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Message-ID: <55EAD753969C41B9A5F39310D689E0BE@george>
From: "George Lendich" <lendich@optusnet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-3288194@logan.com>
Subject: Re: [FlyRotary] Re: IVO Props, etc.
Date: Thu, 13 Nov 2008 11:32:23 +1000
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>I prowled around the test page a bit, & the numbers are really not good
> at all (pitiful, really) if you compare numbers to Lyc powered RVs. The 
> 'best' numbers from the latest chart he supplied (copied below) show 151 
> kts (173mph) tas at 9.3 gph (56 lbs per hr). That speed is roughly what 
> Van claims for a 160hp -6A at 55% power (7.3  gph) at 8000 ft. That's a 
> 26% penalty even if you ignore the 3,000 ft altitude (lower drag) 
> efficiency advantage. At 11,000 ft & that fuel burn, he would  be going 
> around 200 mph with a Lyc.
>
> Since there are 2 big variables (plus airframe/cooling drag) in this 
> equation, you can't tell how much blame to assign to the engine or the 
> prop.
>
> Don't be seduced by the *potential* advantage of a controllable prop. It's 
> already obvious that the cruise/top speed numbers are much worse. I'm a 
> bit too lazy to dig this deep, but you should also compare his climb 
> rate/fuel flow numbers to Van's fixed pitch numbers. Do you really need a 
> climb rate in excess of what the a/c can supply with a fixed pitch prop? 
> If not, the only remaining reason is a drag brake for landing. That's the 
> one area where fixed pitch RV's suffer. High sink rate low speed descents 
> into emergency landing zones are a lot more difficult to achieve, but 
> the -9's already lower landing speed than a -6 should help you there.
>
> Charlie

Charlie,
I looked at the RV6 and the landing speed is lower because of the different 
airfoil, much longer wing, and much bigger flaps. Interesting airfoil 
though.
George ( down under)