X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from smtp102.sbc.mail.ac4.yahoo.com ([76.13.13.241] verified) by logan.com (CommuniGate Pro SMTP 5.3c2) with SMTP id 3978512 for flyrotary@lancaironline.net; Mon, 16 Nov 2009 16:36:13 -0500 Received-SPF: none receiver=logan.com; client-ip=76.13.13.241; envelope-from=bryanwinberry@bellsouth.net Received: (qmail 93613 invoked from network); 16 Nov 2009 21:35:38 -0000 Received: from adsl-232-110-110.asm.bellsouth.net (bryanwinberry@74.232.110.110 with login) by smtp102.sbc.mail.ac4.yahoo.com with SMTP; 16 Nov 2009 13:35:37 -0800 PST X-Yahoo-SMTP: OSuEAS2swBAaBd4uKxevNivslbMG7JXpWjAWZVmoYyRm6qcW_W2VUA-- X-YMail-OSG: fym3RrsVM1mUgSbFcxAlkLBLcLHUh3zLv7x8lsVGpnDgpzm4b0pueqpo8yEfbt22e3GytpGWEQVkuwFBpJn_IRk_NZXsLarH86rdga82yF_plBUimy6WQUJ2M64dkpcCCiY8SzRbLq33UqXUGIKl.uqsFnQiahUrxcVJuIgWMF5oFSqLfnPreZYn_6iJkgWvnTCeZ8UvJWJKd8cedXElyUlmCRx9NPquBDZFRktgH7hojemten7Xbj6elFM4V39V8oasHbzcehi05wnveI.4i6PRbixf3Oxq_hwC_CoEkPVc4jXLn9ymD28vTJp4jigKaCcoHK7YG9c68faXUtUydZUraN2r1KqyjNodJGVJdw-- X-Yahoo-Newman-Property: ymail-3 From: "Bryan Winberry" To: "'Rotary motors in aircraft'" References: Subject: RE: [FlyRotary] Re: Phononic bandgap muffler Date: Mon, 16 Nov 2009 16:35:36 -0500 Message-ID: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0016_01CA66DA.D3613FB0" X-Mailer: Microsoft Office Outlook 11 In-Reply-To: Thread-Index: AcpnAyeTSFzNBVTfRRiBLJalVDu/PwAAVLUg X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_0016_01CA66DA.D3613FB0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 _____ 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 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! _____ 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 >> > > Hi Earnest, > > 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). > > 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. > > 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. > > 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. > > 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. > > If Monty reads this, maybe he can repost his test results & expand on or > correct what I've written here. > > 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. > > Charlie > > -- > 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 ------=_NextPart_000_0016_01CA66DA.D3613FB0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

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

 

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

 

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!

 

 

 

From: MONTY = ROBERTS <montyr2157@windstream.net>
To: Rotary motors in aircraft = <flyrotary@lancaironline.net>
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
>>
>
> Hi Earnest,
>
> 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).
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> If Monty reads this, maybe he can repost his test results & = expand on or
> correct what I've written here.
>
> 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.
>
> Charlie
>
> --
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.h= tml


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



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.h= tml

 

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