Jim Sower wrote (snip)

>uite often stalled, so it produces more drag and less lift).  At cruise >airspeed, the forward velocity of the airplane becomes a component of the >AoA and effectively reduces it making for smaller Cl and Cd, but the >"airspeed" of the airfoil now has the airspeed of the airplane added to >rotational speed, so this higher speed increases total drag >(geometrically).  High Cd at no airspeed and lower Cd at higher airspeed >tend to wash out and we end up with cruise RPM not too far removed from >static RPM.

>Power off:  Let's assume a given airspeed (say 80 kias) on our fixed pitch >prop.
>    Engine "seized":  Our prop is at whatever AoA is determined by >measuring the wind velocity vector and the chord of the airfoil.  It will be >very high - basically 90' less the local pitch of the prop.  The
>drag will correspond to the airfoil drag at ?? AoA (say 50'-80') depending >on where you measure along the span. 

>   Prop "freewheeling":  (more snip).  If our prop is 80% efficient (is that >typical?), and our airplane requires 2400 RPM to cruise at 80 kias, I would >intuit that the terminal rpm of the frictionless freewheeling prop would be >2400/0.8 or about 3000 RPM.

Hay, that's faster than the engine can turn it-me thinks that if this is true, we are getting something for nothing.  But I do agree, a C-123 prop in near FLAT pitch produces  a whole lot of drag.

 

Bob Darrah