X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from qw-out-2122.google.com ([74.125.92.24] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3646568 for flyrotary@lancaironline.net; Tue, 19 May 2009 01:38:01 -0400 Received-SPF: pass receiver=logan.com; client-ip=74.125.92.24; envelope-from=fluffysheap@gmail.com Received: by qw-out-2122.google.com with SMTP id 8so2420334qwh.25 for ; Mon, 18 May 2009 22:37:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=lKSQOJWwQb7WbV9yJCHcDg/nAZXrDeuRPzzw7sqq41s=; b=rGQdNpIt6xj9l+R63ez0ffJefm/sBn4DKJje+jFX+VfNvw6zfNm1wnOsL6qNiXhgO8 NkmnIxYz4gs5u5hd452B22aUBOIqBQxMtji3b6lYJRDFiNBYXCuIyDTv5hTQhnrkryeT Qcqsc4fiCFWghu9bT3VCrXnxA0lGmGO1FiYYw= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=ouQzImDL3XMzLUb1GAKTC8xvFUWe+A3SLO/d0mQ3/GcMhtDyTQwLQtl+5VAgcAAMxX a2k4tEyhDckbgl56mS75wusnRWIPZ3XikyEs9Y5inlct9DRmgV8WhvJQyiWPkMA1PNOu 9tbQjUDBh+/Uz2AIc9OBxVjpCp8x+yrPG8IFk= MIME-Version: 1.0 Received: by 10.220.93.65 with SMTP id u1mr7626217vcm.59.1242711443860; Mon, 18 May 2009 22:37:23 -0700 (PDT) In-Reply-To: References: Date: Mon, 18 May 2009 22:37:23 -0700 Message-ID: Subject: Re: [FlyRotary] Re: 20b Exhaust From: William Wilson To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=0016364ed3862b6f75046a3d4eb2 --0016364ed3862b6f75046a3d4eb2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Well that is sure spiffy. In addition to reducing high frequency noise, it looks like the filter smooths out the frequencies in the lower regions which will make for a less "noisy" sounding exhaust even if it's not actually any quieter. It would probably also be easier for ANR headsets to filter out. You could try experimenting with ceramics. I think PVC and wood have a natural muffling effect that metal pipes won't have. Ceramics can withstand the high temperatures and may be easier to work with, especially in development stage, since clay is very easy to shape. Plus, they do it on the F-117, so it's got to be good. On Mon, May 18, 2009 at 7:30 PM, Ernest Christley wrote: > Tracy Crook wrote: > >> Your mathematics are sound George and using that approach will certainly >> keep back pressure to a minimum. But I think it is doomed to be noisy. >> That's just my understanding about how mufflers generally work and I could >> be wrong. >> During a test of mufflers at a rotary fly-in some years back I was amazed >> at how effective the muffler became and how small the power loss was when we >> installed a 1" diameter muffler outlet pipe on the test stand engine (13B). >> 1" is admittedly too small but we learn by going to extremes sometimes. >> >> Tracy >> >> Maybe there is a way to get both. This is the first results from my > experiments with bandgap filters that I just did today. > > http://ernest.isa-geek.org/Delta/Experiments/PhononicBandgapFilter.html > > > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html > --0016364ed3862b6f75046a3d4eb2 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Well that is sure spiffy.

In addition to reducing high frequency noi= se, it looks like the filter smooths out the frequencies in the lower regio= ns which will make for a less "noisy" sounding exhaust even if it= 's not actually any quieter.=A0 It would probably also be easier for AN= R headsets to filter out.

You could try experimenting with ceramics.=A0 I think PVC and wood have= a natural muffling effect that metal pipes won't have.=A0 Ceramics can= withstand the high temperatures and may be easier to work with, especially= in development stage, since clay is very easy to shape.=A0 Plus, they do i= t on the F-117, so it's got to be good.

On Mon, May 18, 2009 at 7:30 PM, Ernest Chri= stley <echrist= ley@nc.rr.com> wrote:
Tracy Crook wrote:
Your mathematics are sound George and using that approach will certainly ke= ep back pressure to a minimum. But I think it is doomed to be noisy. =A0Tha= t's just my understanding about how mufflers generally work and I could= be wrong.
=A0During a test of mufflers at a rotary fly-in some years back I was amaze= d at how effective the muffler became and how small the power loss was when= we installed a 1" diameter muffler outlet pipe on the test stand engi= ne =A0(13B). =A01" is admittedly too small but we learn by going to ex= tremes sometimes.

Tracy

Maybe there is a way to get both. =A0This is the first results from my expe= riments with bandgap filters that I just did today.

http://ernest.isa-geek.org/Delta/Experiments/Pho= nonicBandgapFilter.html

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