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 5.2.14) with ESMTPS id 3747348 for flyrotary@lancaironline.net; Mon, 06 Jul 2009 22:18:17 -0400 Received-SPF: none receiver=logan.com; client-ip=129.72.10.32; envelope-from=SBoese@uwyo.edu Received: from ponyexpress-ht1.uwyo.edu (ponyexpress-ht1.uwyo.edu [10.84.60.208]) by aspensprings.uwyo.edu (8.14.2/8.14.2) with ESMTP id n672HZbR013183 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Mon, 6 Jul 2009 20:17:35 -0600 (MDT) (envelope-from SBoese@uwyo.edu) Received: from sboesetablet (172.26.4.5) by uwmail.uwyo.edu (10.84.60.198) with Microsoft SMTP Server id 8.1.375.2; Mon, 6 Jul 2009 20:17:31 -0600 From: Steven Boese To: "'Rotary motors in aircraft'" In-Reply-To: Subject: RE: [FlyRotary] Re: Muffler Date: Mon, 6 Jul 2009 20:17:16 -0600 Message-ID: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000C_01C9FE76.C44D5C10" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.2627 Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6001.18049 ------=_NextPart_000_000C_01C9FE76.C44D5C10 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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. 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. 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. 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. 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. 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 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 ------=_NextPart_000_000C_01C9FE76.C44D5C10 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

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.

 

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.

 

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.

 

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.

 

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.

 

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 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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