X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 23 Dec 2005 17:23:58 -0500 Message-ID: X-Original-Return-Path: Received: from systems3.net ([68.98.211.24] verified) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTPS id 893905 for lml@lancaironline.net; Fri, 23 Dec 2005 13:22:03 -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 jBNIJJ7L010666 for ; Fri, 23 Dec 2005 11:19:19 -0700 X-Original-Message-ID: <012701c607ed$ce075b30$5101a8c0@systems0d3b724> From: "Craig Berland" X-Original-To: "Lancair Mail List" Subject: [LML] Re: Where has all the power gone? X-Original-Date: Fri, 23 Dec 2005 11:22:12 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0120_01C607B3.1E910A00" 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 0.86.2/1213/Mon Dec 19 07:48:34 2005 on systems3.net X-Virus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0120_01C607B3.1E910A00 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable "Luckily, your plane won't be flying on the dyno." While you don't fly "on the dyno", you are flying "a dyno". Albeit a = difficult one to calibrate. For a given aircraft, airspeed is = horsepower. For a given RPM torque can be calculated from HP. If you = have a fuel flow meter, you can calculate BSFC. "Can you explain why spark advance is a good idea in auto engines and a = bad one in airplanes?" It is not bad idea, it is good idea...just like in cars. The difference = is how the engines are used and therefore the potential for improvement. = Cars spend a lot of there time at low RPM and low MAP (part throttle). = For this reason, to get best performance/best economy, they need a very = elaborate spark timing control. For example a car engine....WOT at 1500 = RPM may require 18 deg BTDC, WOT at 6000 RPM may require 28 deg BTDC and = 2500 RPM at closed throttle may require 40 deg BTDC and finally it will = want to crank at 0 deg BTDC for best performance. If an electronic = ignition on an aircraft can give "best" timing for all conditions and be = reliable, it is better than a fixed timing mag. However, the benefits = are not as dramatic on airplanes as they are on cars because most of our = time in airplanes is spent at 2500 to 2700 RPM and near WOT. The mags = can be set at optimum timing for that condition. Non turbo engines = benefit more than turbo engines from a variable timing curve. On non = turbo engines, altitude has the same affect as closing the throttle. The = other benefit electronic ignition may have is more spark energy. When = running real rich or real lean, the ignition system is being tested as = to whether or not it can fire the plug or ignite the mixture. If you can = deliver 3X the spark energy to the plug....it will fire at more rich and = more lean conditions as well as poorer plugs will fire. I believe = Walter pointed out, the higher spark energy does increase the burn rate = slightly, therefore the timing curve must be appropriate for the = ignition system. Otherwise you may have timing advance that can be = harmful to engine longevity. The concern I have with current electronic ignitions is reliability, not = "potential" performance. If I could pick the "best" ignition, it would = have 12 coils and very short secondary leads, controlled by a closed = loop computer looking at internal cylinder pressure. The computer would = be programmed for my specific application by a "good" engine development = engineer. Sad to say....I now have mags. After 15 years of developing car engines = with computer tables that included a 1000 variables that modified spark = timing....mags do seem like a step backwards. Craig Berland ------=_NextPart_000_0120_01C607B3.1E910A00 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
"Luckily, your plane won't be flying on = the=20 dyno."
While you don't fly "on the dyno", you = are flying=20 "a dyno".  Albeit a difficult one to calibrate. For a given = aircraft,=20 airspeed is horsepower. For a given RPM torque can be calculated from = HP. If you=20 have a fuel flow meter, you can calculate BSFC.
 
"Can you=20 explain why spark advance is a good idea in auto engines and a bad one = in=20 airplanes?"
It is not bad=20 idea, it is good idea...just like in cars. The difference is how the = engines are=20 used and therefore the potential for improvement. Cars spend a lot = of there=20 time at low RPM and low MAP (part throttle). For this reason, to get = best=20 performance/best economy, they need a very elaborate spark timing = control. For=20 example a car engine....WOT at 1500 RPM may require 18 deg BTDC, = WOT at=20 6000 RPM may require 28 deg BTDC and 2500 RPM at closed throttle may = require 40=20 deg BTDC and finally it will want to crank at 0 deg BTDC for best=20 performance.  If an electronic ignition on an aircraft can give = "best"=20 timing for all conditions and be reliable, it is better than a fixed = timing=20 mag.  However, the benefits are not as dramatic on airplanes as = they are on=20 cars because most of our time in airplanes is spent at 2500 to 2700 RPM = and near=20 WOT. The mags can be set at optimum timing for that condition. Non turbo = engines=20 benefit more than turbo engines from a variable timing curve. On non = turbo=20 engines, altitude has the same affect as closing the throttle. The other = benefit=20 electronic ignition may have is more spark energy.  When running = real rich=20 or real lean, the ignition system is being tested as to whether or not = it can=20 fire the plug or ignite the mixture. If you can deliver 3X the spark = energy to=20 the plug....it will fire at more rich and more lean conditions as well = as poorer=20 plugs will fire.  I believe Walter pointed out, the higher spark = energy=20 does increase the burn rate slightly, therefore the timing curve must be = appropriate for the ignition system.  Otherwise you may have timing = advance=20 that can be harmful to engine longevity.
 
The concern I=20 have with current electronic ignitions is reliability, not "potential"=20 performance.  If I could pick the "best" ignition, it would have 12 = coils=20 and very short secondary leads, controlled by a closed loop computer = looking at=20 internal cylinder pressure.  The computer would be programmed for = my=20 specific application by a "good" engine development=20 engineer.
 
Sad to say....I=20 now have mags.  After 15 years of developing car engines with = computer=20 tables that included a 1000 variables that modified spark timing....mags = do seem=20 like a step backwards.
Craig=20 Berland

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