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Aviation industry tries to go green

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Re: Aviation industry tries to go green

#31

Post by m4rtink »

Ididntdothis wrote: post #28
danaliv wrote: post #24

Earlier quoted context omitted.

The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.

Interesting! I didn't think about volume. Is that why the Saturn V first stage also used kerosene?

Pretty much - the rocket is smaller & you can usually also get more thrust, while loosing some efficiency.

There are were more rockets like this (kerolox for first stage & hydrolox for upper stage), like for example Atlas 5. Other rockets used kerolox boosters, such as for example Energia & IIRc some of the new Chinese rockets.

Re: Aviation industry tries to go green

#32

Post by labster »

Ididntdothis wrote: post #28
danaliv wrote: post #24

Earlier quoted context omitted.

The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.

Interesting! I didn't think about volume. Is that why the Saturn V first stage also used kerosene?

That probably went into the decision, but rocket science is complicated. While not on the Saturn V, you there’s a good discussion on fuel tradeoffs here, after explaining the engine cycles: https://everydayastronaut.com/raptor-engine/

Re: Aviation industry tries to go green

#33

Post by zdragnar »

animalnewbie wrote: post #30
jcampbell1 wrote: post #27

Earlier quoted context omitted.

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

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 not outside the range of most hybrids, and even 40 isn't much far off from, say, a kia optima at all freeway miles. Even low efficiency crossover SUV types get at least half, if not better. As the sector transitions to battery over gas, the situation will only continue to improve, as it has been for years.

That's not to say that proper incentives for car pooling are bad, but it's also no reason to exclude looking at improving the efficiency of planes- especially since fuel costs are so large a portion of their operating costs.

Re: Aviation industry tries to go green

#34

Post by upofadown »

animalnewbie wrote: post #30
jcampbell1 wrote: post #27

Earlier quoted context omitted.

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

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.

Re: Aviation industry tries to go green

#35

Post by JumpCrisscross »

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.

Re: Aviation industry tries to go green

#36

Post by gersh »

It might be better to just capture CO2 from the Ocean or the air, and then use renewable energy to make jet fuel. While the efficiency of the process may not be super high, it will be carbon neutral. See https://www.weforum.org/agenda/2018/02/bill-gates-to-strip-c... and https://www.greencarcongress.com/2014/04/20140408-navy.html.

Re: Aviation industry tries to go green

#37

Post by WalterBright »

imsofuture wrote: post #29
WalterBright wrote: post #19

Earlier quoted context omitted.

I know that for piston engine aircraft, it is critical that the engine be properly warmed up before takeoff. Otherwise, the engine would likely stall shortly after liftoff, leading inevitably to a crash. This is a common cause of accidents. I don't know specifically about jet engines, but as the engine is designed to run while hot, and metal expands when hot, I'd be quite surprised if it wasn't necessary to warm them…

I know that for piston engine aircraft, it is critical that the engine be properly warmed up before takeoff. Otherwise, the engine would likely stall shortly after liftoff, leading inevitably to a crash. This is a common cause of accidents. This is not true. Engine start to takeoff is usually at least a few minutes, but there is no critical temperature factor for the engine (barring extreme heat or cold). It's a lot…

My source is my father, who flew 23 different types of aircraft, single engine, multi engine, piston and jet. He spent some years as a flight instructor, and a crash investigator for the Air Force.

He said not properly warming up the piston engine meant that there was cold oil still in the reservoir, and sucking that into the engine would cause it to stall, usually right after takeoff, causing many accidents.

I've read about it in the paper myself a couple times, the report goes like the engine stalled right after takeoff and the airplane crashed. Didn't warm the engine up.

I can see this in my car. If the engine isn't warmed up, pulling into traffic often meant it would stall right in the middle of the lane I'm trying to cross, leaving me vulnerable to being rammed.

Now, if you're in an airplane overloaded with gas and bombs (and combat missions are always overloading the airplanes), you're going to make darn sure the engines are all at normal operating temperature before you start the roll. And you're going to fly right through the smoke of the previous guy whose engine hiccuped after he was committed.

I've flown in a Cessna a few times, and the pilot will always trundle out to the runway, set the brakes, and run it at full power making sure it's warmed up and both magnetos are working. I'd get out if he didn't :-)

Re: Aviation industry tries to go green

#38

Post by ses1984 »

jcampbell1 wrote: post #27
animalnewbie wrote: post #26

Serious question, pardon my ignorance. How much is the per capita fuel consumption compared to a petrol car? Small steps are good too but I sincerely hope we can spend that effort in safety and perhaps speed. Societies progress as distances get shorter.

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...

Re: Aviation industry tries to go green

#39

Post by redis_mlc »

WalterBright wrote: post #4
gpapilion wrote: post #3

Earlier quoted context omitted.

Fuel saving solutions are always attractive in the industry. Originally it was thought jet engines would fail due to their fuel consumption, but the reduced maintenance requirements made them more attractive.

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 average out. DC-3 operators can maintain their piston engines just fine with one mechanic.

(Large turbofan engines like the 737 MAX uses are basically resurrecting the propeller in terms of moving a large volume of air, rather that relying on only a jet of air.)

I don't think there is a lot of data for larger piston engines. 1,000 HP engines and larger in WW2 had issues at the time, but that was 75 years ago. Metallurgy and production methods have improved since then.

Also WW2 engines were boosted (supercharged and water/alcohol-injected) and the military didn't care about longevity as airliners do today. For example, the American supercharged P-38 was the fastest fighter of WW2, while the version sold to Britain wasn't, and was a dog.

Source: commercially-rated pilot, WW2 student.

Re: Aviation industry tries to go green

#40

Post by sgent »

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…

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...

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