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Doing some math. Regional jets get somewhere around 45.9 seat miles per gallon (1). So 30 seats, going 125 miles would take around 80 gallons of jet fuel. This

Doing some math. Regional jets get somewhere around 45.9 seat miles per gallon (1). So 30 seats, going 125 miles would take around 80 gallons of jet fuel. This is likely low because all the jets listed are bigger and likely flying longer flights that are more efficient but just go with it. Jet fuel has a specific energy of 12 kwh/kg and a density of 6.7 lb/gal (2). So 80 gallons of jet fuel is 536 lb, or 243 kg, and contains 2,916 kwh of energy. Jet engines are not very efficient, so lets say only 30% of this energy actually ends up being used. So 875 kwh. Lets say we are using batteries that are 300 wh/kg (0.3 kwh/kg), which seems on the high side of what electric cars are using now (and that there are no efficiency loses in the electric motors or elsewhere). Now maybe I messed up my unit conversions but I think that means to carry the same energy onboard you would need 6,428 lbs of batteries. And you are still going to carry atleast 1,600 lbs of fuel on top of that. And you have the weight of both electric and conventional engines. I could see this reducing costs like they say but when many big costs are fixed (pilot, hangar, etc.) will this actually make sense? Will airlines fly something that has thousands of pounds less payload than a competitor but lower running costs? I don't know but it will be interesting to see. (1) https://airinsight.com/seat-miles-gallon-fuel-burn-update/ https://airinsight.com/seat-miles-gallon-fuel-burn-update/ (2) https://en.wikipedia.org/wiki/Jet_fuel https://en.wikipedia.org/wiki/Jet_fuel

