Constant Speed Prop vs Variable Engine Timing

On Tue, 2 Mar 2004 07:32:33 -0700, "Bill Daniels"
wrote:

The gear shifted prop was the last gasp of piston engine development before
the turbine age. Look at the Lycoming XR7755, Napier Nomad or the Rolls
Royce Crecy. These were 5000 HP+ monsters that needed every trick in the
engineers bag. Piston engines produce more HP at high RPM at the cost of
fuel consumption but deliver low fuel consumption at low RPMS. Props
produce more thrust at low RPM and most efficiency with the blades at a
single best AOA. That AOA must be maintained over a wide range of
airspeeds. Just too many variables for a CS prop to deal with alone.

The two speed gearbox isn't perfect but it does buy the engineer a bigger
range of options.

Bill Daniels

Bill, are you talking about a two position propeller, as opposed to a
two position reduction drive transmission for the engine?

Early in WWII, some props used a variable pitch mechanism that allowed
the pilot to adjust the pitch, and therefore the engine rpm to any
setting withing the design limits of the prop's pitch. Normally
they'd select fine pitch for takeoff and coarse pitch for cruise. I
suppose some of the props had just those two settings, but most of
them allowed any setting inbetween.

This wasn't a constant speed prop, just an adjustable prop.

Is this what you are referring to?

Thanks, Corky Scott

PS, it isn't a bygone design, there are some adjustable props on the
market for the homebuilt industry today that allow variable pitch, but
are not constant speed props.