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From: Steve Brooks <prvt_pilot@yahoo.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: ***SPAM*** [FlyRotary] Prop design speed
Date: Fri, 2 Jun 2006 20:24:17 -0400
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On Friday 02 June 2006 07:18 pm, Wendell Voto wrote:
Joe,
One thing is for sure on a rotary.  RPM's = HP.  If you aren't getting 5500 + 
RPM's then you are not getting full power.  The RPM versus HP charts that 
I've seen on the 13B show just about a straight line of HP increase with RPM.

I have a ground adjustable IVO prop on mine, and at 4400 RPM static, it feel 
like a sled on the runway and in the air.  Push that up to 5300-5600 and the 
difference is amazing.

It may just be that you are over propped and aren't developing full power from 
the engine.

Steve Brooks
Hoping to fly next weekend
Alternator bearing went out

BTW on a non-flying issue, but still rotary.  I bought a 1990 RX-7 convertable 
yesterday, with less than 37,000 pampered miles on it.  The car looks like 
the day it was new.  It is amazing to drive, but not quite as much power as I 
expected it would have.


>   ----- Original Message -----
>   From: Ernest Christley
>   To: Rotary motors in aircraft
>   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)