X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.3c2) with ESMTP id 3978662 for flyrotary@lancaironline.net; Mon, 16 Nov 2009 18:16:43 -0500 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (sv1-1.per.aanet.com.au [203.24.100.68]) by poplet2.per.eftel.com (Postfix) with ESMTP id 32F36173812 for ; Tue, 17 Nov 2009 07:16:08 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 1EB68BEC00C for ; Tue, 17 Nov 2009 07:16:06 +0800 (WST) Message-ID: <97E3E8E589594C8A8E49DD6E20E9BBD4@ownerf1fc517b8> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Phononic bandgap muffler Date: Tue, 17 Nov 2009 09:16:08 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000C_01CA6766.992A6CE0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5843 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 091116-0, 11/16/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_000C_01CA6766.992A6CE0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Bryan, Cones are good and do what you say - however there must be something to = redirect the sounds so as they can't go directly out the rear. Traveling = through cones alone won't do that. However I ( and Bill Jepson) have used the principle by using a design = that has cones within cones, supplementing with two 2 exhaust = augmentations and a cool tube through the middle. The smaller cones = actually do the redirecting to the outer cones and housing. I haven't tested it yet but I'm glad someone else has stumbled across = the principles to confirm the basis for the design. George (down under) And to piggyback on that thought, what about a cone similar to the = engine (very loud) nacelle of the Convair 880. I'll call it a fluted = cone, but you'll have to google it to get the full picture. Bryan =20 -------------------------------------------------------------------------= ----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] = On Behalf Of Dwayne Parkinson Sent: Monday, November 16, 2009 4:24 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Phononic bandgap muffler =20 Speaking mufflers, has anyone played with a cone shaped "tail pipe?" = NASA/NACA has a paper on the Schneebeli system which uses a silencer of = some sort with a conical exhaust pipe. I think the theory is the cone = acts as a second muffler because the exiting sound waves bounce at = angles off the cone walls rather than heading straight out of the pipe = into your ear drums. The trick would be to level out the exhaust pulses = so the pressure of the exhaust gas as it enters the tail pipe is = relatively constant. With relatively constant pressure, Bernoulli's = principle can apply to the escaping exhaust. Rather than creating back = pressure, the cone shaped tail pipe will cause the exhaust gases to = accelerate out the pipe but remain at the same pressure as when entering = the pipe. Who knows, that may even create extra thrust! =20 =20 =20 -------------------------------------------------------------------------= ----- From: MONTY ROBERTS To: Rotary motors in aircraft Sent: Mon, November 16, 2009 9:42:19 AM Subject: [FlyRotary] Re: Phononic bandgap muffler I'll have to do some digging for my notes and such. That was a couple = computers ago. As I recall, the problem was the high frequency content = of the rotary exhaust. This is present in all ported engines. Think dirt = bike: didinnnnggggdinnngggdinnnnnng. The muffler I made was according to = some NACA papers on silencer design. It was effective at muting the = problem frequencies. Unfortunately the muffler casing did "ring" at the = fundamental frequency the engine hit at about 6000-6500 rpm. I don't = think the thing would have lasted very long ringing like that. It would = have fatigued and disintegrated in short order. The resonator can work, = but the casing will have to be designed not to ring anywhere in the = operating range. The tests were promising, I honestly haven't had a = chance to set down and look at modifying the muffler to eliminate that = problem. The base frequency of the rotary in cruise is comparable to a = Merlin or a V-8 in their respective operating ranges (IIRC 200 Hz or = so). I don't think that it is necessary to muffle the low frequencies. = It would require a large heavy muffler to do so anyway. It is just the = 1500-2000 kHZ that grates on everybody (chainsaw). The higher stuff is = as Charlie said, harmonics of the 1500-2000 kHZ noise. You can't kill = the higher frequencies effectively without an absorption type silencer. = We all know how long they last behind the rotary..... So concentrate on the 1500-2000 kHZ range. It is possible to make a = resonance/band type filter in this range, and taking care of the = fundamental Freq. should take care of the higher harmonics also. The = problem is mostly making something that will stand the thermal and = mechanical abuse. Of course a simple expansion chamber with a restriction on the exhaust = will make it ultra quiet. You will pay a power penalty. Dennis has a combination of things working in his favor. One is the = Renesis' cooler exhaust, the very heavily engineered stock manifold, a = 90 degree turn to kill a lot of the high frequency stuff, and an = absorption type muffler to clean up the rest. I'll do some digging and see what is on my old computer. Monty >>=20 >=20 > Hi Earnest, >=20 > 10-15dB is a very respectable reduction. A 10 dB change is a 10X = power > change and a perceived doubling or halving in volume to the human = ear > (dB's are a logarithmic power measurement). >=20 > However, I doubt that working on the 8k-12k range is going to have = much > effect on the perceived noise from a rotary, for a couple of = reasons. I > can't find the emails & info from Monty Roberts' testing a few years > ago, but IIRC, the problem areas are much lower in frequency. Look = at > the ~1k-2khz area & the ~3.5k-4khz areas. Those areas are much = stronger, > and they are in the 'zone' where human hearing is most sensitive. = When > Monty did his testing, the stuff above 4khz was harmonics radiating = off > the muffler itself (the muffler 'rings' like a bell). The muffler = wasn't > enclosed in a cowling. >=20 > So here's what I think. The 8khz & above stuff is barely audible to > people over 40, or who have rock concerts in their history, or fly > airplanes for any length of time. Additionally, stuff in that = frequency > range hates to turn corners and is easily absorbed by relatively low > mass materials. When you take those two factors into consideration > together, something as simple as enclosing the muffler in a housing = that > won't sustain a resonance (think fiberglass cowling) will kill just > about all of it. The stuff under 4khz, though, is a bit harder to = deal > with, and that spot down below 2khz is really tough. As I mentioned > earlier, those are much more likely to sound offensive, too. >=20 > If you can suppress the 1k-2khz range, the higher freqs will likely = take > care of themselves because they are harmonics of the lower freq = stuff. >=20 > Remember the discussion about Paul Conner's engine with the stock > exhaust manifold? The cast iron was massive enough to absorb all = those > higher order harmonics and the FG cowl finished the work, even with = the > exhaust being dumped out the cowl with just a little 8-10" stub pipe = off > the manifold. It wasn't 'quiet', but it was very pleasing to listen = to, > like a small block V-8. Of course, the downside for a non-renesis = 13B is > the loss of power because you don't get a tuning boost from a = header. > The only other pleasant-sounding rotary plane that I've personally > listened to (other than turbo'd engines) is Dennis Haverlah's = Renesis, > and it uses the stock Renesis exhaust manifold. If you look at the = way > it's constructed, it's made of 3 layers of material, apparently for > noise suppression and heat shielding in one package. >=20 > If Monty reads this, maybe he can repost his test results & expand = on or > correct what I've written here. >=20 > It might be helpful to load a tone generator program & listen to = various > frequencies to get an idea of what each frequency sounds like. If = you > use Audacity or a similar sound editing program, it has a tone = generator > built in. >=20 > Charlie >=20 > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html = -------------------------------------------------------------------------= ------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.425 / Virus Database: 270.14.67/2505 - Release Date: = 11/15/09 19:50:00 -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html =20 ------=_NextPart_000_000C_01CA6766.992A6CE0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Bryan,
Cones are good and do what you say - = however there=20 must be something to redirect the sounds so as they can't go directly = out the=20 rear. Traveling through cones alone won't do that.
 
