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For reference: Model 3 apparently has 75 to 100 kWh. This plane seems to spec out - Li-lon - 900 kWh. For a layman, it sounds like 9 times the battery weight of

For reference: Model 3 apparently has 75 to 100 kWh. This plane seems to spec out - Li-lon - 900 kWh. For a layman, it sounds like 9 times the battery weight of a Model S flying in the sky... Wonder how they made it light enough to be able to fly... https://www.eviation.co/alice/ https://www.eviation.co/alice/

gvb 8y ago
Good question. The Model 3 battery[1] weighs 478 kg so 9x = ~4,300kg. 11 people on board is another 1,000kg (not including the golf clubs). MTOW[2] is 6,350kg so the airframe needs to weigh in at ~1,000kg. I'm sure they can make a battery lighter than a Model 3 battery (optimized for weight rather than cost), but how much lighter??? Unlike liquid fueled aircraft, you won't be able to trade off fuel weight for passenger weight to stay under MTOW. [1] https://evannex.com/blogs/news/tesla-s-battery-pack-is-both-mysterious-and-alluring-work-in-progress https://evannex.com/blogs/news/tesla-s-battery-pack-is-both-... [2] https://en.wikipedia.org/wiki/Maximum_takeoff_weight https://en.wikipedia.org/wiki/Maximum_takeoff_weight
- bronco21016 8y ago
  Excellent point. Often times only enough fuel for the route is taken so more payload can be taken. In a battery setup your max payload is always the same. No trade offs for range.
- rhinoceraptor 8y ago
  I would imagine that planes could have much higher battery cell per battery pack utilization, because the protective shell for the battery packs is less necessary. Some back of the envelope math for the Model 3 battery: it has 4416 2170 cells, 66g each, is 291.5 kg, and the total battery pack weight is 478 kg. So only 60% of the battery pack weight is the actual battery cells.
jetrink 8y ago
That's an interesting statistic. According to Wikipedia, the Tesla's battery is around 500kg, so the aircraft is carrying around 4500kg in batteries. For comparison, the 10-seat Cessna 404 Titan weighs just 2200kg when empty and has a max take-off weight of 3800kg. So the battery alone weighs more than a similar Cessna, full of pax, luggage and fuel. Hm. They list a MTOW of 6350 kg. Less 800kg for 10 fully clothed adults and the weight of the battery, there's only 1000kg left for the plane. Maybe that's possible?
- Robotbeat 8y ago
  About 3.8 tons they say for the battery. They're relying on removing some excess structure from the battery. The thing is about 60% battery by take-off weight. That's not as crazy as it sounds. A 777 is about half fuel at max fuel load.
  - ams6110 8y ago
    It burns that fuel as it flies though, reducing weight which is important for landing safely. The EV aircraft will weigh the same landing as taking off, which presents some complications.
    - Robotbeat 8y ago
      ...but those complications can be overcome. Partially because the airframe is so efficient that the landing speed should be tolerable even with a high landing mass. Materials have improved significantly in the last few decades. There's a lot more possible now than in the past.
aphextron 8y ago
>Wonder how they made it light enough to be able to fly... You get a massive weight savings in the engines and all related components. DC motors are multiple times smaller and lighter than the equivalent powered turbine engine when you consider the entire system. On top of that you totally eliminate the need for variable pitch props and the related transmission parts since electric motors can adjust power instantly. You also negate a lot of hydraulic systems (and their redundant backups) without the need for things like fuel pumps, thrust reversers, etc. It also seems they are not using anything like standard li-po tech. From their site: >Utilizing industry-leading lithium-ion batteries and a proprietary Aluminum-Air system for range, we’ve surpassed the 400Wh/kg mark. For reference this is nearly double Tesla's energy density. Of course the cells will be much more expensive, but that matters a lot less for a low volume, high usage application that can be amortized.
- mveety 8y ago
  Slight quibble: you'd probably still want variable pitch props. Variable pitch props give you a lot of options for noise, speed, efficiency, etc that I wouldn't want to give up just because I have a different power plant. They're also extremely useful for engine-outs (you can feather them which reduces drag significantly) and for landing (you can reverse them which helps which reduces load on your brakes and lets you do questionable things if you need to get into a small strip.)
- captainperl 8y ago
  > DC motors are multiple times smaller and lighter than the equivalent powered turbine engine when you consider the entire system. Airplanes this size can use cruise missile engines, which are very light. See the F-5 for more info (7:1 thrust to weight ratio.) > On top of that you totally eliminate the need for variable pitch props Why is that? Variable pitch props have nothing to do with engine type. They're variable to be more efficient depending on RPM and speed. > You also negate a lot of hydraulic systems (and their redundant backups) without the need for things like fuel pumps, thrust reversers, Not really. A lot of flight controls are boosted with hydraulics, and thrust reversers are for increasing drag (descending faster or slowing down.) None of these depend on engine type. The real issue with electric planes is that they're a fire hazard. Already people have been killed when their electric plane's battery caught fire mid-air: https://www.flyingmag.com/two-people-killed-in-first-crash-electric-airplane https://www.flyingmag.com/two-people-killed-in-first-crash-e... The JAL 787 battery fire was a near-tragedy and resulted in interruption of service to SJC for 2 months: https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_... I find the most erroneous posts on HN to be about airplanes and databases.
dexen 8y ago
The airframe of airplanes is surprisingly lightweight. Engine(s) can easily be around 25% of the (empty) weight, and on anything with decent range, the fuel dominates. Both necessitates a lot of supporting infrastructure. The airplane can probably pack battery cells much denser than Tesla. Tesla uses active, liquid-based cooling; an airplane could employ the airstream for that. Plus I expect a lot less of battery heating; while the capacity is 9x of Model 3, the engine power (thus electrical drain) is around just 3x of Model 3. [1] Also the metal shield under the battery can probably be done away with. As others pointed out, electric engines are much different beast than any hydrocarbon burning ones. You need less support structure (for starters, less vibrations) and also much less auxiliary gear; think of all the cooling systems (either liquid cooling or flaps & openings & shrouds to direct air around); fuel tankage, pipes, valves, pumps & booster pumps; electric generator & possibly hydraulic pumps, and lots and lots of wires to both send electricity and control signals. As electric engines are essentially low-maintenance, you'd save a bunch of weight on monitoring instrumentation & servicing access panels. Maybe i'm reading too much into the renders, but the engine- and prop cowls seem to be very tight fit; both lessening drag and also simply being smaller, lighter parts. Lastly, electric engines can typically be over-loaded way over their continuous power for well understood short stretches of time, facilitating extra power for prompt & safe take-off. Not so with piston or jet engines; the take-off power is typically maybe a dozen percent more than the rated continuous power, and that's about it. You end up carrying through the whole flight engines over-sized (and thus over-weight) just for the sake of take-off power. Small weights savings all over the airframe add up. -- [1] https://en.wikipedia.org/wiki/Tesla_Model_3#Specifications https://en.wikipedia.org/wiki/Tesla_Model_3#Specifications - 258 kW for Model 3 AWD, vs 3x260kW for the airplane.

