Electric commercial flight

[tszaboo]

Also Europe does have a pretty darned good electric rail system, especially compared to north america.. I know you can get pretty much anywhere in Switzerland quickly and efficiently on rail, Japan seems to be really good as well.. North america is essentially in the 3rd world on this

Visiting my parents would be 22 hours by train or 2 hours by plane. With a plane I can literally spend a weekend with them, 4 country away,  leave friday from work, take the early monday plane. Well, I mean normally, not in 2020. Also if you have to go anywhere by train, it is going to cost you an arm and a leg, or you have to fiddle around when you are travelling, or buy like 5 tickets with separate passes for different countries. And DB being DB.
I really think regional turboprops are going to kill long distance trains completely.

[PlainName]

it is going to cost you an arm and a leg, or you have to fiddle around when you are travelling

Trains are massively overpriced. For Xmas dinner with an acquaintance (not this year obvs) we would travel around 50 miles into Central London. Worked out that the petrol cost plus congestion charge plus rip-off NCP parking around Piccadilly Circus was cheaper than the train fare, and I got to go and leave when I wanted, door to door. And that was for one - there are actually two of us so the train fare would be twice as expensive as being more expensive. Plus the rip-off car park price at the rail station...

I can't imagine anyone in their right mind using a train unless... well, can't think of an overriding reason. They'd have to not just pay me to do it by pay me a lot.

[Rx7man]

it is going to cost you an arm and a leg, or you have to fiddle around when you are travelling

Trains are massively overpriced. For Xmas dinner with an acquaintance (not this year obvs) we would travel around 50 miles into Central London. Worked out that the petrol cost plus congestion charge plus rip-off NCP parking around Piccadilly Circus was cheaper than the train fare, and I got to go and leave when I wanted, door to door. And that was for one - there are actually two of us so the train fare would be twice as expensive as being more expensive. Plus the rip-off car park price at the rail station...

I can't imagine anyone in their right mind using a train unless... well, can't think of an overriding reason. They'd have to not just pay me to do it by pay me a lot.

but could you fly there instead?
I don't know exact costs, but i think at least in switzerland you can get a go-anywhere pass with unlimited usage.. same with japan

[PlainName]

If I could fly I'd pay double, and not care about the security timewasting

A daily pass wouldn't help - it's a single (OK, two, since it's a return) train journey. Plus things like daily passes don't cover outside of London. There are season passes but we are talking a huge amount of money for one trip, so that's hardly appropriate.

[vk6zgo]

Conclusion: It's not happening in my lifetime, it's probably not happening in my [putative] children's lifetime. Perhaps there will be short haul (~100 nm) electric commercial flight just within my lifetime.

I think Harbour Air is operating a modified Beaver on electric-only from Vancouver BC to Victoria, I'm not sure if it's truly commercial or for private use, it seems to me the FAA certs to do it carrying the public would be onerous to get.

Electric cars already have pretty poor ranges, we can't make a cell phone that works a whole day on a charge.. I'm not hopeful we'll do trans-atlantic commercial flights on the scale we do today powered by electricity

Electric cars have improved a lot, but, I agree, aren't quite there yet.

"Dumb phones" can last several days---- it is all the "smartphone" overheads that both use up power & require larger screens, limiting battery size that limit the latter.
I have a PC & an iPad, it seems silly to buy a phone which duplicates their capabilities at the expense of compromising the core function of a phone.

[vk6zgo]

I just pulled a number out of my arse for the flight time on a zeppelin style craft... even if it's 3 days, taking a week vacation means you only spend a day at your destination... it's hardly going to be attractive for anything other than deliberately sightseeing on the trip

I also agree that short hop flights like Vancouver-Victoria isn't going to make a dent in emissions from air travel... It's only good for the politicians that have to go to victoria (BC's capital) and gain greenie points

In some countries (like mine) in 2020, you better count on 14 days quarantine at your destination------maybe they'd let you off with 11, if you "quarantine" on the "Zeppelin!"

