X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost03.isp.att.net ([204.127.217.103] verified) by logan.com (CommuniGate Pro SMTP 5.2.11) with ESMTP id 3416020 for flyrotary@lancaironline.net; Wed, 07 Jan 2009 23:55:02 -0500 Received-SPF: pass receiver=logan.com; client-ip=204.127.217.103; envelope-from=bobperk9@bellsouth.net Received: from fwebmail14.isp.att.net ([207.115.9.154]) by isp.att.net (frfwmhc03) with SMTP id <20090108045425H0300dohiae>; Thu, 8 Jan 2009 04:54:25 +0000 X-Originating-IP: [207.115.9.154] Received: from [74.249.209.22] by fwebmail14.isp.att.net; Thu, 08 Jan 2009 04:54:24 +0000 From: "Bob Perkinson" To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] FAW and the Phonoic gap [FlyRotary] Re: Muffler design (was 20B isssues . . ) Date: Thu, 08 Jan 2009 04:54:24 +0000 Message-Id: <010820090454.7223.496586FF000ECE5C00001C3722230650629B0A02D2089B9A019C04040A0DBFC7059D0A9F0D010D@att.net> In-Reply-To: X-Mailer: AT&T Message Center Version 1 (Oct 30 2008) X-Authenticated-Sender: Ym9icGVyazlAYmVsbHNvdXRoLm5ldA== MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_7223_1231390464_0" --NextPart_Webmail_9m3u9jl4l_7223_1231390464_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit Ed, You ought a be able to load that into Excel and crank out muffler dimensions for any airplane {:>) That is what it does ant it??? All this is well over my head... Bob. -------------- Original message from "Ed Anderson" : -------------- > Ernest, keep in mind that the results you get with your sound recording may > not be indicative of what real exhaust pulse would give you. The reason > -the exhaust pulse is a Finite Amplitude Wave - and they do behave > differently in reflecting and refracting than standard sound waves. > > The math is not too intimidating {:>) > > http://www.wikiwaves.org/index.php/Finite_Amplitude_Wave_Theory > > > > Ed Anderson > > Rv-6A N494BW Rotary Powered > > Matthews, NC > > eanderson@carolina.rr.com > > http://www.andersonee.com > > http://members.cox.net/rogersda/rotary/configs.htm#N494BW > > http://www.dmack.net/mazda/index.html > > -----Original Message----- > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On > Behalf Of Ernest Christley > Sent: Wednesday, January 07, 2009 4:07 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] Re: Muffler design (was 20B isssues . . ) > > Tracy Crook wrote: > > Agreed, this is definitely a new concept and I hope it works. > > > > The only thing that bothers me is that, as you pointed out, the > > bandwidth needed for attenuation is about 0 to 12 Khz. That > > represents MANY octaves even if we bump the lower limit to a realistic > > number ( only a closed pipe will work at zero :-). This bandwidth is > > mutually exclusive with the term "tuned". And if by tuned they mean > > low pass, then it is not a new concept since that is covered by > > conventional mufflers. There may be something to this new concept but > > until this contradiction is explained, I would hesitate to start > > cutting parts. > The first parts I'm going to cut are wood sides and PVC pipe baffles. > That'll be good enough to experiment with. I've got a sound sample of a > frequency sweep. I can build a test muffler, play the frequency sweep > in one end, and record it on the other. Displaying both samples in a > sound editor will tell me what, if any, frequencies are attenuated, and > by how much. Losses in the playback speakers and microphone can be > documented by running a test without the intervening muffler. I may > have to spend money on good speakers and a good microphone (Oh, > bummer!). If that shows promise, I replace the PVC with stainless > tubes. If that works, I replace the wood with stainless sheet. > > Which frequencies need to be attenuated? Remember that Monty Roberts > did some work a while back showing a sonagram of a rotary recording? > The sound energies are much higher around 6 and 12kHz. With that in > mind, look at the graphs on the top of page 4 of this report > http://web.mit.edu/course/3/3.042/team1_08f/documents/complete-phononic-band > gap.pdf > > It shows very significant attenuation in frequencies from 4 to 8kHz and > then 10 to 14kHz. This is with 13mm cylinders set in a 30mm square > array. Hollow cylinders showed similar efficacy. Close enough to 1/8" > pipe (mcmaster-carr part# 44635K422 ... cheap!) to make a prototype > almost mandatory. So, my current plan of action is to produce some > sonagrams of rotary exhaust noise, and verify the target frequencies for > attenuation. With the experimental jig, optimize for bandgaps around > those frequencies while using the smallest filling fraction possible. > At that point, I will build a matching prototype. Two sections of steal > sheet, match drilled with 1/2" holes (or whatever size was found to be > optimum). Fill the holes with 3" sections of tube. A bunch of welding > later, a 8.5" wide muffler with a .500 filling fraction will render > about the same flow area as a 4" diameter exhaust pipe. > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html > > __________ Information from ESET NOD32 Antivirus, version of virus signature > database 3267 (20080714) __________ > > The message was checked by ESET NOD32 Antivirus. > > http://www.eset.com > > > > __________ Information from ESET NOD32 Antivirus, version of virus signature > database 3267 (20080714) __________ > > The message was checked by ESET NOD32 Antivirus. > > http://www.eset.com > > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html --NextPart_Webmail_9m3u9jl4l_7223_1231390464_0 Content-Type: multipart/related; boundary="NextPart_Webmail_9m3u9jl4l_7223_1231390464_1" --NextPart_Webmail_9m3u9jl4l_7223_1231390464_1 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable
=20 Ed,
You ought a be able to load that into Excel and crank out muffler di= mensions for any airplane {:>) That is what it does ant it???
