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Aviation industry tries to go green

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Re: Aviation industry tries to go green

#41

Post by riversflow »

ses1984 wrote: post #38
jcampbell1 wrote: post #27

Earlier quoted context omitted.

Airlines get about 40-60 passenger miles per gallon. Not sure if that answers your question.

I was under the impression that metrics like this are too simple to tell the full story. Burning a gallon of ICE fuel at sea level has a different environmental impact than burning a gallon of jet fuel thousands of meters in the air. I think it might be better to compare in terms of "passenger mile per unit of greenhouse effect" but then how do you even get to agreement on how to measure the greenhouse effect...

Additionally, I don’t think jet engines have to pass clean air standards like cars do. I don’t know for certain that this makes a huge difference for global warming, but there are many vectors for environmental damage besides CO2 emissions. Modern gasoline powered ICE vehicles produce fairly clean exhaust thanks to smog regulations.

Re: Aviation industry tries to go green

#42

Post by WalterBright »

redis_mlc wrote: post #39
WalterBright wrote: post #4

Earlier quoted context omitted.

Yup. Piston aircraft engines indeed need tons of maintenance. A huge number of moving parts coupled with trying to minimize the weight and maximize the power is the cause. In WW2 the Germans fitted aircraft engines to their tanks, which worked great when the engines ran, but too often they didn't due to battlefield conditions. (Germany was also terribly short of avgas, which crippled those tanks.)

> Piston aircraft engines indeed need tons of maintenance. Modern small piston aircraft engines under 250 HP have average TBO of 2,000 hours and can be operated beyond that with oil analysis. That's fine for commercial use, and piston engines only use 1/3 to 1/2 the fuel of jet engines, though that may be because of the use of a propeller. So you trade fuel efficiency for engine maintenance, and I think they'd averag…

A Lockheed Constellation had 4 × Wright R-3350-DA3 Turbo Compound 18-cylinder supercharged radial engines, 3,250 hp (2,424 kW) each

https://en.wikipedia.org/wiki/Lockheed_Constellation

That's 72(!) cylinders. Then you've got the superchargers, variable pitch propellers, and on and on. It's a bit of a miracle one could get them all running at the same time :-/

BTW, Lindbergh flew the Atlantic on a single engine. He rejected multi-engine designs because the reliability would be halved. He selected the most reliable engine available at the time.

Re: Aviation industry tries to go green

#43

Post by cgrealy »

JumpCrisscross wrote: post #35
cgrealy wrote: post #8

The big win would obviously be electric aircraft, but I doubt we'll see that in my lifetime (barring a massive breakthrough in battery technology). The problem is even the best batteries have a much lower energy density compared with traditional fuels. Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Real Engineering did a pretty good video on the topic https://www.youtube.com/watch?v=…

> big win would obviously be electric aircraft Why batteries over synthetic jet fuel? Hydrocarbons are great for this purpose. The problem is where the carbon is coming from. Burn jet fuel made from atmospheric carbon and you solve the problem overnight.

Simple answer: I wasn't aware of synthetic jet fuel!

If it can solve the problem, I'm keen to learn more.

Re: Aviation industry tries to go green

#44

Post by rjsw »

Ididntdothis wrote: post #14
cgrealy wrote: post #8

The big win would obviously be electric aircraft, but I doubt we'll see that in my lifetime (barring a massive breakthrough in battery technology). The problem is even the best batteries have a much lower energy density compared with traditional fuels. Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Real Engineering did a pretty good video on the topic https://www.youtube.com/watch?v=…

I think hydrogen would be a candidate but then you have to deal with cooling.

There is some discussion on problems using hydrogen for aircraft in the Ben Rich book "Skunk Works", Lockheed were looking at it [1] before they developed the SR-71.

[1] https://en.wikipedia.org/wiki/Lockheed_CL-400_Suntan

Re: Aviation industry tries to go green

#45

Post by redis_mlc »

WalterBright wrote: post #42
redis_mlc wrote: post #39

Earlier quoted context omitted.

