Return-Path: Received: from cdihost.cdicorp.com ([207.79.152.5]) by truman.olsusa.com (Post.Office MTA v3.5.1 release 219 ID# 0-52269U2500L250S0V35) with SMTP id com for ; Wed, 6 Oct 1999 17:10:10 -0400 Received: from JUPITER by cdihost.cdicorp.com via smtpd (for ns1.olsusa.com [205.245.9.2]) with SMTP; 6 Oct 1999 21:14:08 UT Received: from cdim-pts-mail.cdicorp.com (CDIM-PTS-MAIL [172.17.131.3]) by jupiter.cdicorp.com with SMTP (Microsoft Exchange Internet Mail Service Version 5.5.2448.0) id TMB98CD4; Wed, 6 Oct 1999 17:14:07 -0400 Received: by CDIM-PTS-MAIL with Internet Mail Service (5.5.2448.0) id <4MKZW14F>; Wed, 6 Oct 1999 17:11:52 -0400 Message-ID: From: "Rumburg, William" To: "'lancair.list@olsusa.com'" Subject: LNC2 Main Gear Secondary Attach Point (SB 050-099) Date: Wed, 6 Oct 1999 17:11:50 -0400 X-Mailing-List: lancair.list@olsusa.com Mime-Version: 1.0 <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> Marv - Here is something else that I should have written to the LML a long time ago... Three and one-half years ago, after transporting my LNC2 back from painting, I noticed a distinct squeaking noise whenever the plane was rocked from side-to-side. It was coming from one of the main gear wells. Further snooping led me to the conclusion that the squeaking was due to a shearing movement between the main gear secondary attach point and the bottom spar cap. This, of course, implied that the Hysol bond had broken. However, the separation was not visible. The squeaking noise was the only indication. At the time, I blamed it on a poor "fastbuild" bond, although I now believe it could happen no matter how good a bond. While a severe side load during landing places a tremendous stress on the secondary attach point, another severe stress mode is simply rocking the plane from side-to-side and bond failure could just as well occur then. I saw that a permanent solution was to replace the design attach block (which bonded only to the lower spar cap) with an attachment that spanned the full width of the spar cap (contrary to first impression, a full width attachment would not interfere with access to any other installations in that area of the gear well). If the secondary attach point bond fails, then the primary attach plate must resist the entire torsional load and might also fail, obviously resulting in nasty consequences. I called this in to Lancair at the time, but it went unheeded. Shortly afterward, a Dutch builder/pilot reported almost all of the ten Lancairs in Holland had discovered the condition and recommended the same solution. I wrote this in to Lance almost two years ago, but it took what must have been a rash of failures to prompt the subject SB. The SB requires fitting and installation of a phenolic "brace" between the top of the existing secondary attach block and the spar cap. This avoids having to remove the existing block in order to replace it with a single full-span attachment, which would really be the superior solution. I'm going to replace the existing attach blocks with a single 1" x 2" square phenolic piece, spanning the full width of the spar. I have a sheet of 1/2" phenolic and will fabricate the attachment by bonding two pieces together, then custom fitting it across the spar cap, leaving 1/32" top and bottom for the Hysol/flox bonding mixture. I recommend this for anyone in the building process who still has good access to the gear well. Bill Rumburg N403WR (Sonic bOOm) >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html