X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 24 Apr 2008 10:52:54 -0400 Message-ID: X-Original-Return-Path: Received: from wind.imbris.com ([216.18.130.7] verified) by logan.com (CommuniGate Pro SMTP 5.2.2) with ESMTPS id 2870186 for lml@lancaironline.net; Thu, 24 Apr 2008 10:39:28 -0400 Received-SPF: none receiver=logan.com; client-ip=216.18.130.7; envelope-from=brent@regandesigns.com Received: from [192.168.1.100] (cbl-238-80.conceptcable.com [207.170.238.80] (may be forged)) (authenticated bits=0) by wind.imbris.com (8.14.2/8.12.11.S) with ESMTP id m3OEcgOF079337 for ; Thu, 24 Apr 2008 07:38:48 -0700 (PDT) (envelope-from brent@regandesigns.com) X-Original-Message-ID: <48109AF1.1060704@regandesigns.com> X-Original-Date: Thu, 24 Apr 2008 07:36:33 -0700 From: Brent Regan User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: Re: Window Strength Content-Type: multipart/alternative; boundary="------------030505070407060902070001" This is a multi-part message in MIME format. --------------030505070407060902070001 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit "I am sure 8' deep girders will be sufficient." Leon Moisseiff, Chief Engineer, Tacoma Narrows Bridge "If you cant find 20' lengths of All-Thread then substitute two 10' lengths" Jack D. Gillum, Hayatt Regency hotel "Tea Dance" walkway designer. "Sure, it's a little stronger with the window bonded in, but that small amount of extra strength is not required. The fuselage is strong enough even with the big hole in it." Rob Wolf Rob is correct that the static strength of the fuselage is determined without the windows BUT the windows do have significant "in plane" (npi) shear strength which will have an effect on the torsional stiffness of the fuselage. This, in turn, effects the natural frequency of the empennage. Making the fuselage less stiff by decoupling the window reduces the empennage flutter margin. Only analysis and testing will tell us by how much. Pushing the aircraft faster with bigger engines and making the fuselage less stiff will eventually result in structural failure. I know of at least one IV -P that disintegrated in a 0.63 Mach dive. Rob may be correct that the structural effects are negligible but his confidence is unsupported by analysis or testing. I doubt he has the factory's agreement on this matter. Prudence, and experience, dictates a less cavalier approach to structural modifications. Regards Brent Regan --------------030505070407060902070001 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit "I am sure 8' deep girders will be sufficient." Leon Moisseiff, Chief Engineer, Tacoma Narrows Bridge

"If you cant find 20' lengths of All-Thread then substitute two 10' lengths" Jack D. Gillum, Hayatt Regency hotel "Tea Dance" walkway designer.

"Sure, it's a little stronger with the window bonded in, but that small amount of extra strength is not required. The fuselage is strong enough even with the big hole in it." Rob Wolf

Rob is correct that the static strength of the fuselage is determined without the windows BUT the windows do have significant "in plane" (npi) shear strength which will have an effect on the torsional stiffness of the fuselage. This, in turn, effects the natural frequency of the empennage. Making the fuselage less stiff by decoupling the window reduces the empennage flutter margin. Only analysis and testing will tell us by how much. Pushing the aircraft faster with bigger engines and making the fuselage less stiff will eventually result in structural failure. I know of at least one IV -P that disintegrated in a 0.63 Mach dive.

Rob may be correct that the structural effects are negligible but his confidence is unsupported by analysis or testing. I doubt he has the factory's agreement on this matter.

Prudence, and experience, dictates a less cavalier approach to structural modifications.

Regards
Brent Regan
--------------030505070407060902070001--