However I ( and Bill Jepson) have used = the=20 principle by using a design that has cones within cones, supplementing = with two=20 2 exhaust augmentations and a cool tube through the middle. The smaller = cones=20 actually do the redirecting to the outer cones and housing.
 
I haven't tested it yet but I'm glad = someone else=20 has stumbled across the principles to confirm the basis for the=20 design.
George (down under)

And = to =20 piggyback on that thought, what about a cone similar to the engine = (very loud)=20 nacelle of the Convair 880.  I=92ll call it a fluted cone, but = you=92ll have=20 to google it to get the full picture.

Bryan

 

From:=20 Rotary motors in aircraft = [mailto:flyrotary@lancaironline.net] On=20 Behalf Of Dwayne Parkinson
Sent: Monday, November 16, 2009 = 4:24=20 PM
To: = Rotary motors in aircraft
Subject: [FlyRotary] Re: = Phononic bandgap=20 muffler

 

Speaking mufflers, has = anyone=20 played with a cone shaped "tail pipe?"  NASA/NACA has a paper on = the=20 Schneebeli system which uses a silencer of some sort with a conical = exhaust=20 pipe.  I think the theory is the cone acts as a second muffler = because=20 the exiting sound waves bounce at angles off the cone walls rather = than=20 heading straight out of the pipe into your ear drums.  The trick = would be=20 to level out the exhaust pulses so the pressure of the exhaust gas as = it=20 enters the tail pipe is relatively constant.  With relatively = constant=20 pressure, Bernoulli's principle can apply to the escaping exhaust.=20  Rather than creating back pressure, the cone shaped tail pipe = will cause=20 the exhaust gases to accelerate out the pipe but remain at the same = pressure=20 as when entering the pipe.  Who knows, that may even create extra = thrust!

 

 

 

From: MONTY=20 ROBERTS <montyr2157@windstream.net>
To: Rotary=20 motors in aircraft=20 <flyrotary@lancaironline.net>
Sent: Mon, November 16, 2009 = 9:42:19=20 AM
Subject: = [FlyRotary] Re:=20 Phononic bandgap muffler


