From: BOBPAS26@aol.com
Message-ID: <fc.a48d7be.28a2e1e8@aol.com>
Date: Wed, 8 Aug 2001 14:41:44 EDT
Subject: Re: Hot High Flight
To: lancair.list@olsusa.com
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In a message dated 8/8/01 12:23:50 AM Eastern Daylight Time, Michael D Smith 
writes:

Why also do the CHT rise so much when going from FL 230 to FL 260 with 
everything else keep the same?

Michael, The simple answer is that you're getting up to an altitude where the 
air is too thin to carry away the engine heat. It's a law of nature, and the 
bane of high altitude aviators since shortly after Orville and Wilbur. Your 
turbo-boosted engine continues to produce the same amount of power as you go 
up--until you reach the limit of available boost--when the waste gate fully 
closes and all available air from the turbos is going into the air/fuel 
induction system. Producing this power generates a lot of heat that the 
engine must shed into the oil, exhaust, and surrounding air. The problem is 
that the air at 26,000 feet is less than half as efficient in removing heat 
as it is at sea level. The amount (volume) of air you can blow across the 
cooling fins is approximately constant as you go up, but there aren't enough 
molecules going by to absorb the heat. I haven't flown my IV-P yet, but 
understand from several flyers that engine heating defines the actual ceiling 
of the airplane. I'd also note that heat is an absolute killer of engines and 
other mechanical and electric things--as you've noted. If you hope to run 
your engine to anywhere near it's recommended TBO, don't push the temps, and 
watch them closely. Hope this helps.

Bob Pastusek
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