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 3747070 for flyrotary@lancaironline.net; Mon, 06 Jul 2009 19:17:47 -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: [BULK] [FlyRotary] Muffler MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C9FE98.8C0BE566" Date: Mon, 6 Jul 2009 18:19:07 -0600 Disposition-Notification-To: "Bobby J. Hughes" Content-class: urn:content-classes:message Message-ID: <74120FDE88CAFE4DBDA8814BCE20A3F315E5E3@qnsi-mail.qnsi.net> X-MimeOLE: Produced By Microsoft Exchange V6.5 X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [BULK] [FlyRotary] Muffler Thread-Index: Acn+lJcaRLuBZQE0TluCBzH9E8sJIQAA50KA References: From: "Bobby J. Hughes" To: "Rotary motors in aircraft" This is a multi-part message in MIME format. ------_=_NextPart_001_01C9FE98.8C0BE566 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Steve, =20 About how many hours and gallons of 100LL had this set of plugs seen? =20 Bobby (back from camping in Arkansas) =20 ________________________________ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of sboese Sent: Monday, July 06, 2009 4:48 PM To: Rotary motors in aircraft Subject: [BULK] [FlyRotary] Muffler Importance: Low 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'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. =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 ------_=_NextPart_001_01C9FE98.8C0BE566 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable
Steve,
 
About how many hours and gallons of 100LL had this = set of=20 plugs seen?
 
Bobby (back from camping in = Arkansas)
 

From: Rotary motors in aircraft=20 [mailto:flyrotary@lancaironline.net] On Behalf Of = sboese
Sent:=20 Monday, July 06, 2009 4:48 PM
To: Rotary motors in=20 aircraft
Subject: [BULK] [FlyRotary] = Muffler
Importance:=20 Low

Some of you may remember = that I=20 returned home from the Rotorfest at the end of May to find the internal = baffle=20 of my muffler broken.  I theorized that the broken part may have = partially=20 blocked the outlet and caused a power drop compared to what I should = have been=20 producing.  Pictures of the broken parts and repair were posted on = the list=20 last month.

 

When the weather and my = time off=20 coincided recently, I gave the repaired muffler a flight test after a = ground run=20 to be sure things were working normally.  The flight lasted 9=20 minutes.  The plane was much lighter than when leaving Texas, but = the=20 density altitude was about 9000 ft which is normal for here.  The = plane=20 would barely climb, would not accelerate over 110 kts, and the oil and = coolant=20 temperatures were abnormally high.  This was quite similar to the = data that=20 I posted last month which was a record of the take off and climb upon = leaving=20 the Rotorfest.

 

Since the repair to the = muffler was=20 not a fundamental change in design, blaming the lack of performance on = the=20 damaged muffler was probably incorrect. So what was happening?  = With the=20 engine shut down and still warm, turning it over slowly with the prop = produced a=20 faint clicking noise in a regular pattern.  All indications were = that the=20 noise was coming from internal to the engine.  Compression was fine = on all=20 compression strokes when turning with the prop.  I thought that = maybe the=20 engine had developed chatter marks in the rotor housings to the extent = that the=20 apex seals would make the clicking noise when turning slowly while also = losing=20 compression when turning fast enough that the apex seal could not follow = the=20 uneven surface of the housing.  Pretty remote possibility, I know, = but=20 grasping at straws makes one come up with some pretty weird ideas.  = This=20 was investigated by removing the exhaust headers and looking into the=20 chambers.  No chatter marks were seen.  Everything I could = check short=20 of a complete engine teardown seemed to be normal.  =

 

To make a long story = short,=20 replacing the spark plugs brought things back to normal as demonstrated = by a=20 subsequent flight test.  So the data posted last month is most = likely not a=20 record of operation with increased back pressure as I had indicated, but = rather=20 one of operation with spark plug SAG.  This also is in line with = the=20 observation during the trip to the Rotorfest at one point where I fully = opened=20 the throttle for a short time and observed the RPM to drop off = slightly.  I=20 was under the impression that when SAG occurs, it is sudden and=20 unmistakable.  Apparently with my system, at least, it can be = somewhat=20 insidious.  The SAGGED take off when leaving from Texas = didn’t seem unusual=20 since I’m used to the lower power levels produced at the high = density altitudes=20 here.  The trip around the pattern after SAG developing gradually = during=20 time right around liftoff was memorable.

 

Oh, the clicking = noise?  It=20 turned out to be due to the slight lash in the crank angle sensor gear = when a=20 sensor point was magnetically pulled into alignment with the = pickup.  Being=20 a little more hard of hearing could have saved me a lot of work.=20

 

Steve = Boese

 =20             <= /SPAN>

 

 

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