I'll have to do = some=20 digging for my notes and such. That was a couple computers ago. As I = recall,=20 the problem was the high frequency content of the rotary exhaust. This = is=20 present in all ported engines. Think dirt bike: = didinnnnggggdinnngggdinnnnnng.=20 The muffler I made was according to some NACA papers on silencer = design. It=20 was effective at muting the problem frequencies. Unfortunately the = muffler=20 casing did "ring" at the fundamental frequency the engine hit at about = 6000-6500 rpm. I don't think the thing would have lasted very long = ringing=20 like that. It would have fatigued and disintegrated in short order. = The=20 resonator can work, but the casing will have to be designed not to = ring=20 anywhere in the operating range. The tests were promising, I honestly = haven't=20 had a chance to set down and look at modifying the muffler to = eliminate that=20 problem. The base frequency of the rotary in cruise is comparable to a = Merlin=20 or a V-8 in their respective operating ranges (IIRC 200 Hz or so). I = don't=20 think that it is necessary to muffle the low frequencies. It would = require a=20 large heavy muffler to do so anyway.  It is just the 1500-2000 = kHZ that=20 grates on everybody (chainsaw). The higher stuff is as Charlie said, = harmonics=20 of the 1500-2000 kHZ noise. You can't kill the higher frequencies = effectively=20 without an absorption type silencer. We all know how long they last = behind the=20 rotary.....

So concentrate on the 1500-2000 kHZ range. It is = possible=20 to make a resonance/band  type filter in this range, and taking = care of=20 the fundamental Freq. should take care of the higher harmonics also. = The=20 problem is mostly making something that will stand the thermal and = mechanical=20 abuse.

Of course a simple expansion chamber with a restriction = on the=20 exhaust will make it ultra quiet. You will pay a power = penalty.

Dennis=20 has a combination of things working in his favor. One is the Renesis' = cooler=20 exhaust, the very heavily engineered stock manifold, a 90 degree turn = to kill=20 a lot of the high frequency stuff, and an absorption type muffler to = clean up=20 the rest.

I'll do some digging and see what is on my old=20 computer.


Monty
>>
>
> Hi = Earnest,
>=20
> 10-15dB is a very respectable reduction. A 10 dB change is a = 10X=20 power
> change and a perceived doubling or halving in volume to = the=20 human ear
> (dB's are a logarithmic power measurement).
> =
>=20 However, I doubt that working on the 8k-12k range is going to have=20 much
> effect on the perceived noise from a rotary, for a couple = of=20 reasons. I
> can't find the emails & info from Monty = Roberts'=20 testing a few years
> ago, but IIRC, the problem areas are much = lower in=20 frequency. Look at
> the ~1k-2khz area & the ~3.5k-4khz = areas. Those=20 areas are much stronger,
> and they are in the 'zone' where = human=20 hearing is most sensitive. When
> Monty did his testing, the = stuff above=20 4khz was harmonics radiating off
> the muffler itself (the = muffler=20 'rings' like a bell). The muffler wasn't
> enclosed in a=20 cowling.
>
> So here's what I think. The 8khz & above = stuff=20 is barely audible to
> people over 40, or who have rock concerts = in=20 their history, or fly
> airplanes for any length of time. = Additionally,=20 stuff in that frequency
> range hates to turn corners and is = easily=20 absorbed by relatively low
> mass materials. When you take those = two=20 factors into consideration
> together, something as simple as = enclosing=20 the muffler in a housing that
> won't sustain a resonance (think = fiberglass cowling) will kill just
> about all of it. The stuff = under=20 4khz, though, is a bit harder to deal
> with, and that spot down = below=20 2khz is really tough. As I mentioned
> earlier, those are much = more=20 likely to sound offensive, too.
>
> If you can suppress = the=20 1k-2khz range, the higher freqs will likely take
> care of = themselves=20 because they are harmonics of the lower freq stuff.
>
> = Remember=20 the discussion about Paul Conner's engine with the stock
> = exhaust=20 manifold? The cast iron was massive enough to absorb all those
> = higher=20 order harmonics and the FG cowl finished the work, even with = the
>=20 exhaust being dumped out the cowl with just a little 8-10" stub pipe=20 off
> the manifold. It wasn't 'quiet', but it was very pleasing = to=20 listen to,
> like a small block V-8. Of course, the downside for = a=20 non-renesis 13B is
> the loss of power because you don't get a = tuning=20 boost from a header.
> The only other pleasant-sounding rotary = plane=20 that I've personally
> listened to (other than turbo'd engines) = is=20 Dennis Haverlah's Renesis,
> and it uses the stock Renesis = exhaust=20 manifold. If you look at the way
> it's constructed, it's made = of 3=20 layers of material, apparently for
> noise suppression and heat=20 shielding in one package.
>
> If Monty reads this, maybe = he can=20 repost his test results & expand on or
> correct what I've = written=20 here.
>
> It might be helpful to load a tone generator = program=20 & listen to various
> frequencies to get an idea of what = each=20 frequency sounds like. If you
> use Audacity or a similar sound = editing=20 program, it has a tone generator
> built in.
>
>=20 Charlie
>
> --
> Homepage:  http://www.flyrotary.com/
> Archive and = UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.htm= l


--------------------------------------------------------= ------------------------



No=20 virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.425 /=20 Virus Database: 270.14.67/2505 - Release Date: 11/15/09=20 19:50:00


--
Homepage:  http://www.flyrotary.com/
Archive and = UnSub:  http://mail.lancaironline.net:81/lists/flyrotary/List.htm= l

 

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