X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from EXHUB003-4.exch003intermedia.net ([207.5.74.111] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTPS id 3748023 for flyrotary@lancaironline.net; Tue, 07 Jul 2009 12:44:32 -0400 Received-SPF: none receiver=logan.com; client-ip=207.5.74.111; envelope-from=jwhaley@datacast.com Received: from EXVMBX003-5.exch003intermedia.net ([207.5.74.45]) by EXHUB003-4.exch003intermedia.net ([207.5.74.111]) with mapi; Tue, 7 Jul 2009 09:43:54 -0700 From: Jeff Whaley To: Rotary motors in aircraft Date: Tue, 7 Jul 2009 09:43:54 -0700 Subject: RE: [FlyRotary] SAG was: [FlyRotary] Re: Muffler Thread-Topic: [FlyRotary] SAG was: [FlyRotary] Re: Muffler Thread-Index: Acn+9Cm7C1+MHqxcQpaLquolzQBZuQALH7XA 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_C03ABB0A7362B84BB53D544B3C305E0E01403612F27DEXVMBX0035e_" MIME-Version: 1.0 --_000_C03ABB0A7362B84BB53D544B3C305E0E01403612F27DEXVMBX0035e_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Hey Ed, now might be the time you cleaned a few SAG plugs and tested them? It seems hard to believe that plugs need be thrown out after 25 hours. BTW, up here in Ottawa, I had to pay $17 each ($68 per set) for stock Mazda= plugs, on a trip south I picked up some in Ogdensburg NY around $5 each. Jeff From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Beh= alf Of Ed Anderson Sent: Tuesday, July 07, 2009 7:10 AM To: Rotary motors in aircraft Subject: [FlyRotary] SAG was: [FlyRotary] Re: Muffler There are undoubtedly numerous possibilities as to what is happening/causin= g SAG. However, two things are very clear: 1. 100 LL does definitely reduce the time spark plugs can be used before = SAG occurs. The nominal time period that I have found in my engine is 24-3= 0 hours. You can take the plug out and examine the ceramic cone and see t= he glint of what I believe (but have not done a chemical analysis) of lead = crystals. Folks using MOGAS (such as Tracy) have reported going over 150 h= ours without SAG. So I do believe there is a connection between 100LL and = the short interval of use before SAG. I even attempted to use TCP which is used in some aircraft engines and is r= eportedly suppose to reduce lead deposits. It simply make the problem wors= t, but upon further research I discovered that for this chemical to work th= e cylinder head temperature has to be much higher than what our water coole= d sparkplugs typically see. In my case, the chemical caused further deposi= ts (of some sort) on the sparkplug and I barely got 5 hours out of the set= I used. This may in part explain why our sparkplugs seem to foul more wit= h 100LL than aircraft sparkplugs - they don't get hot enough? 1. If you encounter SAG, then replacing the sparkplugs immediately elimin= ates the SAG problem (for a period of time). So both of those factors lead me to believe it is fouling of spark plugs ra= ther than pre-ignition. If pre-ignition then my dozens of times of SAG (li= ke every 15 minutes on the 5 hour trip from Louisiana) would surely have re= sulted in damage to the engine. In any case, whatever the cause, since I have been replacing my sparkplugs = regularly at 25-30 hour intervals I have encountered no SAG. YMMV Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm ________________________________ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Beh= alf Of William Wilson Sent: Tuesday, July 07, 2009 12:09 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Muffler While the rotary design is a little more resistant to the onset of preignit= ion, once it happens, the rotary is damaged just as easily as a piston engi= ne or even more so. Drag racers suffering preignition have dismantled thei= r motors and found rotors dented in from excess chamber pressure. It is po= ssible that you have been having mild preignition not enough to damage the = engine, I suppose. Do you suppose you have been running really excessively= rich? That would also contribute to plug fouling, low power and low EGT. = If you have fuel injection, a fuel map problem showing up only at high man= ifold pressures (higher than you normally attain in your usual operating re= gime) maybe? You should get WAY more than 10 hours on spark plugs even run= ning 100LL. If combustion were still taking place as you speculate then it would ignite= the incoming mixture during the intake cycle and cause a backfire. So I t= hink that is not it. I assume you've seen this but I found it interesting: http://www.wankel.org/74_Ignition/74-22%20Spark%20plug%20life%20.htm On Mon, Jul 6, 2009 at 7:17 PM, Steven Boese > wrote: I never found the broken muffler part in the outlet of the muffler where it= might have caused increased back pressure even though it was possible for = it to end up in that location by standing the muffler on its end. The symp= toms after repairing the muffler were the same as before the repair was mad= e so at this point, I don't think the broken part was a factor in the perfo= rmance issue. Looking back at the data log, the #2 rotor EGT dropped by ab= out 250 degrees during the power deficit. Back pressure would probably aff= ect both rotors in a similar fashion so that would also point to SAG as the= culprit. In response to your and Bobby's questions, at the onset of SAG, there were = a total of 15 hours on the plugs, 106 gal total of fuel burned, 53 gal of t= hat was 100LL. Ed is most likely right that operating at the increased manifold pressure a= vailable at low altitude made the SAG show up while it didn't at lower mani= fold pressures that I normally see. The relatively small amount of time and fuel that the plugs had seen when S= AG occurred may also be due to the low power levels and correspondingly low= er combustion temperatures permitting more rapid lead deposition on the plu= gs. It looks like I should routinely change plugs every 10 hours or so. I= did have extra plugs along on the Texas trip and it would have been easy t= o have installed them at the rotorfest. The nature of SAG is puzzling. The symptoms of decreased EGT, decreased po= wer output, and increased heat transfer to the oil and coolant are all cons= istent with descriptions of pre-ignition more than that of spark plug misfi= re. In piston engines, pre-ignition can rapidly lead to destruction, but t= he rotary engine may be more tolerant of it. Maybe it isn't a matter of no= ignition due to the spark plug not firing, but a matter of the fire not go= ing out between sparks. The lead in 100LL increases the octane rating by s= lowing the combustion rate and thereby decreasing the tendency for detonati= on. Maybe there is enough gas phase lead in the vicinity of the spark plug= with lead deposited on it that the combustion rate is slowed enough to per= sist from one cycle to the next while the normal combustion rate occurs in = the rest of the chamber. This could result in a process similar to pre-igni= tion. This theory probably has as much probability of being right as the o= ne I had concerning the apex seals clicking. Maybe I can accumulate a pile of SAGGING spark plugs as big as Ed's. That = would be verifiable at least. Steve Boese -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Todd Bartrim Sent: Monday, July 06, 2009 6:23 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Muffler Hi Steve; So you now assume that your power loss is directly attributable to SAG = and not to the partially blocked muffler? Is this correct? I'm curious as I also use a homemade muffler (SpinTech copy) and have = wondered what the result would be if any of the internal came loose. I wond= er if your increased backpressure contributed to the onset of SAG? And do y= ou only burn 100LL, occasionally, or never? Todd C-FSTB RV9 Turbo13B --_000_C03ABB0A7362B84BB53D544B3C305E0E01403612F27DEXVMBX0035e_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Hey Ed, now might be the time you cleaned a few SAG plugs an= d tested them?

