Return-Path: Received: from [24.25.9.103] (HELO ms-smtp-04-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.3c2) with ESMTP id 791854 for flyrotary@lancaironline.net; Sun, 13 Mar 2005 20:12:12 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.103; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-185-127.carolina.rr.com [24.74.185.127]) by ms-smtp-04-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id j2E1BECi027739 for ; Sun, 13 Mar 2005 20:11:15 -0500 (EST) Message-ID: <000401c52832$b7c3de70$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: SAG Report Date: Sun, 13 Mar 2005 20:11:12 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C52808.CDEEB5F0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C52808.CDEEB5F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Dave, Its been know for quite some time (Tracy Crook first identified the = problem several years ago and cause) that the SAG is definitely caused = by the spark plugs. Change the spark plugs and the problem goes away = immediately. Up to this point there is no conjecture - it works every = time! I have had it happen a number of times early-on and initially though it = was an intermittent problem with my fuel injection system due to the = dropping EGTs and lost of power - until Tracy mentioned the cause and = cure. In this case, It is definitely not caused by the ignition system = settings. Now the rest is conjecture on my part - but is my BEST GUESS of what is = happening. Alternative explanations are welcomed! The SAG is apparently caused by the build up of carbon/lead on the = center ceramic electrode - which causes the electrical energy to "bleed" = off before the sufficient voltage potential can develop to cause the = spark to jump the gap at the electrodes. You can clearly see the = ceramic completely covered to the point it appears black with = carbon/lead which we know causes a "fouled" plug.=20 (as a side note - I should have changed the plugs before the trip but = got pressed for time and failed to do so, thinking I had a few more = hours on them.) Stick in a new sparkplug set with clean ceramic cone at you can fly more = than 100 hours with no-lead/mogas or approx 20-30 hours if you use 100LL = avgas (at least that is my experience). Cleaning the electrode should = also work and I have a bunch of plugs that are waiting to be cleaned, = but since they are not $$ aircraft sparkplugs, just have not gotten = around to doing so. My conclusion is that since the symptoms are the same as a piston engine = with excessive retarded ignition timing that is essential what is = happening in this case. However, in this NOT a case of the ignition = timing being excessively retarded by the ignition system setting. Here is my BEST GUESS of what may be happening. We know that higher compression causes a tougher problem for the spark = ignition - it takes more voltage to jump the gap under high compression = condition than lower compression (may sound counterintuitive - but its = been proven). So normally we expect the spark to be timed such that it = fires when the compression is high so we get best combustion = efficiencies. But, that is also the point that puts the most demand on = the ignition system. So when the ceramic cone becomes coated with = sufficient carbon/lead, it bleeds off the electrical energy precluding = the voltage build up sufficient to get the spark jumping the electrode = gap at its intended timing point (at/near the point of highest = compression). However, as the rotor continues to rotate past the point = of intended ignition the pressure now starts to drop considerably - it = finally reaches a point where the remaining electrical energy IS able to = jump the gap (due to the lower compression pressure) and the fuel = mixture starts to burn. However, because you are past the optimum point for converting the = burning fuel into mechanical energy the energy instead ends up as = additional heat which is not blasted out the exhaust as it is normally = because the pressures never get to the normal levels. The burn fuel = instead ends up adding to the heat load of the oil and coolant. (My = speculation about why my temps were elevated during the SAG and the = exhaust temps drop) Could be wrong of course - but that is my best guess about what is = happening. While my explanation may be incorrect, there is no question = that the spark plugs are the source of the SAG problem and the cure and = it is NOT the settings of the ignition system timing (but it does acts = as if the ignition system setting is too retarded).=20 The problem is probably compounded by the type of spark plug used. The = standard 13B plug is shrouded which makes it harder for combustion = gasses to have a cleaning effect on the ceramic cone - compounded by the = fact that the sparkplug is recessed into the rotor housing (to keep the = apex seals from being damaged by an electrode sticking down into the = combustion chamber) - so both factors probably amplify the problem. = There are some "unshrouded" spark plugs that have been mentioned and = used by Racers which may extend the interval before the SAG happens, = but I have not yet tried them. Anyhow, Dave, that is my speculation about what is happening. =20 Best Regards Ed ----- Original Message -----=20 From: David Staten=20 To: Rotary motors in aircraft=20 Sent: Sunday, March 13, 2005 7:12 PM Subject: [FlyRotary] Re: SAG Report So.. did the overtemp cause the SAG? or did the SAG cause the = overtemp? What is causing the over-retarded timing (programming I am = assuming)... =20 Best Guesses are fine as long as they are identified as such... About how many hours had these plugs been running since last swap..? =20 Dave Ed Anderson wrote: Hi Folks Just got back from Florida where spent weekend with Tracy and Laura. = Tracy and I flew to the Leeward Ranch RV Flyin on Saturday. On the way = there I encountered the worst case of spark plug "SAG" ever. We were = cruising at 4500 MSL when the old EGT started south dropping from around = 1650 to below 1400 F. First on the rear rotor then on the front rotor. = Most of the time it only happens on one rotor at a time and will = frequently go away after a few minutes - not this time. I began getting a little concerned when both rotors were in SAG and = seemed content to remain there. I tried backing off the throttle, = switching injector sets on and off with no avail. This had been going = on for several minutes (longer than normal) when I noticed something I = had never noticed before - either because the SAG had never remained = that long on both rotors OR simply had not scan the oil and coolant = temps in previous sags. In any case, I was surprised to find the oil at 190F and the coolant = a 210F when with the OAT and power setting I was carrying they should = have both been around 165-170F. So it clearly looked like the same = symptoms as overly retarded ignition timing. This must have lasted = approx 15 minutes or more. Finally on let down to the Flying location = the SAG went away and temps came down. So on the ground I took out the sparkplugs and it was clear the = ceramic white center was completely coated in lead/carbon - you could = see the lead crystal glint in the sun. Both leading and trailing look = about the same - there was little to no detectable wear on the = electrodes just the ceramic cone black. Installed new spark plugs and flew it back to Tracy's and on home = today without further incident. =20 Just wanted to pass this on because it can sure cause you to think = you may have fuel system problems when in reality its the spark plugs - = especially for any of you using Avgas as I do. Had a great weekend (as always) with the Crooks and was happy to = join them both at a birthday dinner for Laura's father on Saturday = evening. =20 Best Regards Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_0001_01C52808.CDEEB5F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Dave,
 
