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Old 08-09-2019, 04:50 PM
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Huge quantities of carbon emissions emitted by airplanes: Is there any viable alternative?


This Vox article discusses a movement among some environmentalists: "Flight-shaming" - because airplanes emit an enormous quantity of carbon emissions.

Some of the things mentioned (it's a long read):
  • Currently, air travel demand is stronger than ever, especially as previously poor nations become more affluent.
  • By the year 2050, airplane-generated carbon emissions will have jumped a whopping 300-700% compared to the levels of the year 2005.
  • Making airplanes more efficient isn't really an option; modern airliners are already nearly as fuel-efficient as they can possibly be.
  • Short flights generate more carbon emissions, per passenger-mile, than long flights.



Some solutions might be: Use train instead of airplane for short flights. Simply don't travel as much as before. And maybe international business meetings that require people to fly together for a meeting can be replaced with video teleconferencing.

But the pros of air travel are still too great for aviation to ever go away. It is far faster than any other form of transportation (for crossing Pacific or Atlantic, etc.)
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Old 08-09-2019, 04:56 PM
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The other thing is that for moving large numbers of people a very long distance airplanes are actually more efficient that some of the other options.

Aviation has its uses and it isn't going away.

That said, use of trains for intermediate distances would be a good thing. It would also be a good thing if so many people weren't in such a damn hurry all the times.
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Old 08-10-2019, 12:59 AM
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Flight-shaming? This seems like a form of recreational outrage to me.

The article you linked says aviation contributes 2% of total greenhouse gas emissions. That’s not very much.

In any case - the best solution is to enact a revenue-neutral carbon tax, increase it until carbon emissions have dropped to acceptable levels, and bypass this bunch of self-righteous, holier-than-thou environmental fascists running around shaming people for eating meat, driving to work, running the air conditioner, buying products from overseas, taking vacations, etc.
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Old 08-10-2019, 01:34 AM
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The other thing is that for moving large numbers of people a very long distance airplanes are actually more efficient that some of the other options.

Aviation has its uses and it isn't going away.

That said, use of trains for intermediate distances would be a good thing. It would also be a good thing if so many people weren't in such a damn hurry all the times.
Since you have to a) get to the airport and b) get there two hours ahead of time, and c) collect your bags at the other end, I doubt trains would really take that much more time for short haul. But aviation is obviously more efficient for long haul trips.

Anyway, I think everyone on the planet except small skinny people hate flying. Plus the cost makes managers hate to send people on planes even if they get to stay at home themselves. Video conferencing has already become commonplace to avoid flights. Maybe the airplane is a passing thing?
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Old 08-10-2019, 02:12 AM
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Since you have to a) get to the airport and b) get there two hours ahead of time, and c) collect your bags at the other end, I doubt trains would really take that much more time for short haul. But aviation is obviously more efficient for long haul trips.

Anyway, I think everyone on the planet except small skinny people hate flying. Plus the cost makes managers hate to send people on planes even if they get to stay at home themselves. Video conferencing has already become commonplace to avoid flights. Maybe the airplane is a passing thing?
You really think humans will give up something like that so easily?

https://www.cnbc.com/2019/06/18/all-...-customer.html
Quote:
PARIS — The Israeli start-up Eviation announced at the Paris Air Show that U.S regional airline Cape Air is to buy its electric aircraft.

Eviation is developing a nine-passenger aircraft designed to fly up to 650 miles at around 240 knots (276 miles per hour). A commercial jet would cruise around 500 miles per hour. The electric plane — called Alice with a prototype being unveiled at the show this week — is designed for the sort of distances usually conducted by train.
Quote:
Clermont also owns and funds magniX, the firm that manufactures the three electric motors that provide the aircraft with roughly 900 kilowatts of power. Bar-Yohay claimed if there was a problem with the two wing engines, it could continue flying on the rear rotor only.
For sure the longer distances or larger planes are not doable with current tech, but it should be noticed that such progress was not in the cards until recently, I think that a lot of emission reductions will be able to be done for larger passenger planes by using hybrid solutions.

https://www.reuters.com/article/us-a...-idUSKBN1CA16A
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Old 08-10-2019, 06:00 AM
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Originally Posted by pmwgreen View Post
Since you have to a) get to the airport and b) get there two hours ahead of time, and c) collect your bags at the other end, I doubt trains would really take that much more time for short haul. But aviation is obviously more efficient for long haul trips.
I actually started taking the train from Chicago to Detroit at one point because when I ran that very same equation the door-to-door time for the trip was the same or even shorter if I took the train rather than the plane, with a hell of a lot more legroom and a lot less stress. That was back when you only had to be at the airport an hour ahead of time.

