[captainperl]

Airplanes always get most of the energy from ascent back in descent.

VTOL will get less back because it's grossly inefficient.

Note that drag needs to be deducted from the potential energy. There's parasitic and induced drag.

[lmm]

> Airplanes always get most of the energy from ascent back in descent.

Given that the aeroplane ends up stopped on the tarmac at (approximately) sea level with (approximately) empty tanks, how so? A bit of heat I suppose but that's not usable. I'd say current aeroplanes generally deliberately dump energy to the environment (via deliberately increased drag, spoilers etc.) during descent, no?

[DennisP]

They're not recharging batteries but they are extending range. The whole time they're descending, they're moving forward and overcoming air resistance, without needing as much fuel as if they were flying level the same distance and altitudes.

I think that compared to energy expenditure X in level flight at cruising altitude, the aircraft would expend X+Y in the climb and a little less than X-Y in the descent, assuming all horizontal distances are the same.

To the extent that they deliberately increase drag, that wouldn't hold true, but I'm guessing that's mostly on final approach.

[Beltiras]

His context was that the energy was returned to the battery, not in the laws-of-thermodynamics sense.