X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta05-srv.windstream.net ([166.102.165.166] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2463511 for flyrotary@lancaironline.net; Fri, 09 Nov 2007 11:28:34 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.166; envelope-from=montyr2157@alltel.net Received: from ispmxaamta04-gx.windstream.net ([151.213.143.21]) by ispmxmta05-srv.windstream.net with ESMTP id <20071109162753.PYJV19750.ispmxmta05-srv.windstream.net@ispmxaamta04-gx.windstream.net> for ; Fri, 9 Nov 2007 10:27:53 -0600 Received: from Thorstwin ([151.213.143.21]) by ispmxaamta04-gx.windstream.net with SMTP id <20071109162753.GMCG8365.ispmxaamta04-gx.windstream.net@Thorstwin> for ; Fri, 9 Nov 2007 10:27:53 -0600 Message-ID: <001c01c822ed$7c9c7100$6501a8c0@Thorstwin> From: "M Roberts" To: "Rotary motors in aircraft" Subject: Re: Total,duct, Ambient or Velocity???? Date: Fri, 9 Nov 2007 10:27:57 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0019_01C822BB.31D6F960" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0019_01C822BB.31D6F960 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable But, semantics aside, yes, I agree, lower exit pressure is what you are = after and that does not always equate to larger exit duct area. In = fact, if the air heated by the core flows through a nozzle it might even = produce thrust and lower exit pressure using a smaller exit. But, in = general, I still believe that in most of our cases, we are short of the = level of duct design that would reliably permit that. What we need is = someone to invest in one of those $$$$ Computer Fluid Flow software = programs and see what they would reveal. Ed Ed, I have to disagree with the big $$$ CFD idea. Until I see proper exit = ducts and every effort made to do things right inlet wise....CFD is a = waste of time. I have yet to see an installation at the level of = refinement where CFD would start to make sense. You can get to 90% of = optimum by following a few simple guidelines and some fairly simple = math.=20 1.) do a heat balance at the cruise condition to figure out how much air = you need to ingest. 2.) Size your inlet appropriately. 3.) Provide a real exit duct. 4.) Use a cowl flap. 5.) Do some testing with oil and tufts to make improvements. A properly done CFD will only get you another 5% beyond these simple = steps that are within reach of mere mortals. In fact if the guy/gal = doing the CFD work is not intimately familiar with the situation and = what sort of assumptions to make/conditions to assign it is very likely = that the results will be less successful that the empirical method. In other words CFD=3Ddecimal dust. Monty ------=_NextPart_000_0019_01C822BB.31D6F960 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

But, semantics aside, = yes, I agree,=20 lower exit pressure is what you are after and that does not always = equate to=20 larger exit duct area. In fact, if the air heated by the core = flows=20 through a nozzle it might even produce thrust and lower exit = pressure using=20 a smaller exit. But, in general, I still believe that in most of = our=20 cases, we are short of the level of duct design that would reliably = permit=20 that. What we need is someone to invest in one of those $$$$ = Computer=20 Fluid Flow software programs and see what they would reveal.

Ed

Ed,

I have to disagree with the big = $$$ CFD=20 idea. Until I see proper exit ducts and every effort made to do things = right=20 inlet wise....CFD is a waste of time. I have yet to see an installation = at the=20 level of refinement where CFD would start to make sense. You can get to = 90% of=20 optimum by following a few simple guidelines and some fairly simple = math.=20

1.) do a heat balance at the = cruise=20 condition to figure out how much air you need to ingest.

2.) Size your inlet=20 appropriately.

3.) Provide a real exit = duct.

4.) Use a cowl = flap.

5.) Do some testing with oil and = tufts to=20 make improvements.

A properly done CFD will only = get you=20 another 5% beyond these simple steps that are within reach of mere = mortals. In=20 fact if the guy/gal doing the CFD work is not intimately familiar with = the=20 situation and what sort of assumptions to make/conditions to assign it = is very=20 likely that the results will be less successful that the empirical=20 method.

In other words CFD=3Ddecimal=20 dust.

Monty

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