X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: <13brv3@bellsouth.net> Received: from imf24aec.mail.bellsouth.net ([205.152.59.72] verified) by logan.com (CommuniGate Pro SMTP 5.0) with ESMTP id 814186 for flyrotary@lancaironline.net; Thu, 03 Nov 2005 20:51:06 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.152.59.72; envelope-from=13brv3@bellsouth.net Received: from ibm71aec.bellsouth.net ([65.6.194.9]) by imf24aec.mail.bellsouth.net with ESMTP id <20051104015023.BYC13897.imf24aec.mail.bellsouth.net@ibm71aec.bellsouth.net> for ; Thu, 3 Nov 2005 20:50:23 -0500 Received: from rd ([65.6.194.9]) by ibm71aec.bellsouth.net with ESMTP id <20051104015022.UCYR18478.ibm71aec.bellsouth.net@rd> for ; Thu, 3 Nov 2005 20:50:22 -0500 From: "Russell Duffy" <13brv3@bellsouth.net> To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] muffler new info. Date: Thu, 3 Nov 2005 19:50:23 -0600 Message-ID: <000801c5e0e2$1f277f00$6101a8c0@rd> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0009_01C5E0AF.D48D0F00" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.2527 Importance: Normal In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_0009_01C5E0AF.D48D0F00 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable I also had a chance to ring the muffler and see what the resonant = frequency of the structure is. As fate would have it, the fundamental is 2400 hz. = This is a multiple of the 1200 hz resonant frequency of the cavity of the muffler. So it will self excite when the muffler is really working hard. This explains the horrible screech at 6000-6500 rpm. This is also bad = for fatigue life. I should be able to weld a couple of strips of metal to it = and fix that problem. =20 =20 Sorta gives a new meaning to "tuned exhaust" :-) =20 Cheers, Rusty (RV-8 and Zenith XL are now neck and neck)=20 ------=_NextPart_000_0009_01C5E0AF.D48D0F00 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
I also had a chance to ring the muffler = and see=20 what the resonant frequency of the structure is. As fate would have = it, the=20 fundamental is 2400 hz. This is a multiple of the 1200 hz resonant=20 frequency of the cavity of the muffler. So it will self excite when the = muffler=20 is really working hard. This explains the horrible screech at 6000-6500 = rpm.=20 This is also bad for fatigue life. I should be able to weld a = couple of=20 strips of metal to it and fix that problem.
 
 
Sorta gives a=20 new meaning to "tuned exhaust" :-)
 
Cheers,
Rusty (RV-8=20 and Zenith XL are now neck and = neck) 
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