X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 08 Jan 2006 23:11:37 -0500 Message-ID: X-Original-Return-Path: Received: from wind.imbris.com ([216.18.130.7] verified) by logan.com (CommuniGate Pro SMTP 5.0.6) with ESMTPS id 917618 for lml@lancaironline.net; Sun, 08 Jan 2006 12:53:52 -0500 Received-SPF: none receiver=logan.com; client-ip=216.18.130.7; envelope-from=brent@regandesigns.com Received: from [192.168.1.100] (vsat-148-63-101-227.c002.t7.mrt.starband.net [148.63.101.227]) (authenticated bits=0) by wind.imbris.com (8.12.11/8.12.11.S) with ESMTP id k08HqqP4091276 for ; Sun, 8 Jan 2006 09:53:00 -0800 (PST) (envelope-from brent@regandesigns.com) X-Original-Message-ID: <43C15168.5000900@regandesigns.com> X-Original-Date: Sun, 08 Jan 2006 09:52:40 -0800 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 Subject: Re: Fast-Ons et al. Content-Type: multipart/alternative; boundary="------------020609040403070003050400" This is a multi-part message in MIME format. --------------020609040403070003050400 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit When a Fast-On terminal is mated for the first time the material in the "lobes" is strained to the point of yielding, generating a fixed maximum obtainable preload. Thermal cycling, mechanical vibration and corrosion reduce that preload over time. Moisture, drawn into the connector by capillary action, will facilitate corrosion, especially where the stresses are highest, further reducing mechanical clamping force. Repeated mate / demate cycles rapidly deteriorate the connection integrity by wiping off any protective plating, exposing the copper alloy base. The assertion that a Fast-On is somehow "airtight" is false a priori, unless encased in a protective covering such as heat shrink tubing with a thermal adhesive, as the strained spring elements of the connection form open ended tubes. One reason for the failure of the Fast-On connection over time is that the load path for any stress (static or dynamic) is through the electrical path. Any connector designed for a rugged environment will have a separate strain relief load path to protect and mechanically isolate the electrical contacts and reduce contact strain. By definition, connectors function by clamping two conductive elements together so, in a very general way, all connectors are basically the same. The differences come in the details of implementation. The card edge connector, used in the tray on some avionics (e.g. King radios), while not a Fast-On design, is another example where vibration induced strain between the connector elements degrades connector integrity over time. This is evidenced in that the first diagnostic step for a recalcitrant radio is to remove and reinstall it into its tray. I suspect the long term effects of vibration are not fully appreciated by some builders. During certification vibration testing of the Chelton Flight Logic system there was evidence of fretting even in a ARINC-600 (aerospace qualified) tray connector. Post test microscopic examination showed that several of the 150 pins had worn through their 50 micron gold plating. IMHO, the "cost" to make an electrical connection is fixed so you will either "pay now" for a quality connector or the labor to make a cheap connector work or you will "pay later" in hotel rooms, rental cars , commercial flights to get home and the parts to repair after the nose gear collapses because a Fast-On on the hydraulic pressure switch fails at an inopportune time. This is not a hypothetical example, it actually happened. What would happen if a similar connection on a similar pressure switch, say the door seal pressure switch on a IV-P, fails in the flight levels and the cabin pressure gradually drops? Are you SURE you would notice before you lost consciousness? IMHO Fast-Ons have NO place in flight critical and flight safety applications such as pressure switches, gear status switches, hydraulic pump relays, ground connections, engine instrumentation, etc. Use them on your Hobbs meter, cabin lights or cabin speaker if you must. I believe in mitigating as many risks as practical before leaving terra firma. That is just my opinion. Regards Brent Regan --------------020609040403070003050400 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit When  a Fast-On terminal is mated for the first time the material in the "lobes" is strained to the point of yielding, generating a fixed maximum obtainable preload. Thermal cycling, mechanical vibration and corrosion reduce that preload over time.  Moisture, drawn into the connector by capillary action, will facilitate corrosion, especially where the stresses are highest, further reducing mechanical clamping force. Repeated mate / demate cycles rapidly deteriorate the connection integrity by wiping off any protective plating, exposing the copper alloy base.

The assertion that a Fast-On is somehow "airtight" is false a priori, unless encased in a protective covering such as heat shrink tubing with a thermal adhesive, as the strained spring elements of the connection form open ended tubes.

One reason for the failure of the Fast-On connection over time is that the load path for any stress (static or dynamic) is through the electrical path.  Any connector designed for a rugged environment will have a separate strain relief load path to protect and mechanically isolate the electrical contacts and reduce contact strain.

By definition, connectors function by clamping two conductive elements together so, in a very general way, all connectors are basically the same. The differences come in the details of implementation. The card edge connector, used in the tray on some avionics (e.g. King radios), while not a Fast-On design, is another example where vibration induced strain between the connector elements degrades connector integrity over time. This is evidenced in that the first diagnostic step for a recalcitrant radio is to remove and reinstall it into its tray.

I suspect the long term effects of vibration are not fully appreciated by some builders. During certification vibration testing of the Chelton Flight Logic system there was evidence of fretting even in a ARINC-600 (aerospace qualified) tray connector. Post test microscopic examination showed that several of the 150 pins had worn through their 50 micron gold plating.

IMHO, the "cost" to make an electrical connection is fixed so you will either "pay now" for a quality connector or the labor to make a cheap connector work or you will "pay later" in hotel rooms, rental cars , commercial flights to get home and the parts to repair after the nose gear collapses because a Fast-On on the hydraulic pressure switch fails at an inopportune time.  This is not a hypothetical example, it actually happened.

What  would happen if a similar connection on a similar pressure switch, say the door seal pressure switch on a IV-P, fails in the flight levels and the cabin pressure gradually drops? Are you SURE you would notice before you lost consciousness?

IMHO Fast-Ons have NO place in flight critical and flight safety applications such as pressure switches, gear status switches, hydraulic pump relays, ground connections, engine instrumentation, etc. Use them on your Hobbs meter, cabin lights or cabin speaker if you must.  I believe in mitigating as many risks as practical before leaving terra firma.

That is just my opinion.

Regards
Brent Regan
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