Let's consider Cessna-172S ([4]). Its characteristics:
- 130 kW engine, Lycoming_O-360 that weighs 117 kg. For comparison, an electric motor of this range would weigh 11-13 kg (at 10-12 kW/kg, [2]). That saves 100+ kg weight immediately and we can put 50+ kWh batteries instead.
- It carries up to 200 liters of kerosene ([3]), which weighs 164 kg. We can place 82 kWh of batteries instead.
- The engine consumes around 30 liters/hour ([1]), which gives us ~6.7 hours of flight time or the equivalent of 6.7*130=871 kWh for an electric-power plane.
- The fuel tank weighs about ~14 kg (source: an LLM, sorry) and gives us another 7 kWh.
So, we can put 50+82+7=139 kWh. By using modern materials, we can probably increase it to ~180 kWh, which will give us about 1.5 hours of flight time / 300 km range. This is much less than 6.7 hours, but quite practical for recreation and short flights. And it would be much cheaper to run too.
That said, still not practical for medium and long flights.
But the point that CATL makes with this announce is that before this capacity boost, electric planes were a complete joke. Now, they are only somewhat funny.
What I am more excited about is that electrically pumped rockets are now a lot more practical. As an example, Electron is such a rocket ([1]). It can now reduce the weight of the battery pack and increase payload.
I have an imagined invention where battery packs drop off an electric jet as it cruises and they glide to a landing somewhere when they are out of power.
Nuclear waste can be stored on the Moon. Just be careful that it doesn't overheat and turn into a giant rocket, propelling the Moon out of the solar system.
Harbour Air successfully tested electric plane based on De Havilland Beaver. This is still a super short distance but I think the longest route Harbour air has is Vancouver <-> Seattle and it's a 55 minute flight.
The point not considered is the Cessna 172 is an extraordinarily draggy airframe - it didn't need to be clean and laminar because fuel was (relatively) cheap.
Electric aircraft of the future will have half the drag or less. High aspect ratios, flush fairings, streamlined cockpits etc.
> quite practical for recreation and short flights
Perfectly agree with everything, but 1.5hr may be very short if you need to have 30 minutes of reserve at landing. On the saving side, you don’t have to have an alternator to transform ICE energy into energy for the dashboard instruments. On the downside, you now need to heat the cabin manually, rather than reusing the ICE heat.
The electric motor is not 100% efficient so some heat must be available for cabin. Large synchronous generators are 97% efficient not sure about 100 kw e vehicle
Motors
The power requirement at cruising speed would quite a lot less than max power would it not? If cruse consumed 60% of max you'd be using closer to 80kW which would give you over 2 hours flight time.
324 nmi range for the regular variant. Around 65 nmi for the electric version.
This is with older batteries, probably with very bad pack-level energy density. The battery pack can even be swapped. Great to avoid having to wait for charging, but probably terrible for weight.
If you design the aircraft for electric flight from the ground up (see Maxwell X-57 for how you could do that), with a structural battery pack, and with 300-500wh/kg batteries, I'm willing to bet a 2-5 times increase in range is viable.
A lot of people won't fully fuel up their 172 so they can bring more weight, either baggage or passengers. I don't think anyone would fly 6.5 hours in one either, but 2+ is normal for non-training flights.
Well, they were already possible and being sold. But with relatively short but usable ranges. Those now more than double with this battery. Which makes those planes usable in a lot more scenarios.
Consider the Eviation Alice, one of the 9 passenger prototype electrical planes that is currently undergoing test flights (i.e. it definitely works). The advertised range is 250nm. Not amazing. But far enough for a lot of regional flights.
What would happen if you double the battery capacity without increasing the weight? You more than double that range. This is counter intuitive until you realize that you are not going to need more energy for taking off, or reserves. All that extra energy goes into extending cruise range. So you get more than 250nm extra. Basically, it's probably getting closer to 600nm. That's still not amazing but there are a lot of flights every day that are much shorter than that. All of those are now doable with electrical planes. At a fraction of the fuel cost.
