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 5.2.14) with ESMTP id 3646266 for flyrotary@lancaironline.net; Mon, 18 May 2009 18:32:21 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from mail.aanet.com.au (mail.aanet.com.au [203.24.100.34]) by poplet2.per.eftel.com (Postfix) with ESMTP id 0ED051737BF for ; Tue, 19 May 2009 06:31:01 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by mail.aanet.com.au (Postfix) with SMTP id 947E3149C5E2 for ; Tue, 19 May 2009 06:29:59 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: 20b Exhaust Date: Tue, 19 May 2009 08:29:51 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001F_01C9D85B.FAE25410" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 0617-3, 04/28/2006), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_001F_01C9D85B.FAE25410 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Mark, Sorry, I lose track of who has what, is that a 13B or a 20B. If 2" on a = 20B has proven to be fine, then that's the real world proof we need and = indicates that the sound waves are sufficiently staged and the size is = enabling free flow of the exhaust gases. 2" is even good for flowing a = 13B, as I would have suggested 2.5". At what RPM have you flown with this set-up and what size ( volume) is = your muffler. George( down under) My latest exhaust system uses a DNA muffler which has a 3" inlet and = 3" outlet. When I first ran it, I was disappointed at how unacceptably = loud it was. Then I remembered Tracy's statement about most guys using = too large of an exit. So, I reduced the outlet to 2". Sure enough, it = reduced the noise level significantly and there was no detectable loss = of power. I'm still running it with the 2" exit. =20 Mark S.=20 On Mon, May 18, 2009 at 10:14 AM, 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.=20 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.=20 Tracy On Mon, May 18, 2009 at 2:40 AM, George Lendich = wrote: Tracy,=20 The reason I ask is that I like to keep the muffler outlet the = same area size or a little bigger than the exhaust outlet in the rotor = housing which is usually about 2" dia. I do understand the 2 and 3 rotors are staged and the exhaust and = the exhaust (shock) waves are in sequence, but I like to keep the volume = of the muffler and muffler exit to the total of the rotor exits i.e. 3x = Pi.r squared (3x Pi 1 x 1) =3D 9.2 sq" or Radius of 1.71" =3D Dia of = 3.42". I thought 2.25 may have a little too much back pressure, as the = rotary doesn't like back pressure. Probably to do this exercise properly would be to calculate the = volume of the heated and expanded exhaust gases and calculate the timing = of the pulses to see how a particular sized muffler and exit size coped = with the speed and volume of flow. It would be an interesting exercise. George (down under) Too soon to say really. I have not even had time to assemble = the builders log to get ready for the DAR. Lack of engine power is = definitely not what is keeping this thing grounded though : ) Tracy On Sun, May 17, 2009 at 6:01 PM, George Lendich = wrote: Tracy,=20 Any significant back pressure to speak of? George (down under) ----- Original Message -----=20 From: Tracy Crook=20 To: Rotary motors in aircraft=20 Sent: Monday, May 18, 2009 12:11 AM Subject: [FlyRotary] Re: 20b Exhaust In general, the bigger the exit pipe, the louder the exhaust = will be. I used 2.25" which I think is about the minimum for a 20B. Tracy On Sat, May 16, 2009 at 9:28 AM, = wrote: I have fabricated my exhaust manifold/tangential muffler = for my 20b. All I have left is to fit and weld the exhaust pipe. I = would like opinions on the size the exhaust pipe should be. This is in = a pusher application (Velocity) with a relatively short run from the = muffler to the exit point. Similar installation to Al G. Thanks, Joe -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html ------=_NextPart_000_001F_01C9D85B.FAE25410 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Mark,
Sorry, I lose track of who has what, is = that a 13B=20 or a 20B. If 2" on a 20B has proven to be fine, then that's the real = world proof=20 we need and indicates that the sound waves are sufficiently = staged and=20 the size is enabling free flow  of the exhaust gases. 2" is even = good for=20 flowing a 13B, as I would have suggested 2.5".
At what RPM have you flown with this = set-up and=20 what size ( volume) is your muffler.
George( down under)
My latest exhaust system uses a DNA muffler which has a 3" = inlet and=20 3" outlet.  When I first ran it, I was disappointed at how = unacceptably=20 loud it was.  Then I remembered Tracy's statement about most=20 guys using too large of an exit.  So, I reduced = the outlet=20 to 2".  Sure enough, it reduced the noise level significantly and = there=20 was no detectable loss of power.  I'm still = running it=20 with the 2" exit. 
 
Mark S. 

On Mon, May 18, 2009 at 10:14 AM, Tracy Crook = <tracy@rotaryaviation.com>= =20 wrote:
Your=20 mathematics are sound George and using that approach will certainly = keep=20 back pressure to a minimum. But I think it is doomed to be = noisy. =20 That's just my understanding about how mufflers generally work and I = could=20 be wrong.
 During a test of mufflers at a rotary fly-in = some years=20 back I was amazed at how effective the muffler became and how small = the=20 power loss was when we installed a 1" diameter muffler outlet pipe = on the=20 test stand engine  (13B).  1" is admittedly too small but = we learn=20 by going to extremes sometimes.

Tracy

On Mon, May 18, 2009 at 2:40 AM, George = Lendich <lendich@aanet.com.au> wrote:
 Tracy,
The reason I ask is that I like = to keep the=20 muffler outlet the same area size or a little bigger than the = exhaust=20 outlet in the rotor housing which is usually about 2" = dia.
 
I do understand the 2 and 3 = rotors are staged=20 and the exhaust and the exhaust (shock) waves are in = sequence,=20 but I like to keep the volume of the muffler and muffler exit to = the total=20 of the rotor exits i.e. 3x Pi.r squared (3x Pi 1 x 1) =3D 9.2 sq" = or Radius=20 of 1.71" =3D Dia of 3.42".
 
I thought 2.25 may have a little = too much=20 back pressure, as the rotary doesn't like back = pressure.
 
Probably to do this exercise = properly would=20 be to calculate the volume of the heated and expanded exhaust = gases and=20 calculate the timing of the pulses to see how a particular sized = muffler=20 and exit size coped with the speed and volume of flow. It would be = an=20 interesting exercise.
George (down under)
Too=20 soon to say really.  I have not even had time to assemble = the=20 builders log to get ready for the DAR. Lack of engine power is=20 definitely not what is keeping this thing grounded though :=20 )

Tracy

On Sun, May 17, 2009 at 6:01 PM, George = Lendich=20 <lendich@aanet.com.au> wrote:
Tracy,
Any significant back pressure = to speak=20 of?
George (down = under)
-----=20 Original Message -----
From:=20 Tracy Crook=20
To:=20 Rotary=20 motors in aircraft
Sent:=20 Monday, May 18, 2009 12:11 AM
Subject:=20 [FlyRotary] Re: 20b Exhaust

In general, the bigger the exit pipe, the = louder the=20 exhaust will be.  I used 2.25" which I think is about = the=20 minimum for a 20B.

Tracy

On Sat, May 16, 2009 at 9:28 AM, = <jewen@comporium.net> = wrote:
I=20 have fabricated my exhaust manifold/tangential muffler for = my 20b.=20  All I have left is to fit and weld the exhaust pipe. =  I=20 would like opinions on the size the exhaust pipe should = be.=20  This is in a pusher application (Velocity) with a = relatively=20 short run from the muffler to the exit point. =  Similar=20 installation to Al G.

Thanks,
Joe


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