ticulatedspline 29d ago
This graphic always reminds me why it's so hard to beat gasoline and that batteries kinda suck. https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...
- kibwen 28d ago
  Energy density alone is a misleading metric, because what matters is how much energy actually gets delivered to the drive mechanism. It's actually not that hard to beat gasoline, because despite its excellent energy density, gasoline engines are only 30% efficient. First and foremost a gasoline engine is a machine for producing heat and noise, and only incidentally for producing forward motion.
- mrinterweb 28d ago
  I think lithium air batteries will be the real inflection point for aeronautics. Li-air has potential density 12 kWh/kg. CATL is focused on this tech. May be some years before they are able to achieve the full potential density. Still, as the other commenters said, the efficiency of electricity make make up that difference.
- vl 28d ago
  Also for traditional fuel you don’t have to carry half of the fuel - oxidizer comes from air. And then when you spend fuel, you have less weight to carry (which becomes noticeable on the plane).
walrus01 29d ago
If they can get the range to within what, for example, an Alaska Airlines/Horizon Q400 flies from Seattle for regional flights (with reserve for diversion airport), that may be sufficient for some purposes. In terms of operating cost, not just cost of fuel, but if the electric engines can be much less costly in terms of periodic maintenance and overhaul. Maintenance and overhaul costs on turboprop and small jet turbine engines are not cheap.
- class3shock 28d ago
  So if they are doing the hybrid approach and just using the conventional engines during cruise they will have way reduced maintenance costs on them. The need for max thrust during takeoff drives a ton off wear and tear, so removing that would be big. If they are able to do electric only that is even better.
Toutouxc 29d ago
As a rule of thumb, when you find yourself looking at an existing internal combustion vehicle and converting fossil fuel energies and efficiencies using battery gravimetric densities, you’re almost always at the “garbage in” stage of GIGO. This plane isn’t a 737, it isn’t even a jet, it doesn’t run the motors the same way, the flight profiles are all different.
ddlsmurf 29d ago
Yes, it doesn't even make sense to make electric trucks, let alone airplanes. Or they'd be mostly battery.
- ragebol 29d ago
  I read new truck sales in China are about 30% electric and climbing. Apparently it does make sense for them
  - ddlsmurf 28d ago
    What China does hardly indicates economic sense, and you can be sure you won't hear about the down sides or failures. They already very agressively hide car lithium fires but they're very frequent. Economics over there are mostly investment driven with a large dose of ideology and vanity, not demand driven. You can see it everywhere including the massive amounts of empty housings for example
    - dmichulke 28d ago
      This ignores the fact that there are also things that China does better or equal than Western companies. Like robots, solar panels, electric cars (?), AI models, electronics. They must be good at something, otherwise China wouldn't be where it is. So flat out dismissing anything from China is not enough of an argument. Mind you, I'm not saying you're generally wrong, just your "generally" is wrong. ;-)
      - ddlsmurf 28d ago
        I'd dispute they do any of those better, they stole the IP, then used public funds to make cheaper versions in the hope of leading the markets, including by being artificially more affordable while there is any competition. Besides electric cars and solar, it's very debatable wether those will actually be ecological in the end. For ex. they are still opening massive amounts of fossil based electric plants, so the truck that is half battery is actually running on coal anyway. It would take an incredible re-work of the electric grids to accomodate actually transitioning away from thermal cars, including some solution for seasonal storage. If you're impressed by their robots, I don't know what you're looking at, they seem to be ridiculous, not even at the tech level that boston dynamics had decades ago. Finally keep in mind that electric cars are fantastic spying devices, for collecting data, and if you're nefarious, imagine hacking into them. That's why teslas are banned near anything governmental in China. So there is a huge strategic advantage to cornering that market, but not really to save the planet. The AIs are all distilled, USA still leads by far there, and they too are strategic weapons
llukas 28d ago
Check jet engine weight and include in the calculation. One weights 2200-3700 lbs according to same source that quotes 45.9 seat miles per gallon. Vs 125 pounds for electric engine.
- tonyarkles 28d ago
  I’d guess comparable for a 30-seat regional, you’d probably want to compare with a PT6, especially since this aircraft is prop driven. That’s only about 250lb dry.
  - llukas 28d ago
    It seems you're right. Would nice to see breakdown for this plane how it actually maps to real world prototype.
    - class3shock 28d ago
      The thing I quoted is more for bigger jets with much larger engines (it was the first reasonable looking source I found). In any case their hybrid has four engines, two electric, two conventional, so you are really should think of it as needing to haul two extra engines on top of what a conventional only jet would have.
fmpfmp 28d ago
Also consider that an empty battery weighs the same as a charged one. Whereas empty fuel tanks don't. I wonder how annoying this is for the engineers to stay within landing weight limits (MLW)
- bluGill 28d ago
  My guess (I'm not an engineer) is landing weight limits are more then because the airplane will never have more than that anyway. They need a little better suspension in case of a hard landing, and different training for the aircraft (which you need anyway) to account for it handling differently, but otherwise it is still an airplane. Maybe bigger spoilers or some other part as well to better bleed off speed. They need to account for it of course, but it seems more like account for it, not difficult. Any engineer in this space able to comment?
  - 542354234235 28d ago
