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Date: Tue, 10 May 2005 16:14:27 -0600
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
From: Bill Dube <bdube@al.noaa.gov>
Subject: Re: [FlyRotary] Re: center rotor OFF
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>
>Controlling power with throttle means less air in the cylinder, leading to 
>less compression pressure.  Doesn't higher pressure equate to more 
>complete combustion?  Would running 2 cylinders hard be more efficient 
>than running 4 cylinders half as hard?

         If everything else is held the same, the higher the peak pressure 
(compression) the higher the efficiency of the engine. When the throttle is 
further open, the manifold pressure goes up, and this makes the peak 
pressure go up.

         If you are running on fewer cylinders, the throttle is more open 
and the manifold pressure increases. This makes the engine more efficient, 
at least from the standpoint of the thermodynamic cycle.

         You can do this better with an overdrive transmission. This 
reduces the engine speed along with increasing the manifold pressure (for a 
given HP output.) The engine frictional losses are reduced too because the 
RPM is lower.

         I suspect that turning off cylinders was some top-level management 
"bright" idea, perhaps from the marketing department. An overdrive gear in 
the transmission makes much more sense, but I suppose doesn't market as 
well. Not nearly as sexy or high tech.