[PlainName]

I have a PC & an iPad, it seems silly to buy a phone which duplicates their capabilities at the expense of

For the iPad maybe, but I ain't lugging a PC around with me just so I can use a dumb phone

Actually, before the iPhone that's pretty much what people wanted to do - have a PC in the pocket. Hence WinCE and all that followed, which was essentially a Windows desktop in a pocket. The iPhone showed that it wasn't the PC we wanted but the potential provided by a PC - the ability to do 'smart' things on the go, as opposed to taking a desktop simulacrum.

You might find that most people use their phones mostly for non-voice call things, and some have simply replaced the PC with a phone. Phones aren't really phones now - they are mobile computers which can make calls too. And, in fact, with a lot of IoT stuff you simply cannot use your computer with them - the phone is the only way to control or access them.

As such, I don't think the phone is duplicating much if you look at the detail rather than the superficial birds-eye view.

[mzzj]

The majority of electricity serving the majority of the world's population came from burning fossil fuels, and the power plants have an efficiency of around 40%, while a jet engine has around 80% efficiency at cruising speed and altitude.

Electric plane, is thus not very eco friendly after all, unless it enables new paradigms like small group or personal hops between short locations where normally cars would have to burn a lot of fuel to wait in a traffic jam.

To me, this is go (very) small or go home.

80+ efficiency is the "propeller" efficiency alone. Multiplied with the thermal cycle efficiency of the motor (around 50% for current jet engines) you have about 40% overall efficiency.
Electric motor could have 80%*95% = 76% overall efficiency
https://en.wikipedia.org/wiki/Propulsive_efficiency
This lists GE90 turbofan efficiency at 36% https://web.archive.org/web/20161124123017/http://adg.stanford.edu/aa241/propulsion/sfc.html

Still doesn't change the fact that batteries are the weak link with electric flight.

[Siwastaja]

Now the question is, what would be acceptable battery energy density for viable air travel?

I'll just throw two numbers from the top of my head:

Short hauls (continental Europe & similar, 1000km range): 500 Wh/kg
Long hauls (5000km range): 1000 Wh/kg

Current li-ion state-of-the-art is at 300Wh/kg and advancing at about 30%-40% per 10 years. If there is absolutely no breakthroughs but the current slow but non-meaningless progress keeps on, we are there in 2040 for short hauls and 2060 for long hauls.

I remember hearing from sources I don't offhand remember that li-ion would top at around 400 Wh/kg, after which something else is needed. The current technology is approaching this. OTOH, the transistors still keep shrinking by (approximately) Moore's law, despite everyone, experts included, saying that it can't go on for much longer, for many decades now, so as a result, I take expert opinions about approaching hard limits "soon" with a grain of salt.

For long-range above-the-clouds flying, a sudden breakthrough in solar paler efficiency could enable extending the battery range by utilizing solar charging, but I guess this would also require a technological breakthrough which isn't in horizon. But it's an interesting thing to speculate.

[Cerebus]

It's probably easier, and safer, to make predictions about the chemistry of batteries than it is to make predictions about the peculiar (in both senses) physics of very, very, very small transistors.

[sandalcandal]

Now the question is, what would be acceptable battery energy density for viable air travel?

I'll just throw two numbers from the top of my head:

Short hauls (continental Europe & similar, 1000km range): 500 Wh/kg
Long hauls (5000km range): 1000 Wh/kg

Current li-ion state-of-the-art is at 300Wh/kg and advancing at about 30%-40% per 10 years. If there is absolutely no breakthroughs but the current slow but non-meaningless progress keeps on, we are there in 2040 for short hauls and 2060 for long hauls.

I remember hearing from sources I don't offhand remember that li-ion would top at around 400 Wh/kg, after which something else is needed. The current technology is approaching this. OTOH, the transistors still keep shrinking by (approximately) Moore's law, despite everyone, experts included, saying that it can't go on for much longer, for many decades now, so as a result, I take expert opinions about approaching hard limits "soon" with a grain of salt.