Most flights are short haul. And they are, well, short. Which means, all of those are in scope for electrical planes. Small planes work well for these too. You don't have to cram hundreds of people in a plane if you eliminate fuel cost as a major cost factor. That's the only reason we do that. It's not like it's pleasant or comfortable. 20 ten passenger planes can do the work of one passenger jet. But it can do it more flexible and cover more destinations too.
Electrical planes are not about doing exactly the same things that we do with traditional planes but about doing a lot more than that. Basically, less noise, less pollution, less cost, means that a whole lot of flights that would be considered decadent and obscene right now become perfectly feasible and reasonable. A ten minute hop across town. Why not? Live 70 miles from your office? Not a problem, you commute there in under 15 minutes. For the price of a few cups of coffee.
> Most flights are short haul. And they are, well, short. Which means, all of those are in scope for electrical planes.
Exactly. In the EU, Eurocontrol (European Organisation for the Safety of Air Navigation) says 30.6% of flights in 2020 were 0-500km, roughly within the range of the Eviation Alice currently. A further 43.6% of flights in the EU are between 500 and 1500km.
Source [1]
> You don't have to cram hundreds of people in a plane if you eliminate fuel cost as a major cost factor. That's the only reason we do that.
Not only. Gate capacity and runway capacity is an issue too. But that might also be easier to resolve with smaller electric planes. E.g. there's Liliums approach of vertical takeoff from little more than a helipad-sized platform, but even non VTOL planes capable of taking off from short runways would be helpful.
It's not just about runway length. Noise reduction would also make it easier to use smaller local airports. Electric aircraft are already more quiet, but there's probably room for even more reduction by using ducted fans or toroidal propellers.
We may also see a return to more of a hub-and-spoke model. Fly from a smaller, local airport close to you. Fly to some hub near the half-way point, switch to a plane that takes you to a small airport close to your destination. If planes are smaller maybe security can be relaxed too. Total time spent travelling could be comparable to taking a direct flight with a large international airport further from your origin and destination. Then the aircraft doesn't need to be very long range.
The thought of a return to more of a hub-and-spoke model sounds like a total nightmare. It'd take a huge price difference before I'd consider that, personally (EDIT: As in, I usually check "direct flights only" or equivalent and only relent if the cost is ridiculously much higher). Then again my perspective is being near multiple large international airports, so maybe that might appeal to some.
Hub and spoke is primarily used to fill large planes. If you have 10-20 passenger electric planes you'd land at some random county airport, eat a hamburger or a taco while the plane recharges, then get back on the same plane and finish the trip. So you'd have a layover like hub and spoke but all the concerns about missing connections go away.
ICE engines only manage to turn ~15% of the stored energy in gasoline into actual work. A bit of googling suggests that jet engines are about 35% efficient. Stored electricity is much more efficiently turned into mechanical work... Electric engines have 75-90% efficiency. So, you get a lot more work or unit of stored energy.
That factor 6 already seems to include the efficiency of the engine. Pure chemical energy density of kerosene is 12000 W/kg, 24x the new battery's energy densitiy.
Yes. 12kWh/kg chemical energy for kerosene, a little more for avgas. But with a 25% efficiency you are only getting 3kWh out of a kg of fuel. Electric motors tend to have higher efficiency -- maybe up to 75% so you might nearly get 500Wh from a kg of battery.
Yep. Also... kerosene gets spent. Pilots can also dump fuel in emergency when it's too heavy to land. Battery powered planes can't dump electricity, so I'd imagine some trade offs that have to be made.
That is a very good and often overlooked point. So in average on a flight one has to calculate maybe with 60% weight of kerosene, while the battery keeps 100% of its weight during the entire flight.
It gets worse with lithium air batteries that actually gain weight as they discharge because of the formation of solid oxides from the air. Argonne are reporting 1200Wh/kg in the lab though so still worth it.
