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Cyl #3 and #4 show hottest CHT, too hot for my taste during climb

In terms of cooling drag, the specific heat of the cooling medium is the same for all types of engines – because the cooling medium for all of them is air. However, the air cooled engine can be cooled with less air flow because each mass unit of air can be heated to a greater temperature above ambient before it runs out of temperature differential – the air cooled cylinder is 150 F hotter than a radiator.

Water cooling is an advantage for design of an engine in isolation, as opposed to an engine to power an aircraft. It provides higher heat transfer coefficients at the cylinder surface, which allows higher rpm, higher power per cylinder and more waste heat per cylinder. That’s OK as long as you don’t mind adding an extra cooling system, and a gearbox, as well as having a little higher cooling drag,

Water cooling did not become established as better in the 40’s – it was actually at that time when aircraft engines went firmly away from water cooling, for civilian aircraft of up to many times the power of our GA engines. You can make an argument that developments since then have shifted the technical balance back again, but I think it’s more of an expedience based on an interest in adapting car engines to create a product relatively inexpensively. However the resulting products are still more expensive than most GA buyers are ever going to pay based on comparison with other options they already have.

I’ve fixed quite a number of leaky water pumps and radiator hoses, actually more than I could count, but never on an aircraft. I’ve also never adjusted the valves on an aircraft engine, or replaced a gearbox, clutch or timing belt as I’ve done on many other engines – for instance I run five other engines with rubber timing belts like a Mercedes-based aircraft engine. For aircraft service, I intentionally selected the two most robust aircraft engines ever built, the A65 and O-320. They don’t overheat, they don’t break, they don’t require much service and they’re fine for me. Others can spend their money on whatever they’d like.

Last Edited by Silvaire at 02 Nov 00:00
31 Posts
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