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Comment by fdej | Hacker News Reader

That's correct, but note that an electric motor is about twice as efficient as a combustion engine, reducing the factor to about 25x (at least ideally). Typical medium range aircraft burn about 3 kg fuel per km [1], so to fly 1000 km you would need about 3 * 25 * 1000 kg = 75 tonnes of batteries. This should be in the ballpark of what we can pack into an aircraft already, but I guess at least another 2x improvement is needed to make it economical (we want to haul some useful payload, not just the batteries).

[1] https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft

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There are other considerations, though... The thought of a Li fire on board an aircraft is something that would keep me awake nights.

I'd guess that anybody wanting to put Li technology batteries aboard aircraft is likely to spend the next 10 years jumping through regulatory hoops, so unless rechargeable battery technology is "ready to deploy" right now on aircraft, I don't see any way this is happening within a decade.

> The thought of a Li fire on board an aircraft is something that would keep me awake nights.

Whereas you wouldn't think twice about jet fuel fires, because you're used to it rather than because fuel isn't a fire hazard :-)

Jet fuel isn't very flammable unless it's atomized or vaporized, something which only happens in the engine. And it's pretty straightforward to extinguish an engine fire, and all aircraft engines have systems to do this.

And extinguishing a metal fire is not trivial

Doubly surprising given the fear is expressed in a thread specifically about the 50x energy-density differential between jet fuel and Li-on batteries.

Trivia: there was about as much chemical energy in the fuel of either Boeing 767 that struck the twin towers as the gravitational potential energy released by the towers collapsing.

What's the turnaround for the aircraft though? If they can't turn around an aircraft in 15-30 min, we'll need more aircraft or prices will skyrocket (no pun).

Any sensible proposal for electric systems for commercial aircraft is going to aim for batteries to be safely swappable in 10-15 minutes. (Though they can still make delays from unexpected diversions to airports without a stock of batteries worse)

The structural penalties for making "most of the weight of the aircraft" removable will probably lead to a plane that doesn't fly.

... for example, putting the batteries in the existing form-factor of removable cargo containers used in jumbo jets.

Hmmm... I wonder. Let's say they design the aircraft around an existing battery (size/weight). If later technology allows for a lighter battery, would they they have to add the weight back in order to keep the cg correct?

And then charge overnight and be used as energy storage for the time they're not in use. As flight times are very predictable, they should be a good use case for battery storage.

They say they plan to package batteries are packaged as standard freight containers.

Since current turnarounds include freight container swaps, I don't see why a battery swap wouldn't fit in it.

Supercapacitors could solve that, but unfortunately they currently have much less density even than batteries. Apparently graphene supercaps may solve that, but not at the moment.

Tesla style battery swap perhaps?

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