For long-range above-the-clouds flying, a sudden breakthrough in solar paler efficiency could enable extending the battery range by utilizing solar charging, but I guess this would also require a technological breakthrough which isn't in horizon. But it's an interesting thing to speculate.

What are you basing this on? Not that you're far off. Quick research on this subject puts the required breakeven starting at 400kWh/kg for smaller personal aircraft, 750Wh/kg for regional jets

Source: Venkat Viswanathan: Batteries: The Missing Piece for Sustainable Transportation and Aviation March 2018, College of Engineering, Carnegie Mellon University


The above seems to be partially based on this very good NASA study on electric aircraft and their challenges.

"This issue has been somewhat discussed in the prior portions of this paper, with the projection that a 400 Whr/kg battery specific energy density is sufficient to enable meaningful electric and hybrid-electric aircraft."
Mark D. Moore and Bill Fredericks Misconceptions of Electric Propulsion Aircraft and Their Emergent Aviation Markets January 2014, NASA Langley Research Center Hampton, VA, United States
https://ntrs.nasa.gov/citations/20140011913
Key points made in the conference paper are:

• The Design of Electric Aircraft is Different than Existing Aircraft
• Electric and Conventional Propulsion Should NOT be Compared on an Isolated Propulsion System Basis to Achieve Fair Comparisons
• Electric Aircraft Make Financial Sense more sense than Electric Cars [in 2014]
• Electric Storage Energy Density is not THE Issue, or Insufficient for Meaningful Range
• Electric Aircraft Research Should NOT Focus on Large Commercial Transports with a Market Introduction 20 Years from Now

Note: the paper writes statements of the above in a different but equivalent form as negations of misconceptions

I'm working on some first hand back of the envelope calculations to see for myself but I'm no aerospace engineer. I'll post whatever working and results I get when I'm done. I'm not going to be able to do any better models

Edit: From Oct 2019 report on battery technology developments by the Rock Mountain Institute.

Tyson, Madeline, Charlie Bloch. Breakthrough Batteries: Powering the Era
of Clean Electrification. Rocky Mountain Institute, 2019.
https://rmi.org/wp-content/uploads/2019/10/rmi_breakthrough_batteries.pdf

[mzzj]

Now the question is, what would be acceptable battery energy density for viable air travel?

I'll just throw two numbers from the top of my head:

Short hauls (continental Europe & similar, 1000km range): 500 Wh/kg
Long hauls (5000km range): 1000 Wh/kg

Current li-ion state-of-the-art is at 300Wh/kg and advancing at about 30%-40% per 10 years. If there is absolutely no breakthroughs but the current slow but non-meaningless progress keeps on, we are there in 2040 for short hauls and 2060 for long hauls.

I remember hearing from sources I don't offhand remember that li-ion would top at around 400 Wh/kg, after which something else is needed. The current technology is approaching this. OTOH, the transistors still keep shrinking by (approximately) Moore's law, despite everyone, experts included, saying that it can't go on for much longer, for many decades now, so as a result, I take expert opinions about approaching hard limits "soon" with a grain of salt.

For long-range above-the-clouds flying, a sudden breakthrough in solar paler efficiency could enable extending the battery range by utilizing solar charging, but I guess this would also require a technological breakthrough which isn't in horizon. But it's an interesting thing to speculate.

Mid sized jet like 737 burns abts 2500kg jet fuel per hour. Lets say 4000kg for 1000km flight?  12kWh/kg, 50% efficiency = 24000kWh battery needed as replacement. With current li-ion tech that is 72000kg  battery.

[Siwastaja]

It's probably easier, and safer, to make predictions about the chemistry of batteries than it is to make predictions about the peculiar (in both senses) physics of very, very, very small transistors.

Likely, yes.

One reason the transistor predictions failed is because the chip design experts, even transistor experts, had no deep understanding and vision about photolithography processes and probably thought that the wavelength of visible light is the "hard limit".

Battery chemistry predictions could fail due to a similar reason: having even a single false assumption.

But the observed rate of progress is much slower for li-ion energy density (approx 30-40% per 10 years as I said) than it has been for number of integrated transistors (some 40% per year).

