X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from vms044pub.verizon.net ([206.46.252.44] verified) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTP id 894514 for flyrotary@lancaironline.net; Fri, 23 Dec 2005 23:53:36 -0500 Received: from verizon.net ([71.98.169.90]) by vms044.mailsrvcs.net (Sun Java System Messaging Server 6.2-4.02 (built Sep 9 2005)) with ESMTPA id <0IRZ002O9K94SN09@vms044.mailsrvcs.net> for flyrotary@lancaironline.net; Fri, 23 Dec 2005 22:53:28 -0600 (CST) Date: Fri, 23 Dec 2005 23:53:25 -0500 From: Finn Lassen Subject: Re: [FlyRotary] Re: Question for Tracy - was: Off Topic "Switch Placements" In-reply-to: To: Rotary motors in aircraft Message-id: <43ACD445.7000908@verizon.net> MIME-version: 1.0 Content-type: multipart/alternative; boundary=------------040306070500080506040006 X-Accept-Language: en-us, en References: User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax; PROMO) This is a multi-part message in MIME format. --------------040306070500080506040006 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Assuming input to chip is high-impedance, a couple of resistors on the board a factor 10 higher than the pot in parallel with the pot making input to chip mid-range when wiper disconnects. Wouldn't handle the + or ground disconnect, though. More fancy current sensing devices on + or ground side to tell controller that a wire is disconnected is probably overkill. Finn Tracy Crook wrote: > Good question Perry. > > Answer would depend on the exact nature of the 'open' . Open at > ground end, hot end, or wiper. Answers in order: mixture goes full > rich, full lean, wanders around at last set point. The pot used is a > high rel part rated for 500,000 cycles but of course anything can fail. > > Most pot failures are 'dead spots' where the wiper goes open at a > certain spot (usually near where it is used the most). Mixture will > drift at this point and proper pilot response would be to move mixture > to a slightly richer setting, land, get the pot replaced before flying > again. Thanks for the mental nudge, I need to add this to the > instruction manual. > > I have pondered various fail safe strategies for this scenario (for > example, make the B controller fixed at midrange mixture) but so far > have not been satisfied with any of them. Anyone have other ideas to > be considered? > > Tracy --------------040306070500080506040006 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Assuming input to chip is high-impedance, a couple of resistors on the board a factor 10 higher than the pot in parallel with the pot making input to chip mid-range when wiper disconnects. Wouldn't handle the + or ground disconnect, though. More fancy current sensing devices on + or ground side to tell controller that a wire is disconnected is probably overkill.

Finn

Tracy Crook wrote:

Good question Perry.

Answer would depend on the exact nature of the 'open' . Open at ground end, hot end, or wiper. Answers in order: mixture goes full rich, full lean, wanders around at last set point. The pot used is a high rel part rated for 500,000 cycles but of course anything can fail.

Most pot failures are 'dead spots' where the wiper goes open at a certain spot (usually near where it is used the most). Mixture will drift at this point and proper pilot response would be to move mixture to a slightly richer setting, land, get the pot replaced before flying again. Thanks for the mental nudge, I need to add this to the instruction manual.

I have pondered various fail safe strategies for this scenario (for example, make the B controller fixed at midrange mixture) but so far have not been satisfied with any of them. Anyone have other ideas to be considered?

Tracy

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