why isn't fuel delivered in KG

[aslan1982]

Anyone know why fuel from a browser delivers in liters when we use KG.

I know that a liter is a volume and is temperature dependent so 10 liters at 30 deg would be less at 10 degrees.

But it doesn't vary in weight and thats why we use KG so why don't they deliver to us in terms of KG.

Has it something to do with cost per liter

[IO540]

It could be because the metering systems are all volume/displacement based and thus measure volume (litres) and not mass (kg).

At proper airports, the temperature of the fuel is written down on the receipt, anyway.

To deliver a given power, the engine (assuming LOP) will be burning a mass flow, not volume flow.

But thermal expansion of avgas is only 0.1% per degC, so the effect of temperature is not really possible to notice unless one has a fuel totaliser (Shadin type of thing) and is filling up from a pump which is definitely known to be accurate (OK in the UK and N Europe but the airport pump accuracy degrades progressively as one goes south) and flies between two places with widely differing ground/fuel delivery temperatures. The most extreme case possible is something like a N European departure after an overnight soak at -10C, then the tanks are topped off, and then you fly to Greece where the delivery temperature (after ground soak in the tanks) might be +35C. That's a 4.5% change. But you won't find an airport pump in Greece which you can trust to show a 4.5% change :) I know this - I've been doing this for 8 years.

[BackPacker]

Anyone know why fuel from a browser delivers in liters when we use KG.

Depending on the type of aircraft, the location you're in and the purpose, you might be measuring fuel in any of the following quantities:
- pounds
- kilograms
- tonnes
- liters
- US gallons

Gotta learn how to deal with this anyhow.

Also note that the specific mass of Jet-A is different from 100LL, but I have not yet found a manual flight computer that will have the markings for that.

[worrab]

Anyone know why fuel from a browser delivers in liters when we use KG.
Extreeeeemely difficult to measure mass directly on a continuous flow. (Fairly difficult to measure volume accurately for that matter).

[IO540]

I think coriolis mass flow meters can be accurate to a fraction of 1%. They are not cheap though. And nowhere near as primitive and robust as the displacement meters used on bowsers etc.

Whether this is good enough for Weights & Measures I don't know. I vaguely recall the UK regs require 0.2% volume accuracy.

[mm_flynn]

... but I have not yet found a manual flight computer that will have the markings for that.


It would be a very blurry marking as Jet fuel has quite a range of specific gravities compared to avgas