[toothbrush]

So much this. Not to mention the reduced environmental impact. Flying is absolutely catastrophic in terms of greenhouse gas emissions, and the Paris accord doesn't cover even a fraction of it! (because flying occurs in "international space" and so it doesn't appear on any country's "balance sheet"... atrocious.)

[audunw]

> Flying is absolutely catastrophic in terms of greenhouse gas emissions

Uhm, flying is OK in terms of emissions per passenger mile. Not as great as train, but better than driving solo in a gasoline car.

The problem is transcontinental flights. While they're OK in terms of efficiency per mile, the number of miles is staggering.

The problem is, those trips can't be made by train.

So in terms of flying, I think the main focus should be not to fly long distance if it can be avoided. Sure, it's much better to take the train if possible, but if you fly between countries within europe a dozen times a year, that's not a catastrophe.

[cornholio]

I know Boeing proposed Methane turbofans, and they were estimated to have 60% less carbon emissions and cheaper than jet fuel - after eating the large development and infrastructure costs. You could take this even further, producing Hydrogen from clean electric energy is about three times more expensive than methane for the same energy content, leading to a moderate increase in the cost of even a low cost ticket.

But as with all radically new technology, there needs to be a strong industry, government and consumer push. The program that produced the Methane turbofan concept (SUGAR Freeze) has lost any political appeal.

[erezyehuda]

Costs aside, wouldn't replacing carbon emissions with methane be drastically worse? Doing a casual search says that methane is 2000-3000% more potent as a GHG.

[ufo]

I assume the methane would be the fuel, not the byproduct.

[JamesBarney]

I imagine you won't combust 100% of the fuel. So wouldn't it be both.

[rlucas]

Pure methane is a bunch of molecules with just one carbon, which simplifies things a bit vs. a cracked and heterogeneous mix of longer chain (10+) molecules.

You can incompletely combust a 10-carbon molecule and wind up with other hydrocarbons but if you burn up CH4, you're definitely just getting one CO2.

[schiffern]

>The problem is, those trips can't be made by train.

Transcontinental flights (one side of the continent to the other, see [1]) can usually be taken by train. You probably mean intercontinental flights.

[1] https://en.wikipedia.org/wiki/Transcontinental_airspeed_reco...

[ghaff]

You're being pedantic. One can travel from New York to San Francisco (well, Emeryville) by train but it's going to take multiple days and, even if you handwave the existence of high-speed rail through two continental divides among other things, it's a very long trip. That's never going to be a mainstream replacement for even a subsonic 5 to 6 hour flight between a multitude of east coast-west coast city pairs.

[jacobolus]

If there were high-speed trains that could make cross-US trips in, say, 15 hours, and at comparable or cheaper cost vs. airplanes, I can imagine there might be demand. I would be willing to take those overnight.

But even if we could replace most <500 mile flights along the most popular routes (starting by connecting cities up and down the coasts), it would be a huge win as far as fuel economy is concerned.

[schiffern]

And you're being parochial. Who said "continent" was limited to North America?

The claim was that the trip can't be made, not that it can be made but is undesirable as compared with alternatives.

[logfromblammo]

> The problem is, those trips can't be made by train.

They can't now, but they could be. All that is required is a level of capital investment that can't ever be recovered while in competition with air and sea-surface travel...

The transatlantic tunnel has been a sci-fi fantasy since 1895. It could cost as little as $500 billion today.

[PsylentKnight]

> Not as great as train, but better than driving solo in a gasoline car.

It was my understanding that driving is better for shorter trips, because the overhead of taking off and landing is significant. I don't have a source. IIRC I read this in "Doing Good Better."

[llukas]

Is it still competetive vs car for supersonic flight?

[mehrdadn]

I'll point out that although it's indeed atrocious compared to a train ride, flying is still more efficient than driving a car. So if traveling is required and you're debating between driving vs. flying (say SF <-> LA), you should prefer flying unless you can carpool. I don't know the exact numbers since it depends on where you're going and what plane/airline you fly, but I would expect around 50-75 MPG for a reasonably full airplane [1], whereas your car might be more like 25-30 MPG on the highway, so you'd want at least 2-3 (ideally 4) people in the car to make it more efficient.

However the thing about flying is of course that it burns fuel at a much, much faster rate, so if it means the difference between you driving to workplace A vs. flying to workplace B regularly, then you'll be burning one hell of a lot more fuel by flying.

[1] https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Airli...

[mmt]

Interestingly, the efficiency ratio you suggest appears to be reflected in the ratio between the overall cost (including ground transportation at the other end) of flying SFBA-SoCal and driving.

Whenever I've spot-checked, the break-even is at 2 people, which tends to make flying more attractive for time/fatigue reasons (only barely, at some points in history) even for 2, and sometimes worth the cost premium for 3. For a family of 4 or more, even with the increased fuel cost (but generally not other operating costs) of something like a minivan, driving saves too much money to pass up.

[mehrdadn]

That's interesting, thanks for mentioning this!

[Reason077]

That’s true today. But in the coming years and decades, ground transport will be largely electrified and it’s per-mile emissions greatly reduced.

Hopefully, aviation can be electrified too one day (or it’s emissions reduced with hybrid technology), but unlike ground transport, the technology is not quite here yet.

[smolder]

Hybrid tech doesn't help at all with with planes. There is no braking energy to be regained and batteries are too heavy. It has no place there until battery energy density approaches that of fuel, which would require a huuge breakthrough of some kind.

[Reason077]

The idea behind a hybrid aircraft is that eFans (electric fans) are more energy efficient than a turbofan, so you can burn less fuel for a given journey.

Companies including Airbus, Siemens, and Rolls Royce are actively working on this technology with a view to have working prototypes in the early 2020s.

Besides that, there is some "braking" energy to be recaptured during descent or when slowing the aircraft. This technology already exists today: The Pipistrel Electro can regen it's battery during descent. This is similar in principle to the ram air turbine (RAT) in conventional aircraft.

[smolder]

Well thanks for the pertinent info. I was pretty sure of myself that the cost benefit ratio wasn't there but if there are engineering efforts towards it there's at least potentially some merit.

I wonder, does the efficiency gain from efans and a generator apply to a single engine setup as well as it does to multi engine setups?

[mehrdadn]

With battery capacities being what they are you'll also have to hang tight for the moment when they stretch long enough to allow you to even have the choice of driving to the same place you can fly. (Or swap batteries on the way somehow... not sure how well that would work.)

[Reason077]

This is already solved in technology terms. Battery capacities and charging speeds are already good enough for almost all long-distance travel scenarios.

It’s now just a case of getting costs down and infrastructure built out. But that’s the easy part.

[mehrdadn]

> his is already solved in technology terms. Battery capacities and charging speeds are already good enough for almost all long-distance travel scenarios.

Really? It seems to me that decent EV ranges are around 150mi right now, with the best ones going to 300mi... meaning they generally might get you halfway from (say) SF to LA, and you can bet that none of them will get you all the way. And that's not even that long of a distance, depending on what your standards are. Now charging times run into multiple hours, right? How is that even remotely close to gasoline?

[Reason077]

Charging times are around 45 minutes today for 250-300 miles of travel. Most people want to take a break after 4-5 hours of driving anyway, so it’s just a case of having chargers in the right locations.

The new generation of 350kW / 800V chargers will bring that down into the 15-20 minute range.