X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from spam.tierpoint.com ([63.131.235.3] verified) by logan.com (CommuniGate Pro SMTP 6.0.1) with ESMTP id 6064094 for lml@lancaironline.net; Thu, 14 Feb 2013 12:17:43 -0500 Received-SPF: none receiver=logan.com; client-ip=63.131.235.3; envelope-from=brent@regandesigns.com X-ASG-Debug-ID: 1360862228-05c005149112a0fd0001-yPXFKn Received: from wolverine.webiness.com (wolverine.webiness.com [65.61.103.66]) by spam.tierpoint.com with ESMTP id rz4rFpoPcnZkYu1Y; Thu, 14 Feb 2013 09:17:08 -0800 (PST) X-Barracuda-Envelope-From: brent@regandesigns.com X-Barracuda-Apparent-Source-IP: 65.61.103.66 Received: from 50-37-134-165.mscw.id.frontiernet.net ([50.37.134.165]:54446 helo=[192.168.1.40]) by wolverine.webiness.com with esmtpa (Exim 4.80) (envelope-from ) id 1U62Qi-0002bQ-QY; Thu, 14 Feb 2013 09:17:05 -0800 Message-ID: <511D1C15.8080104@regandesigns.com> Date: Thu, 14 Feb 2013 09:17:09 -0800 From: Brent Regan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: Lancair Mailing List Subject: Lancair Door Window Failures References: <41361035E6613244A377D5AC3BF5EFDD4A88C64E@CH1PRD0710MB367.namprd07.prod.outlook.com> X-ASG-Orig-Subj: Lancair Door Window Failures In-Reply-To: <41361035E6613244A377D5AC3BF5EFDD4A88C64E@CH1PRD0710MB367.namprd07.prod.outlook.com> Content-Type: multipart/alternative; boundary="------------090209060704030507030507" X-Barracuda-Connect: wolverine.webiness.com[65.61.103.66] X-Barracuda-Start-Time: 1360862228 X-Barracuda-URL: http://bcvm.tierpoint.com:80/cgi-mod/mark.cgi X-Virus-Scanned: by bsmtpd at tierpoint.com X-Barracuda-BRTS-Status: 1 X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using per-user scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=5.0 tests=HTML_MESSAGE X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.122662 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.00 HTML_MESSAGE BODY: HTML included in message This is a multi-part message in MIME format. --------------090209060704030507030507 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit A little history. The IV-P door latch system was developed empirically and iteratively over the span of several months nearly 20 years ago. I was involved in the process at the concept development level, participated in design reviews and I designed and built a couple of prototype latches. Latch systems were installed in the cycle pressure test article (a fuselage section stuffed with blocks of hard foam to reduce air volume) and then exercised. I am not aware of any FEA studies done. However, due to the elastic nature of the fuselage, variations in builder technique and difficulties in accurately modeling the window to fuselage bond interface I would be highly skeptical of any FEA results. IMHO, testing is the only sure way to qualify the system. I have examined several failed door/windows and repaired one for a friend. During construction, that aircraft and mine were both proof tested to 7.5 PSIG (150% operational) before first flight. During proof testing, my friend's airplane suffered a failure of the aft pressure bulkhead at 6.2 PSIG. Poor bonding of the skin to the core of the factory part resulted in delamination. Moisture present during oven cure was the apparent cause. The bulkhead was replaced and the plane was successfully re-tested. My theory on the failure of door windows is that the latches and their maintenance are at the root of the problem. If a latch does not close fully over-center, under load it can release or fully latch. The shock of this event creates a pressure wave that propagates through the window causing a rupture of the extreme fiber, likely at an imperfection such as a scratch, mounting hole or tool mark. The window then fails like a balloon, albeit a very thick, highly pressurized balloon. Prevention of window failure therefore should be focused on latch maintenance and inspection at regular (100 Hr/ annual) intervals. The latches should be cleaned, inspect and lubricated. Mounting and adjustment fasteners should be checked for torque. Roll pins should be inspected for position and sheer failure. I have seen roll pins "back out" of their holes. Latch preload adjustment should also be checked for uniformity. Finally, preflight inspection should also include a positive confirmation of latch engagement. I use my index finger to feel that the fore and aft top latches are fully engaged after closing the door. On one occasion the aft latch did not fully engage because an article of passenger clothing was caught in the door jam. I believe the IV-P door latch system is satisfactory for a properly constructed and maintained aircraft as is evidenced by the numerous aircraft in service. However the failures show that the door latch system is a critical maintenance item that should be part of the regular maintenance schedule. Regards Brent Regan --------------090209060704030507030507 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit

A little history. The IV-P door latch system was developed empirically and iteratively over the span of several months nearly 20 years ago. I was involved in the process at the concept development level, participated in design reviews and I designed and built a couple of prototype latches. Latch systems were installed in the cycle pressure test article (a fuselage section stuffed with blocks of hard foam to reduce air volume) and then exercised. I am not aware of any FEA studies done. However, due to the elastic nature of the fuselage, variations in builder technique and difficulties in accurately modeling the window to fuselage bond interface I would be highly skeptical of any FEA results. IMHO, testing is the only sure way to qualify the system.

I have examined several failed door/windows and repaired one for a friend. During construction, that aircraft and mine were both proof tested to 7.5 PSIG (150% operational) before first flight. During proof testing, my friend’s airplane suffered a failure of the aft pressure bulkhead at 6.2 PSIG. Poor bonding of the skin to the core of the factory part resulted in delamination. Moisture present during oven cure was the apparent cause. The bulkhead was replaced and the plane was successfully re-tested.

My theory on the failure of door windows is that the latches and their maintenance are at the root of the problem. If a latch does not close fully over-center, under load it can release or fully latch. The shock of this event creates a pressure wave that propagates through the window causing a rupture of the extreme fiber, likely at an imperfection such as a scratch, mounting hole or tool mark. The window then fails like a balloon, albeit a very thick, highly pressurized balloon.

Prevention of window failure therefore should be focused on latch maintenance and inspection at regular (100 Hr/ annual) intervals. The latches should be cleaned, inspect and lubricated. Mounting and adjustment fasteners should be checked for torque. Roll pins should be inspected for position and sheer failure. I have seen roll pins “back out” of their holes. Latch preload adjustment should also be checked for uniformity.

Finally, preflight inspection should also include a positive confirmation of latch engagement. I use my index finger to feel that the fore and aft top latches are fully engaged after closing the door. On one occasion the aft latch did not fully engage because an article of passenger clothing was caught in the door jam.

I believe the IV-P door latch system is satisfactory for a properly constructed and maintained aircraft as is evidenced by the numerous aircraft in service. However the failures show that the door latch system is a critical maintenance item that should be part of the regular maintenance schedule.  

Regards
Brent Regan

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