    Landing weight limits are less than takeoff limits because of the extreme stress it puts on the landing gear. This is why planes that have an issue right after takeoff often need to dump tens of thousands of gallons of fuel before they can land. >Aircraft have two main types of weight limits: the maximum takeoff weight is composed of dry operating weight (DOW) plus payload (passengers and cargo), collectively the zero fuel weight (ZFW), plus the trip fuel, contingency, alternate, final reserve and the block fuel (taxi fuel), and the maximum structural landing weight, with the maximum structural landing weight almost always being the lower of the two. This allows an aircraft on a normal, routine flight to take off at a higher weight, consume fuel en route, and arrive at a lower weight. [0] [0] https://en.wikipedia.org/wiki/Fuel_dumping https://en.wikipedia.org/wiki/Fuel_dumping
- insanetake 28d ago
  > an empty battery weighs the same as a charged one Technically, an empty battery weighs less than a charged one. In practice, the difference is negligible.
kvemkon 28d ago
> Lets say we are using batteries that are 300 wh/kg (0.3 kwh/kg) 400 Wh/kg are almost there [1]. [1] https://youtu.be/nM86DBOqgPM?t=541 https://youtu.be/nM86DBOqgPM?t=541
- Gibbon1 28d ago
  People are working on solid state batteries which puts you at 500-600 wh/kg. For cars the economics is a dicey proposition. Because $/wh is important. The extra range (dubious) or lower weight has to cover the cost difference. But for electric aircraft there is a lot to be gained by weight savings.
athrowaway3z 28d ago
The economics to do what planes do today make no sense; but i think that's making the analysis the wrong way around. There are opportunities for which airplanes have never made economic sense because they have big fixed costs like pilot, hangar, fuel-infra, engine(-maintenance). So will small short haul (?pilot-less) rechargeable planes have enough allure to beat out alternatives where planes were never considered before? probably not at any major scale in a future where it competes with other autonomous transport, but that's me guessing at numbers. There will be enough of a market to build these things for niche constraints (eg the fuel-infra if small modular reactors become widespread).
- bluGill 28d ago
  The big problem with autonomous airplanes is they still require airports. I don't have a runway in my backyard, and I can't build one because someone else has a house there. My closest runway is about 20 minutes away, and then once I get to the far airport it is another 20 minutes to get where I'm going. This is why commute by airplane will always be a niche only a few people can do. In turn this means airplanes will never scale to be as cheap as cars are (a new Cesna stationair HD MSRP is over $700k - I submit that if they were building 40 per hour like many SUVs are built the cost would be around $70k) Even a farmer is unlikely to be willing to give up that much space from their farmer operation. I do know farmers who have their own private runways, but they love flying and so are willing to give up some income to have a runway. They are giving up thousands of dollars in gross income to have that runway. I happen to have a backyard that is big enough for a helicopter (I think - I never measured but I think I'm at the minimums the FAA requires), but I have an oversized yard. There are a lot more places for a helicopter. Most local parks have enough space, but I think communities would object to regular use. (if used only a couple times a month no problem, but more that and the noise and need to clear everyone else out will make it an objection)
horsawlarway 28d ago
They discuss quite a bit of this in the video. I actually thought it was a decent walk through of why they're targeting the space they're targeting, and how they're thinking about exactly these problems. Some items to consider from the video 1. short flights spend an large amount of energy simply having the engines running during taxi to/from the runway. 2. Take-off also consumes much more fuel than cruising. 3. 1 & 2 combine to push airlines to prefer larger & larger planes making longer trips when using fuel (it's how they're managing that 45.9 seat mile number - it get much worse for shorter trips). 4. They're already pushing the 400kwh/kg range for batteries (I believe he makes an offhand comment in the video that they're using 8 packs, with roughly the capacity/weight of 4 tesla battery packs - which would put their batteries in the ~4k lb range if we estimate by teslas pack weights. They are likely pushing to go lower than that. I think it's not crazy to consider they're targeting a production weight ~50% below your guess - in the high 3000s) 5. On top of fuel savings, one of his more compelling points is that maintenance on their engines will be much, much lower. Jet engines are expensive to service, maintain, and repair (thousands of parts, complicated designs, extreme operating conditions). Their motors are basically 450kg dc motors - it's a giant drone motor mounted on an airframe. 6. they seem to have quite a bit of interest from existing airlines (ex - united) so apparently this does seem compelling to them. 7. He quotes a $5 take-off cost in electrical power. Something like an Embraer ERJ-135 uses ~20 - 30 gallons of jet fuel for the same thing (~$100). If they target a plane that's doing very frequent takeoffs/landings, operating costs could be considerably lower, not just lower. --- Personally - I don't know if they'll make it work, but it's definitely an interesting play, with more real thought put into it than most attempts I've seen.
- class3shock 28d ago
  1-3. Agreed 4. Remember my predicted number is on the low side of how much juice they would need. Of course they get much better efficiency than a conventional jet on taxi and takeoff, so maybe it ends up being closer to what you are saying. I wish they had some more hard data. 5. Yep, commented on this in another post but even just removing takeoff wear and tear on a conventional engine would be big. 6. I would take that with a big dose of salt. United has a deal with Boom (a complete fraud of a company in my view) to purchase planes. So maybe not the best metric. 7. I haven't done the math but the $5 takeoff doesn't pass the smell test for me. $5 doesn't buy much juice (50 kWh? So like a gallon of jet fuel?) and getting a 30k+ lb plane to cruising altitude is not trivial. "Personally - I don't know if they'll make it work, but it's definitely an interesting play, with more real thought put into it than most attempts I've seen." Totally agree, which I never thought I would say about an aerospace startup.
thefourthchime 28d ago
There's a lot more to it than that. Just going around on the taxi, Take off and landing burns a ton of fuel for these for traditional jet engines. This plane is designed specifically to cost less to operate. I'm pretty sure they figured it out, which is why they have over 9b in order commitments.