This is more about day to day operations than emergencies. For an electric plane, your MTOW (max takeoff weight) is equal to your MLW (max landing weight). An ICE plane can take off with "bonus" fuel that it can't land with for structural reasons, while an electric plane can't.
Electric planes could recharge using solar or wind. As efficiency increases with these technologies, it would mean planes wouldn't require carrying the same watt-for-watt energy as fuel.
> Electric planes could recharge using solar or wind. As efficiency increases with these technologies, it would mean planes wouldn't require carrying the same watt-for-watt energy as fuel.
Those are pipe dreams :-)))
Solar recharging for electric cars is not realistic, let alone for electric planes.
Wind charger... maybe there's something there, but the fact that nobody has tried it probably means it's not good enough.
Planes have a much larger surface area to carry solar panels, and they fly above clouds, so have clearer access to sunlight than cars do.
Wind charging is more of a pipe dream, but there's no reason a plane couldn't glide for a period of time to get some energy back, similar to regenerative breaking.
There have been experiments in both areas, and while it's certainly unfeasible today for any large aircraft, the technology and efficiency will only improve. It would be wrong to discard these as an impossibility.
The concepts of potential energy and kinetic energy make the "wind charging" idea ... difficult.
The extra weight and structural challenges imposed by solar panels on aircraft don't seem worth it. The math on (174 sqft) * ideal theoretical power (250 W /m2) yields an optimistic ideal 4000 Watts. A conservative 75% power usage of a 172 engine is around 100kW. 4% under ideal circumstances.
Recharging would take a lot of energy but it's not unthinkable to have 1-3 GW supplied to an airport (which is what a reactor would likely supply), large metropolitan areas and large industrial factories already get to similar amounts. It's a couple of transmission lines and most large airports are close to population centers anyway.
The challenge would be getting the right amount at the right time, like now with quick charging. Like there, you'd probably have buffer storage at the airport so that it consumes electricity when available (e.g. during the day from solar) and dispenses it to aircrafts when needed. Luckily, most airports in the world have nearly all take offs and landings during the day, so there's a big overlap. Dubai would be an example where likely all would come from solar but a lot is needed over night (if we ever get electric long-haul flights).
So overall I don't think that this would be the limiting factor. But I guess larger airliners are more likely to run on synthetic fuels than electricity for a long time. And I guess that's fine, we have a lot of areas where cheap and/or dense batteries can help us much more in the short term (grid storage, cars, trucks).
Why does it have to be poison? Wouldn't having an airport nearby be a blessing for anyone with solar panels on their roof? Just like an industrial zone, it'd be a nonstop load ready to buy from anyone, anytime. (Yes I understand the infrastructure would need to change a lot.)
It's way cheaper and more efficient for electricity consumers to purchase power from the grid, and for the grid to figure out the most optimal way to produce and deliver the power.
Solar and wind are in many areas a) only available during certain hours b) expensive.
To ensure you have a stable power cost, and stable power availability, you as a large consumer (In the EU) make PPA agreements with power producers for specific KW rates, for specific KWh amounts, for specific times. These are complicated agreements.
A few panels on some warehouses and hangers close to an airport could keep the lights and the A/C on in the terminal, but that's about it. No one is putting up wind turbines anywhere close to an airport.
I feel that synthetic kerosene via electrolysis is a far more viable path to sustainable aviation than battery-electric engines. The energy-inefficiency doesn’t really matter as long as you can keep the total cost of the flight within consumer reach.
Carbon neutral synthetic fuels might make sense for airliners, because they're already pretty efficient, reliable and incomprehensibly powerful and there's tons of other stuff in them that'd require maintenance even if you took out the engines.
They don't make sense for general aviation planes that are usually a fifty year-old engine design that requires expensive overhauls and guzzles expensive fuel wrapped in a bit of aluminum.
But do we really need to focus on general aviation? I don't have numbers but believe it to be a pretty small part overall. In transportation, it's also fine if we keep some gasoline speciality vehicles for a long time, as long as we're able to convert the vast majority of cars and trucks.
