Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2955041 for flyrotary@lancaironline.net; Thu, 29 Jan 2004 08:46:55 -0500 Received: from edward (clt78-020.carolina.rr.com [24.93.78.20]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i0TDkrjF002565 for ; Thu, 29 Jan 2004 08:46:53 -0500 (EST) Message-ID: <000e01c3e66e$60dea1a0$2402a8c0@edward> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Streamline Ducts Date: Thu, 29 Jan 2004 08:47:03 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000B_01C3E644.77C10950" 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 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_000B_01C3E644.77C10950 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable -----=20 From: Finn Lassen=20 To: Rotary motors in aircraft=20 Sent: Wednesday, January 28, 2004 10:12 PM Subject: [FlyRotary] Re: Streamline Ducts I found that going from a bell shape curve to a straight wedge to my = oil cooler the oil temps dropped somewhat. If I understand it correctly, the 7.5 degree max rule is to ensure = that the airflow stay attached to the duct walls (no turbulence). = According to Bernie Kerr's experiments, that is true for an open duct = (e.g. a wind tunnel). However, as soon as you put a restriction in there = (a screen or a radiator) that rule no longer holds true and you can have = a much steeper angle with the flow still staying attached. He observed = this by tufting the walls of a test duct. An experiment anybody could = do. Shamelessly copied from http://www.rotaryaviation.com/bernie_kerr.htm = (see pictures there): That Bernie is some guy. From what I understand about the topic , I = agree with Bernie regarding the 7.5 deg angle and wind tunnels. The = characteristics of the core of the radiator does indeed have an effect = on the diffusion process through its resistance to air flow. Seeing the = tuffs from Bernie's radiator would appear to indicate he is getting = decent air flow (at least at low velocities). Again, as I have = mentioned several times, if you have sufficient air mass flow through = your core, you WILL cool. However, you could at the same time also = incurr large cooling drag. =20 The difference between an adequate cooling system and a great cooling = system (both keep the engine from meltdown) is the amount of cooling = drag. That is where careful attention to ducts, diffusers, exit and = cooling core characteristcs comes to play. =20 Clearly a system that fails to cool the engine is inadequate. Keep in = mind you could have the best duct design, diffuser pressure recovery, = etc, all optimized - BUT, if you radiator is too small for the BTUs you = need to reject then the system will fail to cool you engine. =20 Ed Anderson ------=_NextPart_000_000B_01C3E644.77C10950 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
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From:=20 Finn=20 Lassen
Sent: Wednesday, January 28, = 2004 10:12=20 PM
Subject: [FlyRotary] Re: = Streamline=20 Ducts

I found that going from a bell shape curve to a = straight wedge=20 to my oil cooler the oil temps dropped somewhat.

If I = understand it=20 correctly, the 7.5 degree max rule is to ensure that the airflow stay = attached=20 to the duct walls (no turbulence). According to Bernie Kerr's = experiments,=20 that is true for an open duct (e.g. a wind tunnel). However, as soon = as you=20 put a restriction in there (a screen or a radiator) that rule no = longer holds=20 true and you can have a much steeper angle with the flow still staying = attached. He observed this by tufting the walls of a test duct. An = experiment=20 anybody could do.

Shamelessly copied from http://www.rotarya= viation.com/bernie_kerr.htm=20 (see pictures there):

That Bernie is = some=20 guy.   From what I understand = about the=20 topic , I agree with Bernie regarding the 7.5 deg angle and wind=20 tunnels.  The characteristics of the core of the radiator does = indeed=20 have an effect on the diffusion process through its resistance to air=20 flow.  Seeing the tuffs from Bernie's radiator would appear to = indicate=20 he is getting decent air flow (at least at low velocities).  = Again, as I=20 have mentioned several times, if you have sufficient air mass flow = through=20 your core, you WILL cool.  However, you could at the same=20 time also incurr large cooling drag. 
 
The difference between an adequate = cooling=20 system and a great cooling system (both keep the engine from meltdown) = is the=20 amount of cooling drag.  That is where careful attention to = ducts,=20 diffusers, exit and cooling core characteristcs comes to play. =20
 
Clearly a system that fails to = cool the engine=20 is inadequate.  Keep in mind you could have the best duct design, = diffuser pressure recovery,  etc, all optimized - BUT, if you = radiator is=20 too small for the BTUs you need to reject then the system will fail to = cool=20 you engine. 
 
Ed Anderson
 
 
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