X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 13 Oct 2010 11:52:37 -0400 Message-ID: X-Original-Return-Path: Received: from web57510.mail.re1.yahoo.com ([66.196.100.77] verified) by logan.com (CommuniGate Pro SMTP 5.3.9) with SMTP id 4504193 for lml@lancaironline.net; Wed, 13 Oct 2010 08:27:12 -0400 Received-SPF: none receiver=logan.com; client-ip=66.196.100.77; envelope-from=casey.gary@yahoo.com Received: (qmail 15929 invoked by uid 60001); 13 Oct 2010 12:26:35 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=hHNa48/4/kW+Xzjr3cja2HTY3y4kK62+ALdvrgtqn0PtfS8ye7T+THcXisFfUDYEUTQoJmFMtrEn5irkJP9Dm/MJyTQmotmt+vQhMfzqcycZ0dobimWY6VpWDOLymQnHNKTxjvteNTg+4HSPf5uPv6SH/3tKd30ZxehUYxFSYhY=; X-Original-Message-ID: <394174.9908.qm@web57510.mail.re1.yahoo.com> X-YMail-OSG: D8M.7nUVM1kPqQK6cKUXrfpCdX.IgaQxC.QGIImasSHC5Lk 86VYyqcDMnESiRcN4uo4fUGMUoHCOz8K03eMhaGoEErhCSElI7PMd7_IIuip 4kMdmLGdgFeqO8Lslj6jYQIujpinNqNzD41fXFACNwY9YOtNa_qt2_zD5DPL gEESFxnhb3E3k68LXs8sbXX48sj6vMcCrHzyPKd72GQf6XSBM3oPn7DJIDHK oLOdkCg3FfIc_Nf.bgKlMDg-- Received: from [97.122.152.1] by web57510.mail.re1.yahoo.com via HTTP; Wed, 13 Oct 2010 05:26:35 PDT X-Mailer: YahooMailRC/504.5 YahooMailWebService/0.8.106.282862 References: X-Original-Date: Wed, 13 Oct 2010 05:26:35 -0700 (PDT) From: Gary Casey Subject: Re: Slick Magneto and Spark Plugs X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-2088066425-1286972795=:9908" --0-2088066425-1286972795=:9908 Content-Type: text/plain; charset=us-ascii I agree that a big factor (negative one at that) is the capacitance of the plug wires. It slows the buildup of voltage at the plug, making the system more susceptible to fouling. And having a resistor in the plug has a (slight, in my opinion) benefit in that regard (is that current "shaping?"). But any stress in the magneto is due to high voltage - the least stress would be to ground the plug wire and the most stress is with an open plug wire. The current during the spark event has essentially no effect, as the coil is current-limited by its own inductance. The most effective "improvement" might be to implement a secondary air gap in the plug to prevent current flow until voltage has built up to some value. A trick from the automotive dark ages. I can't imagine that removing the resistor will cause any distress in the magneto, although it will increase the rate of erosion in the plug, and the distributor rotor air gap). Given that, I think the advice to check the resistance (a 2,000 Ohm max limit is probably as good as any) of any plug that is removed for service is good, and I will do it from now on. Gary The person at Aircraft Magneto Service told me the spark plug resistor isn't there so much for RFI suppression as it is for current limiting and shaping. He said the ignition harness acts as a capacitor, and the harness + resistor + spark plug form an RC network and thus affect the shape of the current pulse(s) inside the magneto. He said removing the resistor not only leads to rapid spark plug wear, but also stresses the magneto and associated components. At least that's what I think he was telling me..... I have no intention of substituting a 0 ohm resistor in the spark plug....i was just wondering if any of our Reno racers really do it and see any difference. -isaac --0-2088066425-1286972795=:9908 Content-Type: text/html; charset=us-ascii
I agree that a big factor (negative one at that) is the capacitance of the plug wires.  It slows the buildup of voltage at the plug, making the system more susceptible to fouling.  And having a resistor in the plug has a (slight, in my opinion) benefit in that regard (is that current "shaping?").  But any stress in the magneto is due to high voltage - the least stress would be to ground the plug wire and the most stress is with an open plug wire.  The current during the spark event has essentially no effect, as the coil is current-limited by its own inductance.  The most effective "improvement" might be to implement a secondary air gap in the plug to prevent current flow until voltage has built up to some value.  A trick from the automotive dark ages.  I can't imagine that removing the resistor will cause any distress in the magneto, although it will increase the rate of erosion in the plug, and the distributor rotor air gap).  Given that, I think the advice to check the resistance (a 2,000 Ohm max limit is probably as good as any) of any plug that is removed for service is good, and I will do it from now on.
Gary

The person at Aircraft Magneto Service told me the spark plug resistor isn't there so much for RFI suppression as it is for current limiting and shaping.  He said the ignition harness acts as a capacitor, and the harness + resistor + spark plug form an RC network and thus affect the shape of the current pulse(s) inside the magneto.  He said removing the resistor not only leads to rapid spark plug wear, but also stresses the magneto and associated components.  At least that's what I think he was telling me.....

I have no intention of substituting a 0 ohm resistor in the spark plug....i was just wondering if any of our Reno racers really do it and see any difference.

-isaac

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