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Comment by nradov | Hacker News Reader

The part about air intakes doesn't make any sense. In order to move the airplane forward it has to suck air in at the front and accelerate it out the back. That's just basic physics, regardless of whether the power comes from batteries or liquid fuel.

(Obviously rocket powered airplanes don't need air intakes but that's not what we're discussing here.)

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I presume whatever Musk said was referring to something legitimate, but to put a finer point on your comment: in normal jet engines, only a fraction of air actually goes into the combustion chamber. The rest is just pushed out the back (faster than it came in) by turbine blades that are driven by that combustion. Indeed, modern jet engines are "high by-pass" which I think means that the large majority (>80%) of air isn't part of the combustion.

Performance of internal combustion engines varies greatly depending on altitude due to thinner air. This is even worse on hot days. That's not the case with an electric motor. As you get higher, you need to push more air, but since the air is thinner, it's easier to push. Most likely and electric motor with a variable pitch propeller would be extremely efficient. Electric planes would get all the benefits of high altitude flight (namely thin air means less friction) and none of the downsides.

As someone else mentioned, if the batteries get too cold you run into other issues.

I think the point is that combustion engines require the thicker atmosphere to oxidize the fuel in combustion. The electric planes just need inertial reaction, they don't need oxygen.

No that's not how it works. Turbine engines can and have been designed to run fine at very high altitudes (>100000ft). So electric propulsion holds no particular advantage there.

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