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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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