ORIGINAL: Jezmo
You're right. New deal on the wind tunnel test folks. It needs to be with an idling engine and then with the engine off.
I was thinking of the comparison with the heli rotor in auto and that's where the freewheeling idea came from. My BAD.
My prediction is that as the engine, or motor idles slower and slower, the braking will increase until a point is reached where the blades are at such a high angle of attack to the airflow that they stall. At that point, the propeller will "let go" of the air and the windmilling torque will dramatically go down and the braking force will dramatically go down as well.
On some full scale airplanes with props pitched for high speed, you actually hear the engine suddenly slow down as the airspeed increases to a certain point because the blades are suddenly not in a partial stall.