X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao107.cox.net ([68.230.241.39] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2467993 for flyrotary@lancaironline.net; Mon, 12 Nov 2007 13:37:29 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.39; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao107.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20071112183649.RJHF5798.fed1rmmtao107.cox.net@fed1rmimpo01.cox.net> for ; Mon, 12 Nov 2007 13:36:49 -0500 Received: from BigAl ([72.192.143.193]) by fed1rmimpo01.cox.net with bizsmtp id Bucp1Y00T4AaN600000000; Mon, 12 Nov 2007 13:36:50 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Diffuser Configuration Comparison Date: Mon, 12 Nov 2007 10:37:05 -0800 Message-ID: <000001c8255b$0687bdb0$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C82517.F866EEB0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C82517.F866EEB0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: Rotary motors in aircraft Subject: [FlyRotary] Re: Diffuser Configuration Comparison =20 I especially liked the comment in the report where it says that the higher the pressure drop across the core, the higher the diffuser efficiency. I interpret this as 'thicker core is better than thinner!' Of course there is a point of diminishing returns where flow is simply too low as Ed has pointed out but in an application where diffuser efficiency is such an important factor, this pushes that point in the direction of 'thick'. =20 Tracy (back from the dragon and sorry to bring up the thick vs thin thing again :>) =20 Again I feel compelled to caution against over-simplification and generalities (I=92m not just trying to be a contrarian; really!). In a = myriad of factors, drawing that conclusion based on one configuration and one parameter can certainly be misleading. What is your criteria? I can say that generally increased pressure drop equates to increased drag. Also =93thickness=94 and =93pressure drop=94 are not equatable (is that a = word?). The very thick P-51 rad with large hexagonal passages is in no way = comparable to the same thickness of modern radiators with =BD=94 between tubes and 16 = fins/in. =20 The most detailed, sophisticated analysis of radiators for our = application that I have seem was done by Fred Moreno back in =9299; but = unfortunately it also was done for a specific case of 220 KTAS and 10 fins/in. What it suggests is there is an optimum thickness (minimum drag), and that is roughly 3=94. That=92s for 10 fins/in.; I concluded that my 16 fins/in = rad should be thinner, and went with 2.5=94 thckness. It works = exceptionally well. The 2.5=94 to 3=94 thickness seems common for rads made by Ron = Davis and Griffin for racing applications. That seems consistent. =20 But likely, obtaining minimum drag is beyond the sophistication that = most of us can achieve in our applications. If we can get it to cool adequately we=92ve done a good job; and that is probably mostly a function of = scoops, diffuser and exit configurations. =20 FWIW, =20 Al G ------=_NextPart_000_0001_01C82517.F866EEB0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Diffuser Configuration Comparison

 

I especially liked the comment in the report where it says that = the

higher the pressure drop across the core, the higher the = diffuser

efficiency.=A0=A0 I interpret this as 'thicker core is better than

thinner!'=A0=A0 Of course there is a point of diminishing returns = where

flow is simply too low as Ed has pointed out but in an = application

where diffuser efficiency is such an important factor, this = pushes

that point in the direction of 'thick'.

 

Tracy (back from the dragon and sorry to bring up the thick vs thin

thing again :>)

 

Again I feel compelled to caution against over-simplification and generalities (I’m not just trying to be a contrarian; really!). =A0In a myriad of factors, drawing that conclusion = based on one configuration and one parameter can certainly be misleading. What is = your criteria?=A0 I can say that generally increased pressure drop equates to increased drag. Also “thickness” and “pressure = drop” are not equatable (is that a word?).=A0 The very thick P-51 rad with = large hexagonal passages is in no way comparable to the same thickness of modern = radiators with =BD” between tubes and 16 fins/in.

 <= /font>

The most = detailed, sophisticated analysis of radiators for our application that I have seem = was done by Fred Moreno back in ’99; but unfortunately it also was = done for a specific case of 220 KTAS and 10 fins/in. What it suggests is there is = an optimum thickness (minimum drag), and that is roughly 3”.=A0 = That’s for 10 fins/in.; I concluded that my 16 fins/in rad should be thinner, = and went with 2.5” thckness.=A0 It works exceptionally well.=A0 The = 2.5” to 3” thickness seems common for rads made by Ron Davis and = Griffin for racing applications.=A0 That seems consistent.

 <= /font>

But likely, = obtaining minimum drag is beyond the sophistication that most of us can achieve in = our applications. If we can get it to cool adequately we’ve done a good job; and = that is probably mostly a function of scoops, diffuser and exit = configurations.

 <= /font>

FWIW,

 <= /font>

Al = G

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