3 ms·

You can't convert between kWh and kW. 100 kWh = 6 MW for one minute... so there is plenty of power if the flight is short enough. They said the plane has 4 Tesl

You can't convert between kWh and kW. 100 kWh = 6 MW for one minute... so there is plenty of power if the flight is short enough. They said the plane has 4 Tesla's worth of battery power, let's assume they are 80KWh packs then that's 320kWh that they could use for a short flight. That's a fair amount of juice, they definitely won't be flying long in a 25 ton aircraft without starting up the auxiliary motor but I have no doubt it will be able to get off the ground on $5 worth of electricity. To be fair though it is more likely to be 50 kWh just for the take-off, so that's probably where their $5 figure came from (at $0.10 / kWh). For comparison: a single gallon of Jet-A = ~150MJ. 320 kWh = 320,000 W for one hour so 3600 * 320,000 = 1150MJ, or about 40 gallons and I suspect that these electric motors are quite efficient. So it does pencil out, I think. Or maybe my pencil is broken and no doubt HN will correct my math.

dghlsakjg 1mo ago
The specific claim from the company is that the entire 27 min flight was done with $5 worth of power using an all electric power system with a power output exceeding one megawatt. https://www.heartaerospace.com/newsroom/heart-aerospace-completes-first-flight-of-world-s-largest-electric-aircraft https://www.heartaerospace.com/newsroom/heart-aerospace-comp... I still think it is an amazing achievement. I just don’t see how they were able to get it done on $5 worth of power, or they just quoted the wrong price.
- Toutouxc 1mo ago
  I still don’t see what the problem is. The entire flight was likely just a few patterns and your earlier figure of 100 kWh (let’s assume they get their electricity for cheap) is already a serious amount of energy. It takes 100 kWh of energy to lift a 10.4ton object by about 3.2 km, so we’re obviously in the same ballpark for the maiden flight, and the rest is just drag. For drag, I’ll approximate the plane fuselage as two EVs that I drive. A 737 has a lower drag coefficient than my car, but a plane also has wings, so let’s say that evens out. Out of that 100 kWh, we probably only needed like a half for pure altitude, so we have 50 kWh for drag. An EV can sustain 200 km/h with about 60 kW of power, so let’s say 120 kW for the plane, and the flight was less than half an hour. Also, the plane got to convert all the potential energy back to kinetic energy on descent, so that was “free”. Again, I believe that the napkin math checks out.
  - echoangle 1mo ago
    > A 737 has a lower drag coefficient than my car Drag coefficient is about the shape and needs to be multiplied by area to get drag. Your car is a lot smaller when viewed from the front than a 737. And there's no way a plane flying at the speed it does has the same drag losses as two EVs.
    - Toutouxc 1mo ago
      That’s why I approximated the fuselage as two EVS (the frontal area) and I only looked up the drag coefficient of a 737 because it’s a well-known narrow-body airliner. I don’t know what speeds they flew, but AFAIK most maiden flights are very tame. My point stands, low hundreds of kilowatthours of energy seems like the right ballpark.
      - echoangle 1mo ago
        > That’s why I approximated the fuselage as two EVS (the frontal area) Have you ever seen a car and a plane? The Tesla model x has a frontal area of 2.6 sqm and a 737 fuselage alone, without any wings is already 11 sqm. With all attachments it’s at least 20 sqm. And half of the energy for altitude gain and half for drag is way too optimistic. The flight cost more than $5 in energy.
        Toutouxc 1mo ago
        The electric plane isn’t a 737, the fuselage looks quite slender.
  - dghlsakjg 1mo ago
    The 100kwh number was based on a rate of electricity that is 1/6th the average cost of electricity in the area they did the flight. Even the absolute cheapest rate in that region is 4x the price I used. The price I quoted was a little less than the cheapest published electrical rate in North America, which isn’t in the United States. So you can barely make it work if you price electricity at a rate that doesn’t exist in the country they did it, using an amount of power that much, much smaller planes usually require to stay aloft (A Cesnna 172, which will struggle with 4 adults, uses 145hp/115kw for takeoff and climbout at a much lower speed). A plane of comparable size and capacity uses 1500-2000 hp turbine engines. That lines up with their own megawatt plus claim. Regular rates in the area they operate in get them less than 25kwh. They would have had to negotiated a hell if a discount to have pulled it off. And even so, it would be a deceptive claim. It’s like claiming that you doubled the cost efficiency of a 737 (by getting a sponsorship from Shell).
kvemkon 1mo ago
> more likely to be 50 kWh just for the take-off 1.6 MW power [1]. Would be 2 minutes for take-off realistic? [1] https://youtu.be/nM86DBOqgPM?t=475 https://youtu.be/nM86DBOqgPM?t=475
- jacquesm 1mo ago
  Depends on how high you go ;)

