X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from tomcat.al.noaa.gov ([140.172.240.2] verified) by logan.com (CommuniGate Pro SMTP 4.3.4) with ESMTP id 1010591 for flyrotary@lancaironline.net; Wed, 22 Jun 2005 17:44:39 -0400 Received-SPF: none receiver=logan.com; client-ip=140.172.240.2; envelope-from=bdube@al.noaa.gov Received: from mungo.al.noaa.gov (mungo.al.noaa.gov [140.172.241.126]) by tomcat.al.noaa.gov (8.12.11/8.12.0) with ESMTP id j5MLhsMG005259 for ; Wed, 22 Jun 2005 15:43:54 -0600 (MDT) Message-Id: <6.2.1.2.0.20050622145851.03c8a318@mailsrvr.al.noaa.gov> X-Mailer: QUALCOMM Windows Eudora Version 6.2.1.2 Date: Wed, 22 Jun 2005 15:42:46 -0600 To: "Rotary motors in aircraft" From: Bill Dube Subject: Re: [FlyRotary] Re: PSRU adapter plate In-Reply-To: References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed At 02:43 PM 6/22/2005, you wrote: >The error in reasoning here (7075 is twice as strong as 6061 so it can be >half as thick) is that the bending strength of a plate is far more >influenced by its thickness than by material strength. This is in >addition to the fit problems pointed out by Dean. > >Just not a good idea. True. Deflection varies with the reciprocal of the cube of the thickness. A plate half as thick deflects 8 times as much under the same load. Thus, you can't simply reduce the plate thickness. However, you could use a 1/2 inch thick 7075 plate and then machine away low-stress portions, leaving stiffening ribs in just the right places. With this approach, you could cut the weight of the plain 6061 plate about in half, maybe more. Wouldn't want to do it without the FEA, (including vibration modes) of course. Bill Dube'