X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3747098 for flyrotary@lancaironline.net; Mon, 06 Jul 2009 19:41:44 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Received: from computername ([75.191.186.236]) by cdptpa-omta04.mail.rr.com with ESMTP id <20090706234107654.PPYJ2041@cdptpa-omta04.mail.rr.com> for ; Mon, 6 Jul 2009 23:41:07 +0000 From: "Ed Anderson" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] SAG was: [FlyRotary] Muffler Date: Mon, 6 Jul 2009 19:41:24 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0030_01C9FE71.BF33C390" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Thread-Index: Acn+kP9gzmf4eGvFRtacJWLrnJQYDwAAf1xQ Message-Id: <20090706234107654.PPYJ2041@cdptpa-omta04.mail.rr.com> This is a multi-part message in MIME format. ------=_NextPart_000_0030_01C9FE71.BF33C390 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Steve, =20 It just dawned on me that flying at a density altitude of 9000 MSL, you = have only approx =BD the pressure than we folks at sea level have. That = would of course reduce pressure in the combustion chamber and would perhaps give = you more time between plug changes before SAG sits in. So that might be one reason you did not encounter it until you ventured to the low lands. =20 Ed =20 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 =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson Sent: Monday, July 06, 2009 7:25 PM To: Rotary motors in aircraft Subject: [FlyRotary] SAG was: [FlyRotary] Muffler =20 Hi Steve, =20 Isn=92t this stuff fascinating? =20 I=92ve had many encounters with SAG all the way from one memorable take = off fully loaded on a hot summer day (but not 9000 ft density altitude) in Tennessee. Both rotors decided to go into SAG at the same time =96 = really gets your attention. Being fully loaded for my trip to Memphis and with = a full load of fuel, my rate of climb was about 500 fpm. I was really puckered until I recalled that flying the old C-150, if I could GET 500 = fpm on a hot day, I thought I was doing great. So I relaxed and climbed to altitude over the air port, whereupon pulling back on the power caused = the SAG to go away and I flew on to Memphis where Tracy was kind enough to provide me with a set of non-sagged plugs. I now do not fly without at least two complete plug changes. It=92s tough to pull back on power = during take off {:>) =20 But, it seems to happen most frequently at high power settings but will gradually extend to every phase of flight including cruise. =20 My theory is that at high power settings your manifold pressure and therefore your combustion pressure is at its highest. As you know a = spark has a harder time of jumping the gap when pressures are high. So I = believe as the plug fouls over with lead on the ceramic cone accumulating, it becomes easier for at least some of the charge to bleed off before it = builds high enough to jump the gap. Pull back on the throttle, pressure = decreases and the plug fires normally =96 at least for a while. =20 I once flew back from Louisiana without having changed my plugs at my nominal 25-30 hour point. I was encountering SAG symptoms about every = 15 minutes. I discovered that if I use the ignition check switch to turn = off the leading plugs spark (firing on only the trialing) that the EGT would increase from about 1575-1600F to over 1700F. After restoring the = leading spark system, I could fly another 15 or so minutes before the SAG = symptoms started again. I don=92t really know why that made a difference =96 did = I change the combustion conditions and cause higher temps burning off some = of the deposits =96 I don=92t know. =20 But typically, the first thing I notice is a change in the drone of the engine, the second most noticeable thing is the EGT on the affect rotor = will be on its way down typically dropping around 300F deg. The rpm will decrease as well somewhere around 150-200 rpm (this on one affected = rotor), don=92t recall what it did during take off with two sagging. = Generally, if at full power, reducing the throttle seems to help. Then frequently it = will occur - last for a minute or so and then disappear again. The intervals will generally become shorter and the effects periods longer. You can easily think you have a fuel or injector problem when its really not. =20 I never get use to the engine making un-normal sounds, so to reduce seat cushion wear, I change my plugs around 25-30 hours, but remember I use = 100LL almost exclusively =96 autogas seems to give much extended plug use = before SAG occurs. =20 YMMV =20 Ed =20 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 =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of sboese Sent: Monday, July 06, 2009 6:48 PM To: Rotary motors in aircraft Subject: [FlyRotary] Muffler =20 Some of you may remember that I returned home from the Rotorfest at the = end of May to find the internal baffle of my muffler broken. I theorized = that the broken part may have partially blocked the outlet and caused a power drop compared to what I should have been producing. Pictures of the = broken parts and repair were posted on the list last month. =20 When the weather and my time off coincided recently, I gave the repaired muffler a flight test after a ground run to be sure things were working normally. The flight lasted 9 minutes. The plane was much lighter than when leaving Texas, but the density altitude was about 9000 ft which is normal for here. The plane would barely climb, would not accelerate = over 110 kts, and the oil and coolant temperatures were abnormally high. = This was quite similar to the data that I posted last month which was a = record of the take off and climb upon leaving the Rotorfest. =20 Since the repair to the muffler was not a fundamental change in design, blaming the lack of performance on the damaged muffler was probably incorrect. So what was happening? With the engine shut down and still = warm, turning it over slowly with the prop produced a faint clicking noise in = a regular pattern. All indications were that the noise was coming from internal to the engine. Compression was fine on all compression strokes when turning with the prop. I thought that maybe the engine had = developed chatter marks in the rotor housings to the extent that the apex seals = would make the clicking noise when turning slowly while also losing = compression when turning fast enough that the apex seal could not follow the uneven surface of the housing. Pretty remote possibility, I know, but grasping = at straws makes one come up with some pretty weird ideas. This was investigated by removing the exhaust headers and looking into the = chambers. No chatter marks were seen. Everything I could check short of a = complete engine teardown seemed to be normal. =20 =20 To make a long story short, replacing the spark plugs brought things = back to normal as demonstrated by a subsequent flight test. So the data posted = last month is most likely not a record of operation with increased back = pressure as I had indicated, but rather one of operation with spark plug SAG. = This also is in line with the observation during the trip to the Rotorfest at = one point where I fully opened the throttle for a short time and observed = the RPM to drop off slightly. I was under the impression that when SAG = occurs, it is sudden and unmistakable. Apparently with my system, at least, it = can be somewhat insidious. The SAGGED take off when leaving from Texas = didn=92t seem unusual since I=92m used to the lower power levels produced at the = high density altitudes here. The trip around the pattern after SAG = developing gradually during time right around liftoff was memorable. =20 Oh, the clicking noise? It turned out to be due to the slight lash in = the crank angle sensor gear when a sensor point was magnetically pulled into alignment with the pickup. Being a little more hard of hearing could = have saved me a lot of work.=20 =20 Steve Boese =20 =20 =20 __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ------=_NextPart_000_0030_01C9FE71.BF33C390 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Hi = Steve,

