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. Joe Hull
Cozy Mk-IV #991 (In Phase1 Flight Test - 23.8 hrs flown) Redmond (Seattle), Washington


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