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?

Engine power is taken from curves supplied by the
engine manufacture. In general the torque curve of a
typical aircraft engine is very close to flat, often
still rising as you pass the rated rpm (redline?).
This is not surprising since the cam and valve lift on
these engines are not much different than the average
pickup truck auto engine,which usually peak above 2700
rpm. On mildly tuned engines a number very close to 1
ft lb per cubic inch is quite typical over a wide
range of rpm.
"torque peak" ia almost an oxymoron - usually a rather
gentle curve unless peaked by resonant intake or
exhaust. The 210 hp Cont IO 360 is a good example of
this - using a "bundle of snakes" intake it pushes a
bump up a bit past 1 ft lb per cube near design rpm.
Vance

 
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