Return-Path: Received: from gull.mail.pas.earthlink.net ([207.217.120.84] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2883645 for flyrotary@lancaironline.net; Tue, 09 Dec 2003 13:44:11 -0500 Received: from h-68-166-182-146.sfldmidn.covad.net ([68.166.182.146] helo=richard) by gull.mail.pas.earthlink.net with smtp (Exim 3.33 #1) id 1ATmq8-0000m8-00 for flyrotary@lancaironline.net; Tue, 09 Dec 2003 10:44:08 -0800 Message-ID: <005901c3be84$8ea8e620$6601a8c0@richard> From: "Eric Ruttan" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Air Density at altitude Date: Tue, 9 Dec 2003 13:45:02 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 DeltaDeltaT, like delta T, cant be measured from any absolute point, but is a degree measurment between points. We assume that the behavior going from -30 to -20 is the same as from 90 to 100 (assume all degree C). This is not exactly true but very close. From: Subject: [FlyRotary] Re: Air Density at altitude > Wouldn't the percentage change in DeltaT (DeltaDeltaT?) have to be measured from absolute 0? An 80degree change would then represent...what?... about 20%? > From: Ed Anderson > Subject: [FlyRotary] Re: Air Density at altitude > > Heat transfer equation Q =W*DeltaT*Cp, with W = mass flow down > > by 30%. So to get rid of the same Q of heat (and since Cp doesn't > > change that much) it would appear that means the delta T term > > would need to increase by 30% for Q quantity to remain the same. > > But, I don't know exactly how a 79Deg colder incoming air would > > affect the Delta T term.