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
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