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Date: Fri, 26 Aug 2005 11:29:05 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fire extinguishers
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Hans Conser wrote:

>
> Actually liquid cooled engines need a great volume of air than air 
> cooled engines.  This is because the temperature differential (Delta 
> T) of the aircooled engine is much greater.  In other words it takes 
> less air to cool 400 degree cooling fins vs 220 degree coolant.
>

Hans, if I've learned nothing else from the cooling discussions on this 
list, I've learned that it's is never as simple as it should be. It's 
true that the DeltaT is much greater, but that's not the whole story.  
Compare the surface area available to transfer the heat and you'll see 
that it's a wash.  The benefit of liquid cooling is that you CAN (but 
not necessarily will) design air ducts that directs the air around the 
cooling surfaces so that not as much of the inertial energy is lost.  
With an air cooled engine, you're pretty much stuck with an 
'un'aerodynamic cylinder sticking out in the wind, causing all sorts of 
vortices and turbulance, wasting a lot of energy and allowing a large 
portion of the cooling air to leave without taking any of that heat 
energy with it.

Even more to the point, water cooled makes it possible to design the 
system (radiator placement, airduct entrances and exits) to benefit the 
aerodynamics of the airplane.  For example, I'm moving the radiators 
toward the rear of my Delta so that I don't have to pour lead in the 
tailpost.  With an air cooled, you pretty much stuck with opening right 
behind the propeller.

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