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 3645646 for flyrotary@lancaironline.net; Mon, 18 May 2009 11:15:20 -0400 Received-SPF: pass receiver=logan.com; client-ip=74.125.92.24; envelope-from=rwstracy@gmail.com Received: by qw-out-2122.google.com with SMTP id 8so2152961qwh.25 for ; Mon, 18 May 2009 08:14:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to :content-type; bh=M0aBJT3RLUrkDLCwt6YZ/1c94+RVlGsW9/NhlQe7W7c=; b=FRTAN/HVWCro5LH1PX6ayDglh4PCpUVvgcbtaQCmEZs+GlmygWOzP/cnMqL0E8f07R EV2gQhsQAi7cK06YALANJOjyuRVaBasnAxP/ShRU+XTxIQDlUs5Au0ycwdWuEucYrI6D Nnr9u4B4m5Ln3wnJRsOt2om/L/UY8czxnjjPQ= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type; b=g+xHYwN+20HuLNLil2hDClQmAiWimGRUWZIznVYgZpKXrbAex5akXHMniL42/3ndwx MiTIZksS1+UA8sLYwFFRi4FuiWi8RHR9tVtuaDaRO8nOXykf4o2fuIAFQb5IoroZDlZc ArZbPkGvF6AWNENE1Aoy0s78ZM+pbina7ORQ0= MIME-Version: 1.0 Sender: rwstracy@gmail.com Received: by 10.224.11.77 with SMTP id s13mr6399539qas.244.1242659685926; Mon, 18 May 2009 08:14:45 -0700 (PDT) In-Reply-To: References: Date: Mon, 18 May 2009 11:14:45 -0400 X-Google-Sender-Auth: c4ed69993e642c68 Message-ID: <1b4b137c0905180814w278cb92y6e791ec91ab3f384@mail.gmail.com> Subject: Re: [FlyRotary] Re: 20b Exhaust From: Tracy Crook To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=0015175cd62a2811cf046a314118 --0015175cd62a2811cf046a314118 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit 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 On Mon, May 18, 2009 at 2:40 AM, George Lendich wrote: > Tracy, > 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) = 9.2 sq" or Radius of 1.71" = 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, >> Any significant back pressure to speak of? >> George (down under) >> >> ----- Original Message ----- >> *From:* Tracy Crook >> *To:* Rotary motors in aircraft >> *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 >>> >> >> > --0015175cd62a2811cf046a314118 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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.=A0 Tha= 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).=A0 1" is admittedly too small but we learn by going to ex= tremes sometimes.

Tracy

On Mon, May 18, 2009 at 2:40 AM= , George Lendich <lendich@aanet.com.au> wrote:
=A0Tracy,
The reason I ask is that I like to kee= p the muffler=20 outlet the same area size or a little bigger than the exhaust outlet in the= =20 rotor housing which is usually about 2" dia.
=A0
I do understand the 2 and 3 rotors are= staged and=20 the exhaust and the exhaust (shock)=A0waves are=A0in sequence, but I like= =20 to keep the volume of the muffler and muffler exit to the total of the roto= r=20 exits i.e. 3x Pi.r squared (3x Pi 1 x 1) =3D 9.2 sq" or Radius of 1.71= " =3D Dia of=20 3.42".
=A0
I thought 2.25 may have a little too m= uch back=20 pressure, as the rotary doesn't like back pressure.
=A0
Probably to do this exercise properly = would be to=20 calculate the volume of the heated and expanded exhaust gases and calculate= the=20 timing of the pulses to see how a particular sized muffler and exit size co= ped=20 with the speed and volume of flow. It would be an interesting=20 exercise.
George (down under)
Too=20 soon to say really.=A0 I have not even had time to assemble the builders= =20 log to get ready for the DAR. Lack of engine power is definitely not what= is=20 keeping this thing grounded though : )

Tracy

On Sun, May 17, 2009 at 6:01 PM, George Lendic= h <lendich@aanet.com.au>=20 wrote:
Tracy,
Any significant back pressure to s= peak=20 of?
George (down under)
-----=20 Original Message -----
From:=20 Tracy Crook
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.=A0 I used 2.25" which I think is about the mini= mum for=20 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 =A0All I have left is to fit and weld the exhaust pipe. =A0I would= =20 like opinions on the size the exhaust pipe should be. =A0This is in= a=20 pusher application (Velocity) with a relatively short run from the= =20 muffler to the exit point. =A0Similar installation to Al=20 G.

Thanks,
Joe


--
H= omepage:=20 =A0http://w= ww.flyrotary.com/
Archive and UnSub: =A0=20 http://mail.lancaironline.net:81/lists/flyrotary/List= .html



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