From: "Todd Bartrim bartrim@gmail.com" <flyrotary@lancaironline.net>
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Date: Thu, 21 Nov 2019 14:08:12 -0800
Message-ID: <CALYfWBtSJ74A9gFZa6DNP14bHPy08944Rmjz0QM6eOxsVw-nfQ@mail.gmail.com>
Subject: Re: [FlyRotary] Re: Mufflers
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Hi Neil and other Rotorheads;
  Sorry for the delayed reply, had a busy week with my kid in a hockey
tournaments, as well as my own beer league. I love this season.....
I was using an AeroTurbine 2525 several feet downstream of my modified
stock turbo until recently. It's a long story why and how, but I had this
muffler inside a housing to keep it out of the air stream for aerodynamics
and to keep it out of the cowl. Hard to describe and it was a half-baked
idea, that I would not do again, but it was successful in that I had no
visible muffler hanging below that aircraft and it was very quiet. I had
strived to have a quiet aircraft and was quite satisfied with this aspect
and many other pilots on the airport grounds had made very positive
comments about how quiet it was when I would taxi past and also on take-off
and climb out. I only ever had one cranky old guy say that it was loud, but
it was clearly a case of it being different and not like a conventional
aircraft noise, so to him it was obviously not good and must be loud. I
think we can dismiss this one complaint.
Unfortunately I've not got any proper decibel measurements from a proper
meter, but I did install a decibel meter app on my phone and took some
measurements from inside the cockpit during a full power run while tied
down just before I removed the muffler, for some before and after
comparisons.
   Why did I remove it? Well again it's back to that darn half-baked
muffler housing idea. The radiant heat from the muffler would radiate into
the cockpit alongside my leg and despite having the muffler ceramic coated
as well as firewall insulation on the housing it would get a little warm on
hot summer days. That and I decided that it was time for my aircraft to go
on a diet and start shedding some pounds, so I decided that it was time to
see how bad it was without a muffler as I had never run it before without a
muffler. Before the AeroTurbine I had a home made version of a SpinTech.
  Anyways the not-so-hard data that you're looking for.
With the muffler in place I saw a max of 83db, without it I saw a max of
89db. According to the app this is equivalent to an alarm clock?
Keep in mind that this from a cell phone app that I had just downloaded
moments before the test and had made no attempt to calibrate it so really
can only be used for before and after comparison.
So it was only a 6db increase in noise. It has always been possible to talk
easily with the pax without the use of headsets during cruise flight. So
with such a small increase in noise, I modified the exhaust pipe to come
straight out of the rear of the cowl and went for a flight. One of my old
cowboy buddies has a small ranch right under the departure end of one of
the runways, so I notified him I was going for a flight and to go outside
to take a listen and tell me how it sounds. I didn't tell him why, but he
knows that I've always wanted to make sure I was quiet. So afterwards I
stopped by for a beer and first thing he says is that it sounds quieter
now. WTF? Since he's not very technical, I'm thinking again that it's just
a different tone and he has interpreted it as being quieter.
   So I have a co-worker who lives under the downwind leg of the circuit
and he is much more technical minded (he converted his own truck to
electric about 10 years ago) so his opinion is probably more relevant.
However since he's below the downwind leg, it's at a point where I have
reduced power, so is already much quieter that when climbing over my other
friends place. Anyways this guy has previously reported to me that he feels
my plane is a little quieter than most, but mostly it is a different tone
that is easy to tune out as he finds it less obnoxious than many of the GA
planes that fly over. So I asked him a few weeks after I made the change if
he'd seen me flying over recently and how did it sound? He said he hadn't
noticed any difference, but wasn't paying attention to the sound anymore.
So while that's not very scientific, it tells me that any increase in sound
or change in tone hasn't been enough to make anyone take notice. So for all
that reason, I think I'm going to make this a permanent weight loss.
   So clearly the stock turbo does provide some muffling. Another thing to
note is that the thin wall 321SS pipe is about 30" long and has 5 elbows in
it as it weaves it's way out. I'm not sure that would have much effect, but
I imagine it's better than a straight pipe.
I see Dave has also responded and while I believe he has a stock turbine
housing, the turbine and compressor wheel are not stock at all, so I don't
know how much, but I suspect this would have some effect on sound.
  As far as the longevity of the AeroTurbine, It showed no signs of damage
at after about 25 hours of flight and probably another 15 hours of ground
running. That was before I sent it out to have it ceramic coated and I then
put about another 10 hours on it (ground and flight) before I removed it.
It shows no sign of damage or flaking of the ceramic coating. I'll probably
use it on an old Jeep that my kid and I are rebuilding for him when he
turns 16.
  Based on my experience, I would clearly chose to pack the useful weight
of a turbo, than that of a muffler. Although that comes with it's own
challenges as well.

