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Old 18th Oct 2018, 18:19
  #29 (permalink)  
EMIT
 
Join Date: Aug 2007
Location: The Netherlands
Age: 63
Posts: 287
Originally Posted by krismiler View Post
Possibly some energy could be returned to the batteries by windmilling propellors on the descent in the same way electric vehicles can recharge their batteries by using the motor as a brake.

Electric cars can recharge to around 80% very quickly, it's the last few percent which takes time to trickle in.
Yet another conceptual mistake, such as you find everywhere in the green madness of todays world!

A car driver that approaches a red traffic light at 50 mph and then brakes to stop the car is wasting the kinetic energy that is in the car - he should have started coasting early enough to come to a stop right at the traffic light without any braking. Because this method is impractical in normal traffic, hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery.

An airplane that descends from cruise level to landing does use the coast technique already, the engines are already just idling, it cannot be done more efficiently. If you want to “brake” by using the propellor to drive the e-motor as a generator, your aircraft will have more drag, thus descend more steeply than the idle glide path. You will have to expend (=waste) energy either before starting descent, by staying level longer, or by flying level at the bottom of the descent.

There is no such thing as a free lunch!
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