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Comment by chris_va | Hacker News Reader

Yes, though try telling a pilot that their plane will get heavier as the flight goes along.

(am a occasionally ga pilot and have been watching metal air batteries for a while)

Actually that’s great! Considering takeoff is the most taxing part of flight.

It is normal for a long range airliner to take off with more weight than it can safely land with, necessitating a fuel dump if for some reason it needs to return to the airport shortly after leaving.

Sure, but even these batteries won't allow long range which is why short haul was specified. It's unlikely that batteries will _ever_ get energy density anywhere near enough to make long haul all electric flights possible, even with big efficiency increases. You just can't compete with using 100% of your mass as storage.

fun fact, the SR-71's tires could not handle the weight of the plane with a full fuel tank, so it could not takeoff or land filled up, which is why they always refueled them in midair.

I would have loved to be in the room when that was discussed.

Hey, I know a way we can save X lbs. of weight; this is going to sound a bit nutty but ...

The reality is probably that it was an obvious choice to everyone schooled in the art but from the outside it seems kind of genius.

I always thought the reason they had to dump fuel was in case of a fire or explosion upon landing.

Most situations where an airliner returns to the airport don't involve any sort of crash landing, and don't have a significantly higher risk than normal of igniting fuel in the tanks.

To use the 787 Dreamliner[0] as an example, the maximum landing weight is around 120,000 pounds less than the maximum take-off weight. Even a 737 [1] has to fly an hour or so to burn off enough fuel for landing (assuming it is fully loaded to begin with), or dump it into the air if it's urgent.

[0] https://modernairliners.com/boeing-787-dreamliner/boeing-787...

[1] https://modernairliners.com/boeing-737/boeing-737-specificat...

>> Considering takeoff is the most taxing part of flight.

You must have pretty strange takeoff technique, and perfect landing skills ;-)

Presumably they mean taxing to the aircraft, rather than the pilots.

That's astounding. Any good reading material on this phenomena?

I'm not sure what to tell you. It is chemistry of the battery itself..

I think it’s because the way the battery works involves oxidization of the lithium. So the weight comes from collecting oxygen from the surrounding air as a form of rust.

Also the fact that lithium is a light element compared to oxygen, so the weight increases by quite a substantial amount.

It is, however, quite easy to program a drone to compensate for this!

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