Checkboard - not exactly.
If the propeller is stationary it will produce only form drag, the amount depending upon the profile of the blade faces. If, however, the propeller is windmilling, the combination of its rotational velocity and the TAS of the aircraft to which it is attached result in a relative airflow which produces a negative angle of attack and, therefore, an aerodynamic reaction. The component of this reaction parallel with the longitudinal axis of the aircraft adds to the drag forces and might be termed 'windmilling drag' whilst the component in the plane of rotation of the propeller acts in the direction of rotation and represents the force which keeps the propeller rotating against the compression of the engine, what might be termed the 'windmilling force'. Thus a windmilling propeller produces significantly more drag than a stationary one.
I think that's the way Harvey Spirit described it but it really is easier with diagrams!
Dan Winterland - good to know you're still around, haven't seen you since Scampton.
[This message has been edited by rolling circle (edited 13 July 1999).]