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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)
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