X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from aspensprings.uwyo.edu ([129.72.10.32] verified) by logan.com (CommuniGate Pro SMTP 5.3.9) with ESMTPS id 4487498 for flyrotary@lancaironline.net; Thu, 30 Sep 2010 11:14:48 -0400 Received-SPF: none receiver=logan.com; client-ip=129.72.10.32; envelope-from=SBoese@uwyo.edu Received: from ponyexpress-ht2.uwyo.edu (ponyexpress-ht2.uwyo.edu [10.84.60.209]) by aspensprings.uwyo.edu (8.14.4/8.14.4) with ESMTP id o8UFE8ix026574 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Thu, 30 Sep 2010 09:14:08 -0600 (MDT) (envelope-from SBoese@uwyo.edu) Received: from ponyexpress-mb5.uwyo.edu ([fe80::9813:248c:2d68:a28b]) by ponyexpress-ht2 ([10.84.60.209]) with mapi; Thu, 30 Sep 2010 09:14:07 -0600 From: "Steven W. Boese" To: Rotary motors in aircraft Date: Thu, 30 Sep 2010 09:14:06 -0600 Subject: RE: [FlyRotary] New SAG Theory Discussions of SAG Thread-Topic: [FlyRotary] New SAG Theory Discussions of SAG Thread-Index: ActgrnIA7giPtgE0RdqgSQTyEC9rdAAAU+zY Message-ID: References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: multipart/alternative; boundary="_000_E1AA3B1AF41D8049B1E3FBD5E225626004E2453FE1ponyexpressmb_" MIME-Version: 1.0 --_000_E1AA3B1AF41D8049B1E3FBD5E225626004E2453FE1ponyexpressmb_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed, You take good notes. Just a couple of clarifications: The decrease in the thermal conductivity = of the copper core may be the result of thermal cycling causing development= of porosity within the copper. This is independent of the corrosion going= on between the Mn alloy electrode sheath and the insulator. So there are = two essentially independent mechanisms contributing to the heat range chang= e of the spark plug with age. The development of the porosity within the copper is not particularly affec= ted by the type of fuel whereas the corrosion between the Mn alloy sheath a= nd the insulator is accelerated by the use of 100LL. The cure is still to install new spark plugs. I have colder spark plugs from Racing Beat that are recommended for prolong= ed use in high RPM high power applications. At best, the colder plugs will= merely delay the onset of SAG but won't prevent it from happening eventual= ly. It will be some time before the results of using those plugs will be k= nown. Steve Boese ________________________________ From: Rotary motors in aircraft [flyrotary@lancaironline.net] On Behalf Of = Ed Anderson [eanderson@carolina.rr.com] Sent: Thursday, September 30, 2010 8:46 AM To: Rotary motors in aircraft Subject: [FlyRotary] New SAG Theory Discussions of SAG In a nut shell, Steve's excellent data gathering (how many of use have acce= ss to a scanning electron microscope or spectrum analyzer {:>)) and analysi= s indicates a possible alternative reason for SAG other than fouling. It basically boils down to a theory of pre-ignition based on the deteorati= ng heat removal capacity of the plug. There is a copper core (the photos showing the two cores) in the center of = the ceramic cone which is responsible for conducting 90% of the heat away f= rom the center electrode. Based on Steve's' electron microscope viewing of= two cores (one new and one having been used in a 100LL environment), it ap= pears that the plug using leaded gasoline has corrosion occurring on the bo= undary between this copper core and the surrounding (hot) elements. This l= ayer of corrosion hinders heat removal from the plug leading to parts of th= e plug becoming hot enough to trigger pre-ignition. This SAG tends to happened at high power settings and reducing power tends = to make it go away (for a while). Steve's theory is that the plug encounte= rs max heat and temperature at high power settings and that reducing the po= wer permits the plug to cool off enough for the pre-ignition to go away (fo= r a while). So we now have two theories - one is the fouled plug and one of the overhea= ted plug causing SAG. Preignition generally leads to detonation which does= not appear to be happening (at least no one is finding the typical detonat= ion damage to the rotary engine). A possible reason is the quenching effec= t of the less than optimum shape of the rotary combustion space may tend to= delay or prevent the onset of detonation damage that one would expect from= continuous preignition caused by a too hot plug. I believe Steve intends to see if he can find some colder plugs (the ones t= hat conduct heat better) and see if that extends the time between SAG. Cur= rently I find that roughly 25-30 hours is about the max I can get using 100= LL before SAG sets in, whereas Tracy and others have well over 150 hours us= ing unleaded Mogas. So if the colder plugs extend the time before SAG, I w= ould say that pretty much would suggest Steve's theory is correct - if Not,= then perhaps the fouled Plug theory still has merit or it could be some ot= her phenomena happening. Steve, my apologies if I did not present your case as well as you could Ed Edward L. Anderson Anderson Electronic Enterprises LLC 305 Reefton Road Weddington, NC 28104 http://www.andersonee.com http://www.eicommander.com . From: Bill Bradburry Sent: Thursday, September 30, 2010 9:59 AM To: Rotary motors in aircraft Subject: [FlyRotary] Discussions of SAG I understand that there was a presentation on SAG at the meeting. Can some= one go over the alternative theory with the ones of us that were not in att= endance? It looked like someone had a scanning electron microscope photo t= hat they were showing! Wow! Are we getting sophisticated or what!! Was t= his an explanation of the cause, or ideas for prevention, both?? Bill B --_000_E1AA3B1AF41D8049B1E3FBD5E225626004E2453FE1ponyexpressmb_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed,
 
