WRONG PERSPECTIVE
AlexD10
Technically it is probably possible to "harvest" electrical energy with reverse generation, but what is the use?
Coming in from high altitude, the aircraft basically glides in at idle power. If the propellers would be used as windmills, then the aircraft would have much higher drag, so the path would be steeper.
In order to have that steeper path available, the aircraft would have to stay at higher cruise level for a longer time, which would require cruise thrust in stead of idle.
Furthermore, in order to store all the harvested energy, the aircraft would have to haul along, all the time, a massive pack of batteries, which would also cost extra energy.
Elecric cars are a "succes" only because of all the government subsidies given on them, keep that bull manure out of aviation please!