From: "Neil Unger 12348ung@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Mufflers
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
References: <list-13191362@logan.com>
Message-ID: <6d6721c6-173c-2583-45b4-cb36b6b1f07f@gmail.com>
Date: Tue, 19 Nov 2019 12:25:28 +1100
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Andrew,

                    all very interesting,  What noise do you get back in 
the cab?  bearable, loud or great?  Neil.

On 11/19/2019 11:31 AM, Andrew Martin andrew@martinag.com.au wrote:
> Neil, I stumbled on a system that seems to work quite well. In my head 
> I think it works similar to an ANR headset where the noise is not 
> muffled as such but reflected to cancel it out.
> Important bit is exhaust enters & exits at same end. In my case I used 
> a 65mm ss pipe inside a 100mm pipe about 150mm long, but longer would 
> be better again as outlet on outer pipe does see some holes on inner 
> pipe so noise has direct escape path. 65 mm pipe has 10mm holes with 
> about twice area of pipe to try to minimize back pressure.
> Theory is that exhaust pulses are broken into smaller bits as they see 
> holes in inner pipe, but then hit the blanked off end and are 
> reflected just like in ANR. Not sure if this is correct or not, but it 
> seems to work in use quite well.
> My exhaust system is quite short as tailpipe exits just behind prop 
> similar to PT6 turboprop. I made exit pipe from 65mm also but think 
> smaller may be better as I think the exhaust gas flows much better 
> after the pulses are broken up.
> Andrew
>
> On Tue, 19 Nov 2019 at 5:20 am, Neil Unger 12348ung@gmail.com 
> <mailto:12348ung@gmail.com> <flyrotary@lancaironline.net 
> <mailto:flyrotary@lancaironline.net>> wrote:
>
>     Attn Todd Bartrim,
>
>                                            When in doubt check the
>     instruction book!!  I finally checked the archives to find that
>     Todd you
>     are way in front of me.  I am definitely going to put a turbo on my
>     renesis, but am still looking for a muffler. Depending on what Lynn
>     suggestes, but your experience with the spintech or your latest
>     version
>     is appreciated.  Do you have any tests with a decibel meter?  My
>     exhaust
>     noise is just too loud, fine for me but passengers do not exactly
>     que up
>     for another ride.
>
>     So design starts all over again, but I do have another engine to play
>     with to keep mine in the air while I experiment.    Here again
>     Todd you
>     have the electric water pump --- thoughts?
>
>     Neil.
>
>
>     --
>     Homepage: http://www.flyrotary.com/
>     Archive and UnSub:
>     http://mail.lancaironline.net:81/lists/flyrotary/List.html
>
> -- 
> Regards Andrew Martin Martin Ag

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    <p>Andrew,</p>
    <p>                   all very interesting,  What noise do you get
      back in the cab?  bearable, loud or great?  Neil.<br>
    </p>
    <div class="moz-cite-prefix">On 11/19/2019 11:31 AM, Andrew Martin
      <a class="moz-txt-link-abbreviated" href="mailto:andrew@martinag.com.au">andrew@martinag.com.au</a> wrote:<br>
    </div>
    <blockquote type="cite" cite="mid:list-13191362@logan.com">
      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
      <div>
        <div>
          <div dir="auto">Neil, I stumbled on a system that seems to
            work quite well. In my head I think it works similar to an
            ANR headset where the noise is not muffled as such but
            reflected to cancel it out.</div>
        </div>
        <div dir="auto">Important bit is exhaust enters &amp; exits at
          same end. In my case I used a 65mm ss pipe inside a 100mm pipe
          about 150mm long, but longer would be better again as outlet
          on outer pipe does see some holes on inner pipe so noise has
          direct escape path. 65 mm pipe has 10mm holes with about twice
          area of pipe to try to minimize back pressure.</div>
      </div>
      <div dir="auto">Theory is that exhaust pulses are broken into
        smaller bits as they see holes in inner pipe, but then hit the
        blanked off end and are reflected just like in ANR. Not sure if
        this is correct or not, but it seems to work in use quite well.</div>
      <div dir="auto">My exhaust system is quite short as tailpipe exits
        just behind prop similar to PT6 turboprop. I made exit pipe from
        65mm also but think smaller may be better as I think the exhaust
        gas flows much better after the pulses are broken up. </div>
      <div>
        <div dir="auto">Andrew</div>
        <div><br>
          <div class="gmail_quote">
            <div dir="ltr" class="gmail_attr">On Tue, 19 Nov 2019 at
              5:20 am, Neil Unger <a href="mailto:12348ung@gmail.com"
                target="_blank" moz-do-not-send="true">12348ung@gmail.com</a>
              &lt;<a href="mailto:flyrotary@lancaironline.net"
                target="_blank" moz-do-not-send="true">flyrotary@lancaironline.net</a>&gt;
              wrote:<br>
            </div>
            <blockquote class="gmail_quote" style="margin:0 0 0
              .8ex;border-left:1px #ccc solid;padding-left:1ex">Attn
              Todd Bartrim,<br>
              <br>
                                                     When in doubt check
              the <br>
              instruction book!!  I finally checked the archives to find
              that Todd you <br>
              are way in front of me.  I am definitely going to put a
              turbo on my <br>
              renesis, but am still looking for a muffler. Depending on
              what Lynn <br>
              suggestes, but your experience with the spintech or your
              latest version <br>
              is appreciated.  Do you have any tests with a decibel
              meter?  My exhaust <br>
              noise is just too loud, fine for me but passengers do not
              exactly que up <br>
              for another ride.<br>
              <br>
              So design starts all over again, but I do have another
              engine to play <br>
              with to keep mine in the air while I experiment.    Here
              again Todd you <br>
              have the electric water pump --- thoughts?<br>
              <br>
              Neil.<br>
              <br>
              <br>
              --<br>
              Homepage:  <a href="http://www.flyrotary.com/"
                rel="noreferrer" target="_blank" moz-do-not-send="true">http://www.flyrotary.com/</a><br>
              Archive and UnSub:   <a
                href="http://mail.lancaironline.net:81/lists/flyrotary/List.html"
                rel="noreferrer" target="_blank" moz-do-not-send="true">http://mail.lancaironline.net:81/lists/flyrotary/List.html</a><br>
            </blockquote>
          </div>
        </div>
      </div>
      -- <br>
      <div dir="ltr" class="gmail_signature"
        data-smartmail="gmail_signature">Regards
        Andrew Martin
        Martin Ag</div>
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