Comment by rappatic
4 days ago
> the Boeing 737-800 had just 220kg of fuel left in its tanks... enough for just five or six minutes of flying
Maybe I'm just unaware, but it's crazy to me that these planes burn 40 kilograms of jet fuel per minute.
4 days ago
> the Boeing 737-800 had just 220kg of fuel left in its tanks... enough for just five or six minutes of flying
Maybe I'm just unaware, but it's crazy to me that these planes burn 40 kilograms of jet fuel per minute.
I don’t think that’s so much? A car burns 1 liter to travel 15 kilometer’ish, and carries 4 people.
An airplane burns 40 liters to travel 15 kilometers too (900 kph), but carries 160 people.
That’s about 40x more than the car, so the fuel economy per passenger is about the same.
Of course jet fuel is probably a bit more polluting, but it’s still interesting how close it is.
The greenhouse effects of flying is about 3-5x the effect of just burning the fuel.
Could you explain why this is?
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What do you mean by this? What else than burning the fuel contributes to the greenhouse effect?
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In commercial aviation (passenger/cargo), typically about half the take-off weight is fuel. That's not half the payload weight (pax + cargo + fuel), it's half the takeoff weight.
For a medium-range flight (say ~2000 mi / 3200 km) each passenger incurs somewhat more than their own weight in fuel.
I don't think that's correct. The MTOW (Maximum Take-Off Weight) of an A320ceo is 78,000 kg, while the max fuel capacity is approximately 24,210 litres. Using Jet A-1's density of roughly 0.804 kg/L, that's about 19,460 kg of fuel, which represents only 25% of the take-off weight. The OEW (Operating Empty Weight) for that aircraft is approximately 42,600 kg, which means you'd need the fuel to weigh around 35,400 kg for your "half the take-off weight is fuel" claim to be true—nearly double the actual fuel capacity.
Even for a long-range aircraft like the A350-900, with an MTOW of 280,000 kg and a fuel capacity of approximately 138,000 litres (roughly 111,000 kg at 0.804 kg/L), fuel represents about 40% of the take-off weight. The OEW is approximately 155,000 kg, meaning even a completely empty plane (except for crew) loaded with maximum fuel still wouldn't reach your claimed 50% fuel fraction.
Yeah, when people say "flying has a high carbon footprint", they're not kidding. It's really quite massive.
I don't fly any more.
Want to bake your noodle?
Because the market responds to your behavior by slightly lowering the cost of flying to fill those seats, demand increases to match from slightly lower income people. Because they then organize their lives slightly more around cheap flights, it gets even harder to lower the impact of flying.
Paradoxically, rich people like us (you're a tech worker too...) flying more, because we're less sensitive to price, leave more room for pricing in carbon reduction strategies in the tickets/taxes. If you have more seats from the lower end of the market... you don't have as much flexibility in solutions.
Which is a strong argument for a carbon tax on (fossil) fuels. Indexed to consumption over greenhouse gas emissions targets.
Taxes are one way to make markets internalise externalities.
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That might be true within a certain band, but if enough people stop flying, there's only so much elasticity there. Eventually they stop flying as many planes.
(Of course, subsidies probably throw a wrench in all of this.)
> leave more room for pricing in carbon reduction strategies in the tickets/taxes
that is politically driven and has nothing to do with whether rich or poor bums are on seats.
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Clearly you have thought a lot about carbon reduction, so I have a question for you.
Is a plug in hybrid or EV less polluting if you don’t have rooftop solar?
edit: I think I know the general answer, but I’m splitting hairs comparing a replacement car for an ICE vehicle that I have.
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Don't look up the carbon footprint of driving then. That is even higher in comparison to most passenger flights.
The data on https://ourworldindata.org/travel-carbon-footprint disagrees, do you have a source?
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Well, I don't drive either, except for a longer distance trip once or twice a year...
Especially crazy considering the 737 is not a particularly large commercial aircraft.
40kg/minute is around 12 gallons (47 liters) of fuel per minute. Meanwhile a 777 burns around 42 gallons (160 liters) per minute. A 747 burns 63 gallons (240 liters) per minute - more than a gallon per second!
Is that at cruising altitude?
Yes
Each of the four F1 engines on the Saturn V burned 1.8 metric tonnes of liquid oxygen and 0.8 tonnes of rocket fuel every second.
And each engine's propellant pumps required 55,000 HP to deliver that propellant.
40kg of fuel per minute is a lot but airplanes carry a lot of people.
Web searches suggest a 737-800 gets about 0.5mpg at cruise. With 189 passengers in a one-class layout that’s 95mpg per passenger. With 162 in a two-class layout that’s 81mpg per passenger.
This is better than a single person in a car but four people in a Prius gets 50mpg * 4 = 200 mpg.
This is what vexes me about the lack of emphasis on highway self-driving. Everyone's obsessed with robo taxis.
An overnight trip that's automated could go at 40 mph and get seriously good gas mileage. I mean man with four people would probably get almost 100 miles per gallon.
And this would eliminate a lot of short-range flights
It should be a lot easier to implement than having to worry about a whole class of problems that robo taxis in cities have
Sounds like a train.
The robo taxi links the last few miles to transit.
I recently travelled from my house in Seattle to my office in SF without ever getting in a car. I walked more in the airport than I did anywhere else.
Home -> Walk 11 min -> Metro Bus -> light rail -> SEA -> SF -> BART -> Walk 2 min to Hotel.
Next time I go down I’m going to take Amtrak. I couldn’t this time because it was full. In 2024 360,000 people rode that route on 730 trips for an average of about 500 people per trip. Looks like Amtrak gets between 0.6 and 2mpg. That’s 300mpg to 1000mpg per person which is better than a Prius’ 200mpg at 40mph.
Seattle to SF is 1019 miles. At 40mph that’s 25 hours, which is an hour slower than the Amtrak schedule.
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That is why some people avoid flying for environmental reasons. Planes use crazy amounts of fuel.
Look at it (2.5 t/h) by volume (0.82 kg/L): 3 kL/h (790 gal/h) == 50 L/m (13 gal/m) == 830 mL/s (0.9 qt/s), and then divide the total flow rate by 2 for rate per engine.
Or divide the total by the number of passengers (~189) flying to consider effective fuel economy (per passenger) or 13 kg/pax/h or 3.6 g/pax/s.
They must plan to never land with less than 30 minutes of fuel, or about 1.25 t, and I'd say they should never, ever land with less than 15 minutes in their career during a pan/mayday bingo fuel emergency.
> 40 kilograms of jet fuel per minute.
That is going to vary considerably between cruising and ascending.