dghlsakjg 1mo ago

The specific claim from the company is that the entire 27 min flight was done with $5 worth of power using an all electric power system with a power output exceeding one megawatt. https://www.heartaerospace.com/newsroom/heart-aerospace-completes-first-flight-of-world-s-largest-electric-aircraft https://www.heartaerospace.com/newsroom/heart-aerospace-comp... I still think it is an amazing achievement. I just don’t see how they were able to get it done on $5 worth of power, or they just quoted the wrong price.

Toutouxc 1mo ago
I still don’t see what the problem is. The entire flight was likely just a few patterns and your earlier figure of 100 kWh (let’s assume they get their electricity for cheap) is already a serious amount of energy. It takes 100 kWh of energy to lift a 10.4ton object by about 3.2 km, so we’re obviously in the same ballpark for the maiden flight, and the rest is just drag. For drag, I’ll approximate the plane fuselage as two EVs that I drive. A 737 has a lower drag coefficient than my car, but a plane also has wings, so let’s say that evens out. Out of that 100 kWh, we probably only needed like a half for pure altitude, so we have 50 kWh for drag. An EV can sustain 200 km/h with about 60 kW of power, so let’s say 120 kW for the plane, and the flight was less than half an hour. Also, the plane got to convert all the potential energy back to kinetic energy on descent, so that was “free”. Again, I believe that the napkin math checks out.
- echoangle 1mo ago
  > A 737 has a lower drag coefficient than my car Drag coefficient is about the shape and needs to be multiplied by area to get drag. Your car is a lot smaller when viewed from the front than a 737. And there's no way a plane flying at the speed it does has the same drag losses as two EVs.
  - Toutouxc 1mo ago
    That’s why I approximated the fuselage as two EVS (the frontal area) and I only looked up the drag coefficient of a 737 because it’s a well-known narrow-body airliner. I don’t know what speeds they flew, but AFAIK most maiden flights are very tame. My point stands, low hundreds of kilowatthours of energy seems like the right ballpark.
    - echoangle 1mo ago
      > That’s why I approximated the fuselage as two EVS (the frontal area) Have you ever seen a car and a plane? The Tesla model x has a frontal area of 2.6 sqm and a 737 fuselage alone, without any wings is already 11 sqm. With all attachments it’s at least 20 sqm. And half of the energy for altitude gain and half for drag is way too optimistic. The flight cost more than $5 in energy.
      - Toutouxc 1mo ago
        The electric plane isn’t a 737, the fuselage looks quite slender.
- dghlsakjg 1mo ago
  The 100kwh number was based on a rate of electricity that is 1/6th the average cost of electricity in the area they did the flight. Even the absolute cheapest rate in that region is 4x the price I used. The price I quoted was a little less than the cheapest published electrical rate in North America, which isn’t in the United States. So you can barely make it work if you price electricity at a rate that doesn’t exist in the country they did it, using an amount of power that much, much smaller planes usually require to stay aloft (A Cesnna 172, which will struggle with 4 adults, uses 145hp/115kw for takeoff and climbout at a much lower speed). A plane of comparable size and capacity uses 1500-2000 hp turbine engines. That lines up with their own megawatt plus claim. Regular rates in the area they operate in get them less than 25kwh. They would have had to negotiated a hell if a discount to have pulled it off. And even so, it would be a deceptive claim. It’s like claiming that you doubled the cost efficiency of a 737 (by getting a sponsorship from Shell).

kvemkon 1mo ago

> more likely to be 50 kWh just for the take-off 1.6 MW power [1]. Would be 2 minutes for take-off realistic? [1] https://youtu.be/nM86DBOqgPM?t=475 https://youtu.be/nM86DBOqgPM?t=475

jacquesm 1mo ago
Depends on how high you go ;)