Its been know  for quite some = time (Tracy=20 Crook first identified the problem several years ago and cause) that the = SAG is=20 definitely caused by the spark plugs.  Change the spark plugs and = the=20 problem goes away immediately. Up to this point there is no = conjecture - it=20 works every time!
I have had it happen a number of times = early-on and=20 initially though it was an intermittent problem with my fuel injection = system=20 due to the dropping EGTs and lost of power - until Tracy mentioned = the=20 cause and cure. In this case,  It is definitely not caused by = the=20 ignition system settings.
 
Now the rest is conjecture on my part - = but is my=20 BEST GUESS of what is happening.  Alternative explanations are=20 welcomed!
 
The SAG is apparently caused by the = build up of=20 carbon/lead on the center ceramic electrode - which causes the = electrical energy=20 to "bleed" off before the sufficient voltage potential can develop to = cause the=20 spark to jump the gap at the electrodes.  You can clearly see the = ceramic=20 completely covered to the point it appears black with carbon/lead which = we know=20 causes a "fouled" plug. 
 
(as a side note - I should have changed = the plugs=20 before the trip but got pressed for time and failed to do so, thinking I = had a=20 few more hours on them.)
 
Stick in a new sparkplug set with clean = ceramic=20 cone at you can fly more than 100 hours with no-lead/mogas or approx = 20-30 hours=20 if you use 100LL avgas (at least that is my experience).   = Cleaning=20 the electrode should also work and I have a bunch of plugs that are = waiting to=20 be cleaned, but since they are not $$ aircraft sparkplugs, just have not = gotten=20 around to doing so.
 
My conclusion is that since the = symptoms are the=20 same as a piston engine with excessive retarded ignition timing that is=20 essential what is happening in this case.  However, in = this NOT a case=20 of the ignition timing being excessively retarded by the ignition system = setting.
 
Here is my BEST GUESS of what may be=20 happening.
 
We know that  higher compression = causes a=20 tougher problem for the spark ignition - it takes more voltage to jump = the gap=20 under high compression condition than lower compression (may sound=20 counterintuitive - but its been proven).  So normally we expect the = spark=20 to be timed such that it fires when the compression is high so we get = best=20 combustion efficiencies.  But, that is also the point that puts the = most=20 demand on the ignition system.  So when the ceramic cone becomes = coated=20 with sufficient carbon/lead, it bleeds off the electrical energy = precluding the=20 voltage build up sufficient to get the spark jumping the electrode gap = at its=20 intended timing point (at/near the point of highest = compression). =20 However, as the rotor continues to rotate past the point of intended = ignition=20 the pressure now starts to drop considerably - it finally reaches a = point where=20 the remaining electrical energy IS able to jump the gap (due to the = lower=20 compression pressure) and the fuel mixture starts to burn.
 
