I don't off hand but you can always make your own

prop. Many people

have. George Graham and Perry Mick come to mind.

Also

if there is enough money involved some of the prop

makers would make

you a custom prop I am sure. I know Klause would. If

diameter is a problem

due to landing gear limitations you could go to

wider blades or a

three blade prop.

BTW what is intrinsically wrong with cruising at

6000 RPM? We don't

really know the limits of the rotary engine. For all

we know it will

cruise at 75% power at 6000 RPM for 2000 hours. The

four rotor Lemans
engine

ran with this RPM schedule for 24 hours with little

or no wear.

This engine is still winning races ten years later.

It sure is easy to get a lot more power at 7000 RPM

then it is

at 6000 RPM. A lot of the gyro guys running rotaries

are running 2.85:1

PSRU ratios with multi blade Warp Drive props. They

don't seem to have

any engine problems.

Paul Lamar

Tracy Crook wrote:

True, I don't think there is a problem with the engine
running 6000
continuous.  Note that Mazda's research showed that
stress on the rotor and
stationary gears is very low at this speed (see
Yamamoto's book).  Also true
that the prop makers will try anything you want (for a
price). The problem
is that they really have zero experience with the type
of prop needed with
low prop rpm because there has been no demand for such
a thing.

Another problem is the wide spread of engine speeds
you encounter with high
ratio gear drives and fixed pitch props.  I'm cheering
you guys on with the
variable pitch prop project and hopeing for the best
but for now we have to
work with what is available at a reasonable cost which
means a fixed pitch
prop.  If you prop for good takeoff and climb
performance, the top end and
high altitude rpm goes through the roof and fuel burn
is high.  From real
world examples, this tendancy is greater with high
ratio drives.

Also true that you can make your own prop.  My
congratulations to those who
have.   But for me (to again quote Dirty Harry), A
man's got to know his own
limitations.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

Agreed on the fixed pitch compromise between take off and climb performance
verses top speed.

Usually larger diameter props are out of the question because of
landing gear length considerations. That leaves more pitch, wider
blades or more blades.

Things are not as bad as Vance makes out. Yes the high pitch prop may
be stalled but it is still generating thrust and that is a function
of the HP going in. If the prop static RPM is 6000  instead of 5000 RPM
the engine is putting more power into the prop.

The classic example is the high bypass ducted fan air liner. Yes the duct is horribly
inefficient at low speeds but the engine has a zillion HP.

Klause's Varieze is another example. His fixed pitch prop is optimized
for 250 MPH and yes his airplane does not take off as well as a Varieze
with a prop optimized for 200 MPH. He still gets out of SZP with
a 2000 foot runway with room to spare. Not only that he runs his prop
up to 3100 RPM or so so the diameter is not large.

Paul Lamar
 
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