But we'll see. It's a fact that a lot more money is going in battery R&D than ever before, and it's likely sooner or later we see some minor or major breakthrough. But it's best not to hold your breath while waiting, let alone believe each press release.

[Siwastaja]

What are you basing this on? Not that you're far off.

My 500 Wh/kg and 1000Wh/kg numbers? Well, just intuition. Have done some literature research about it; have given it a thought or two; have done some quick napkin calculations just for fun. Napkins are in waste bin. Doing a proper scientifically valid, even remotely so, analysis with sources would be work for at least 100 hours. I like doing such quick&dirty "expert intuition" things even on subjects where I really am not an expert (but which might coincide with expertise I have, such as li-ion battery technology and electric motor drives).

Where I base "currently 300 Wh/kg" and 30-40%/decade numbers? Observations of actual market of cells I can buy.

45-gram 3.65V 3.5-3.6Ah 18650 cells are currently available from Samsung, LG and Panasonic; have been for a few years now, this is 290 Wh/kg for 2018 off-the-shelf. I'm assuming even more modern cells such as ones developed by Tesla now easily hit 300Wh/kg.

30-40% increase per decade can be observed if you look at past products. My observations are some 160 Wh/kg in 2000, 230 Wh/kg in 2010, and 300 Wh/kg in 2020. This is not very precise, though, because COTS cell launch dates are difficult to find, especially retrospectively.
 

Quick research on this subject puts the required breakeven starting at 400kWh/kg for smaller personal aircraft, 750Wh/kg for regional jets

Sounds like something I could agree with.

[PlainName]

The mistake y'all are making is trying to have batteries emulate oil-fueled systems. That's like trying to have a computer emulate pen and paper instead of having it's own paradigm.

So, back to the drawing board, and the problem is you only have enough energy density for short powered flight. Ergo, the answer is to have much more un-powered flight. BFO railgun at the start, sub-orbital mid-flight and you can use your Amazon powerbank to go around in case your first landing glide fails. The real breakthrough is going to be in acceleration couches (and maybe in-flight waste disposal).

[sandalcandal]

The mistake y'all are making is trying to have batteries emulate oil-fueled systems. That's like trying to have a computer emulate pen and paper instead of having it's own paradigm.

So, back to the drawing board, and the problem is you only have enough energy density for short powered flight. Ergo, the answer is to have much more un-powered flight. BFO railgun at the start, sub-orbital mid-flight and you can use your Amazon powerbank to go around in case your first landing glide fails. The real breakthrough is going to be in acceleration couches (and maybe in-flight waste disposal).

You're either trolling or going really off the rails there.

[PlainName]

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

A bit of fun can often be a bit of fun. Trolling is malicious.

[sandalcandal]

My bad I thought you might have been serious.

[tszaboo]

Mid sized jet like 737 burns abts 2500kg jet fuel per hour. Lets say 4000kg for 1000km flight?  12kWh/kg, 50% efficiency = 24000kWh battery needed as replacement. With current li-ion tech that is 72000kg  battery.

You can also calculate with about 2.5L kerosene/seat/100km. For regional flights on the more modern 319neo and similar planes. But if you compare this to a car, it uses less than a car with a 1-2 passengers. And planes dont have the issue like cars, that they have to be small and have to handle well.
But then the plane lands. And you need to charge it up. Planes dont make money on the ground, so better do it fast. There are 500.000 Airplanes / year on Frankfurt airport. That's more than 1000 / day, or 62/hour. Counting with 65/ hour, that is 1500MW continuous charging. That's about 2-3 nuclear reactors operated next to the airport.
And you need to have the same charging facilities at remote locations, or they cannot accept electric planes. How are you going to convince the companies, that are hanging by a thread, with minimal margins defaulting in 2020 to install all this infrastructure? Who is going to do it first?

[mzzj]

Mid sized jet like 737 burns abts 2500kg jet fuel per hour. Lets say 4000kg for 1000km flight?  12kWh/kg, 50% efficiency = 24000kWh battery needed as replacement. With current li-ion tech that is 72000kg  battery.

