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

Well, this is an updated curve, and another interesting design for direct
drive with a wankel.

I think I have an answer to some of the results I found puzzling. The
direct drive prop uses a Wankel power cuve from some of the
posted data. The Wankel, like most all conversions, has a different
shape to the power curve than a classic aircraft engine (as used for
the 68 inch 2700 rpm case). The torque peak of a "Lycosaurus"
is frequently above the rated rpm, and the curve is essentially a
straight line. The near stock Mazda curve shohs max torque about
4000 rpm with breathing limited poer arcing over between there
and the power peak a bit over 6000. Thus at static, the little prop
is moving down to a higher percent of rated power, than the big
engine over the same percent rpm. This, and the fact that the blades
are not stalling, pushes static thrust up closer to the constant speed
prop curve. The big prop, with it's steep pitch, is stalled over most
of the blade, the extra drag of the stalled blade is slowing it more
and the poer curve is droppig away faster. The static thrust on the
big prop is incresed about 50 percent by reducing pitch, and
allowing rated rpm and power, while the little prop only gains
only about 25 percent.

The other picture is a concept by Bob Archer( justifiably well
known for his antenna work). Bob has had a geared, turbo
wankel with a controllable pitch prop  on a trailer test
stand for at least 25 years. but this design was based on direct
drive. Unfortunately both tasks have been tabled.

Vance

 
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