X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [66.219.56.253] (HELO mail.qnsi.net) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3747326 for flyrotary@lancaironline.net; Mon, 06 Jul 2009 22:35:53 -0400 Received-SPF: none receiver=logan.com; client-ip=66.219.56.253; envelope-from=bhughes@qnsi.net Return-Receipt-To: "Bobby J. Hughes" Subject: RE: [FlyRotary] Re: Muffler MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C9FEB4.38C1CA44" Date: Mon, 6 Jul 2009 21:37:13 -0600 Disposition-Notification-To: "Bobby J. Hughes" Content-class: urn:content-classes:message X-MimeOLE: Produced By Microsoft Exchange V6.5 Message-ID: <74120FDE88CAFE4DBDA8814BCE20A3F315E5E5@qnsi-mail.qnsi.net> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [FlyRotary] Re: Muffler Thread-Index: Acn+sdu9hxV58FLpSVaQZCe7Rr4MSwAAW7Tg References: From: "Bobby J. Hughes" To: "Rotary motors in aircraft" This is a multi-part message in MIME format. ------_=_NextPart_001_01C9FEB4.38C1CA44 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Steve, =20 The increased oil and water temp's are interesting. I am not sure this has been reported before.=20 =20 Bobby ________________________________ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Steven Boese Sent: Monday, July 06, 2009 8:17 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Muffler 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 symptoms after repairing the muffler were the same as before the repair was made so at this 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 about 250 degrees during the power deficit. Back pressure would probably affect both rotors in a similar fashion so that would also point to SAG as the culprit. =20 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 that was 100LL. =20 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 lower manifold pressures that I normally see. =20 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 or so. I did have extra plugs along on the Texas trip and it would have been easy to have installed them at the rotorfest. =20 The nature of SAG is puzzling. The symptoms of decreased EGT, decreased power output, and increased heat transfer to the oil and coolant are all consistent with descriptions of pre-ignition more than that of spark plug misfire. In piston engines, pre-ignition can rapidly lead to destruction, but the 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 going 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 the spark plug with lead deposited on it that the combustion rate is slowed enough to persist 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-ignition. This theory probably has as much probability of being right as the one I had concerning the apex seals clicking. =20 Maybe I can accumulate a pile of SAGGING spark plugs as big as Ed's. That would be verifiable at least. =20 =20 Steve Boese =20 =20 =20 =20 -----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 =20 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 wonder if your increased backpressure contributed to the onset of SAG? And do you only burn 100LL, occasionally, or never? =20 Todd C-FSTB RV9 Turbo13B=20 =20 ------_=_NextPart_001_01C9FEB4.38C1CA44 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable
Steve,
 
The increased oil and water temp's are = interesting. I am=20 not sure this has been reported before.
 
Bobby

From: Rotary motors in aircraft=20 [mailto:flyrotary@lancaironline.net] On Behalf Of Steven=20 Boese
Sent: Monday, July 06, 2009 8:17 PM
To: Rotary = motors=20 in aircraft
Subject: [FlyRotary] Re: = Muffler

I never found = the=20 broken muffler part in the outlet of the muffler where it might have = caused=20 increased back pressure even though it was possible for it to end up in = that=20 location by standing the muffler on its end.  The symptoms after repairing = the muffler=20 were the same as before the repair was made so at this point, I = don’t think the=20 broken part was a factor in the performance issue.  Looking back at the data log, = the #2=20 rotor EGT dropped by about 250 degrees during the power deficit.  Back pressure would probably = affect both=20 rotors in a similar fashion so that would also point to SAG as the=20 culprit.

 

In response = to your and=20 Bobby’s questions, at the onset of SAG, there were a total of 15 = hours on the=20 plugs, 106 gal total of fuel burned, 53 gal of that was=20 100LL.

 

Ed is most = likely right=20 that operating at the increased manifold pressure available at low = altitude made=20 the SAG show up while it didn’t at lower manifold pressures that I = normally=20 see.

 

The = relatively small=20 amount of time and fuel that the plugs had seen when SAG occurred may = also be=20 due to the low power levels and correspondingly lower combustion = temperatures=20 permitting more rapid lead deposition on the plugs.  It looks like I should = routinely change=20 plugs every 10 hours or so.  I did=20 have extra plugs along on the Texas trip and it = would have=20 been easy to have installed them at the rotorfest.

 

The nature of = SAG is=20 puzzling.  The symptoms of = decreased=20 EGT, decreased power output, and increased heat transfer to the oil and = coolant=20 are all consistent with descriptions of pre-ignition more than that of = spark=20 plug misfire.  In piston = engines,=20 pre-ignition can rapidly lead to destruction, but the rotary engine may = be more=20 tolerant of it.  Maybe it = isn’t a=20 matter of no ignition due to the spark plug not firing, but a matter of = the fire=20 not going out between sparks.  = The=20 lead in 100LL increases the octane rating by slowing the combustion rate = and=20 thereby decreasing the tendency for detonation.  Maybe there is enough gas = phase lead in=20 the vicinity of the spark plug with lead deposited on it that the = combustion=20 rate is slowed enough to persist from one cycle to the next while the = normal=20 combustion rate occurs in the rest of the chamber. This could result in = a=20 process similar to pre-ignition.  = This theory probably has as much probability of being right as = the one I=20 had concerning the apex seals clicking.

 

Maybe I can = accumulate=20 a pile of SAGGING spark plugs as big as Ed’s.  That would be verifiable at = least.     

 

Steve Boese  

 

   

 

-----Original=20 Message-----
From: = Rotary=20 motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Todd = Bartrim
Sent: Monday, July 06, 2009 6:23=20 PM
To: Rotary motors = in=20 aircraft
Subject: = [FlyRotary]=20 Re: Muffler

 

Hi=20 Steve;
    So you now assume that your power loss is = directly=20 attributable to SAG and not to the partially blocked muffler? Is this=20 correct?
     I'm curious as I also use a = homemade=20 muffler (SpinTech copy) and have wondered what the result would be if = any of the=20 internal came loose. I wonder if your increased backpressure contributed = to the=20 onset of SAG? And do you only burn 100LL, occasionally, or never?

 

Todd
C-FSTB
RV9 Turbo13B=20

 

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