Vance Jaqua wrote:

Vance why would your fixed pitch and constant speed
props have about the
same eff. at 30, 60 and 90  MPH? I think you are off
here.
I think you are way off.  I think you forgot to
increase the eff.
for the constant speed prop. Put a HP column in
there for the constant
speed prop.

Let us define our terms here.

Theory thrust is = HP * 550/FPS.

Prop eff is = actual thrust/ theory thrust

Paul Lamar

Paul - What I am trying to stress is that constant
speed props are not more "efficient" than fixed pitch
props. Horsepower for both the constant speed and the
variable gear box is 160 over the entire range - they
let you operate the engine at full power, and that is
where they get more thrust - NOT with better
efficiency . Efficiency is output power - thrust times
speed versus shaft INPUT power at that point - not
rated power - Vance

 If the engine is running
at peak power RPM.... input power and rated power are the same.

I think you are wrong about the efficiency of the constant
speed prop. So does Martin Hollman and a host of other people
that have written books on the subject. As the pitch of the
constant speed prop is reduced the peak efficiency of around 80%
moves down on the MPH scale.


Take the climb chart I uploaded for the Lancair 320 and calculate the 
additional prop thrust required to climb at the higher rate at the various
speeds. All the input data needed is right there in that chart. 

I have the flu today so I don't want to do it right now
but I will soon.

Paul Lamar
 
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