From: "Andrew Martin andrew@martinag.com.au" <flyrotary@lancaironline.net>
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Date: Tue, 19 Nov 2019 08:31:03 +0800
Message-ID: <CAJxaVD0NVuu_jn8fVQaCDYRQetEJJGowuF4_jC1oyXhXWNs_Xw@mail.gmail.com>
Subject: Re: [FlyRotary] Mufflers
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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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 <
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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<div><div><div dir=3D"auto">Neil, I stumbled on a system that seems to work=
 quite=C2=A0well. In my head I think it works similar to an ANR headset whe=
re the noise is not muffled as such but reflected to cancel it out.</div></=
div><div dir=3D"auto">Important bit is exhaust enters &amp; exits at same e=
nd. 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 hole=
s 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=3D"auto">Theory is that exhaust pulses are broken into smaller bit=
s 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 see=
ms to work in use quite well.</div><div dir=3D"auto">My exhaust system is q=
uite short as tailpipe exits just behind prop similar to PT6 turboprop. I m=
ade 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.=C2=A0</div><=
div><div dir=3D"auto">Andrew</div><div><br><div class=3D"gmail_quote"><div =
dir=3D"ltr" class=3D"gmail_attr">On Tue, 19 Nov 2019 at 5:20 am, Neil Unger=
 <a href=3D"mailto:12348ung@gmail.com" target=3D"_blank">12348ung@gmail.com=
</a> &lt;<a href=3D"mailto:flyrotary@lancaironline.net" target=3D"_blank">f=
lyrotary@lancaironline.net</a>&gt; wrote:<br></div><blockquote class=3D"gma=
il_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-lef=
t:1ex">Attn Todd Bartrim,<br>
<br>
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 When in doubt check the <br>
instruction book!!=C2=A0 I finally checked the archives to find that Todd y=
ou <br>
are way in front of me.=C2=A0 I am definitely going to put a turbo on my <b=
r>
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.=C2=A0 Do you have any tests with a decibel meter?=C2=A0 My =
exhaust <br>
noise is just too loud, fine for me but passengers do not exactly que up <b=
r>
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.=C2=A0=C2=A0=C2=A0 Here aga=
in Todd you <br>
have the electric water pump --- thoughts?<br>
<br>
Neil.<br>
<br>
<br>
--<br>
Homepage:=C2=A0 <a href=3D"http://www.flyrotary.com/" rel=3D"noreferrer" ta=
rget=3D"_blank">http://www.flyrotary.com/</a><br>
Archive and UnSub:=C2=A0 =C2=A0<a href=3D"http://mail.lancaironline.net:81/=
lists/flyrotary/List.html" rel=3D"noreferrer" target=3D"_blank">http://mail=
.lancaironline.net:81/lists/flyrotary/List.html</a><br>
</blockquote></div></div>
</div>-- <br><div dir=3D"ltr" class=3D"gmail_signature" data-smartmail=3D"g=
mail_signature">Regards
Andrew Martin
Martin Ag</div>

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