Thank you folks. Smart community .
Well... Why propeller airplanes don't have a sort of case (duct) around the propeller, like some propeller used in scale model planes (electric ducted fan) that trys to mimic a turbine's look ?
I found a intesting thing about human power vehicles. Helicopter powered by humans :
A solar powered attempt :
(should had put solar cells in the propeller's blades )
You only need to be strong and slin lightweight at same time, and enjoy trips of 10 seconds. But it's impressive anyway.
Why bikes used in record breacking don't also use arms power, like this human powered helicopter ?