How are you going to convince the companies, that are hanging by a thread, with minimal margins defaulting in 2020 to install all this infrastructure? Who is going to do it first?

No need to go that far with the speculation. 737 with 72000kg battery is not able to get off the ground. 80000kg maximum take-off weight,  possible battery weight could be something like 20000kg. Still would need about 4x improvement even for short flights.
Slow the planes down and make them more like gliders would help but then it is not any faster than train.

[mzzj]

Further "back of the envelope" numbers: Li-ion batteries cost at the moment around 200 usd/kWh.
737 24 MWh battery pack would cost 4.8 million USD with a maybe 500 flights per battery pack. (you can currently forget about Tesla-like battery lifetime in a airplane where battery weight is extremely critical and every discharge is going to be nearly 100% capacity) 
Battery cost 48 usd per passenger per 1000km flight.  Jet fuel at current prices would be  20 kg per passenger and 7 usd.

Costs (and big part of natural resource use) are obviously somewhere else than jet fuel.

[sandalcandal]

Those seem like bad assumptions.

Further "back of the envelope" numbers: Li-ion batteries cost at the moment around 200 usd/kWh.
737 24 MWh battery pack would cost 4.8 million USD with a maybe 500 flights per battery pack. (you can currently forget about Tesla-like battery lifetime in a airplane where battery weight is extremely critical and every discharge is going to be nearly 100% capacity) 
Battery cost 48 usd per passenger per 1000km flight.  Jet fuel at current prices would be  20 kg per passenger and 7 usd.

Costs (and big part of natural resource use) are obviously somewhere else than jet fuel.

I can't imagine planes literally being completely flat as they land, a significant safety margin is clearly required. The lifetime-cost is also greatly improved for moderate penalties to energy density which is something anyone seriously considering such a system would take. I'd see a penalty to specific energy of 30% as reasonable but assuming 100% DoD is completely out.

No need to go that far with the speculation. 737 with 72000kg battery is not able to get off the ground. 80000kg maximum take-off weight,  possible battery weight could be something like 20000kg. Still would need about 4x improvement even for short flights.
Slow the planes down and make them more like gliders would help but then it is not any faster than train.

Also the comparison of fuel vs. battery weight alone is way off due to the complete lack of accounting for the differences in efficiency and weight of other power train components. The previously linked NASA paper cites 3-4x efficiency and 6x motor power to weight compared to state-of-the-art engines. I suggest at least reading that paper to clear major counter intuitive misconceptions before attempting an analysis. https://ntrs.nasa.gov/citations/20140011913

[mzzj]

Those seem like bad assumptions.

Also the comparison of fuel vs. battery weight alone is way off due to the complete lack of accounting for the differences in efficiency and weight of other power train components. The previously linked NASA paper cites 3-4x efficiency and 6x motor power to weight compared to state-of-the-art engines. I suggest at least reading that paper to clear major counter intuitive misconceptions before attempting an analysis. https://ntrs.nasa.gov/citations/20140011913

NASA paper is written from small 4-person recreational aircraft point of view and we were lately talking about medium sized 737 commercial passenger jets on "short" 1000km distances.  Small aircraft with piston engines and stoneage design just purely suck.
Cirrus SR-22 is apples to oranges..potatoes comparison in this regard.

10x cheaper fuel source? Sure if you compare to 100 octane low lead avgas.  Jet fuel is 6 times cheaper than  100LL. And engines are roughly twice as efficient.

6x Engine power to weight ratio ?
Emrax 268 brushless AC motor has amazing (for electric motor) 11.56 kW/kg power to weight ratio and I'm not sure how well this would scale to larger units. https://www.nextbigfuture.com/2015/04/siemens-and-emrax-claim-best-power-to.html
Jet engines are bit tricky to calculate but Pratt & Whitney PW150 turboprop: 4.76 kW/kg

[sandalcandal]

Those seem like bad assumptions.

