Seems to me that if you run a coarse pitch prop at high RPM and low airspeed it will stall as the relative airflow will approach the blades from greater than the critical angle and the blades will loose their aerodynamic efficiency. This could certainly be the situation at low speed on take off or in a tailslide. If you stop a prop in flight the relative airflow will be from directly ahead (plus or minus a bit of aircraft angle of attack and or sideslip) so the prop will be stalled aerodynamically in the braking sense ie in reverse! The first case is analagous to an aeroplane stalling in errect flight, the second to an aircraft stalling inverted; both stalls but two very different situations!
DB6, the helical twist on a prop is mostly there to alter the pitch angle of the blade so that the relative airflow approaches the blade element at the same, aerodynamically efficient, angle of attack along the entire length of the blade from root to tip. The change in blade profile (thickness/chord ratio and the use of a different aerofoil section along the blade) also helps. The fact that the blade is going more slowly near the root does not change the fact that it will be at its most aerodynamically efficient at a particular angle of attack to the relative airflow.
Happy landings!!
Last edited by 3 Point; 10th Dec 2004 at 18:54.