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Comment by Toutouxc | Hacker News Reader

Sorry, but you’re still weirdly switching from power (kilowatts) to energy (kilowatt hours). The electric plane could easily pull 1.5 megawatts for two minutes (on takeoff) and consume 50 kWh of energy, then spend the next 45 kWh cruising around and descend on the rest. (Or similar numbers, of course.)

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I understand that energy and instantaneous power draw aren’t the same. I’m working with the numbers given: over a megawatt of power draw, and the price of energy in kilowatt hours. I’m not saying that they are flying on 100kw. I’m saying that using absurdly optimistic - unrealistic, really - pricing they have alln energy budget of 100kwh to use for the entire flight of 27 min. That means that average power consumption for the entire flight is just over 200kw if they are paying slightly less than the lowest power rate on the continent (which isn’t available in the country they did this test in). We both understand that energy is power * time.

100kwh was an extremely generous amount of energy to allow for $5. Actual, real world, best case scenario industrial pricing in the region they are in would give them 50kwh for $5.

Look at your numbers again with the fantasy pricing. You are saying that they took off with a normal amount of power for a plane that size, then cruised around using an amount of power (45kw) that wouldn’t keep a two person plane 1/20th the weight airborne. Now cut that budget in half.

Even the most efficient planes on earth - single person powered gliders - need about 15-25kw to maintain level flight at much lower speeds. Keep in mind that drag increases with the square of speed, and this plane is traveling significantly faster than any of the low power planes I’m citing. Citing drag from a Tesla is kind of irrelevant because the whole way an airplane works is by creating lift via drag. The Tesla has wheels to hold the weight, so incurs a much lower penalty for weight.

The reason I’m so skeptical is that I have done the engineering calculations to convert my own very small (sub 1k pound gross) plane. It would need about 30kw/h to maintain level flight with just 1 person in it.

Again, I am incredibly impressed with the engineering and what they have accomplished. I just think that one of their marketing figures was pulled out of someone’s ass.

> You are saying that they took off with a normal amount of power for a plane that size, then cruised around using an amount of power (45kw) that wouldn’t keep a two person plane 1/20th the weight airborne.

No, I’m not saying anything about 45 kW, you’re, again mistaking kW for kWh.

> Citing drag from a Tesla is kind of irrelevant because the whole way an airplane works is by creating lift via drag.

That’s already included in the drag coefficient that I quoted, and I know what induced drag is. Airliners are incredibly slippery because of their shape, a Skyhawk (or any other small GA plane) is a brick compared to that.

I’m not arguing about the $5 figure, it might as well be $20, I don’t know where they buy their electricity, but it’s still a very low number compared to anything burning Jet-A or avgas, and it’s absolutely a “low hundreds of kilowatt hours” number.

You were arguing for the 100kwh derived from $5 a few comments up. Now you are arguing for low hundreds of kWh?

So you are now in agreement that $5/100kwh is unrealistic? That was my whole point the entire time.

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