Quote:
Anyway, I think everyone on the planet except small skinny people hate flying.
I'm a small skinny person and I hate flying commercial. (Being in the cockpit myself is a different story.)

Quote:
Plus the cost makes managers hate to send people on planes even if they get to stay at home themselves. Video conferencing has already become commonplace to avoid flights. Maybe the airplane is a passing thing?
No, it's not - because people fly for more than one reason.
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Old 08-10-2019, 07:04 AM
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To me it seems that carbon neutral liquid fuels could be an answer. I'm not sure if we currently have the technology to produce large quantities efficiently enough, or if it could ever be possible to do so.

Maybe someone more knowledgeable can comment on this.
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Old 08-10-2019, 08:42 AM
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To me it seems that carbon neutral liquid fuels could be an answer. I'm not sure if we currently have the technology to produce large quantities efficiently enough, or if it could ever be possible to do so.

Maybe someone more knowledgeable can comment on this.
We can make biofuels that run just fine in jet engines. They're just more expensive than the fossil stuff.

More expensive would be carbon capture from a concentrated non-fossil source (e.g. a fermenter), followed by reduction of carbon dioxide, followed by Fischer–Tropsch. Or syngas to methanol, then methanol-to-gas (I don't recall if anyone had promised that for jet fuel.)

Or if you want to get real pricey, direct air capture followed by the above.

If there were a price on carbon, the relative prices change.

The chemical processes all take more energy than you get out, before someone starts nattering about free energy. If you have too much electricity your can store that energy in liquid fuels for a hefty loss in round trip efficiency.

Last edited by Ruken; 08-10-2019 at 08:44 AM.
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Old 08-10-2019, 10:21 AM
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they're working on rechargeable fluid batteries that are 1.5 times denser than Lithium so electric planes for short flights are highly likely if they're cost effective. The idea is to use a conventional "gas tank" system but filled with a liquid that can be repeatedly recharged.

A hybrid plane/train seems like a good idea on paper. Instead of laying track on graded beds we put up overhead wires and fly lifting bodies closer to ground level but above current traffic corridors. It would be like a reverse electric train with the trailing wire going up to the plane.

All of this is on top of what we're already seeing and that is the transition from gas to electric vehicles. This is going to happen at the same evolutionary speed the cell phone exhibited. Maybe faster. The price barrier has already been broken by high performance electric cars and it's just a matter of time before batteries catch up the price point and refueling needs of daily drivers.

Last edited by Magiver; 08-10-2019 at 10:22 AM.
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Old 08-10-2019, 12:03 PM
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Electrification of aviation faces some steep barriers, regardless of whether using a conventional battery, redox flow battery, or fuel cell. Those all have their own challenges, including energy density. But regardless of storage medium, the motors and power electronics aren't really up to snuff. People are working on this.
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Old 08-10-2019, 12:25 PM
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With the relative energy densities of hydrocarbons vs. even very good batteries, I suspect that the only viable option for long-range (including intercontinental) travel is going to be hydrocarbon fuels offset by some sort of sequestration process. Yeah, it'll be a lot more expensive than it is currently, but battery airplanes would probably be much more expensive yet.
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Old 08-10-2019, 12:39 PM
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Electrification is less bad for smaller planes. If we see any electrification at all, it will start with short flights.
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Old 08-10-2019, 01:05 PM
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Electrification is less bad for smaller planes. If we see any electrification at all, it will start with short flights.
It's easy to put a motor behind a prop so commuters are the logical progression. Also, I think they they rely on freight loads like wide body aircraft do. So there should be more space available for energy storage.
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Old 08-10-2019, 09:32 PM
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It's easy to put a motor behind a prop so commuters are the logical progression. Also, I think they they rely on freight loads like wide body aircraft do. So there should be more space available for energy storage.
that should read: commuters DON'T rely on freight loads like wide body aircraft do.
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Old 08-11-2019, 07:20 AM
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Space isn't the issue; it's weight. Gravimetric (or specific) energy density of storage. And of all the electrical systems. Even the wiring weight is a problem. You need high voltage to keep the wire diameter down. At those altitudes, dielectric breakdown of air is a problem, which would steer you away from high voltage. It's a very hard problem.
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Old 08-11-2019, 08:27 AM
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Space isn't the issue; it's weight. Gravimetric (or specific) energy density of storage. And of all the electrical systems. Even the wiring weight is a problem. You need high voltage to keep the wire diameter down. At those altitudes, dielectric breakdown of air is a problem, which would steer you away from high voltage. It's a very hard problem.
Yes, weight is the issue. But larger aircraft use their available space/weight for cargo. It is less so with commuter aircraft. In other words, larger aircraft are based on both passenger and cargo revenue. Their cargo bays are filled with freight. They will run a higher density in their belly compartments than a commuter plane will.

