----- Original Message -----
Sent: Friday, June 02, 2006 2:16 PM
Subject: [FlyRotary] Re: ***SPAM***
[FlyRotary] Prop design speed
Joe Hull wrote:
>>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
>>
>
The 80%
figure may be Craig being conservative. Tony Bingelis says the
slip
may increase to 85%-90% under favorable conditions. Which I'm sure
you're
doing at WOT. Mathematically, that would take you up to around
150mph. But still, you're getting the speed without the prop
RPMs. It
sounds like there is more pitch in this prop than what is
advertised.
--
Joe,
Do you have wheel pants installed?
Wendell (Cozy builder - hoping to need a prop some
day)