gvb 8y ago

Good question. The Model 3 battery[1] weighs 478 kg so 9x = ~4,300kg. 11 people on board is another 1,000kg (not including the golf clubs). MTOW[2] is 6,350kg so the airframe needs to weigh in at ~1,000kg. I'm sure they can make a battery lighter than a Model 3 battery (optimized for weight rather than cost), but how much lighter??? Unlike liquid fueled aircraft, you won't be able to trade off fuel weight for passenger weight to stay under MTOW. [1] https://evannex.com/blogs/news/tesla-s-battery-pack-is-both-mysterious-and-alluring-work-in-progress https://evannex.com/blogs/news/tesla-s-battery-pack-is-both-... [2] https://en.wikipedia.org/wiki/Maximum_takeoff_weight https://en.wikipedia.org/wiki/Maximum_takeoff_weight

bronco21016 8y ago
Excellent point. Often times only enough fuel for the route is taken so more payload can be taken. In a battery setup your max payload is always the same. No trade offs for range.
rhinoceraptor 8y ago
I would imagine that planes could have much higher battery cell per battery pack utilization, because the protective shell for the battery packs is less necessary. Some back of the envelope math for the Model 3 battery: it has 4416 2170 cells, 66g each, is 291.5 kg, and the total battery pack weight is 478 kg. So only 60% of the battery pack weight is the actual battery cells.

jetrink 8y ago

That's an interesting statistic. According to Wikipedia, the Tesla's battery is around 500kg, so the aircraft is carrying around 4500kg in batteries. For comparison, the 10-seat Cessna 404 Titan weighs just 2200kg when empty and has a max take-off weight of 3800kg. So the battery alone weighs more than a similar Cessna, full of pax, luggage and fuel. Hm. They list a MTOW of 6350 kg. Less 800kg for 10 fully clothed adults and the weight of the battery, there's only 1000kg left for the plane. Maybe that's possible?

