Speaking of 6000 rpm props, I promised to look at the difference

between

constant speed and fixed props in this range, and the results should

be

below. this was for a near stock Mazda with 160 bhp at 6000 rpm for
a 200mph capable plane on that power. The fixed prop was 34 inch
dia with about 42 in pitch. The constant speed was simulated by the
same blade area with the pitch changed to match speed. This is for a
clean installation, with free flow - interference from the fuselage
can severely degrade these predictions. The results are not half bad
for this little prop, and the gain from varible pitch appears less

than

what one would expect at a lower disk loading.
Vance J

Vance,

Can you add a curve for a conventional 68" dia fixed prop at
'conventional' a/c engine rpms (around 2800rpm max)
optimized for the same 200mph cruise? I'm interested in how
much is actually lost in static & takeoff thrust by going to
the small high rpm prop.

The same pair of curves assuming 200 hp would be useful as
well.

Thanks,

Charlie England

You read my mind Charlie. Yes by all means Vance and a 68 dia CS
prop while your are at it. Please.

Paul Lamar

Paul and guys - I am working both of those questions for 160hp and 200hp
with both direct drive 6000 rpm class and 2700 rpm types. I am coming up
with some suprizing answers, The fixed pitch "slow" props are not as much
better at slow speeds as I expected, and they do not converge as much at 200
mph as I had expected. The low end performance of the small props is
helped by the fact that they are not stalled, and let the engine rev further
up the power curve (equivalent). At the other end, it appears that the
disc loading losses persist further up the speed range than I expected.
Because of these unexpected results, I am running more cases with
small differences to convince myself that these are not artifacts of
the program theory - curves will be posted soon - Vance

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