ticulatedspline 29d ago

This graphic always reminds me why it's so hard to beat gasoline and that batteries kinda suck. https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...

kibwen 28d ago
Energy density alone is a misleading metric, because what matters is how much energy actually gets delivered to the drive mechanism. It's actually not that hard to beat gasoline, because despite its excellent energy density, gasoline engines are only 30% efficient. First and foremost a gasoline engine is a machine for producing heat and noise, and only incidentally for producing forward motion.
mrinterweb 28d ago
I think lithium air batteries will be the real inflection point for aeronautics. Li-air has potential density 12 kWh/kg. CATL is focused on this tech. May be some years before they are able to achieve the full potential density. Still, as the other commenters said, the efficiency of electricity make make up that difference.
vl 28d ago
Also for traditional fuel you don’t have to carry half of the fuel - oxidizer comes from air. And then when you spend fuel, you have less weight to carry (which becomes noticeable on the plane).

walrus01 29d ago

If they can get the range to within what, for example, an Alaska Airlines/Horizon Q400 flies from Seattle for regional flights (with reserve for diversion airport), that may be sufficient for some purposes. In terms of operating cost, not just cost of fuel, but if the electric engines can be much less costly in terms of periodic maintenance and overhaul. Maintenance and overhaul costs on turboprop and small jet turbine engines are not cheap.

class3shock 28d ago
So if they are doing the hybrid approach and just using the conventional engines during cruise they will have way reduced maintenance costs on them. The need for max thrust during takeoff drives a ton off wear and tear, so removing that would be big. If they are able to do electric only that is even better.

Toutouxc 29d ago

As a rule of thumb, when you find yourself looking at an existing internal combustion vehicle and converting fossil fuel energies and efficiencies using battery gravimetric densities, you’re almost always at the “garbage in” stage of GIGO. This plane isn’t a 737, it isn’t even a jet, it doesn’t run the motors the same way, the flight profiles are all different.

ddlsmurf 29d ago

Yes, it doesn't even make sense to make electric trucks, let alone airplanes. Or they'd be mostly battery.

ragebol 29d ago
I read new truck sales in China are about 30% electric and climbing. Apparently it does make sense for them
- ddlsmurf 28d ago
  What China does hardly indicates economic sense, and you can be sure you won't hear about the down sides or failures. They already very agressively hide car lithium fires but they're very frequent. Economics over there are mostly investment driven with a large dose of ideology and vanity, not demand driven. You can see it everywhere including the massive amounts of empty housings for example
  - dmichulke 28d ago
    This ignores the fact that there are also things that China does better or equal than Western companies. Like robots, solar panels, electric cars (?), AI models, electronics. They must be good at something, otherwise China wouldn't be where it is. So flat out dismissing anything from China is not enough of an argument. Mind you, I'm not saying you're generally wrong, just your "generally" is wrong. ;-)
    - ddlsmurf 28d ago
      I'd dispute they do any of those better, they stole the IP, then used public funds to make cheaper versions in the hope of leading the markets, including by being artificially more affordable while there is any competition. Besides electric cars and solar, it's very debatable wether those will actually be ecological in the end. For ex. they are still opening massive amounts of fossil based electric plants, so the truck that is half battery is actually running on coal anyway. It would take an incredible re-work of the electric grids to accomodate actually transitioning away from thermal cars, including some solution for seasonal storage. If you're impressed by their robots, I don't know what you're looking at, they seem to be ridiculous, not even at the tech level that boston dynamics had decades ago. Finally keep in mind that electric cars are fantastic spying devices, for collecting data, and if you're nefarious, imagine hacking into them. That's why teslas are banned near anything governmental in China. So there is a huge strategic advantage to cornering that market, but not really to save the planet. The AIs are all distilled, USA still leads by far there, and they too are strategic weapons

