3 ms·

Is "thousands" of gallons even remotely accurate? The numbers I can find are that a 747 uses 1 gal/second, so a single excess 5-hour flight is like 18,000 gall

Is "thousands" of gallons even remotely accurate? The numbers I can find are that a 747 uses 1 gal/second, so a single excess 5-hour flight is like 18,000 gallons. Even a ~45% efficiency reduction on that for more modern planes gives 10,000 gallons per excess flight. Multiply that by however many excess flights per airline per day and then by many airlines are doing this (I dunno, let's say 5 flights for 5 airlines? though this feels generous) and suddenly you have like 250,000 gallons/day being wasted per day. Multiplied by however many days they're doing this (idk, 10? though that also sounds generous) that's already like 2.5 million gallons every couple of weeks. Did they mean "millions"?

labawi 7y ago
Generalizing total plane consumption from instantaneous consumption doesn't seem like a good idea. Their engines have high dynamic range between take-off, climb, steady flight and glide. 4.5l/s (1gal/s) seem like a lot, would that be take-off/climb consumption? Then again, a 747 is huge and usually heavy, carrying a lot of people and cargo..
- mehrdadn 7y ago
  I mean, if you're aware of more accurate numbers, I'm all ears. These are just the numbers I was able to find, and I doubt that I'm off by 100x-1000x.
  - labawi 7y ago
    I think the instantaneous fuel consumption at take-off vs. a very long glide down could in fact be 1000x, but is at least 100x. So I ask, what do your numbers represent? EDIT: "747-400 has eight fuel tanks, with a combined capacity of 57,164 gallons of Jet-A fuel"[1]. So around 30-40k gal for a typical trans-oceanic flight? Meaning 1 gal per 1 second of flight time should be within order of magnitude, but far from take-off or peak consumption. [1] http://www.boeing-747.com/boeing-747-internals/fuel-system.html http://www.boeing-747.com/boeing-747-internals/fuel-system.h...
    - mehrdadn 7y ago
      > So I ask, what do your numbers represent? And I said, it's right there if you actually take 5 seconds to Google. Literally the top result [1] says [2] that for a medium-haul flight (3,240–6,300 km), a 747-800 burns 9.9 kg/km of fuel, which at 917 km/h and 0.81 kg/L density, comes out to 0.82 gal/s if I'm doing my math correctly. So I guess my bad for being off by a whopping... 20%? Like I said, I'm all ears if you have better numbers, but it's quite inconsiderate to just casually dismiss what people say with so little effort and force them to spend 20 minutes to respond. [1] https://www.google.com/search?q=plane+fuel+consumption https://www.google.com/search?q=plane+fuel+consumption [2] https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Medium-haul_flights https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Mediu...
      - senordevnyc 7y ago
        I mean, didn’t this entire thread start because you took issue with the word “thousands” in the headline, even though it’s technically correct? :)
        maxfan8 7y ago
        It sounded like dataflow was doing a Fermi estimate, which usually need to be within one order of magnitude of the real answer to be considered decent. I think the reason why they didn’t like the headline was because it seemed like it was several orders of magnitude off.

labawi 7y ago

Generalizing total plane consumption from instantaneous consumption doesn't seem like a good idea. Their engines have high dynamic range between take-off, climb, steady flight and glide. 4.5l/s (1gal/s) seem like a lot, would that be take-off/climb consumption? Then again, a 747 is huge and usually heavy, carrying a lot of people and cargo..

mehrdadn 7y ago
I mean, if you're aware of more accurate numbers, I'm all ears. These are just the numbers I was able to find, and I doubt that I'm off by 100x-1000x.
- labawi 7y ago
  I think the instantaneous fuel consumption at take-off vs. a very long glide down could in fact be 1000x, but is at least 100x. So I ask, what do your numbers represent? EDIT: "747-400 has eight fuel tanks, with a combined capacity of 57,164 gallons of Jet-A fuel"[1]. So around 30-40k gal for a typical trans-oceanic flight? Meaning 1 gal per 1 second of flight time should be within order of magnitude, but far from take-off or peak consumption. [1] http://www.boeing-747.com/boeing-747-internals/fuel-system.html http://www.boeing-747.com/boeing-747-internals/fuel-system.h...
  - mehrdadn 7y ago
    > So I ask, what do your numbers represent? And I said, it's right there if you actually take 5 seconds to Google. Literally the top result [1] says [2] that for a medium-haul flight (3,240–6,300 km), a 747-800 burns 9.9 kg/km of fuel, which at 917 km/h and 0.81 kg/L density, comes out to 0.82 gal/s if I'm doing my math correctly. So I guess my bad for being off by a whopping... 20%? Like I said, I'm all ears if you have better numbers, but it's quite inconsiderate to just casually dismiss what people say with so little effort and force them to spend 20 minutes to respond. [1] https://www.google.com/search?q=plane+fuel+consumption https://www.google.com/search?q=plane+fuel+consumption [2] https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Medium-haul_flights https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Mediu...
    - senordevnyc 7y ago
      I mean, didn’t this entire thread start because you took issue with the word “thousands” in the headline, even though it’s technically correct? :)
      - maxfan8 7y ago
        It sounded like dataflow was doing a Fermi estimate, which usually need to be within one order of magnitude of the real answer to be considered decent. I think the reason why they didn’t like the headline was because it seemed like it was several orders of magnitude off.