"Jim Logajan" wrote in message
.. .
Charles Talleyrand wrote:
Alternatively, there must be planes that have used both fixed and
constant-speed props. Anyone know the difference?

Don't know about the Cessna 150, but I'm pretty sure some owners of
experimentals (such as the RV series) have tried both fixed and later
constant speed props on the same engine and airframe. If interested, I
suspect one could find numbers mentioned on the forums on this web site:
http://www.vansairforce.net/

As an RV builder/owner I 've seen that discusion a hundred times. I
selected a fixed pitch prop with a cruise pitch for my airplane. My
airplane cruises as fast and efficiently as any 160 HP RV-6 you'll find,
regardless of fixed pitch or constant speed prop. However, my airplane's
acceleration and climb performance is far inferior to RV's with constant
speed prop's.

In my airplane, the takeoff run is made at full throttle, which delivers
about 2200 RPM and 29" of MP. That's probably 75% power or less. The
constant speed guys are turning 2700 RPM and are also showing 29" of MP.
They are getting 100% power. That extra 40 ponies makes a huge difference
until I get my airplane closer to its ideal speed regime, which is 140+
knots and allows the engine to turn up to 2500+ RPM. In level flight with a
wide open throttle and at 1000 MSL on a standard day, the engine will spin
my prop to slightly over 2700 RPM, which pulls the airplane along at 175+
knots...

KB