this post was submitted on 30 Jul 2024
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Air New Zealand becomes first major carrier to drop climate goal (www.bbc.com)
submitted 3 months ago* (last edited 3 months ago) by MicroWave@lemmy.world to c/world@lemmy.world
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Air New Zealand has abandoned a 2030 goal to cut its carbon emissions, blaming difficulties securing more efficient planes and sustainable jet fuel.

The move makes it the first major carrier to back away from such a climate target.

The airline added it is working on a new short-term target and it remains committed to an industry-wide goal of achieving net zero emissions by 2050.

The aviation industry is estimated to produce around 2% of global carbon dioxide emissions, which airlines have been trying to reduce with measures including replacing older aircraft and using fuel from renewable sources.

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[–] HK65@sopuli.xyz 6 points 3 months ago* (last edited 3 months ago) (1 children)

They still descent with flaps and spoilers out, instead of trading off altitude for speed slowly. They fly with speeds of 400+kts, but just like with cars, going slower saves fuel.

I agree with you wholeheartedly that aviation fuel subsidies must end, and train travel should be prioritized above all else.

That said, it's not true that going slower saves fuel, for multiple reasons.

  • One is that the primary resistance planes encounter is air resistance, which is lowest in the highest parts of the atmosphere, because the air is thinner. But since planes use air pressure differences to stay up, thinner air means you have to go faster if you want to stay aloft.
  • Even discounting that, going slower means a higher angle of attack for the plane, meaning the plane will pitch up more to maintain altitude. This actually increases drag, and that's true for everything from airliners to small propeller planes. Point is, the speed where fuel consumption is minimal for a given distance is not going to be near the lower end of the scale, more likely you'll find it in the upper third, above 400 knots for an airliner.
  • The first point may be valid, but since going higher saves fuel, steep descents may actually also save fuel, as an idling engine will still consume a lot of fuel. In fact, I'd be willing to bet that going 400kts at altitude, then cutting the engines idle, and extending flaps and spoilers reduces flight time and thus fuel consumed compared to just cutting the engines and slowly descending. BTW you need flaps and spoilers to land, so it's more of a when rather than an if you'll open them.
  • And finally, air pilots and airlines already optimise for fuel consumption, because that's in their interest as well. Fueling an airliner is hella expensive even with the massive subsidies. It should be more expensive, we agree on that, but slowing down airliners is just going to make fuel consumption and emissions even worse.
[–] admin@lemmy.thefloatinglab.world 1 points 3 months ago (1 children)

All you say might be true for the current design of airplanes. But it is like saying, "this formula 1 race car is really more efficient on the race track than in urban traffic, hence driving cars faster is more efficient.". I agree flying higher is more efficient. There is however no rule that you need to get to 400kts in order to be able to fly at FL350. It all depends on the design of the airplane. In general, for every form of transportation, road vehicles, boats, airplanes, going faster always means "spending progressively more fuel". I built my own airplane. And sure enough, flying it at 160kts instead of 140kts costs more fuel, at any altitude. And, not insignificantly, my small propeller airplane has a lower fuel consumption per passenger per mile than the airliners do, despite the latter flying higher and faster... What is the reason of that? There was also the Concorde. It could fly even faster, and higher, but... it used way more fuel. But this also doesn't mean that flying the Concorde close to its stall speed would be more efficient. There is no way to fly the Concorde at the same efficiency as a 737, at any speed or altitude, because it is designed to fly high and fast, and burn more fuel to make that possible.

So, I'm pretty sure, if we would not optimize the design of airplanes for a certain speed, but for the lowest fuel consumption, you might indeed end up with airplanes that fly slower (and maybe lower) than the designs we have now, and we could have airplanes that use less fuel per passenger per mile.

[–] HK65@sopuli.xyz 1 points 3 months ago

An airliner is not an F1 car though, that's a jet fighter. All I'm saying is that I think if Ryanair could get a plane that would eat less fuel but take twice as long to make a trip, they would jump at it. The Concorde shows exactly that, while some airlines might want the prestige, mostly they just want to provide the cheapest service they can get away with.

And, not insignificantly, my small propeller airplane has a lower fuel consumption per passenger per mile than the airliners do, despite the latter flying higher and faster… What is the reason of that?

Are you carrying enough fuel while doing that to do a trans-Atlantic flight? Airliners do. Can you fly over the troposphere to avoid significant weather that, beyond having people throw up, would have planes divert and use a lot more fuel as well? Airliners can. There are other reasons, of course, but these are just off the top of my head. All that said, of course fuel efficiency is but one of the things airliners are optimized for, and there are other concerns, but speed is not really one of them for the sake of it.