. Chimborazo (don't have precise values for there). It might be 10.4 lbf/ft³ at some place on the moon, but nobody measures water in those units on Earth so we wouldn't do so on the moon either.

A kilogram force is exactly 9.80665 newtons (not capitalized in English).

That's little g, not big G. But what's a one g field? How precisely do you know it? This g, the local acceleration of gravity, varies by

0.53% even if you limit yourself to SEA LEVEL ON EARTH.

In order to have a well-defined pound force, you need to specify some standard acceleration of free fall to use for this purpose. That's something that was never done until around the turn of the 20th century, the time when the CGPM in 1901 officially defined grams force using 980.665 cm/s² for this purpose. Nobody has ever officially chosen such a value to use for defining pounds force, though one of the values often used is the one which is official for defining grams force (however, others such as 32.16 ft/s² are also used).

The pound foot is a normally a unit of torque, not of force. A foot pound is either a unit of torque, or a unit of work or energy.

Why didn't you address this, Ron? It could have showed you exactly where most of your errors lie--an utter failure to understand the simple linguistics fact that "weight" is an ambiguous word, one with more than one meaning.

Gene Nygaard

Gentlemen of the jury, Chicolini here may look like an idiot, and sound like an idiot, but don't let that fool you: He really is an idiot. Groucho Marx

Reminds me of an interesting story from a few years ago. An Air Canada Airbus had a new for the time glass cockpit. Unfortunately, the fuel guages weren't working, and the fuel load was measured on the ground with a dipstick. Apparently, between the pilot and the groundcrew, there was a slipup between English/Metric, and the pilot took off thinking he had about twice as much fuel as he really had. Luckily, he was able to set the plane down at an abandoned airport when the engines quit. Kim M

Operation American Freedom-Where is our regime change?

In snipped-for-privacy@mb-m27.aol.com, Royabulgaf posted this drivel:

A made-for-tv-movie was made out of this story (_Falling from the Sky: Flight 174_) ... The fuel measurement system wasn't working, so the ground crew had converted from pounds to liter, while the flight crew were in a Boeing B-767-233ER, the first Air Canada model that measured the fuel in KILOS, and the flight crew used kilo to liter conversion. The result was that the flight crew had less than half the fuel it thought it had. The incident occurred 23 Jul 1983.

Similar situation with NASA Mars probe...

-- Doug Semler I hate spam, standard email address munging applied.

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Dang this is complicated! Just to confuse the subject, the fuel guys tell me that the lb. is the preferred measure of fuel since a lb in Kuwait is a lb in Newfoundland but gallons vary with temp and altitude. Therefore, when you put X000 lbs of fuel into an F16, you don't have to take temp and altitude into consideration.

Fuel is delivered and priced by volume. The units depend on whether the airport is in a metric country. Kuwait delivers fuel in litres. I do not know about Newfoundland.

Fuel weight is obtained from volume by local calculation. The units depend on the choice of the captain. Aircraft operated by US airlines use lb, most others use kg.

The main interest in the weight of fuel is because the weight and balance of an aircraft are critical to safe and efficient performance. Some smaller aircraft have displays in volume units (gallons or litres) and do not have displays of weight units.

No, actually by "standard volume" in most cases--that is, the volume it would have at some specified temperature. The delivery pumps usually include automatic temperature correction.

So this "standard volume" together with the identification of a particular kind of fuel (density varies with different types) is really equivalent to a measurement of mass.

Litres also. At the time of the "Gimli glider" incident, it was imperial gallons in Canada. But in that case, the improbable, unending pile of errors after the inoperative fuel gauge included conversions between U.S. gallons (for a Canadian airline on a domestic flight) and litres, as well as pounds and kilograms, and inches and centimetres on the dripstick and the tables for interpreting that measurement.

The conversion factor depends on the type of fuel--but not on the temperature, if fuel were priced and delivered on the basis of ambient temperature.

These kilograms are, of course, the proper SI units for this "weight"--and that's something a lot of people have difficulty getting a handle on, the simple linguistics fact that weight is an ambiguous word with more than one meaning. Of course, these kilograms are units of mass; the once acceptable kilograms force are NOT a part of the modern metric system, the International System of Units. Of course, the pounds used in some places are also units of mass, legally defined as 0.45359237 kg.

"Mass balance" is another relevant term, helping you understand the meaning of "weight" in this case.

Gene Nygaard

I believe it was a Boeing 767, or did it happen more than once?