 

It just dawned on me that flying at = a density altitude of 9000 MSL, you have only approx ½ the pressure = than we folks at sea level have.  That would of course reduce pressure = in the combustion chamber and would perhaps give you more time between plug = changes before SAG sits in.  So that might be one reason you did not = encounter it until you ventured to the low lands.

 

Ed

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Monday, July 06, = 2009 7:25 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] SAG = was: [FlyRotary] Muffler

 

Hi = Steve,

 

Isn’t this stuff = fascinating?

 

I’ve had many encounters with = SAG all the way from one memorable take off fully loaded on a hot summer day = (but not 9000 ft density altitude) in Tennessee.  Both rotors decided to go into SAG at the same time – really gets = your attention.  Being fully loaded for my trip to Memphis and with a full load of = fuel, my rate of climb was about 500 fpm.  I was really puckered until I recalled = that flying the old C-150, if I could GET 500 fpm on a hot day, I thought I = was doing great.  So I relaxed and climbed to altitude over the air = port, whereupon  pulling back on the power caused the SAG to go away and = I flew on to Memphis where Tracy was kind enough to provide me with a set of non-sagged plugs.  I now do not fly without at least two complete = plug changes.  It’s tough to pull back on power during take off = {:>)

 

But, it seems to happen most = frequently at high power settings but will gradually extend to every phase of flight including cruise.

 

My theory is that at high power = settings your manifold pressure and therefore your combustion pressure is at its highest.  As you know a spark has a harder time of jumping the gap = when pressures are high.  So I believe as the plug fouls over with lead = on the ceramic cone accumulating, it becomes easier for at least some of the = charge to bleed off before it builds high enough to jump the gap.  Pull back = on the throttle, pressure decreases and the plug fires normally – at = least for a while.

