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Comment by manigandham | Hacker News Reader

Electric drivetrains have the unique ability to recover energy, often used in braking for EV cars. Is there any corollary for recovering potential energy for electric planes?

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There is at least one commercial EV aircraft that can do it, but frankly it won't be as big a deal as it is with cars. Cars are speeding up and slowing down all the time. Aircraft generally speed up, stay fast, and then slow down at the very end of the flight. And for most aircraft, the entire flight is powered from takeoff to landing. It could be useful in emergency situations where the pilot is at risk of overshooting the runway.

For aerobatic aircraft it could be a big deal. High power motors and the desire to be as light as possible will probably drive power recovery and even crazier stunts at airshows.

The reason energy recovery in cars makes sense is that you're constantly stopping and starting. In a plane you definitely don't want the engine to stop running while you're in the air.

Isn't altitude ultimately a function of energy? If you're decreasing altitude wouldn't that be a decent amount of recovery?

Gas turbines need to keep running to sustain combustion but electric motors can start and stop instantly with current flow; it seems possible to use this as part of the dynamic control of the aircraft.

You don’t change altitude frequently enough and even if you could recover 80% of the energy you spent on reaching cruising altitude when you perform your landing approach it won’t be much, and probably won’t be worth the extra complexity and weight of an energy recovery system.

Unless we’re talking about very short flights the majority of your energy would be expanded at cruising altitude especially since electric engines have a fairly flat efficiency curve.

Actually, why don't planes cycle climbing to a height, switch off the engines, glide for X miles, restart engines to climb, etc ...

Pretty sure I used to do that when I used to fly in my Microprose F-15 and was short on fuel.

Because it’s not a very efficient or pleasant flight experience, and it’s probably too much of a risk.

Generally, you don't want to stop an engine that's running fine. It might just not restart...

Kindof. Currently used for emergency recovery: https://en.wikipedia.org/wiki/Ram_air_turbine

Potentially on descent, but I think it's a much smaller potential benefit in an airplane, and perhaps tricky because you don't want to extract so much energy that you lose speed and stall.

Electric planes don't really need much breaking, except when coming in for a landing.

At that point, your flight is over and you don't need any extra range.

Planes don’t brake (except for a brief moment while landing), so no.

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