X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 29 Dec 2005 22:01:08 -0500 Message-ID: X-Original-Return-Path: Received: from systems3.net ([68.98.211.24] verified) by logan.com (CommuniGate Pro SMTP 5.0.5) with ESMTPS id 905327 for lml@lancaironline.net; Thu, 29 Dec 2005 13:32:46 -0500 Received-SPF: none receiver=logan.com; client-ip=68.98.211.24; envelope-from=cberland@systems3.net Received: from systems0d3b724 ([192.168.1.81]) by systems3.net (8.13.4/8.13.4/Debian-3) with SMTP id jBTIU17G003900 for ; Thu, 29 Dec 2005 11:30:01 -0700 X-Original-Message-ID: <011001c60ca6$48c8ee30$5101a8c0@systems0d3b724> From: "Craig Berland" X-Original-To: "Lancair Mail List" Subject: [LML] Re: Where has all the power gone? X-Original-Date: Thu, 29 Dec 2005 11:32:50 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_010B_01C60C6B.995757F0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1506 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1506 X-Virus-Scanned: ClamAV 0.86.2/1219/Wed Dec 28 15:57:59 2005 on systems3.net X-Virus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_010B_01C60C6B.995757F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Brent wrote: Aircraft engines have dual ignition systems for increased = detonation margins, NOT for reliability from redundancy. Aircraft = combustion chambers are so freaking big that by the time a flame front = has traversed the chamber the remaining gas has been compressed and = heated to the point of detonation. Starting the fire in two places = shortens the combustion time significantly and reduces the opportunity = for detonation. This is also the mechanism for the RPM drop during a mag = check. When you turn off one mag the combustion event takes longer = which has a similar effect as starting the process later, AKA "retarding = the timing". =20 =20 Hi Brent, From what little I know about the combustion process, the above = paragraph seems to contradict it's self. Retarding the spark timing = helps to prevent detonation. If turning off one mag has the same effect = as retarding the timing (as you stated above), wouldn't running on one = mag help to prevent detonation rather than contribute to it? After all, = peak cylinder pressure will be lower while running on one mag and = thetaPP will move further away from TDC. Lower pressure means lower = CHT's which should also improve the detonation margin. I think = redundancy and improved fuel efficiency may be the reason two mags are = used on aircraft engines. =20 Ron Laughlin Legacy N44L (res)=20 Ron, in response to a good question. If the engine is tuned for dual = ignition, that is, the timing is set to produce best power and best = economy when both plugs are firing, then shutting off one plug will = retard the effective timing and reduce the engines tendency to detonate. = If the engine is tuned to run on one plug, the timing must be advanced = relative to the dual ignition timing to get back to best power and best = economy. The engine will be more likely to detonate at this more = advanced timing even though it may be making slightly less power. = Therefore it is correct to say a dual ignition engine will increase the = detonation margin over a single ignition engine. In my opinion, what is = missing is, this is true when both engines have there timing set to = produce best power and economy. Craig Berland ------=_NextPart_000_010B_01C60C6B.995757F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Brent wrote: Aircraft engines have dual = ignition systems=20 for increased detonation margins, NOT for reliability from redundancy. = Aircraft combustion chambers are so freaking big that by the time a = flame=20 front has traversed the chamber the remaining gas has been compressed = and=20 heated to the point of detonation.  Starting the fire in two = places=20 shortens the combustion time significantly and reduces the opportunity = for=20 detonation. This is also the mechanism for the RPM drop during a mag=20 check.  When you turn off one mag the combustion event takes = longer which=20 has a similar effect as starting the process later, AKA "retarding the = timing". 

 
Hi Brent,
 
From what little I know about the combustion process, the above = paragraph=20 seems to contradict it's self. Retarding the spark timing helps to = prevent=20 detonation. If turning off one mag has the same effect as retarding the = timing=20 (as you stated above), wouldn't running on one mag help to prevent = detonation=20 rather than contribute to it? After all, peak cylinder pressure will be = lower=20 while running on one mag and thetaPP will move further away from TDC. = Lower=20 pressure means lower CHT's which should also improve=20 the detonation margin. I think redundancy and improved fuel = efficiency may=20 be the reason two mags are used on aircraft engines.  =
Ron=20 Laughlin
Legacy N44L (res)
 
Ron, in response to a good question.  If the engine is tuned = for dual=20 ignition, that is, the timing is set to produce best power and best = economy when=20 both plugs are firing, then shutting off one plug will retard the = effective=20 timing and reduce the engines tendency to detonate.  If the engine = is tuned=20 to run on one plug, the timing must be advanced relative to the dual = ignition=20 timing to get back to best power and best economy.  The engine will = be more=20 likely to detonate at this more advanced timing even though it may be = making=20 slightly less power. Therefore it is correct to say a dual ignition = engine will=20 increase the detonation margin over a single ignition engine. In my = opinion,=20 what is missing is, this is true when both engines have there timing set = to=20 produce best power and economy.
Craig Berland
 
 
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