"Jay" wrote in message
om...
Seems to me that some of the benefits of the constant speed prop were
based on the limitiations of timing (ignition and valve) of the
Lyco/Conti engines. If your engine was designed to have a large
dynamic range of efficient operation, you won't need the articulated
prop as much.

Prop blades are just rotating wings. The goal is to run the blades at their
most efficient angle of attack for the RPM and aircraft airspeed. The
performance of the prop is best at low RPM but the piston engine driving it
is likely to be most efficient at a higher RPM. That is the reason that
high performance piston aircraft have both PRSU's and constant speed props.

Some experimental powerplant/prop systems included a two speed gearbox in
addition to the CS prop to run the engine at high RPM at takeoff and low RPM
for cruise. These experimental engines also shifted the cam and ignition
timing for the two PRSU ratios. This helped the prop blades stay at the
best AOA to maximize thrust and optimized the engine at two set points, high
RPM for takeoff and low RPM for long range cruise. This was at the very end
of large piston engine development and an attempt to wring the last bit of
performance out of these monsters.

Having an engine with a wide "dynamic range" is nice for a car but less
useful for an airplane where it is best to optimize the engine for one RPM
and let the CS prop and PRSU operate the prop in the most efficient way.

Bill Daniels