On 23 Feb 2004 09:32:01 -0800, (Jay) wrote:

For props, bigger is better for static thrust (look at a helecopter)
but what about for top speed, a more desireable figure of merit for
fixed wing aircraft? I seem to remember hearing somewhere that for
top speed there is an optimal prop length that is not infinite. You
need to generate a stream of air that is going faster than the speed
that you want to fly.

You just described the reason no piston engined WWII fighter ever flew
faster than the speed of sound. The prop needed to produce enough
thrust to pull the airplane into supersonic speed, but the prop was
running into the wall of drag as the tips neared supersonic speed and
the fuselage was producing enormous drag too.

The prop tips would have to go supersonic if the airplane was to go
that fast too, and props of that era were not designed for supersonic
speeds.

Even going straight down at full power, just too much drag. They went
fast enough to scare the bajeebers out of a number of pilots though.
:-) They also went fast enough to lock up the controls and in some
cases, cause the destruction of the airplane... and the pilot.

Corky Scott