Since there is no break on the motor of the Aerobird, even if the motor is off, you will often get spin on the prop as you fly, like a pinwheel in the breeze. In this case it is the moving air that is turning the prop, not the motor.

This is called windmilling. It is actually working as a break. When you finally come in for a landing, if the prop has actually stopped, then you are windmilling. The prop is not providing any thrust in this situation.

On gliders that are launched with electric motors, they either use folding props or a break on the motor to prevent this and reduce drag. I have considered trying to fit a folding prop to the Aerobird since I sometimes like to thermal soar with it. It would do so much better if I could stop this effect.