Also the comparison of fuel vs. battery weight alone is way off due to the complete lack of accounting for the differences in efficiency and weight of other power train components. The previously linked NASA paper cites 3-4x efficiency and 6x motor power to weight compared to state-of-the-art engines. I suggest at least reading that paper to clear major counter intuitive misconceptions before attempting an analysis. https://ntrs.nasa.gov/citations/20140011913

NASA paper is written from small 4-person recreational aircraft point of view and we were lately talking about medium sized 737 commercial passenger jets on "short" 1000km distances.  Small aircraft with piston engines and stoneage design just purely suck.
Cirrus SR-22 is apples to oranges..potatoes comparison in this regard.

10x cheaper fuel source? Sure if you compare to 100 octane low lead avgas.  Jet fuel is 6 times cheaper than  100LL. And engines are roughly twice as efficient.

6x Engine power to weight ratio ?
Emrax 268 brushless AC motor has amazing (for electric motor) 11.56 kW/kg power to weight ratio and I'm not sure how well this would scale to larger units. https://www.nextbigfuture.com/2015/04/siemens-and-emrax-claim-best-power-to.html
Jet engines are bit tricky to calculate but Pratt & Whitney PW150 turboprop: 4.76 kW/kg

Fair enough, the paper was primarily about smaller aircraft rather than commercial passenger jets like the 737. The model used to get 400 Wh/kg is 200 mile (321 km) range. The paper did quote "SOA" engines so I'm don't think "Small aircraft with piston engines and stoneage design" is fair so say but I can see large jet engines achieving much better efficiencies.

Since you've bothered to read sources and add info and calculations I'll try calculations of my own for 1000km range
Cessena Grand Caravan EX 14 seater turboprop https://cessna.txtav.com/en/turboprop/grand-caravan-ex
Range 1689km, Cruising speed 343km/h, Usable fuel weight 1019kg, full fuel payload 583kg, Engine power 647k W, dry engine weight 175kg
Full range fuel energy = 1019*12 = 12 000kWh
Electric full range energy = 12 200/4 = 3000kWh (Also full range flight time = 1689/343=4.9h, full range energy = 4.9*647=3170kWh)

Electric Range-Energy Efficiency = 1689/3000 = 0.563km/kWh
Energy for 1000km = 1000/0.563=1800 kWh
Minimum engine weight = 647/11.56= 56kg
Engine weight saving = 175-56 =119kg
Available weight = 1019+119=1138kg
Minimum specific energy for 1000km range = 1800/1138 = 1600Wh/kg

Maximum energy with 400Wh/kg = 1138*0.4=455kWh
Maximum range with 400Wh/kg = 256km

Edit2: Didn't add reserve margins for electric but should roughly scale through with built in fuel margins.

It would seem the 400kWh/kg minimum target really is a minimum for viable electric aircraft. I'm not sure how the 750Wh/kg then comes about. However, these calculations as based off an existing turboprop airframe and as also discussed in the NASA paper, electric enable fundamentally different design paradigms which could greatly reduce required power overall not just engine inefficiency.
"NASA’s aeronautical innovators hope to validate the idea that distributing electric power across a number of motors integrated with an aircraft in this way will result in a five-time reduction in the energy required for a private plane to cruise at 175 mph [281km/h]." https://www.nasa.gov/image-feature/nasas-x-57-electric-research-plane
Even halving energy would be immense let alone 5 times reduction.

Edit: Even in very recent news NASA is still sticking to that "goal of a 500 percent increase in high-speed cruise efficiency" 2 Nov 2020 https://www.nasa.gov/aeroresearch/all-electric-x-57-propeller-designs-undergo-wind-tunnel-tests

[Rx7man]

Another "gotcha" in battery systems is that often there are tradeoffs between recharge cycles, capacity, and current draw, as well as diminishing efficiency when you demand more current from them.. If they are getting charged and discharged a couple times a day (which would be needed in order to be viable options), their lifespan might be quite short.
I can't speak as to how each of those details are going to play with each other, but it would certainly be something engineers think about