Compated to jet fuel, avgas is more expensive today because there's almost no market for it. When synthesized, it's probably cheaper to produce than jet fuel.
The best application I've seen for the currently available electric airplanes are flight schools. One plane I looked into has a flight time of 1.5hrs, which is plenty for training. When I last priced out instructor time, 30% of the cost was the fuel. This means that flight schools could cut prices by up to 25% or so. That being said, the plane I looked into was $250k, while a student level ICE plane could be had for $20-50k.
I don’t think Musk has given a writeup of his reasons for thinking 400wh/kg is the magic number, but a lot of research has been done that says similar numbers. This paper https://www.sciencedirect.com/science/article/pii/S2666691X2... is a good review; it cites researchers saying 800wh/kg for an electric Airbus A320, NASA saying 400Wh/kg for general aviation and 750Wh/kg for regional aviation, and other researchers saying 600Wh/kg for commercial regional aircraft and 820Wh/kg for commercial narrow-body aircraft.
That paper also sketches out the argument for electric flight at close to current battery densities rather than close to kerosene energy densities. It goes:
Jet fuel gets roughly 28% final efficiency while electric gets roughly 90%, so divide jet fuel by 3 to get 4,000 effective Wh/kg.
That is getting close to current energy densities of batteries. You only need to find one more ~2x improvement that electric flight can obtain over jet fuel to bring it into the range of 500Wh/kg, which CATL is saying they have in production right now.
(Presumably Musk’s magic 400Wh/kg number involved another 2.5x improvement, though I don’t know where specifically he thought it would come from. The internet seems to think he said you can go higher because you don’t need oxidizer from the air to burn jet fuel, but that doesn’t sound right since you still need to push on the air with your fans and you’ll run out of that at high altitude before you run out of oxygen, so it must be coming from somewhere else. Regardless, the point is that jet fuel imposes design constraints that trap you in a local maximum of aircraft efficiency, and electric engines allow you to explore a wider space which may have much much higher maximums.)
I assume it's a limit motivated more by how far you can go rather than the cost of fueling/charging. Like, above a certain weight/energy store ratio, it's either too heavy to fly or would just have an incredibly limited range.
Soaring is currently making the switch, not only as sustainers, but also for starting. There are models from major manufacturers, like the Schleicher AS 33/34 me [1] or Antares [2].
The point isn't necessarily to equal or beat kerosene in terms of weight and range, but rather to be good enough that electric aircraft are usable for many or most use cases.
Planes tend to be very expensive to operate, due to maintenance and fuel costs. Some people would be happy to trade range for dramatically lower operating costs.
Nope, the variable is cost per passenger. Large jets only exist because fuel is really expensive. The cost per passenger gets astronomical with smaller planes. That's why only rich people can afford that. Big planes are more economical. Because of the fuel.
This is simply not true with electrical planes. A mega watt hour of power is about 60-100$. And much cheaper than that with renewables. Not at retail prices of course. But if you consume power by the mwh, you'd be investing in your own generation (solar + storage) pretty soon. A mwh is about what you need to move a small electrical plane a few hundred miles. The kerosene cost for a similar journey in a small jet is going to be hundreds of dollars, even for a small jet. The smallest jets burn 50-100 gallons of fuel per hour (in cruise). Depending where you get your fuel, that ranges from 3-5$ per gallon. That's why small jets are only for rich people. Even a very short flight sets you back hundreds of dollars. A simple propeller plane is cheaper. But we're still talking 5-10 gallons per hour. That's why people talk about 100$ hamburgers. Because that's what it costs to take your tiny plane out to grab a burger somewhere.
Big big jets are a bit more economical with fuel than small ones. But they only makes sense if you can distribute fuel cost among many passengers.
With electrical, you can use lots of smaller planes cost effectively rather than having to put lots of people in a few bigger ones. For the same reason, you don't need big airports either. Or worry about pollution. And even the noise of small electrical planes is not as much of a problem. And with autonomous flight, we won't even need pilots long term. Small electrical planes are good enough and much nicer for passengers, more flexible to operate, etc.