With electric propulsion there are a number of metrics that change. The size of electric motors allows more options for placement so they can be used to increase lift by means other than accelerating the wing forward. They can be used to move air over the wing using many smaller propellers or angled to directly lift the plane. Commuter planes are a logical platform for electric motor propulsion.
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Old 08-12-2019, 08:31 AM
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Didn't the Air Force or NASA build a nuclear powered air craft in like the 60's? I seem to recall it had some major radiation issues, but that's nothing in the face of current carbon emissions. We could do that. I mean, what could go wrong???

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Old 08-12-2019, 09:13 AM
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Didn't the Air Force or NASA build a nuclear powered air craft in like the 60's?
There was a lot of research on nuclear powered aircraft but nobody built a working prototype. The closest they came was the Convair NB-36H which carried an operational nuclear reactor, but wasn't actually powered by it. They demonstrated that the aircraft could carry a reactor and sufficient radiation shielding to keep the crew safe, but concerns remained for contamination in case of a crash.

I wouldn't dismiss the concept out of hand though. Nuclear thermal generators are used on many spacecraft, and several have survived rocket explosions without causing any contamination. Of course an actual reactor is larger and more difficult to make crash-proof.

Last edited by scr4; 08-12-2019 at 09:15 AM.
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Old 08-12-2019, 09:40 AM
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Does anyone know how much Co2 per passenger mile for short/long haul?
Compared to trains/automobile/buses?
and air freight?
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Old 08-12-2019, 10:17 AM
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Does anyone know how much Co2 per passenger mile for short/long haul?
Compared to trains/automobile/buses?
and air freight?
It beats driving solo in a big car, and nothing else:
https://www.aef.org.uk/downloads/Gra...ortmodesUK.pdf
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Old 08-12-2019, 10:21 AM
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Flight-shaming? This seems like a form of recreational outrage to me.

The article you linked says aviation contributes 2% of total greenhouse gas emissions. That’s not very much.
It's not very much in absolute numbers, but those 2% are produced by a very small portion of humanity.

With one trip across the Atlantic and back you add to your personal carbon budget as much as the average for one person for a whole year in a majority of the world's countries.

Adding to that the emissions from airplane engines have additional negative influences due to where they are emitted.
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Old 08-12-2019, 07:24 PM
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If the U.S. had decent high-speed trains like the rest of the developed world does, a lot of short-to-medium-distance flights would be superfluous. You'd still want to fly from NYC to L.A., but NYC to Chicago or Atlanta would be just as fast by train.
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Old 08-13-2019, 07:30 AM
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If the U.S. had decent high-speed trains like the rest of the developed world does, a lot of short-to-medium-distance flights would be superfluous. You'd still want to fly from NYC to L.A., but NYC to Chicago or Atlanta would be just as fast by train.
I'd love to learn about where I can travel that far, that fast. Because NYC to Chicago is 800 miles in 2.5 hours. That's like Paris to Vienna. Rome to Prague. Tokyo to Kumamoto.

The fastest train in Europe* runs Naples--Milano, connecting Italy's three most populous cities and five of its top eight. That takes over four hours and is the equivalent of leaving NYC and crossing into OH from PA but not making it to Columbus. I guess you can also stop in Pittsburgh or . . . Allentown? The flight to Columbus takes <2 h. Maybe if you're the type who arrives at the airport super early and are starting/ending near the train station you could make that work out.

*According to this: https://www.railway-technology.com/f...ins-in-europe/

Yes, our trains suck, but let's not make other trains out to be what they aren't. There was a wapo article earlier this month about "flight shame" that mentioned a guy traveling from Stockholm to Austria who skipped the 2 hour flight for about 30 hours combined trains, bus, and ferry. A car would have been faster.
https://www.washingtonpost.com/world...2d3_story.html

Now that's longer than your "short" examples. More like NYC to Minneapolis or Des Moines.
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Old 08-13-2019, 07:34 AM
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With electric propulsion there are a number of metrics that change. The size of electric motors allows more options for placement so they can be used to increase lift by means other than accelerating the wing forward. They can be used to move air over the wing using many smaller propellers or angled to directly lift the plane. Commuter planes are a logical platform for electric motor propulsion.
Some relevant literature:
10.1177/0954410017721254
10.2514/6.2018-1652
10.2514/6.2014-2851

I know beans about aerodynamics, so I'll just take everyone's word for it that there are significant gains to be made via magical (to ignorant me) placement of light motors. See also NASA X-57.