Todd Bartrim


On Thu, Nov 21, 2019 at 10:34 AM Jeff Whaley jwhaley@datacast.com <
flyrotary@lancaironline.net> wrote:

> Not Tracy, but FWIW I have about 100 hrs on my 13B with an Aero Turbine
> 2525 muffler attached.  It is holding up well, is better than nothing but
> don't expect it to create a quiet exhaust; put it this way, I extended my
> exhaust pipe and Fish-tailed or whale-tailed if you like (with
> perforations) as it is compressed on the horizontal plane Vs the vertical
> to get further noise reduction.
> Jeff
>
>     IIRC, Tracy's been flying one on the 20B powered RV-8 for a number of
> years. That's what motivated me to purchase one, but it hasn't seen any
> exhaust gas yet.
>
>     Charlie
>
>
>   Charlie,,
>       Any idea how many hours Tracy has on his AeroTurbine
> 2525.............?
> --
> Kelly Troyer
> Dyke Delta_"Eventually"
> 13B_RD1C_EC2_EM2
>
> --
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>

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<div dir=3D"ltr">Hi Neil and other Rotorheads;<div>=C2=A0 Sorry for the del=
ayed reply, had a busy week with my kid in a hockey tournaments, as well as=
 my own beer league. I love this season.....</div><div>I was using an AeroT=
urbine 2525 several feet downstream of my modified stock turbo until recent=
ly. It&#39;s a long story why and how, but I had this muffler inside a hous=
ing to keep it out of the air stream for aerodynamics and to keep it out of=
 the cowl. Hard to describe and it was a half-baked idea, that I would not =
do again, but it was successful=C2=A0in that I had no visible muffler hangi=
ng below that aircraft and it was very quiet. I had strived to have a quiet=
 aircraft and was quite satisfied with this aspect and many other pilots on=
 the airport grounds had made very positive comments about how quiet it was=
 when I would taxi past and also on take-off and climb out. I only ever had=
 one cranky old guy say that it was loud, but it was clearly a case of it b=
eing different and not like a conventional aircraft noise, so to him it was=
 obviously=C2=A0not good and must be loud. I think we can dismiss this one =
complaint.=C2=A0</div><div>Unfortunately I&#39;ve not got any proper decibe=
l measurements from a proper meter, but I did install a decibel meter app o=
n my phone and took some measurements from inside the cockpit during a full=
 power run while tied down just before I removed the muffler, for some befo=
re and after comparisons.</div><div>=C2=A0 =C2=A0Why did I remove it? Well =
again it&#39;s back to that darn half-baked muffler housing idea. The radia=
nt heat from the muffler would radiate into the cockpit alongside my leg an=
d despite having the muffler ceramic coated as well as firewall insulation =
on the housing it would get a little warm on hot summer days. That and I de=
cided that it was time for my aircraft to go on a diet and start shedding s=
ome pounds, so I decided that it was time to see how bad it was without a m=
uffler as I had never run it before without a muffler. Before the AeroTurbi=
ne I had a home made version of a SpinTech.=C2=A0</div><div>=C2=A0 Anyways =
the not-so-hard data that you&#39;re looking for.=C2=A0</div><div>With the =
muffler in place I saw a max of 83db, without it I saw a max of 89db. Accor=
ding to the app this is equivalent to an alarm clock?</div><div>Keep in min=
d that this from a cell phone app that I had just downloaded moments before=
 the test and had made no attempt to calibrate it so really can only be use=
d for before and after comparison.<br></div><div>So it was only a 6db incre=
ase in noise. It has always been possible to talk easily with the pax witho=
ut the use of headsets during cruise flight. So with such a small increase =
in noise, I modified the exhaust pipe to come straight out of the rear of t=
he cowl and went for a flight. One of my old cowboy buddies has a small ran=
ch right under the departure end of one of the runways, so I notified him I=
 was going for a flight and to go outside to take a listen and tell me how =
it sounds. I didn&#39;t tell him why, but he knows that I&#39;ve always wan=