However, because you are past the = optimum point for=20 converting the burning fuel into mechanical energy the energy instead = ends up as=20 additional heat which is not blasted out the exhaust as it is normally = because=20 the pressures never get to the normal levels.  The burn=20 fuel instead ends up adding to the heat load of the oil and = coolant. (My=20 speculation about why my temps were elevated during the SAG and the = exhaust=20 temps drop)
 
Could be wrong of course - but that is = my best=20 guess about what is happening.  While my explanation may be = incorrect,=20 there is no question that the spark plugs are the source of the SAG = problem and=20 the cure and it is NOT the settings of the ignition system timing (but = it=20 does acts as if the ignition system setting is too=20 retarded). 
 
The problem is probably compounded by = the type of=20 spark plug used.  The standard 13B plug is shrouded which makes it = harder=20 for combustion gasses to have a cleaning effect on the ceramic cone - = compounded=20 by the fact that the sparkplug is recessed into the rotor housing (to = keep the=20 apex seals from being damaged by an electrode sticking down into the = combustion=20 chamber) - so both factors probably amplify the problem.  There are = some=20 "unshrouded" spark plugs that have been mentioned and used by = Racers which=20 may  extend the interval before the SAG happens, but I have not yet = tried=20 them.
 
Anyhow, Dave, that is my speculation = about what is=20 happening. 
 
Best Regards
 
Ed
----- Original Message -----
From:=20 David=20 Staten
Sent: Sunday, March 13, 2005 = 7:12=20 PM
Subject: [FlyRotary] Re: SAG = Report

So.. did the overtemp cause the SAG? or did the SAG = cause the=20 overtemp? What is causing the over-retarded timing (programming I am=20 assuming)...
 
Best Guesses are fine as long as they are = identified=20 as such...

About how many hours had these plugs been running = since last=20 swap..?
 
Dave

Ed Anderson wrote:
Hi Folks
 
Just got back from Florida where = spent weekend=20 with Tracy and Laura.  Tracy and I flew to the Leeward Ranch RV = Flyin=20 on Saturday.  On the way there I encountered the worst case of = spark=20 plug "SAG" ever.  We were cruising at 4500 MSL when the old EGT = started=20 south dropping from around 1650 to below 1400 F.  First on the = rear=20 rotor then on the front rotor.  Most of the time it only = happens on one=20 rotor at a time and will frequently go away after a few = minutes  - not=20 this time.
 
I began getting a little concerned = when both=20 rotors were in SAG and seemed content to remain there.  I tried = backing=20 off the throttle, switching injector sets on and off with no = avail. =20 This had been going on for several minutes (longer than normal) when = I=20 noticed something I had never noticed before - either because the = SAG had=20 never remained that long on both rotors OR simply had not scan the = oil and=20 coolant temps in previous sags.
 
In any case, I was surprised to = find the oil at=20 190F and the coolant a 210F when with the OAT and power setting I = was=20 carrying they should have both been around 165-170F.  So it = clearly=20 looked like the same symptoms as overly retarded ignition=20 timing.   This must have lasted approx 15 minutes or = more. =20 Finally on let down to the Flying location the SAG went away and = temps came=20 down.
 
So on the ground I took out the = sparkplugs and=20 it was clear the ceramic white center was completely coated in = lead/carbon -=20 you could see the lead crystal glint in the sun.  Both leading = and=20 trailing look about the same - there was little to no detectable = wear on the=20 electrodes just the ceramic cone black.
 
Installed new spark plugs and flew = it back to=20 Tracy's and on home today without further incident.  =
 
Just wanted to pass this on because = it can sure=20 cause you to think you may have fuel system problems when in reality = its the=20 spark plugs - especially for any of you using Avgas as I = do.
 
Had a great weekend (as always) = with the Crooks=20 and was happy to join them both at a birthday dinner for Laura's = father on=20 Saturday evening. 
 
Best Regards
 
Ed
 
Ed Anderson
Rv-6A N494BW Rotary=20 Powered
Matthews, NC
eanderson@carolina.rr.com

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