The problem still is jet fuel has a specific energy of 12 kWh/kg wheareas Li-ion batteries are something like <0.3.
That doesn't preclude a hybrid system with a non-driving internal combustion generator, or fuel cells, which aren't really up to snuff yet. But people are working on this.

The range/payload tradeoff also depends on power density. Magical propellors may reduce the required peak power (during takeoff), but I couldn't tell you how much. There are also people working on better motors.

So yes, commuter planes are a more logical platform for electric motor propulsion than larger planes, but we can't do it with existing technology. Yet.
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Old 08-13-2019, 07:59 AM
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Ruken, what are those numbers you posted?
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Old 08-13-2019, 08:01 AM
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I'd love to learn about where I can travel that far, that fast. Because NYC to Chicago is 800 miles in 2.5 hours. That's like Paris to Vienna. Rome to Prague. Tokyo to Kumamoto.
It should be noted that the 2.5 hours you list is flight time, it does not include the wait time at the airport, going through security, taxiing after landing, waiting to retrieve your luggage, etc. What people often forget about train travel is that there is less waiting when it comes to boarding and disembarking as well as less time to reach your final destination since train stations are in cities, as opposed to outside them like airports usually are.

Although high-speed trains are not necessarily the solution to air travel, comparing flight times to transit times on trains is not an accurate comparison. Total travel to and from a destination is needed to have an accurate comparison and discussion about the benefits and drawbacks of the two.

//i\\
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Old 08-13-2019, 09:34 AM
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Ruken, what are those numbers you posted?
https://en.wikipedia.org/wiki/Digital_object_identifier
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Old 08-13-2019, 10:30 AM
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It should be noted that the 2.5 hours you list is flight time, it does not include the wait time at the airport, going through security, taxiing after landing, waiting to retrieve your luggage, etc. What people often forget about train travel is that there is less waiting when it comes to boarding and disembarking as well as less time to reach your final destination since train stations are in cities, as opposed to outside them like airports usually are.
I leave 90 minutes before my flight, same for the train, and don't check luggage for 95% of my trips, and rarely need to be smack in the middle of a city. YMMV

DC (since I'm more familiar with it) rather than NYC, but I can leave the house at 7a EDT and be at a meeting in Des Planes, IL at 10:30a CDT. No train is going to do that. I do take trains along the NE corridor and would love faster ones, but trains in other directions just don't have the population density that other, train-heavy parts of the world see. NYC to Chicago sure doesn't. NYC to DC does. But DC to Atlanta does not.

That Italian train would be like going from here to Indy. So even faster than Chicago. Their 4.5 hours is a hell of a lot better than our 18+ that you could do today on Amtrak if you really wanted. But even at 4.5 hours, that makes it damn hard to make a day trip of it like I can on a plane. And nobody would put a fast route in there anyway because it travels through a whole lot of not-a-whole-lot, as opposed to 20+% of the population. Maybe I just shouldn't expect to make day trips to Indy. But a fast train is certainly not an equivalent substitute to what I have available now.

I would love to take more trains. Right now, it's easier for me to fly to Philly, rent a car, and drive to a meeting near Princeton than it is for me to take Amtrak to Trenton followed by regional rail or taxi/uber. It's easier for me to drive to a meeting in Morgantown or Pittsburgh (downtown -- I fly if I'm near PIT airport.) RDU seems like it should be train-able but it's not. And east-coast-to-Chicago would be cool but it's just silly given the distances and populations involved.
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Old 08-13-2019, 12:35 PM
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I'd love to learn about where I can travel that far, that fast. Because NYC to Chicago is 800 miles in 2.5 hours. That's like Paris to Vienna. Rome to Prague. Tokyo to Kumamoto.
NYC to Chicago by air in 2.5 hours? Sure, if you can just walk into the airport and get on your plane. Used to be able to do that before 9/11. Now, not so much.
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Old 08-13-2019, 01:16 PM
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NYC to Chicago by air in 2.5 hours? Sure, if you can just walk into the airport and get on your plane. Used to be able to do that before 9/11. Now, not so much.
I already addressed this. But that's essentially what anyone with pre-check does.

Last edited by Ruken; 08-13-2019 at 01:18 PM.
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