 

I once flew back from Louisiana without having changed my = plugs at my nominal 25-30 hour point.  I was encountering SAG symptoms about = every 15 minutes.  I discovered that if I use the ignition check switch = to turn off the leading plugs spark (firing on only the trialing) that the EGT = would increase from about 1575-1600F to over 1700F.  After restoring the = leading spark system, I could fly another 15 or so minutes before the SAG = symptoms started again.  I don’t really know why that made a = difference – did I change the combustion conditions and cause higher temps = burning off some of the deposits – I don’t = know.

 

But typically, the first thing I = notice is a change in the drone of the engine, the second most noticeable thing is = the EGT on the affect rotor will be on its way down typically dropping = around 300F deg.  The rpm will decrease as well somewhere around 150-200 rpm = (this on one affected rotor), don’t recall what it did during take off with = two sagging.   Generally, if at full power, reducing the throttle = seems to help.  Then frequently it will occur - last for a minute or so = and then disappear again.  The intervals will generally become shorter and = the effects periods longer.  You can easily think you have a fuel or = injector problem when its really not.

 

I never get use to the engine = making un-normal sounds, so to reduce seat cushion wear, I change my plugs = around 25-30 hours, but remember I use 100LL almost exclusively – autogas = seems to give much extended plug use before SAG = occurs.

 

YMMV

 

Ed

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of sboese
Sent: Monday, July 06, = 2009 6:48 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] = Muffler

 

Some of you may remember that I returned home from = the Rotorfest at the end of May to find the internal baffle of my muffler broken.  I theorized that the broken part may have partially = blocked the outlet and caused a power drop compared to what I should have been producing.  Pictures of the broken parts and repair were posted on = the list last month.

 

When the weather and my time off coincided recently, = I gave the repaired muffler a flight test after a ground run to be sure things = were working normally.  The flight lasted 9 minutes.  The plane was = much lighter than when leaving Texas, but the density altitude was about 9000 ft which is normal for = here.  The plane would barely climb, would not accelerate over 110 kts, and the oil = and coolant temperatures were abnormally high.  This was quite similar = to the data that I posted last month which was a record of the take off and = climb upon leaving the Rotorfest.

 

Since the repair to the muffler was not a fundamental = change in design, blaming the lack of performance on the damaged muffler was = probably incorrect. So what was happening?  With the engine shut down and = still warm, turning it over slowly with the prop produced a faint clicking = noise in a regular pattern.  All indications were that the noise was coming = from internal to the engine.  Compression was fine on all compression = strokes when turning with the prop.  I thought that maybe the engine had = developed chatter marks in the rotor housings to the extent that the apex seals = would make the clicking noise when turning slowly while also losing = compression when turning fast enough that the apex seal could not follow the uneven = surface of the housing.  Pretty remote possibility, I know, but grasping at = straws makes one come up with some pretty weird ideas.  This was = investigated by removing the exhaust headers and looking into the chambers.  No = chatter marks were seen.  Everything I could check short of a complete = engine teardown seemed to be normal. 

 

To make a long story short, replacing the spark plugs brought things back to normal as demonstrated by a subsequent flight test.  So the data posted last month is most likely not a record of operation with increased back pressure as I had indicated, but rather = one of operation with spark plug SAG.  This also is in line with the observation = during the trip to the Rotorfest at one point where I fully opened the throttle for = a short time and observed the RPM to drop off slightly.  I was under = the impression that when SAG occurs, it is sudden and unmistakable.  Apparently with my system, at least, it can be somewhat insidious.  = The SAGGED take off when leaving from Texas didn’t seem unusual since I’m used to the lower power levels produced at the high density altitudes here.  The trip around the = pattern after SAG developing gradually during time right around liftoff was = memorable.

 

Oh, the clicking noise?  It turned out to be due = to the slight lash in the crank angle sensor gear when a sensor point was = magnetically pulled into alignment with the pickup.  Being a little more hard of hearing could have saved me a lot of work.

 

Steve Boese

              <= /span>

 

 



__________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com



__________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

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