It seems hard to believe that plugs need be thrown out after= 25 hours.

BTW, up here in Ottawa, I had to pay $17 each ($68 per set) = for stock Mazda plugs, on a trip south I picked up some in Ogdensburg NY around= $5 each.

Jeff

 

From: Rotary motors= in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anders= on
Sent: Tuesday, July 07, 2009 7:10 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] SAG was: [FlyRotary] Re: Muffler

 

There are undoubtedly numerous possibilities as to what is happening/causing SAG.  However, two things are very clear:=

 

  1. 100 LL doe= s definitely reduce the time spark plugs can be used before SAG occurs.  The nominal time period that I have found in my engine i= s 24-30 hours.  You can take the plug out and examine the ceramic  cone and see the glint of what I believe (but have not done a chemical analysis) of lead crystals.  Folks using MOGAS (such as Tracy) have reported going over 150 hours without SAG.  So I do believe there is a connection between 100LL and the short interval of = use before SAG.

 

I even attempted to use TCP wh= ich is used in some aircraft engines and is reportedly suppose to reduce lead deposits.  It simply make the problem worst, but upon further research= I discovered that for this chemical to work the cylinder head temperature has= to be much higher than what our water cooled sparkplugs typically see.  I= n my case, the chemical caused further deposits (of some sort)  on the sparkplug and I barely got 5 hours out of the set I used.  This may in part explain why our sparkplugs seem to foul more with 100LL than aircraft sparkplugs – they don’t get hot enough?   =

 

  1. If you enc= ounter SAG, then replacing the sparkplugs immediately eliminates the SAG prob= lem (for a period of time). 

