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Comment by fsh | Hacker News Reader

Anything but airplanes. Current airliners have a fuel fraction between 24 and 47%, so any decrease in energy density massively compromises performance. The energy density of jet fuel is two orders of magnitude higher than modern batteries, and jet engines have efficiencies of a few ten percent.

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Nonetheless, folks are working the problem. Albeit most of the current designs look more like short-haul passenger craft or automated cargo drones to connect remote communities.

It feels like this would be a very tricky problem, seeing as it seems most large planes have "it's much lighter when landing than taking off" as part of the design constraints, seeing as maximum takeoff weight > maximum landing weight for most airliners (generally speaking, I think). It's probably not insurmountable, but it seems unclear how we fix this when takeoff weight == landing weight for electric planes.

Higher landing weight mostly just means you need stronger landing gear and wings (which adds weight, which reduces range...) It's an unfortunate cycle, but not insurmountable.

All commercial aircraft are capable of landing at takeoff weight (to deal with aborted takeoff, and other similar emergency scenarios). They just aren't certified to do so routinely, and doing so repeatedly may put a lot of stress on the landing gear and airframe.

And the breaks notably may melt besides the landing gear suffering irreparable damage (to where you need to replace the landing gear). That's planned for and to be handled by the required fire fighting truck coming out and hosing them down if they start any signs of starting a fire, even though that will shatter the brake discs that were still good. The certified landing weight is about what weight they can be and still take off with no maintenance needed and just a regular refueling and perhaps crew change due to shift limits. But nothing done to the plane besides refueling. And yeah, it's because the extra capacity is just for extra fuel for extra range, so it's not worth the spendings on landing it more than just safely once.

> Anything but airplanes.

Well, rockets are even worse, of course. :)

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