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RE: Exhaust &

> From:          "Laurence W. Coen" <lwcoen@freewwweb.com>

> There are two factors that I think you should consider in deciding
> what mixture you should use in a liquid cooled system.  Protecting
> to 18deg F on the ground could get you into trouble while flying
> trouble while flying. At, say 15,000 ft., the OAT is -30degF. and a

Yes, but. At 50% power, you're still pumping out more than a quarter 
million BTU/hr into the cooling system. And the purpose of the 
variable outlet is to reduce airflow through the system (And 
therefore reduce drag.) so just there's just enough air to remove
the heat generated.

With the standard atmosphere, it's about 5degF at 15,000. So if it's 
-30degF, then the ground temp should be around 24degF. That's a 
fairly uncommon daytime temperature in my neck of the woods and not 
that regularly even at night.

My point about coolant and variable outlets aren't hard and fast 
rules, just something to think about when you want to get the last 
bit of efficiency possible. Power lost to coolant pumping may not be 
enough for the added worry about the viscosity and cold nights, but 
the pump does take a fair number of HP. I'd think flow control would 
be more important, though I don't have any hard numbers there either.

David Parrish