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Date: Fri, 02 Jun 2006 15:16:16 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: ***SPAM*** [FlyRotary] Prop design speed
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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
>Cozy Mk-IV #991 (In Phase1 Flight Test - 23.8 hrs flown) 
>Redmond (Seattle), Washington
>
>
>--
>Homepage:  http://www.flyrotary.com/
>Archive and UnSub:   http://mail.lancaironline.net/lists/flyrotary/
>
>  
>
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.

http://64.233.161.104/search?q=cache:_vgwpK7XvqcJ:members.eaa.org/home/homebuilders/authors/bingelis/1The%2520Fixed%2520Pitch%2520Propellor%2520Dillemma.html+airplane+propeller+slip+efficiency&hl=en&gl=us&ct=clnk&cd=16&client=firefox-a

-- 
         ,|"|"|,               Ernest Christley     |
----===<{{(oQo)}}>===----     Dyke Delta Builder    |
        o|  d  |o          www.ernest.isa-geek.org  |