Airliners have already moved away from the hub-and-spoke model to a point-to-point model where smaller narrowbodies fly direct from small airport to small airport (E.g. Southwest in the US). They do this specifically because of the increased efficiencies of smaller aircraft.
If you can further lower the per passanger cost of small planes, you can make smaller airports more viable, and fly point-to-point from more odd routes. Think Oxford, UK (OXF), to Gothenburg, Sweden (GSE).
And more non trivial amounts of money on parts, maintenance and inspections. Lots of moving parts. Lots of complexity. Lots of engineering hours spent on keeping it all running smoothly. Electrical planes still need inspections but they are a lot more robust and the complexity of maintaining, inspecting, and operating them is at least an order of magnitude lower. And they break down in less and less expensive ways and probably less often too.
The third expensive component is staffing. Pilots are expensive and for complex aircraft they need lots of training. So, simple electrical airplanes lower the training cost and make it easier to train and find new pilots. And complexity is also a reason you often need two pilots. Smaller/simpler airplanes can be one pilot operations. And of course replacing pilots entirely when these things become autonomous brings further cost savings. The flip side is that lots of small planes require more pilots.
Finally, big airports are expensive. You have to pay landing fees in lots of places. And service fees. And missing your assigned slot because of delays is expensive. That too goes away if you start flying from less busy/cheaper airports.
So, there a few additional savings here beyond fuel. But that is the biggest one.
IMHO this is going to be a repeat of the EV revolution a decade ago. But minus a lot of the emotional bickering about range anxiety, etc. Most planes are operated by for profit businesses. The second something cheap becomes available, they'll be all over it. In the same way using electrical vans vs. ice vans is not a topic of debate in the industry. You get the electrical van if you can. They are cheaper to operate. There's zero uncertainty on that front so you see essentially all large fleets transitioning to electrical vans as soon as they can get it done.
With electrical flight, a lot of this stuff is bottle necked on product development (happening), certification (starting to happen), and volume production (not happening yet). Better batteries increase the demand further. But without volume production, demand is not the issue. Supply is. This is and will be supply constrained for a long time.
Not at this density. This is the minimum requirement for medium length large airplanes. Small aircraft are already viable with mass produced batteries.
As they scale production of these, hopefully they can get 20% additional improvements at the cell/pack level, reaching potential to replace the most common flights.
Video[0] isn't a direct answer, but I found it helpful for understanding the trade offs that come when considering using electric power for a plane vs regular fuel. They show the math in an easy to follow diagram.
tl;dr for their small kit aircraft the weight of batteries they would need to match the stored energy of equivalent fuel (even with a battery at 500wh/kg) would be 5-10x heavier, and also not get lighter during the flight. They said for long range it doesn't make sense, but that there are lots of companies iterating in the short range electric space.
Seems like marketing hype to me. An 8-hour transatlantic flight requires something like 600MWhr of energy. That's about 75MW, which is in small nuclear reactor territory.
Replacing transatlantic flights is out of the question (for batteries for now). But there exists shorter routes, and according to this list [1] on Wikipedia, the busiest route in the world is 449km long. That's probably also not doable now, but maybe in some years?
For the first years it will probably only be a few wierd, short routes in rich countries like Norway with 110% financial support from the state. But when they can safely fly 5-600km there is a actually quite a number of routes with a lot of passengers out there.
The US very nearly built a 60MW nuclear reactor for use in airplanes after their scaled down design at 2.5MW was successfully built, ran, and tested. This was done in the 1950s and, incidentally, required inventing molten salt reactors. https://en.m.wikipedia.org/wiki/Aircraft_Reactor_Experiment
(They actually planned to go all the way to 350MW, which could theoretically run a transatlantic passenger jet with 2,000 passengers, assuming it’s even possible to build such an airframe.)
Seems like it would still annihilate the payload/range.