Hacker News Reader

Comment by ddalex | Hacker News Reader

Normally for airliners you compare fuel burn per distance per passenger.

At 200 passengers you'd get 2.3 l per 100km per passenger (100 miles per gallon per passenger), in line with a small sedan car.

View on HN

I flew from Ohio to Melbourne back in ~2001. It was CMH-DEN-LAX-MEL. The leg from DEN to LAX was a 747 and there were probably 30 passengers in the entire plane. I was near the back of the plane and it gave me an entirely new perspective of just how much they bend and twist in flight. You could see the walls above the wings sort of bow in when lifting off.

Probably tied with hot air balloons for least efficient transport I've ever taken.

(For the leg from LAX to MEL i had the aisle seat beside the shitter galley in the back. 14 hours of people fanning their farts in my face.)

You should see what a big plane does fully laden.

The fuselage and wing of a cargo jet in turbulence basically "banana" in perpendicular planes.

I flew on a 757 from ORD to ROC years ago as the only passenger on the plane. The flight attendant just came and sat down next to me to do the safety briefing, told me she was sorry but no refreshment service, and then went up front. I didn't see another soul again until we were getting ready to land. That was a very eerie two hours.

I am not able to verify the accuracy of your calculations, but for comparison, Delta circa 2018 marketed how its entire fleet (flying at a pretty high capacity factor) averaged ~44 passenger miles per gallon.

I don’t know how air freight is factored into fuel efficiency calculations, but it has become an increasing part of passenger airlines’ business models in the past decade, too.

(Source: I spent way too much time keeping tabs on Delta as a top level frequent flier)

Personally I think it's useful to use scales & dimensions people already know & grasp. I'm having a hard time combining all the factors you're smooshing together. I haven't figured out- 2.3 what per 100km per passenger? I haven't run any numbers to run that have gotten me 2.3 anythings.

Using my figure, if you want to get per-passenger, if we say it seats 200, we can multiply .217km/l by (1 plane/200 persons) and get 43.4 km/l / person, or, 102mpg/p, which I think most people will understand reasonably intuitively, compared to what they already know. This is indeed a rather impressive claim. It makes me wonder why they don't just call this thing the 100mpg plane, if true.

> Personally I think it's useful to use scales & dimensions people already know & grasp.

To the best of my knowledge, most of the world reports transport efficiency in l/100km. And the poster even nicely included the US-centric mpg value for people in not-most-of-the-world.

Some (most?) regions compare fuel efficiency by how much fuel in liters is needed to travel 100km.

English speaking countries (or at least most of them) usually do it the other way around and compare the distance one can travel by fuel unit.

distance per fuel quantity ~~ efficiency

fuel quantity per distance ~~ inefficiency or cost

The US and UK are probably the only English-speaking countries that measure efficiency in miles per gallon (and not even the same gallon). Everywhere else uses litres per 100 km. I believe my car (2003 VW Jetta TDI diesel) gets about 4.5 L/100 km, which is quite good compared to a typical truck that gets 15+ L/100 km.

Australia and New Zealand only use L/100km, so it's not a language thing.

You weren’t able to divide 1 by 43.4 and multiply by 100 to get 2.3L per 100km?

First I considered that 2.3l/100km is pretty great. But when actually scaling it to full car with 4 persons in it doesn't feel that special anymore about 9.1 l/100km. Which really isn't anything to write home about even in larger sedans.

If fuel economy is your goal, you can take a glider.

A skilled glider pilot can go (slowly) as far as they like with no fuel. The typical limit is when you get tired and need to sleep (gliding can't yet be done well by a computer, because it takes quite some skill to find the necessary thermals and wind currents).

There are also terrain and weather conditions.

Typically it is very hard to glide at night since a large part of gliding is the air movement caused by local and regional thermal differences.

Ardupilot (or one of its offshoots, I can't recall exactly) does have a lift detecting autopilot in beta. I don't know how it works with a specific route, but it seems to lock in thermals pretty well.

Now this is something I'd like to see. A permanent glider, in the sky for years on end. Obviously with humans onboard you'd have to resupply it with food and water.

But with a computer - train ML on human pilot behaviours? - it could stay there for quite some time.

Well, yes, but this doesn't drive on a road at 130km/h, it files through the sky at close to speed of sound

As long as you fill your car with 4 people, then yes it pollutes less.

> At 200 passengers

Unfortunately, most planes fly far from their maximum capacity (even though most passengers are in fact flying in overcrowded planes).

Even that is only a fair comparison when comparing specific routes, as an airliner has the significant penalty of having to carry aloft its own fuel, and therefore becomes less fuel efficient on longer routes.

This doesnt make sense. I divided range by fuel capacity. There's no longer range possible.

Right, but the max range for an airliner is the distance at which its least fuel efficient, as it has to carry its max fuel load. Shorter routes will be much more efficient due to the lower fuel loading.

Reply on news.ycombinator.com