 

So both of those factors lead me to believe it is fouling of sp= ark plugs rather than pre-ignition.  If pre-ignition then my dozens of tim= es of SAG (like every 15 minutes on the 5 hour trip from Louisiana) would sure= ly have resulted in damage to the engine. 

 

In any case, whatever the cause, since I have been replacing my sparkplugs regularly at 25-30 hour intervals I have encountered no SAG.&nbs= p; YMMV

 

Ed

 

 

From: Rotary motors= in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of William Wilson
Sent: Tuesday, July 07, 2009 12:09 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Muffler

 

While the rotary design= is a little more resistant to the onset of preignition, once it happens, the rot= ary is damaged just as easily as a piston engine or even more so.  Drag ra= cers suffering preignition have dismantled their motors and found rotors dented = in from excess chamber pressure.  It is possible that you have been havin= g mild preignition not enough to damage the engine, I suppose.  Do you suppose you have been running really excessively rich?  That would als= o contribute to plug fouling, low power and low EGT.  If you have fuel injection, a fuel map problem showing up only at high manifold pressures (higher than you normally attain in your usual operating regime) maybe?&nbs= p; You should get WAY more than 10 hours on spark plugs even running 100LL.
If combustion were still taking place as you speculate then it would ignite= the incoming mixture during the intake cycle and cause a backfire.  So I t= hink that is not it.

I assume you've seen this but I found it interesting:
http://www.wankel.org/74_Ignition/74-22%20Spark%20plug%20life%20.htm<= /a>

On Mon, Jul 6, 2009 at 7:17 PM, Steven Boese <sboese@uwyo.edu> wrote:

I never found the broken muffler part in the outlet of the muffler where it m= ight have caused increased back pressure even though it was possible for it to e= nd up in that location by standing the muffler on its end.  The symptoms = after repairing the muffler were the same as before the repair was made so at thi= s point, I don’t think the broken part was a factor in the performance issue.  Looking back at the data log, the #2 rotor EGT dropped by abou= t 250 degrees during the power deficit.  Back pressure would probably af= fect both rotors in a similar fashion so that would also point to SAG as the culprit.

 

In response to your and Bobby’s questions, at the onset of SAG, there we= re a total of 15 hours on the plugs, 106 gal total of fuel burned, 53 gal of tha= t was 100LL.

 

Ed is most likely right that operating at the increased manifold pressure available at low altitude made the SAG show up while it didn’t at low= er manifold pressures that I normally see.

 

The relatively small amount of time and fuel that the plugs had seen when SAG occurred may also be due to the low power levels and correspondingly lower combustion temperatures permitting more rapid lead deposition on the plugs.  It looks like I should routinely change plugs every 10 hours o= r so.  I did have extra plugs along on the Texas trip and it would have = been easy to have installed them at the rotorfest.

 

The nature of SAG is puzzling.  The symptoms of decreased EGT, decreased p= ower output, and increased heat transfer to the oil and coolant are all consiste= nt with descriptions of pre-ignition more than that of spark plug misfire.&nbs= p; In piston engines, pre-ignition can rapidly lead to destruction, but the ro= tary engine may be more tolerant of it.  Maybe it isn’t a matter of n= o ignition due to the spark plug not firing, but a matter of the fire not goi= ng out between sparks.  The lead in 100LL increases the octane rating by slowing the combustion rate and thereby decreasing the tendency for detonation.  Maybe there is enough gas phase lead in the vicinity of t= he spark plug with lead deposited on it that the combustion rate is slowed eno= ugh to persist from one cycle to the next while the normal combustion rate occu= rs in the rest of the chamber. This could result in a process similar to pre-i= gnition.  This theory probably has as much probability of being right as the one I ha= d concerning the apex seals clicking.

 

Maybe I can accumulate a pile of SAGGING spark plugs as big as Ed’s.  = That would be verifiable at least.     

 

Steve Boese  

 

   

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lan= caironline.net] On Behalf Of Todd Bartrim
Sent: Monday, July 06, 2009 6:23 PM
To: Rotary motors in aircraft

Subject: [FlyRotary] R= e: Muffler

 

Hi Steve;
    So you now assume that your power loss is directly attributable to SAG and not to the partially blocked muffler? Is this corre= ct?
     I'm curious as I also use a homemade muffler (Spin= Tech copy) and have wondered what the result would be if any of the internal cam= e loose. I wonder if your increased backpressure contributed to the onset of = SAG? And do you only burn 100LL, occasionally, or never?

 

Todd
C-FSTB
RV9 Turbo13B

 

 

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