Originally Posted by
Lord Lucan
I am not sure what sort of efficiency you are referring to. Air Nautical Miles per kWh? Could you elaborate a bit on this efficiency loss.
Every time you convert energy there is a wastage. Considering windmilling: you take off and climb to cruise - chemical energy to electrical to kinetic and the kinetic to electrical to chemical. At each of these changes energy is lost (friction, noise, heat, drag). By windmilling you are doubling the points at which energy can be lost - why not start your power off descent earlier (ie shorten your cruise phase) and glide to the runway rather than deplete your batteries longer in the cruise and then try to recapture it using windmilling in the descent. Recuperative technology makes sense in road vehicles due to the frequency with which deceleration is required. In an aircraft ideally there is no deceleration requirement nor is there a thrust requirement until you wish to go around on a missed approach/balked landing/reverse. In practice we keep gas turbine engines running to supply the various systems and due to the long start up times but in an aircraft powered electrically, these limitations would not apply. Glide the machine down to landing as much as is possible with the minimum drag possible (ie no big wind turbine hanging from the wing!)