ted to make sure I was quiet. So afterwards I stopped by for a beer and fir=
st thing he says is that it sounds quieter now. WTF? Since he&#39;s not ver=
y technical, I&#39;m thinking again that it&#39;s just a different tone and=
 he has interpreted it as being quieter.</div><div>=C2=A0 =C2=A0So I have a=
 co-worker who lives under the downwind leg of the circuit and he is much m=
ore technical minded (he converted his own truck to electric about 10 years=
 ago) so his opinion is probably more relevant. However since he&#39;s belo=
w the downwind leg, it&#39;s at a point where I have reduced power, so is a=
lready much quieter that when climbing over my other friends place. Anyways=
 this guy has previously reported to me that he feels my plane is a little =
quieter than most, but mostly it is a different tone that is easy to tune o=
ut as he finds it less obnoxious than many of the GA planes that fly over. =
So I asked him a few weeks after I made the change if he&#39;d seen me flyi=
ng over recently and how did it sound? He said he hadn&#39;t noticed any di=
fference, but wasn&#39;t paying attention to the sound anymore. So while th=
at&#39;s not very scientific, it tells me that any increase in sound or cha=
nge in tone hasn&#39;t been enough to make anyone take notice. So for all t=
hat reason, I think I&#39;m going to make this a permanent weight loss.=C2=
=A0</div><div>=C2=A0 =C2=A0So clearly the stock turbo does provide some muf=
fling. Another thing to note is that the thin wall 321SS pipe is about 30&q=
uot; long and has 5 elbows in it as it weaves it&#39;s way out. I&#39;m not=
 sure that would have much effect, but I imagine it&#39;s better than a str=
aight pipe.=C2=A0</div><div>I see Dave has also responded and while I belie=
ve he has a stock turbine housing, the turbine and compressor wheel are not=
 stock at all, so I don&#39;t know how much, but I suspect this would have =
some effect on sound.</div><div>=C2=A0 As far as the longevity of the AeroT=
urbine, It showed no signs of damage at after about 25 hours of flight and =
probably another 15 hours of ground running. That was before I sent it out =
to have it ceramic coated and I then put about another 10 hours on it (grou=
nd and flight) before I removed it. It shows no sign of damage or flaking o=
f the ceramic coating. I&#39;ll probably use it on an old Jeep that my kid =
and I are rebuilding for him when he turns 16.</div><div>=C2=A0 Based on my=
 experience, I would clearly chose to pack the useful weight of a turbo, th=
an that of a muffler. Although that comes with it&#39;s own challenges as w=
ell.</div><div><br></div><div><div><div dir=3D"ltr" class=3D"gmail_signatur=
e" data-smartmail=3D"gmail_signature"><div dir=3D"ltr">Todd Bartrim</div></=
div></div><br></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" c=
lass=3D"gmail_attr">On Thu, Nov 21, 2019 at 10:34 AM Jeff Whaley <a href=3D=
"mailto:jwhaley@datacast.com">jwhaley@datacast.com</a> &lt;<a href=3D"mailt=
o:flyrotary@lancaironline.net">flyrotary@lancaironline.net</a>&gt; wrote:<b=
r></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex=
;border-left:1px solid rgb(204,204,204);padding-left:1ex">Not Tracy, but FW=
IW I have about 100 hrs on my 13B with an Aero Turbine 2525 muffler attache=
d.=C2=A0 It is holding up well, is better than nothing but don&#39;t expect=
 it to create a quiet exhaust; put it this way, I extended my exhaust pipe =
and Fish-tailed or whale-tailed if you like (with perforations) as it is co=
mpressed on the horizontal plane Vs the vertical to get further noise reduc=
tion.<br>
Jeff<br>
<br>
=C2=A0 =C2=A0 IIRC, Tracy&#39;s been flying one on the 20B powered RV-8 for=
 a number of years. That&#39;s what motivated me to purchase one, but it ha=
sn&#39;t seen any exhaust gas yet.<br>
<br>
=C2=A0 =C2=A0 Charlie<br>
<br>
<br>
=C2=A0 Charlie,,<br>
=C2=A0 =C2=A0 =C2=A0 Any idea how many hours Tracy has on his AeroTurbine 2=
525.............?<br>
-- <br>
Kelly Troyer<br>
Dyke Delta_&quot;Eventually&quot;<br>
13B_RD1C_EC2_EM2<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>

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