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From: "Joe Hull" <joeh@pilgrimtech.com>
To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
Subject: RE: ***SPAM*** [FlyRotary] Prop design speed
Date: Fri, 2 Jun 2006 11:23:11 -0700
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> My rough calculations, with an estimated 20% slip, says this prop with =
a
> 76" pitch, is good for 121 MPH with a 2.85 drive and 160 MPH with a =
2.17
> drive assuming a 6000 RPM cruise???
> Where am I going wrong?

I'm not the prop designer - that would be Craig Catto. He knows his =
stuff so
I'm trusting his numbers. My guess is that there may be a couple =
variables
that are missing or need adjusting in the numbers. The slip % may be =
less
and the 76" may be at the 1/3 distance mark and there may be more twist =
on
the outer 2/3's. One thing I do know is that at full throttle I can't =
get
much over 5000RPM at 4000ft and about 140kts IAS (approx 160mph). The =
design
speed for the prop is 5,800RPM (with my 2.17 PSRU).

Cozy's aren't known for their drag - so it isn't the airframe that's =
holding
it back. Either the engine is way under-delivering on power or the prop =
is
way over pitched or both.=20

Joe Hull
Cozy Mk-IV #991 (In Phase1 Flight Test -=A023.8 hrs flown)=20
Redmond (Seattle), Washington