llukas 28d ago

Check jet engine weight and include in the calculation. One weights 2200-3700 lbs according to same source that quotes 45.9 seat miles per gallon. Vs 125 pounds for electric engine.

tonyarkles 28d ago
I’d guess comparable for a 30-seat regional, you’d probably want to compare with a PT6, especially since this aircraft is prop driven. That’s only about 250lb dry.
- llukas 28d ago
  It seems you're right. Would nice to see breakdown for this plane how it actually maps to real world prototype.
  - class3shock 28d ago
    The thing I quoted is more for bigger jets with much larger engines (it was the first reasonable looking source I found). In any case their hybrid has four engines, two electric, two conventional, so you are really should think of it as needing to haul two extra engines on top of what a conventional only jet would have.

fmpfmp 28d ago

Also consider that an empty battery weighs the same as a charged one. Whereas empty fuel tanks don't. I wonder how annoying this is for the engineers to stay within landing weight limits (MLW)

bluGill 28d ago
My guess (I'm not an engineer) is landing weight limits are more then because the airplane will never have more than that anyway. They need a little better suspension in case of a hard landing, and different training for the aircraft (which you need anyway) to account for it handling differently, but otherwise it is still an airplane. Maybe bigger spoilers or some other part as well to better bleed off speed. They need to account for it of course, but it seems more like account for it, not difficult. Any engineer in this space able to comment?
- 542354234235 28d ago
  Landing weight limits are less than takeoff limits because of the extreme stress it puts on the landing gear. This is why planes that have an issue right after takeoff often need to dump tens of thousands of gallons of fuel before they can land. >Aircraft have two main types of weight limits: the maximum takeoff weight is composed of dry operating weight (DOW) plus payload (passengers and cargo), collectively the zero fuel weight (ZFW), plus the trip fuel, contingency, alternate, final reserve and the block fuel (taxi fuel), and the maximum structural landing weight, with the maximum structural landing weight almost always being the lower of the two. This allows an aircraft on a normal, routine flight to take off at a higher weight, consume fuel en route, and arrive at a lower weight. [0] [0] https://en.wikipedia.org/wiki/Fuel_dumping https://en.wikipedia.org/wiki/Fuel_dumping
insanetake 28d ago
> an empty battery weighs the same as a charged one Technically, an empty battery weighs less than a charged one. In practice, the difference is negligible.

kvemkon 28d ago

> Lets say we are using batteries that are 300 wh/kg (0.3 kwh/kg) 400 Wh/kg are almost there [1]. [1] https://youtu.be/nM86DBOqgPM?t=541 https://youtu.be/nM86DBOqgPM?t=541

Gibbon1 28d ago
People are working on solid state batteries which puts you at 500-600 wh/kg. For cars the economics is a dicey proposition. Because $/wh is important. The extra range (dubious) or lower weight has to cover the cost difference. But for electric aircraft there is a lot to be gained by weight savings.

athrowaway3z 28d ago

The economics to do what planes do today make no sense; but i think that's making the analysis the wrong way around. There are opportunities for which airplanes have never made economic sense because they have big fixed costs like pilot, hangar, fuel-infra, engine(-maintenance). So will small short haul (?pilot-less) rechargeable planes have enough allure to beat out alternatives where planes were never considered before? probably not at any major scale in a future where it competes with other autonomous transport, but that's me guessing at numbers. There will be enough of a market to build these things for niche constraints (eg the fuel-infra if small modular reactors become widespread).

