Paul wrote:

Too soon to say whether I believe it or not. I need
to get
out there and take some actual take off data. So far
I am still in bed.
The data I do have you dismiss as advertising hype.

Based on the chart of runs you made and uploaded
showing such a small advantage
to a constant speed prop over a fixed pitch prop
raised my doubts.
This goes against my considerable flying experience
with constant speed
props verses fixed pitch props.

The biggest problem I have is with your efficiency
numbers and the lack
of RPM column and pitch column for the constant
speed prop. Constant speed implies
max RPM with max HP for the constant speed prop. I
know from experience
that constant speed props rev higher on takeoff and
therefore the engine
is generating way more HP.

I also have the same problems with the var gear
columns.

Here again is your chart.

fixed pitch 70X78             const spd   var gear
   mph  rpm   bhp f lbs eff    f lbs eff  f lbs

eff

    0   1940  108  407   0      603   0    525   0
   30   1950  109  393  28      530  26    505  25
   60   1960  110  353  51      480  50    460  47
   90   2080  118  327  66      425  63    420  62
  120   2400  130  307  76      366  73    365  73
  160   2500  149  283  81      299  80    299  80
  190   2720  160  268  83      268  83    268  83

Paul Lamar

 Both the constant speed and variable gear box used
the 160 hp for the whole range- about 2700 engine rpm
the constant speed pitch was set to roughly set the
160 hp 2700 rpm at all points varying from a bit under
50 inches at static (flatter would over rev the engine
- same blade area as the fixed prop) up to 78 inches
at top speed - when you get your airplane back
together you might be able to simulate fixed pitch at
static if it will let you pull full throttle rpm down
to about 2000 - Vance

 Gary Casey wrote:

I have been following the "great propeller debate" and I think I
understand the chart.  What it's saying, if I'm not mistaken, is that the
twist in a constant speed prop cannot be optimum at all pitch angles and
this is why the fixed pitch prop is slightly more efficient at many
operating points.  What seems to be a bit excessive is the static thrust
difference of almost 50% between the fixed and variable pitch props.
Your chart shows that the engine is producing 311 ft-lbs of torque at
2700 rpm, but only 292 ft-lbs at 1940 rpm.  I would have thought that
with an engine of the "aircraft type" with a mild cam and fixed spark
advance that the torque at 2000 rpm would be higher than at 2700 rpm.  Is
your data from actual engine tests?

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