Return-Path: Received: from imf25aec.mail.bellsouth.net ([205.152.59.73] verified) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 563442 for flyrotary@lancaironline.net; Sat, 11 Dec 2004 14:30:32 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.152.59.73; envelope-from=ceengland@bellsouth.net Received: from [209.215.61.105] by imf25aec.mail.bellsouth.net (InterMail vM.5.01.06.11 201-253-122-130-111-20040605) with ESMTP id <20041211193002.IEUM2130.imf25aec.mail.bellsouth.net@[209.215.61.105]> for ; Sat, 11 Dec 2004 14:30:02 -0500 Message-ID: <41BB4AB9.7080906@bellsouth.net> Date: Sat, 11 Dec 2004 13:30:01 -0600 From: Charlie England User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: exhaust design question References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit I was hoping the same thing, but at the rotary roundup, Tracy's engine still had a lot of that sharp edged bite as the rpm came up. Not as strong as the old 13B, but still there. Standing to the side of the plane, it almost sounded like the muffler tube (it's exposed under the fuselage) was resonating at the upper midrange pitch that's irritating. Higher frequencies are usually easier to control & damp out than low freqs, so I wonder if the sound would be as bad if the muffler was inside the fiberglas cowling. That way, the cowl itself could become part of the silencing system by damping the sound radiated by the muffler. Charlie Dennis Haverlah wrote: > I would expect the Renesis engine with the split/side exhaust is not > as irritating. What is the experience? I have not heard either a 13B > or Renesis takeoff or fly-by. > Dennis H. > > Charlie England wrote: > >> Russell Duffy wrote: >> >>> So it appears its as much the nature of the Rotary "bark" as it is >>> the sound level. >>> >>> >>> I completely agree, and I've tried to get people around the airport >>> to understand this. Since the engine doesn't sound like a "normal" >>> engine, everyone takes note. Since they noticed it, they assume >>> it's primarily because it must be louder than other engines. This >>> isn't necessarily true of course. Glad you got your power back. >>> Rusty (yawn) >> >> >> >> >> This phenomenon is widely understood by audiophiles & (ex)sound >> engineers. Certain frequencies, and certain harmonic structures added >> to any sound, are much more irritating to the ear than others. The >> 'bark' or 'edge' in the sound of a 2stroke or rotary is the harmonic >> structure of the sound, not the actual level. I suspect that if you >> fed a microphone into an oscilloscope, you'd see something like a >> sine or triangle wave from a 4stroke piston engine & something >> approaching a square wave from a 2stroke or rotary. We can run that >> experiment here at Slobovia the next time we have a visit from a rotary. >> >> I suspect that's why Paul Conner's exhaust is actually a pleasing >> sound while most rotaries 'hurt' your ears. His iron manifold is >> probably filtering out the irritating harmonics & 'rounding off' the >> waveform. >> >> Charlie >