X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 2 [X] Return-Path: Sender: To: lml Date: Fri, 02 Feb 2007 03:29:04 -0500 Message-ID: X-Original-Return-Path: Received: from smtp114.sbc.mail.mud.yahoo.com ([68.142.198.213] verified) by logan.com (CommuniGate Pro SMTP 5.1.5) with SMTP id 1805636 for lml@lancaironline.net; Fri, 02 Feb 2007 00:04:29 -0500 Received-SPF: none receiver=logan.com; client-ip=68.142.198.213; envelope-from=elippse@sbcglobal.net Received: (qmail 94599 invoked from network); 2 Feb 2007 05:03:42 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=sbcglobal.net; h=Received:X-YMail-OSG:Message-ID:From:To:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=lgXfG2WQRAKtp7wKyt5v3STah/ekkya4bYaSV611dyWCYvBXaVFkJuAwtrM+GO5Bkm/O3+SipNYcUvU/F/ez8HprmsNVa8Av4MAOg1RYAaLdbz+Wru7Fb07qhmSeoJbsvBqt5sswIabY7I4hI8nIgiHF6mGLVU5JZ3UMnQY8a8g= ; Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@75.15.115.83 with login) by smtp114.sbc.mail.mud.yahoo.com with SMTP; 2 Feb 2007 05:03:41 -0000 X-YMail-OSG: hOqUfyoVM1lviy6SJxbhAfRC7BdiQn3ygrnqT9Bwhdzq2bSIKPs.v6qwhRtw4tJNcxoDv.9wVfDJ4Wj5USsFzCr7xc3ZKdSQFuBS8eOkJh6yRXV_SRXrIhtFNEWe0w1QWXGHXoFxdUoyxvA- X-Original-Message-ID: <001101c74687$836a2790$53730f4b@Computerroom> From: "Paul Lipps" X-Original-To: "Marv Kaye" Subject: Wing pressure X-Original-Date: Thu, 1 Feb 2007 21:03:37 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000E_01C74644.71CB2E50" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_000E_01C74644.71CB2E50 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable I knew that post would start something! Let's take three cases of a = HOLLOW wing flying at sea level, where the pressure is 2116 PSF. Case 1. = Pressure in the wing, 2116 PSF, pressure on top of wing, 2076 PSF, = pressure on the wings bottom, 2196 PSF. The air inside the wing pushes = up on the top surface at 40 PSF while it pushes down on the bottom = surface at 20 PSF. Net lift, 20 PSF up. Case 2. Same pressures on the = top and bottom of the wing, but the pressure in the wing is reduced to = 2076 PSF. No pressure differential across the top skin, so no force on = it, but there is 20 lb upward acting on the bottom skin. Net lift, = 20PSF. Case 3. Same pressure on the outside, but 2196 PSF inside. No = differential across the bottom skin, but 20 PSF up across the top skin. = Net upward force, 20 PSF on the top skin! Sure, you can define the lift = as the pressure difference between the top and bottom surfaces, but that = won't tell you where the stresses are! If there was no upward force = against the top skin, it wouldn't be necessary to lace the fabric on the = ribs of fabric-covered wings. Look at the lift; it acts on the fabric, = then passes to the ribs, and from them to the spar, and then to the = fuselage. Oh well! Old ideas die hard! ------=_NextPart_000_000E_01C74644.71CB2E50 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable

I knew that post would start something! = Let's take=20 three cases of a HOLLOW wing = flying at sea=20 level, where the pressure is 2116 PSF. Case 1. Pressure in = the wing, 2116=20 PSF, pressure on top of wing, 2076 PSF, pressure on the wings bottom, = 2196 PSF.=20 The air inside the wing pushes up on the top surface at 40 PSF while it = pushes=20 down on the bottom surface at 20 PSF. Net lift, 20 PSF up. Case 2. = Same=20 pressures on the top and bottom of the wing, but the pressure in the = wing is=20 reduced to 2076 PSF. No pressure differential across the top skin, so no = force=20 on it, but there is 20 lb upward acting on the bottom skin. Net lift,=20 20PSF. Case 3. Same pressure on the outside, but 2196 PSF inside. = No=20 differential across the bottom skin, but 20 PSF up across the top skin. = Net=20 upward force, 20 PSF on the top skin! Sure, you can define the lift as = the=20 pressure difference between the top and bottom surfaces, but that = won't=20 tell you where the stresses are! If there was no upward force against = the top=20 skin, it wouldn't be necessary to lace the fabric on the ribs of = fabric-covered=20 wings. Look at the lift; it acts on the fabric, then passes to the ribs, = and=20 from them to the spar, and then to the fuselage. Oh well! Old ideas die=20 hard!

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