bluGill 28d ago
The big problem with autonomous airplanes is they still require airports. I don't have a runway in my backyard, and I can't build one because someone else has a house there. My closest runway is about 20 minutes away, and then once I get to the far airport it is another 20 minutes to get where I'm going. This is why commute by airplane will always be a niche only a few people can do. In turn this means airplanes will never scale to be as cheap as cars are (a new Cesna stationair HD MSRP is over $700k - I submit that if they were building 40 per hour like many SUVs are built the cost would be around $70k) Even a farmer is unlikely to be willing to give up that much space from their farmer operation. I do know farmers who have their own private runways, but they love flying and so are willing to give up some income to have a runway. They are giving up thousands of dollars in gross income to have that runway. I happen to have a backyard that is big enough for a helicopter (I think - I never measured but I think I'm at the minimums the FAA requires), but I have an oversized yard. There are a lot more places for a helicopter. Most local parks have enough space, but I think communities would object to regular use. (if used only a couple times a month no problem, but more that and the noise and need to clear everyone else out will make it an objection)

horsawlarway 28d ago

They discuss quite a bit of this in the video. I actually thought it was a decent walk through of why they're targeting the space they're targeting, and how they're thinking about exactly these problems. Some items to consider from the video 1. short flights spend an large amount of energy simply having the engines running during taxi to/from the runway. 2. Take-off also consumes much more fuel than cruising. 3. 1 & 2 combine to push airlines to prefer larger & larger planes making longer trips when using fuel (it's how they're managing that 45.9 seat mile number - it get much worse for shorter trips). 4. They're already pushing the 400kwh/kg range for batteries (I believe he makes an offhand comment in the video that they're using 8 packs, with roughly the capacity/weight of 4 tesla battery packs - which would put their batteries in the ~4k lb range if we estimate by teslas pack weights. They are likely pushing to go lower than that. I think it's not crazy to consider they're targeting a production weight ~50% below your guess - in the high 3000s) 5. On top of fuel savings, one of his more compelling points is that maintenance on their engines will be much, much lower. Jet engines are expensive to service, maintain, and repair (thousands of parts, complicated designs, extreme operating conditions). Their motors are basically 450kg dc motors - it's a giant drone motor mounted on an airframe. 6. they seem to have quite a bit of interest from existing airlines (ex - united) so apparently this does seem compelling to them. 7. He quotes a $5 take-off cost in electrical power. Something like an Embraer ERJ-135 uses ~20 - 30 gallons of jet fuel for the same thing (~$100). If they target a plane that's doing very frequent takeoffs/landings, operating costs could be considerably lower, not just lower. --- Personally - I don't know if they'll make it work, but it's definitely an interesting play, with more real thought put into it than most attempts I've seen.

class3shock 28d ago
1-3. Agreed 4. Remember my predicted number is on the low side of how much juice they would need. Of course they get much better efficiency than a conventional jet on taxi and takeoff, so maybe it ends up being closer to what you are saying. I wish they had some more hard data. 5. Yep, commented on this in another post but even just removing takeoff wear and tear on a conventional engine would be big. 6. I would take that with a big dose of salt. United has a deal with Boom (a complete fraud of a company in my view) to purchase planes. So maybe not the best metric. 7. I haven't done the math but the $5 takeoff doesn't pass the smell test for me. $5 doesn't buy much juice (50 kWh? So like a gallon of jet fuel?) and getting a 30k+ lb plane to cruising altitude is not trivial. "Personally - I don't know if they'll make it work, but it's definitely an interesting play, with more real thought put into it than most attempts I've seen." Totally agree, which I never thought I would say about an aerospace startup.

thefourthchime 28d ago

There's a lot more to it than that. Just going around on the taxi, Take off and landing burns a ton of fuel for these for traditional jet engines. This plane is designed specifically to cost less to operate. I'm pretty sure they figured it out, which is why they have over 9b in order commitments.