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Comment by chrisseaton | Hacker News Reader

These batteries don't get lighter as they fly though do they?

I heard that airliners can't land with a full load of fuel and they have to dump it to land in an emergency. I wonder if that means you can't even replace max fuel weight with the same battery weight because then it'd be permanently too heavy to land.

I wonder if airliners could drop exhausted battery packs by parachute over designated DZs as they fly across the continent or ocean?

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Not all airliners can dump fuel. Some have to burn it off to get under maximum landing weight, or just risk land over the prescribed MLW.

These batteries don't get lighter as they fly though do they?

Technically they do - the battery of a Chevy Volt loses half a microgram from full to empty :)

https://physics.stackexchange.com/a/34424/6210

That’s obviously not going to be significant at all and clearly not what I meant.

Hence the "technically" and the smiley :)

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>I heard that airliners can't land with a full load of fuel and they have to dump it to land in an emergency

I think the main reason they do that is that way there's less stuff to burn if there's a fire or explosion.

No the main reason is with equal weight it is way harder on the airframe to land than take off.

Electric airplanes are small so it's not as a big of a deal, but it will limit their ability to scale.

Jettisonable batteries (or lift magazines of battery + motor) are one design that's been explored. Take-off and initial climb is a major fuel-demand flight phase.

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