You take good notes.
 
Just a couple of clarifications: = ; The decrease in the thermal conductivity of the copper core may be the re= sult of thermal cycling causing development of porosity within the cop= per.  This is independent of the corrosion going on between the Mn alloy electrode sheath and the insulator.  So there= are two essentially independent mechanisms contributing to the heat range = change of the spark plug with age. 
 
The development of the porosity withi= n the copper is not particularly affected by the type of fuel whereas the c= orrosion between the Mn alloy sheath and the insulator is accelerated = by the use of 100LL.
 
The cure is sti= ll to install new spark plugs. 
&= nbsp;
I have colder s= park plugs from Racing Beat that are recommended for prolonged use in = high RPM high power applications.  At best, the colder plugs will mere= ly delay the onset of SAG but won't prevent it from happening eventually.  It will be some time before the results of usi= ng those plugs will be known.
 
Steve Boese
 
  
=  
From: Rotary moto= rs in aircraft [flyrotary@lancaironline.net] On Behalf Of Ed Anderson [eand= erson@carolina.rr.com]
Sent: Thursday, September 30, 2010 8:46 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] New SAG Theory Discussions of SAG

In a nut shell, Steve's excellent data gathering = (how many of use have access to a scanning electron microscope or spectrum = analyzer {:>)) and analysis indicates a possible alternative reason for = SAG other than fouling. 
 
 It basically boils down to a theory of pre-= ignition based on the deteorating heat removal capacity of the plug. 
 
There is a copper core (the photos showing the tw= o cores) in the center of the ceramic cone which is responsible for conduct= ing 90% of the heat away from the center electrode.  Based on Steve's'= electron microscope viewing of two cores (one new and one having been used in a 100LL environment), it appears that= the plug using leaded gasoline has corrosion occurring on the boundary bet= ween this copper core and the surrounding (hot) elements.  This layer = of corrosion hinders heat removal from the plug leading to parts of the plug becoming hot enough to trigger pre-i= gnition.
 
This SAG tends to happened at high power settings= and reducing power tends to make it go away (for a while).  Steve's t= heory is that the plug encounters max heat and temperature at high power se= ttings and that reducing the power permits the plug to cool off enough for the pre-ignition to go away (for a while).=
 
So we now have two theories - one is the fouled p= lug and one of the overheated plug causing SAG.  Preignition generally= leads to detonation which does not appear to be happening (at least no one= is finding the typical detonation damage to the rotary engine).  A possible reason is the quenching effect of = the less than optimum shape of the rotary combustion space may tend to dela= y or prevent the onset of detonation damage that one would expect from cont= inuous preignition caused by a too hot plug.
 
I believe Steve intends to see if he can find som= e colder plugs (the ones that conduct heat better) and see if that extends = the time between SAG.  Currently I find that roughly 25-30 hours is ab= out the max I can get using 100LL before SAG sets in, whereas Tracy and others have well over 150 hours using unlea= ded Mogas.  So if the colder plugs extend the time before SAG, I would= say that pretty much would suggest Steve's theory is correct - if Not, the= n perhaps the fouled Plug theory still has merit or it could be some other phenomena happening.
 
Steve, my apologies if I did not present your cas= e as well as you could
 
Ed
 
Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.anderson= ee.com
http://www.eicomma= nder.com
 
.
 
 

Sent: Thursday, September 30, 2010 9:59 AM
Subject: [FlyRotary] Discussions of SAG

I understand th= at there was a presentation on SAG at the meeting.  Can someone go ove= r the alternative theory with the ones of us that were not in attendance?  It looked like someone had a scanning electr= on microscope photo that they were showing!  Wow!  Are we getting= sophisticated or what!!  Was this an explanation of the cause, or ide= as for prevention, both??

&= nbsp;

Bill B

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