X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [69.171.52.140] (account marv@lancaironline.net) by logan.com (CommuniGate Pro WebUser 5.0.6) with HTTP id 915018 for lml@lancaironline.net; Fri, 06 Jan 2006 01:30:07 -0500 From: "Marvin Kaye" Subject: Re: [LML] Idle power descent? To: lml X-Mailer: CommuniGate Pro WebUser v5.0.6 Date: Fri, 06 Jan 2006 01:30:07 -0500 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Posted for Walter Atkinson : We believe shock cooling to be a myth. That said, there are two issues. 1) how can you shock cool something that's not hot to start with? Keep CHTs under 380 and you can't cool 'em off fast enough to hurt anything, and 2) Look at all of the years we have pulled the mixture in twins during training with no known ill effects. We *think* we know where this OWT came from. When the first TC'd piston twins hit the market (Twin Cessnas) we were not accustomed to flying for extended periods in the flight levels. Even in the summer, the fuel would cool off to below zero temps while at altitude. The pilot would descend rapidly to pattern altitude with low FF whereupon he would shove the mixture to full rich before landing as per the POH. This big blast of very cold fuel would hit the side of the warm intake chamber and the results were cracks in the intake housing. We never saw CYLINDER or head problems, we saw intake area cracks. As soon as pilots quite shoving the mixture to full rich, the problem disappeared... it also disappeared when the misguided idea of reducing power in 1"MP increments every two minutes slowed the rate of descent enough that the pilot was altering the mixture slowly instead of all at once. There were never any reports in NA airplanes. Why? Shock cooling cylinders from low power descents does not exist. Heck, I can leave 17k feet at 90% power, descend at over 1000 fpm at very low power and not have CHTs change more than 70-80 degrees over 15 minutes. How can you shock cool something that's not hot to start with? This, as with most OWT's started with an accurate observation but an inaccurate causal assignment. Walter