X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao103.cox.net ([68.230.241.43] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2462797 for flyrotary@lancaironline.net; Fri, 09 Nov 2007 01:10:24 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.43; envelope-from=alventures@cox.net Received: from fed1rmimpo02.cox.net ([70.169.32.72]) by fed1rmmtao103.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20071109060945.QFNC5967.fed1rmmtao103.cox.net@fed1rmimpo02.cox.net> for ; Fri, 9 Nov 2007 01:09:45 -0500 Received: from BigAl ([72.192.143.193]) by fed1rmimpo02.cox.net with bizsmtp id AW9j1Y00J4AaN600000000; Fri, 09 Nov 2007 01:09:44 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Total,duct, Ambient or Velocity???? Date: Thu, 8 Nov 2007 22:09:50 -0800 Message-ID: <002201c82297$236fe180$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0023_01C82254.154EEB70" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 In-reply-to: This is a multi-part message in MIME format. ------=_NextPart_000_0023_01C82254.154EEB70 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =20 It would seem "reasonable" that a low pressure area at the exit will = help flow through a duct - no argument on that point. What the report = appeared to say is that the after a certain point opening the exit area wider = does not appear to have any additional benefit. (Exit "area" and exit = "pressure" are not interchangeable terms) That if the duct is capable of "using up" = all of the kinetic energy in your air flow by obstructions, pressure drops = and friction losses then enlarging the exit does not necessarily add to the flow. =20 Remember you can not suck air through a duct, you can only blow it = through. (Of course you can suck air through a duct - I do it after (and = sometimes before) every flight with the fan I have on the back side of the = radiator) So in effect if the straw is pinched you can "suck" on it all you want = but it won't increase flow {:>). =20 =20 If I understood the report, it appears that enlarging the exit area = beyond the frontal area of your core provides little if any additional benefit. That does not mean cowl flaps never work or provide benefit. In fact it appears that the better your duct, the more benefit the cowl flaps = appear to have, the worst your duct, the lesser benefit - just the opposite of = what you might think. Ed; =20 Don't mean to be picky, but some of these generalities are making me nervous:-). These things are applicable only when the duct/diffuser is operating at max efficiency - which is rarely the case. Lot's of good info. Thanks. You're right; it's some kind of magic, and = you don't know for sure until you built it and try it. Al ------=_NextPart_000_0023_01C82254.154EEB70 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

It  would seem "reasonable" that a low pressure area at the exit  will = help flow through a duct - no argument on that point.  What the report = appeared to say is that the after a certain point opening the exit area wider = does not appear to have any additional benefit. (Exit “area” and exit “pressure” are not interchangeable = terms) That if the duct = is capable of "using up" all of the kinetic energy in your air flow by obstructions, pressure drops  and friction losses then enlarging = the exit does not necessarily  add to the flow.

 

Remember you can not suck = air through a duct, you can only blow it through. (Of course you can suck air through a duct – I = do it after (and sometimes before) every flight with the fan I have on the = back side of the radiator) So in effect if the straw is pinched you = can "suck" on it all you want but it won't increase flow {:>).  

 

If I understood the report, =  it appears that enlarging the exit area beyond the frontal area of your = core provides little if any additional benefit.  That does not mean cowl = flaps never work or provide benefit.  In fact it appears that the better = your duct,  the more benefit the cowl flaps appear to have, the worst = your duct, the lesser benefit - just the opposite of what you might = think.

Ed;

 

Don’t mean to be picky, but = some of these generalities are making me nervousJ.  These = things are applicable only when the duct/diffuser is operating at max = efficiency – which is rarely the case.

Lot’s of good info.  Thanks.  You’re right; it’s some = kind of magic, and you don’t know for sure until you built it and try = it.

Al

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