Return-Path: Sender: (Marvin Kaye) To: flyrotary Date: Wed, 05 Mar 2003 20:33:06 -0500 Message-ID: X-Original-Return-Path: Received: from fed1mtao07.cox.net ([68.6.19.124] verified) by logan.com (CommuniGate Pro SMTP 4.0.6) with ESMTP id 2044753 for flyrotary@lancaironline.net; Wed, 05 Mar 2003 18:55:46 -0500 Received: from smtp.west.cox.net ([172.18.180.51]) by fed1mtao07.cox.net (InterMail vM.5.01.04.05 201-253-122-122-105-20011231) with SMTP id <20030305235546.XDVG6215.fed1mtao07.cox.net@smtp.west.cox.net> for ; Wed, 5 Mar 2003 18:55:46 -0500 From: X-Original-To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] Re: Starter solenoid X-Original-Date: Wed, 5 Mar 2003 18:55:41 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Original-Message-Id: <20030305235546.XDVG6215.fed1mtao07.cox.net@smtp.west.cox.net> Al Gietzen wrote: > ... It may more than double > the failure probability because the return spring in the starter solenoid is > much more robust than the one in the contactor; so which is more likely to > fail closed? > ... This comparison overlooks the relative masses that each spring has to move. The tiny mass of the contactor core represents a much smaller load (perhaps even proportionally) on its spring. It could reasonably be expected to endure more cycles of being energized/deenergized before failure. Moreover, it is a small matter to mount the contactor such that gravity adds its small piece to the dis-engaging force - the way Ford did during the '50s. Of course, such an arrangement could mask incipient failure of the contactor - but in that case, if one hears the starter attempt to engage during a negative-G maneuver, one would know to check the contactor, right? My $.02 Dale