> Piston aircraft engines indeed need tons of maintenance. Modern small piston aircraft engines under 250 HP have average TBO of 2,000 hours and can be operated beyond that with oil analysis. That's fine for commercial use, and piston engines only use 1/3 to 1/2 the fuel of jet engines, though that may be because of the use of a propeller. So you trade fuel efficiency for engine maintenance, and I think they'd averag…

A Lockheed Constellation had 4 × Wright R-3350-DA3 Turbo Compound 18-cylinder supercharged radial engines, 3,250 hp (2,424 kW) each https://en.wikipedia.org/wiki/Lockheed_Constellation That's 72(!) cylinders. Then you've got the superchargers, variable pitch propellers, and on and on. It's a bit of a miracle one could get them all running at the same time :-/ BTW, Lindbergh flew the Atlantic on a single engine. He re…

You're using Wright and Lindbergh as examples?

Pedant.

Re: Aviation industry tries to go green

#46

Post by redis_mlc »

sgent wrote: post #40
redis_mlc wrote: post #39

Earlier quoted context omitted.

> Piston aircraft engines indeed need tons of maintenance. Modern small piston aircraft engines under 250 HP have average TBO of 2,000 hours and can be operated beyond that with oil analysis. That's fine for commercial use, and piston engines only use 1/3 to 1/2 the fuel of jet engines, though that may be because of the use of a propeller. So you trade fuel efficiency for engine maintenance, and I think they'd averag…

I don't know what the data is, but the DHC-8/Q-400 is a fairly popular regional airplane outside the US, and depending on the model goes from 1300 - 5000hp. https://www.pwc.ca/en/products-and-services/products/regiona...

Both the DHC-8 and Q-400 are turbo-prop (ie. jet-engined) airplanes, not piston.

Re: Aviation industry tries to go green

#48

Post by tonyedgecombe »

Aviation looks like the industry least likely to go green to me. I doubt electric planes are ever going to be viable for anything other than a short hop which would be better done by train. Synthetic fuels sounds interesting until you look at how much fuel they consume.

The trend is quite obviously in the wrong direction: https://www.statista.com/statistics/655057/fuel-consumption-...

It's often quoted as 2% of global emissions, my (admittedly back of the envelope) calculations come out 50% higher without the cost of burning it at high altitude nor refining the fuel nor the infrastructure on the ground to support air travel.

My guess is emissions from air travel will continue to rise as the world develops and they will take an increasing share of the total as other sectors decarbonise.

This all leads on to political problems, how are you going to convince the poor to reduce their emissions when they see their rich neighbours jetting across the world on holiday.

Re: Aviation industry tries to go green

#49

Post by ShorsHammer »

cgrealy wrote: post #8

The big win would obviously be electric aircraft, but I doubt we'll see that in my lifetime (barring a massive breakthrough in battery technology). The problem is even the best batteries have a much lower energy density compared with traditional fuels. Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Real Engineering did a pretty good video on the topic https://www.youtube.com/watch?v=…

It is a certainly an untenable problem for longhaul, though with the current pace of advances in battery tech (mainly driven by smartphone companies of all things) shorthaul electric flight could certainly find some support in the near future.

Electric offers dramatic reductions in engine noise and maintenance, along with far more reliability/safety. I can see that being a selling point to some aviation execs, Norway has been trying it out, hope it works for them.

> Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty.

Offtopic: The discussion on that fact is an excellent question/answer to read on SE: https://physics.stackexchange.com/questions/34421/does-the-m...

Re: Aviation industry tries to go green

#50

Post by maccard »

upofadown wrote: post #34
animalnewbie wrote: post #30

Earlier quoted context omitted.

It does exactly. Thank you. This is 4 times that of a singly occupied car. Probably more effort should go towards car pooling. And maybe electric scooters.

That's only a meaningful comparison if you drive across oceans to different continents. People tend to fly much much longer distances than they drive. Supposedly a single long over ocean flight costs something the same as a whole year of driving in terms of carbon emission.

> That's only a meaningful comparison if you drive across oceans to different continents. People tend to fly much much longer distances than they drive.

Distance isn't everything, many many flights are avoidable/suitable for alternative modes of transport. This [0] estimates that 18% of flights of adults in the UK are "long haul". 40% were either domestic or short haul in Europe, both of which are replacable by trains. The longest domestic flight in the UK is from Gatwick to Inverness, and takes just under 2 hours, or an 8 hour train journey.

[0] https://fullfact.org/economy/do-15-people-take-70-flights/ - (Note this was just the first source I found)

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