Robotbeat 8y ago
About 3.8 tons they say for the battery. They're relying on removing some excess structure from the battery. The thing is about 60% battery by take-off weight. That's not as crazy as it sounds. A 777 is about half fuel at max fuel load.
- ams6110 8y ago
  It burns that fuel as it flies though, reducing weight which is important for landing safely. The EV aircraft will weigh the same landing as taking off, which presents some complications.
  - Robotbeat 8y ago
    ...but those complications can be overcome. Partially because the airframe is so efficient that the landing speed should be tolerable even with a high landing mass. Materials have improved significantly in the last few decades. There's a lot more possible now than in the past.

aphextron 8y ago

>Wonder how they made it light enough to be able to fly... You get a massive weight savings in the engines and all related components. DC motors are multiple times smaller and lighter than the equivalent powered turbine engine when you consider the entire system. On top of that you totally eliminate the need for variable pitch props and the related transmission parts since electric motors can adjust power instantly. You also negate a lot of hydraulic systems (and their redundant backups) without the need for things like fuel pumps, thrust reversers, etc. It also seems they are not using anything like standard li-po tech. From their site: >Utilizing industry-leading lithium-ion batteries and a proprietary Aluminum-Air system for range, we’ve surpassed the 400Wh/kg mark. For reference this is nearly double Tesla's energy density. Of course the cells will be much more expensive, but that matters a lot less for a low volume, high usage application that can be amortized.

mveety 8y ago
Slight quibble: you'd probably still want variable pitch props. Variable pitch props give you a lot of options for noise, speed, efficiency, etc that I wouldn't want to give up just because I have a different power plant. They're also extremely useful for engine-outs (you can feather them which reduces drag significantly) and for landing (you can reverse them which helps which reduces load on your brakes and lets you do questionable things if you need to get into a small strip.)
captainperl 8y ago
> DC motors are multiple times smaller and lighter than the equivalent powered turbine engine when you consider the entire system. Airplanes this size can use cruise missile engines, which are very light. See the F-5 for more info (7:1 thrust to weight ratio.) > On top of that you totally eliminate the need for variable pitch props Why is that? Variable pitch props have nothing to do with engine type. They're variable to be more efficient depending on RPM and speed. > You also negate a lot of hydraulic systems (and their redundant backups) without the need for things like fuel pumps, thrust reversers, Not really. A lot of flight controls are boosted with hydraulics, and thrust reversers are for increasing drag (descending faster or slowing down.) None of these depend on engine type. The real issue with electric planes is that they're a fire hazard. Already people have been killed when their electric plane's battery caught fire mid-air: https://www.flyingmag.com/two-people-killed-in-first-crash-electric-airplane https://www.flyingmag.com/two-people-killed-in-first-crash-e... The JAL 787 battery fire was a near-tragedy and resulted in interruption of service to SJC for 2 months: https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_... I find the most erroneous posts on HN to be about airplanes and databases.

dexen 8y ago

The airframe of airplanes is surprisingly lightweight. Engine(s) can easily be around 25% of the (empty) weight, and on anything with decent range, the fuel dominates. Both necessitates a lot of supporting infrastructure. The airplane can probably pack battery cells much denser than Tesla. Tesla uses active, liquid-based cooling; an airplane could employ the airstream for that. Plus I expect a lot less of battery heating; while the capacity is 9x of Model 3, the engine power (thus electrical drain) is around just 3x of Model 3. [1] Also the metal shield under the battery can probably be done away with. As others pointed out, electric engines are much different beast than any hydrocarbon burning ones. You need less support structure (for starters, less vibrations) and also much less auxiliary gear; think of all the cooling systems (either liquid cooling or flaps & openings & shrouds to direct air around); fuel tankage, pipes, valves, pumps & booster pumps; electric generator & possibly hydraulic pumps, and lots and lots of wires to both send electricity and control signals. As electric engines are essentially low-maintenance, you'd save a bunch of weight on monitoring instrumentation & servicing access panels. Maybe i'm reading too much into the renders, but the engine- and prop cowls seem to be very tight fit; both lessening drag and also simply being smaller, lighter parts. Lastly, electric engines can typically be over-loaded way over their continuous power for well understood short stretches of time, facilitating extra power for prompt & safe take-off. Not so with piston or jet engines; the take-off power is typically maybe a dozen percent more than the rated continuous power, and that's about it. You end up carrying through the whole flight engines over-sized (and thus over-weight) just for the sake of take-off power. Small weights savings all over the airframe add up. -- [1] https://en.wikipedia.org/wiki/Tesla_Model_3#Specifications https://en.wikipedia.org/wiki/Tesla_Model_3#Specifications - 258 kW for Model 3 AWD, vs 3x260kW for the airplane.