All thi= s is well over my head...
Bob.

-------------- Original message from "Ed Anderson" <eanderson@carolina.= rr.com>: --------------


> Ernest, keep in mind that the results you get with your sound reco= rding may
> not be indicative of what real exhaust pulse would give you. The = reason
> -the exhaust pulse is a Finite Amplitude Wave - and they do behave
> differently in reflecting and refracting than standard sound waves= .=20=20
>=20
> The math is not too intimidating {:>)
>=20
> http://www.wikiwaves.org/index.php/Finite_Amplitude_Wave_Theory
>=20
>=20
>=20
> Ed Anderson
>=20
> Rv-6A N494BW Rotary Powered
>=20
> Matthews, NC
>=20
> eanderson@carolina.rr.com
>=20
> http://www.andersonee.com
>=20
> http://members.cox.net/rogersda/rotary/configs.htm#N494BW
>=20
> http://www.dmack.net/mazda/index.html
>=20
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.ne= t] On
> Behalf Of Ernest Christley
> Sent: Wednesday, January 07, 2009 4:07 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Muffler design (was 20B isssues . . )
>=20
> Tracy Crook wrote:
> > Agreed, this is definitely a new concept and I hope it works.
> >
> > The only thing that bothers me is that, as you pointed out, t= he=20
> > bandwidth needed for attenuation is about 0 to 12 Khz. That= =20
> > represents MANY octaves even if we bump the lower limit to a = realistic=20
> > number ( only a closed pipe will work at zero :-). This band= width is=20
> > mutually exclusive with the term "tuned". And if by tuned th= ey mean=20
> > low pass, then it is not a new concept since that is covered = by=20
> > conventional mufflers. There may be something to this new co= ncept but=20
> > until this contradiction is explained, I would hesitate to st= art=20
> > cutting parts.
> The first parts I'm going to cut are wood sides and PVC pipe baffl= es.=20=20
> That'll be good enough to experiment with. I've got a sound sampl= e of a=20
> frequency sweep. I can build a test muffler, play the frequency s= weep=20
> in one end, and record it on the other. Displaying both samples i= n a=20
> sound editor will tell me what, if any, frequencies are attenuated= , and=20
> by how much. Losses in the playback speakers and microphone can b= e=20
> documented by running a test without the intervening muffler. I m= ay=20
> have to spend money on good speakers and a good microphone (Oh,=20
> bummer!). If that shows promise, I replace the PVC with stainless= =20
> tubes. If that works, I replace the wood with stainless sheet.
>=20
> Which frequencies need to be attenuated? Remember that Monty Robe= rts=20
> did some work a while back showing a sonagram of a rotary recordin= g?=20=20
> The sound energies are much higher around 6 and 12kHz. With that = in=20
> mind, look at the graphs on the top of page 4 of this report
> http://web.mit.edu/course/3/3.042/team1_08f/documents/complete-pho= nonic-band
> gap.pdf
>=20
> It shows very significant attenuation in frequencies from 4 to 8kH= z and=20
> then 10 to 14kHz. This is with 13mm cylinders set in a 30mm squar= e=20
> array. Hollow cylinders showed similar efficacy. Close enough to= 1/8"=20
> pipe (mcmaster-carr part# 44635K422 ... cheap!) to make a prototyp= e=20
> almost mandatory. So, my current plan of action is to produce som= e=20
> sonagrams of rotary exhaust noise, and verify the target frequenci= es for=20
> attenuation. With the experimental jig, optimize for bandgaps aro= und=20
> those frequencies while using the smallest filling fraction possib= le.=20=20
> At that point, I will build a matching prototype. Two sections of= steal=20
> sheet, match drilled with 1/2" holes (or whatever size was found t= o be=20
> optimum). Fill the holes with 3" sections of tube. A bunch of we= lding=20
> later, a 8.5" wide muffler with a .500 filling fraction will rende= r=20
> about the same flow area as a 4" diameter exhaust pipe.
>=20
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub:
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>=20
> __________ Information from ESET NOD32 Antivirus, version of virus= signature
> database 3267 (20080714) __________
>=20
> The message was checked by ESET NOD32 Antivirus.
>=20
> http://www.eset.com
>=20
>=20=20
>=20
> __________ Information from ESET NOD32 Antivirus, version of virus= signature
> database 3267 (20080714) __________
>=20
> The message was checked by ESET NOD32 Antivirus.
>=20
> http://www.eset.com
>=20=20
>=20
>=20
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrot= ary/List.html
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