Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Aviation industry tries to go green

phys.org

Post reply on HN
Print view View original

81–90 of 106 posts

Re: Aviation industry tries to go green

#81

Post by fulafel »

dangus wrote: post #78
fulafel wrote: post #75

Earlier quoted context omitted.

I hope blimps make a comeback, they have a lot of potential. Especially considering high speed rail is bound to stay limited to busiest connections, given the fixed costs and required high passenger volumes.

Blimps are slow. That means they’d probably cost more than commercial jets, because the crew is being paid for a longer period of time. It also seems like jets can fly in far more inclement weather than blimps, but I’m no expert in that.

Of course everything currejntly costs more than commercial jets now because we aren't pricing in the havoc to the fuel cost, this can't be the criterion.

Also, the Hindenburg went at 100+ km/h in the 30's, we're already using many kinds of vehicles that go at similar speeds and don't cost more than commercial jets. Hopefully we could beat the 30's technology in speed, that's just the lower bound.

edit: also, correcting my terminology, I should have talked about "rigid airships" instead of "blimps" apparently - blimps are like balloons with little engines, and the Hindenburg & modern credible air travel blimpy looking designs are "rigid airships".

Re: Aviation industry tries to go green

#82

Post by imtringued »

usrusr wrote: post #64
riversflow wrote: post #41

Earlier quoted context omitted.

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.

Non-CO2 emissions are bad for us now, but their long-term impact on the future is insignificant. They are more bad now precisely because they don't just stick around forever, unlike CO2 they still contain bound energy and will happily participate in all kinds of undesirable reactions.

This implies that synthetic jet fuel isn't the answer either because it will still create local pollution. Does using hydrogen prevent these types of emissions?

Re: Aviation industry tries to go green

#83

Post by danaliv »

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?

Oh, good question - not a rocket scientist but this history seems to say that’s the case: https://history.nasa.gov/SP-4206/ch7.htm

”Liquid hydrogen was only one half as dense as kerosene. This density ratio indicated that, for the necessary propellant, an LH2 tank design would require a far larger tank volume than required for RP-1. The size would create unacceptable penalties in tank weight and aerodynamic design. So, RP-1 became the fuel.”

(RP-1 And Jet A are almost identical.)

In applications where cross-sectional area is an exponential factor (read: atmospheric flight), volume is significant!

Re: Aviation industry tries to go green

#84

Post by bluGill »

cgrealy wrote: post #43
JumpCrisscross wrote: post #35

Earlier quoted context omitted.

> 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.

https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_proces...

Problem is it used a lot more energy than pumping oil out of the ground. In theory we can get the energy from solar or something, but still it needs a lot of energy.

Good news it the process as been successfully used on the scale of providing fuel for entry countries. Thus we know it scales to something larger. There are other options that look promising in a test tube but don't seem to work at larger scales yet.

Re: Aviation industry tries to go green

#85

Post by bluGill »

benhurmarcel wrote: post #53
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.

> This is 4 times that of a singly occupied car. How do you get that? A normal modern car does 5.5 L/100km (~40 mpg) nowadays.

While cars that get ~40mpg exist, they are not common - at least not in North America. SUVs that get less than 20 are more common than cars that get > 40.

That still isn't 4x though. You can find SUVs that get 4x worse, but they are generally heavy duty trucks doing things that cars cannot do. Per useful mass moved they do better than anything else.

Re: Aviation industry tries to go green

#86

Post by bluGill »

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…

Takeoff is when an airplane engine needs to be at full power. Thus the time when you need the engine warmed up the most is right after startup.

Re: Aviation industry tries to go green

#87

Post by byroot »

davidgh wrote: post #77
kypro wrote: post #66

Earlier quoted context omitted.

In Europe train is already quite a nice way to get around. I live in the UK and caught a train to London then a Eurotunnel train to Paris and it was probably quicker and easier when you account for time spent in departures and going through airport security.

I’m often surprised at the ticket prices on trains in Europe. As I’ve traveled around there, it’s not uncommon for me to see a route by train at approximately 100 EUR and the same route by air by for less than half that. Causing additional confusion is that when I take the train, there are often a significant number of empty seats. It seems that the cost of an additional passenger on a train is almost zero, so why do…

> It seems that the cost of an additional passenger on a train is almost zero

It is. But the cost of the first passenger is massive.

Think of all these rails (and the terrain under it you have to pay a hefty price for), all the bridges etc.

You mention the Paris-London train, just the tunnel did cost $21 billions, add the high speed rails before and after it and you are probably at close to $40 billions in infrastructure before the first train can do the trip.

Trains are orders of magnitude greener than planes, but unless you massively tax planes, or massively subsidize trains, they'll always be more expensive than planes.

Re: Aviation industry tries to go green

#88

Post by econcon »

tonyedgecombe wrote: post #48

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 globa…

First of all there is no need for people to trottle globe needlessly, all Instagram culture and people every person on earth dreaming of seeing same locations as photographed on Instagram is vanity.

Why we've to damage our planet so much just to see some locations?

Re: Aviation industry tries to go green

#89

Post by dredmorbius »

dangus wrote: post #78
fulafel wrote: post #75

Earlier quoted context omitted.

I hope blimps make a comeback, they have a lot of potential. Especially considering high speed rail is bound to stay limited to busiest connections, given the fixed costs and required high passenger volumes.

Blimps are slow. That means they’d probably cost more than commercial jets, because the crew is being paid for a longer period of time. It also seems like jets can fly in far more inclement weather than blimps, but I’m no expert in that.

They're also fragile, handle poorly in adverse conditions, and have little excess lifting capacity.

In a world in which heavier-than-air flight becomes less affordable, there might be some niche uses. In general, my sense is that lighter-than-air craft are simply too close to the limits of potential engineering and materials.

Re: Aviation industry tries to go green

#90

Post by rezgi »

dangus wrote: post #79
jeromegv wrote: post #58

Earlier quoted context omitted.

Only solution is to have some type of carbon tax on local travels and use it to reinvest in a train network. A lot of the air flights in North America would be better served by high speed trains. We won’t have an alternative to long distance flights, but there is one for shorter flights.

I’d argue that not a lot of air flights in the United States would be served better by train when you think of some of these distances. The east coast is already covered by an excellent train line. That line could be made faster to be more competitive but it already handles far more passengers than air. Now let’s look at some other popular routes. Chicago to LA? 2,000 miles. That would take around 10 hours nonstop on…

Chicago > LA flights look like they take 5h (time on the plane.) Add the time to go through the security theater, transfers from and to the airport, and you're not that far off from how long it would take by train.

I'm not even considering the delays because of weather, technical, etc.

Trains don't have as much potential for being delayed (train schedules have a lot less variance because the track is pretty much fixed and the timetables too), and they take you right from the city center to the destination's city center.

Comfort doesn't compare either, you don't have to pay extra so you can actually sit down like a human being and retain your dignity.

And if the trains were electric instead of diesel like they are in the US, I wouldn't be surprised if it was also cheaper than flying.

As a counterexample to China, Switzerland has an amazing rail network. Trains going from anywhere to anywhere, comfortably, reliably, quickly, and multiple times a day. And yet, the country is very mountainous, and has lots and lots of smaller cities.

Post reply on HN