Paul wrote:

Hi, fellow rotary enthusiasts....I am looking for information regarding
the best prop dia and pitch selection for my SQ2000 canard.  I
presently have a 3 blade 64 x 78 Performance wood prop.  With
my new manifold, I am now able to get a static rpm of 4800 rpm's (The
second attempt gave me 5000 rpm's, and the third attempt gave me 4800
before rising temperatures caused me to discontinue
testing). I have a Ross 2.19:1 PSRU, so I figure I got between 2191
rpm's and 2283 rpm's with a 64 x 78 prop.  Anyone care to decipher
these results?
    I got an email from Ron Gowan, and he was using a Performance 3
blade 62x72 prop with a 2.19:1 redrive and he stated that he was able
to do 195 mph at 1500 feet altitude at 6000 rpm's.  I doubt
that my prop would unload that much in the air (to get 6000 rpm's).
    Ed Anderson, I believe was using a 68 x 72 prop, and Perry Mick's
new prop is 62 x 68.  Just wondering if my 64 x 78 is too much prop,
or?
    I should mention that my primary concern is for a good cruise
prop.  I don't care about a climb prop....I figure I spend a lot more
time at cruise than climbing, so I would like the optimum
performance to enhance my cruise performance.
    Unfortunately, on my first flight the engine was not developing
adequate power (max 4200 rpm's), so I can't provide any flight data
for this prop.  Just trying to find out what prop sizes
others are using that have aircraft designed for speeds around 200 mph.
    My engine is now running considerably better and developing more
power after I changed intake manifolds, so I would like to try to
match prop to engine and aircraft, of course.  Thanks in
advance for all replies and suggestions.  sincerely,  Paul Conner,
rotary powered SQ2000 in Mobile, AL

All depends on how much HP you have Paul. All those people you mentioned
including yourself
have widely different intake manifolds. It is not like every body had an
O-360.
Before you make a decision I think you should make some top speed runs
and note
the RPM.

Paul Lamar

I took mine up to 5500' yesterday and let it go WOT for awhile. 6170 rpm
= 2843 prop rpm, GPS gs 156 knots, indicated 142 knots. With a pitch of
68" this rpm is 268 fps = 183 mph = 159 knots. So the GPS and RPM agree
again. This is pretty typical of a LEZ with an O-235 engine, which is
what I used as a basis for sizing the prop.

Paul, if you don't care about climb and mostly about cruise, your prop
might be about right. 2800 RPM * 78" = 303 fps = 207 mph. Your gearbox
ratio is basically the same as mine. After you get your engine tuned and
producing full power, if it can't turn the prop up to the desired RPM,
you could trim the tips slightly to reduce diameter a little, but the
pitch sounds about right.

Static RPM is worthless as a comparison, I can't get mine to do anything
static because it's stalled so bad. It doesn't even turn up correctly
until I'm going down the runway about 40-50 knots.

I think from the few reports I've heard my plane is much quieter now.
Fan tip speed was around 900 fps, with the new prop even at 6170 engine
RPM tip speed is only 769 fps, not including the vector addition of
forward velocity. During a 100 knot climb the engine is only 5500 RPM
with a tip speed of only 686 fps. Al Wick heard me fly over his house
when I was at 12,500' a couple years ago, so that must have been
supersonic tip speed noise. With the fan my family could hear me from
inside the house when I flew over at 4500'.

Perry

Thanks you Paul and Perry for the prop advice.  Perry mentioned that his
prop doesen't turn up correctly until he's going down the runway about 40-50
knots.  Think I'll do that next.  If the prop starts to unload and pick up
rpm's, I'll go ahead and fly it as Paul Lamar suggested.  

Unfortunately on
my first flight the climb was so pitiful, it left me somewhat distrusting
this prop.  I realize it's not the prop's fault that I was not able to
advance the throttle beyond 1/2 without the engine faultering....that was
manifold related.  Now that I have considerably more power and I am able to
actually move the throttle lever to full power (and get more power), I think
you guys are correct in that I should give this prop a try. Maybe it ain't
broke, as they say.

       Thanks to Perry for running the numbers for me regarding the pitch vs
rpm, fpm=mph.  Obviously I need more test results at altitude.
    I guess I was considering all rotaries to be similar, but as Paul Lamar
mentioned, there are too many variables, such as intake manifold
configurations, etc.   I'll give it another shot now that I am able to
produce full power.  Thanks to all for your input and suggestions.    Paul
Conner, rotary powered SQ2000 in Mobile, AL

A lot of fixed pitch props have that problem. Particularly
on high speed air planes. What works for cruise and top speed may stall
at static. Note the curves that Vance just uploaded. Actually it is kind of 
dangerous to optimize a prop for static thrust in certain circumstances.

What sort of problems were you having with your intake manifold?
Here are some old file photos of it.

Paul Lamar
 
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