X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 31 Dec 2005 17:02:25 -0500 Message-ID: X-Original-Return-Path: Received: from smtp109.sbc.mail.mud.yahoo.com ([68.142.198.208] verified) by logan.com (CommuniGate Pro SMTP 5.0.5) with SMTP id 907286 for lml@lancaironline.net; Sat, 31 Dec 2005 12:42:11 -0500 Received-SPF: none receiver=logan.com; client-ip=68.142.198.208; envelope-from=elippse@sbcglobal.net Received: (qmail 2881 invoked from network); 31 Dec 2005 17:41:26 -0000 Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@66.122.72.111 with login) by smtp109.sbc.mail.mud.yahoo.com with SMTP; 31 Dec 2005 17:41:25 -0000 X-Original-Message-ID: <005b01c60e31$6cacd410$6f487a42@Computerroom> From: "Paul Lipps" X-Original-To: Subject: more ignition stuff X-Original-Date: Sat, 31 Dec 2005 09:41:25 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0058_01C60DEE.5E068160" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0058_01C60DEE.5E068160 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Did you know: The capacitor(condenser) across the points is not there to "protect" = them! It forms a resonant circuit with the primary inductance. Its job = is to keep the current flowing through the primary in a reduced manner = so that the voltage generated by this current collapse, across the = points, does not exceed the breakdown voltage across the points as they = open. Don't believe me? Take out the capacitor and see if you can get = the engine to run. The typical dielectric breakdown voltage of air at STP is about = 50,000V/in. across smooth, rounded terminals. Pointed terminals reduce = the required breakdown voltage. When the points become pitted, with = little points, the breakdown voltage decreases to the point where the = primary voltage across them will arc, sustaining primary current. So the = current change necessary to generate the secondary (high) voltage is = reduced. This causes a weak spark and occasional missing or rough = running. Keep the points smooth, just as you used to in your car! Don't = ignore magneto maintenance! The "P" (points) lead from the magneto has all of the primary = voltage across it. With wide plug gaps and high manifold pressure, this = can get into the hundreds of volts across the points. On my old = Cadillac, with 4 Amps primary current and primary reactance of 60 ohms, = the peak, open-loop voltage would get to 240V! The "P" lead should be = shielded and the shield connected to the body of the magneto and the = ground connector on the switch. Grounding the shield of this lead to the = airframe or the ground bus makes a new path for the current to return to = the magneto, generating lots of radio interference. Ground the shield at = the magneto, and at the switch, don't connect it to the airplane ground! = Wired correctly, there is no need for a filter in the "P" lead. Widening the plug gap, as was pointed out in a previous ms., = increases the voltage that has to rise on the primary and secondary of = the coil. This can lead to breakdown across the points, the coil, or at = the rotor and cap, or in the ignition leads, or, as someone wisely = pointed out, across cigarettes in the plugs that were handled and not = cleaned. Even though a wider gap will give a larger flamefront and = promote better ignition, it is better to stick with the miniscule gap = recommended by the magneto and plug makers. Keep in mind, too, that as = you go up in altitude, the lower density decreases the breakdown voltage = across these places, so that an ignition that operates well at lower = altitudes may show roughness up in the 'teens or twenties. Turbo-ed = systems pretty much should have pressurized magnetos and the wider plugs = which are available. "Course if you operate above 90,000' to 120,000', = the breakdown voltage starts back up. Our x-band slot antennas on the = Atlas booster, fed by a 2kW peak transponder, used to show breakdown = across the narrow dimension in this altitude range, muddying-up the = pulse waveform.=20 If you haven't started installing conductors from a rear-mounted = battery to the starter, see if you can get a download of the article in = the Feb. 1995 Kitplanes which discusses lighter, less expensive = conductors for installation in non-conductive airframes. Also, if you're = interested in inexpensive flashers you can make for your landing or = recognition lights, go to the EAA Ch. 170 web-site and download the = article there. Sorry, for you of that persuasion, this is not the = raincoat/overcoat type of flasher! ------=_NextPart_000_0058_01C60DEE.5E068160 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Did you know:
    The capacitor(condenser) = across the=20 points is not there to "protect" them! It forms a resonant circuit with = the=20 primary inductance. Its job is to keep the current flowing through the = primary=20 in a reduced manner so that the voltage generated by this current = collapse,=20 across the points, does not exceed the breakdown voltage across the = points as=20 they open. Don't believe me? Take out the capacitor and see if you can = get the=20 engine to run.
    The typical dielectric = breakdown=20 voltage of air at STP is about 50,000V/in. across smooth, rounded = terminals.=20 Pointed terminals reduce the required breakdown voltage. When = the=20 points become pitted, with little points, the breakdown voltage = decreases to the=20 point where the primary voltage across them will arc, sustaining primary = current. So the current change necessary to generate the secondary = (high)=20 voltage is reduced. This causes a weak spark and occasional missing or = rough=20 running. Keep the points smooth, just as you used to in your car! Don't = ignore=20 magneto maintenance!
    The "P" (points) lead from = the magneto=20 has all of the primary voltage across it. With wide plug gaps and high = manifold=20 pressure, this can get into the hundreds of volts across the=20 points. On my old Cadillac, with 4 Amps primary current and primary = reactance of 60 ohms, the peak, open-loop voltage would get to = 240V! The=20 "P" lead should be shielded and the shield connected to the body of the = magneto=20 and the ground connector on the switch. Grounding the shield of this = lead to the=20 airframe or the ground bus makes a new path for the current to return to = the=20 magneto, generating lots of radio interference. Ground the shield at the = magneto, and at the switch, don't connect it to the airplane = ground! Wired=20 correctly, there is no need for a filter in the "P" lead.
    Widening the plug gap, as was = pointed=20 out in a previous ms., increases the voltage that has to rise on the = primary and=20 secondary of the coil. This can lead to breakdown across the points, the = coil, or at the rotor and cap, or in the ignition leads, or, as = someone=20 wisely pointed out, across cigarettes in the plugs that were handled and = not=20 cleaned. Even though a wider gap will give a larger flamefront and = promote=20 better ignition, it is better to stick with the miniscule gap = recommended by the=20 magneto and plug makers. Keep in mind, too, that as you go up in = altitude, the=20 lower density decreases the breakdown voltage across these places, so = that an=20 ignition that operates well at lower altitudes may show roughness up in = the=20 'teens or twenties. Turbo-ed systems pretty much should have pressurized = magnetos and the wider plugs which are available. "Course if you operate = above=20 90,000' to 120,000', the breakdown voltage starts back up. Our x-band = slot=20 antennas on the Atlas booster, fed by a 2kW peak transponder, = used to=20 show breakdown across the narrow dimension in this altitude range, = muddying-up=20 the pulse waveform. 
 
    If you haven't started = installing=20 conductors from a rear-mounted battery to the starter, see if you can = get a=20 download of the article in the Feb. 1995 Kitplanes which discusses = lighter, less=20 expensive conductors for installation in non-conductive airframes. Also, = if=20 you're interested in inexpensive flashers you can make for = your=20 landing or recognition lights, go to the EAA Ch. 170 web-site and = download the=20 article there. Sorry, for you of that persuasion, this is not the=20 raincoat/overcoat type of flasher!
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