Return-Path: Received: from [24.25.9.102] (HELO ms-smtp-03-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2904519 for flyrotary@lancaironline.net; Wed, 24 Dec 2003 20:27:21 -0500 Received: from o7y6b5 (clt78-020.carolina.rr.com [24.93.78.20]) by ms-smtp-03-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id hBP1R6ow017632 for ; Wed, 24 Dec 2003 20:27:18 -0500 (EST) Message-ID: <000a01c3ca85$d4f39460$1702a8c0@WorkGroup> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] seven degree divergence? Date: Wed, 24 Dec 2003 20:24:14 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0007_01C3CA5B.E5E60E80" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0007_01C3CA5B.E5E60E80 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable =20 From: kevin lane=20 To: Rotary motors in aircraft=20 Sent: Wednesday, December 24, 2003 7:38 PM Subject: [FlyRotary] seven degree divergence? I keep seeing reference to 7 degree duct divergence, and the carpenter = in me can't figure out how you place a typically straight-sided = protractor against a curve to measure it. anyone know? seems to me = something is missing, such as "per inch" so that the curve can be broken = down into a series of small triangles. Kevin Lane Portland, OR e-mail-> n3773@comcast.net web-> http://home.comcast.net/~n3773 (browse w/ internet explorer) Kevin, In some early studies on ducts, experimentation showed that if the = straight walls (in this case not curved) of a duct did not diverge more = than 7 Deg from the intake to the cooler core that losses would be at a = minimum. Apparently 7 Deg was the magic angle (I have seen references = that indicated you might get away with as much as 10 Deg) which if you = did not exceed would provide flow with no boundary layer separation. It is not 7 Deg per inch ( that would make it much more useable for = aircraft), but 7 deg total. So as you might imagine with only 7Deg if = you core were any size at all the inlet would have to be many inches = away. Probably OK for wind tunnels {:>) That is one reason why attempts were made to find low loss diffusion = configurations that provided for shorter ducts. I personally have never = seen the original study, but I have seen it referenced in many NACA = studies on radiators, diffusers and ducts. Ed Anderson ------=_NextPart_000_0007_01C3CA5B.E5E60E80 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
 
From:=20 kevin = lane=20
Sent: Wednesday, December 24, = 2003 7:38=20 PM
Subject: [FlyRotary] seven = degree=20 divergence?

I keep seeing reference to 7 degree = duct=20 divergence, and the carpenter in me can't figure out how you place a = typically=20 straight-sided protractor against a curve to measure it.  anyone=20 know?  seems to me something is missing, such as "per inch" so = that the=20 curve can be broken down into a series of small = triangles.
Kevin Lane  Portland, OR
e-mail-> = n3773@comcast.net
web-> http://home.comcast.net/~n3773
(browse=20 w/ internet explorer)
 
Kevin,
 
    In some early studies on = ducts,=20 experimentation showed that if the straight walls (in this case not = curved)=20  of a duct did not diverge more than 7 Deg from the intake to the = cooler=20 core that losses would be at a minimum. Apparently 7 Deg was the = magic=20 angle (I have seen references that indicated you might get away = with as=20 much as 10 Deg) which if you did not exceed would provide = flow with=20 no boundary layer separation.
 
  It is not 7 Deg per inch ( that = would make=20 it much more useable for aircraft), but 7 deg total.  So as you = might=20 imagine with only 7Deg if you core were any size at all the inlet = would have=20 to be many inches away.  Probably OK for wind tunnels=20 {:>)
 
 That is one reason  why attempts = were made to=20 find low loss diffusion configurations that provided for shorter = ducts. =20 I personally have never seen the original study, but I have seen=20 it referenced  in many NACA studies on radiators, diffusers = and=20 ducts.
 
 
Ed Anderson
 
 
------=_NextPart_000_0007_01C3CA5B.E5E60E80--