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Just for point-of-reference, have any
of you guys used your dB meters around Lyc & Cont powered a/c?
Checking an RVx or EZ with similar HP at roughly the same
positions relative to the exhaust should give you some perspective
on relative sound energy vs the rotary. If there's one available,
also check a Cessna 180 on takeoff, also at the same distance from
the plane as from the homebuilts on takeoff.
Now if you want to know why the rotary *seems* so loud, download a
realtime spectrum analyzer on your phone. You'll need to take
those measurements at some distance away from the plane(s) to get
realistic readings (the phone can't handle 100+ dB levels very
well at all), but I'll bet you see some significant differences
between the spectrum of a rotary and the RV/EZ group, and some at
least passing similarity between the rotary and a C180, if the 180
driver is using full throttle & rpm during the takeoff run.
Similar situation for a T6 (Harvard) doing a high speed pass at
full rpm.
Charlie
On 1/19/2020 2:51 PM, Neil Unger 12348ung@gmail.com wrote:
Mat,
Picked up the muffler that Chris uses and I am
amazed that it works. Chris seems to have a gift of falling on
his feet. It is very simple and he claims it is very quiet, but
with a slight power loss. Will photograph it, but is based on
an ATC OZ muffler. Checked my DB readings last week, and only
got as far as 3000 RPM which is the quiet range! 2000 RPM 85
DB 2500 RPM 95 DB, 3000 rpm 100 DB and outside the cab 110
DB. NO wonder at full noise it gets annoying. Obviously my
system is useless for noise reduction, with certainly no back
pressure at all. I am guessing that to have noise reduction I
will have to wear some restriction which is power loss. Same
story -- just what compromise can I live with?
Will attempt to describe the muffler once I have measured it on
the bench. MY thanks to Chris for loaning this to me.
Neil.
Have started on the exhaust.
Made all three primaries 2" double slip joints (that alone
took almost a whole day with welder). The big can (CA - Centrifugal Accumulator) rolled into
a 5" can and we'll secure it to the engine with straps.
The inside pipe is 2.75"
which has an area of 5.94sq". I'm not sure if there's a
magic number, but all the holes I drilled equaled to just
under double the area (11sq"). Most are 3/8, but I did add
some 1/2 to get the total area up. Could we get away with drilling
less holes? Not sure. I'll be able to drill out one side end
of the CA and pull out the inner tube and change out. Will experiment later with less holes and
monitor back pressure. Will weld a npt bung on the CA and
use the wideband bung to measure the different.
The previous exhaust with
just an Aero Turbine
2525XL, measured ~113dBA. With nothing, was closer to
120dBA. Funny around 2000 prop rpm was louder then at 2300
full static.
- Matt Boiteau
On 2020-01-07
12:19:23 AM, Matt Boiteau mattboiteau@gmail.com <flyrotary@lancaironline.net>
wrote:
Okay I'll make all 3 primary tubes (2" diameter)
all double slip fit. Welding batwing tabs
(picture below) on to either side on the slips, will
hold the muffler to the header but allow expansion.
Having
troubles finding 2.75" bends in 321, so I might have
to just switch to 3" downpipe that is more common.
Vband clamp before downpipe for easier removal and
under the plane to allow adding additional exhaust
setups (long pipe with holes drilled in it,
fishmouth tailpipe, etc)
Batwing tabs
- Matt Boiteau
On
2020-01-03 4:22:18 PM, Neil Unger 12348ung@gmail.com <flyrotary@lancaironline.net>
wrote:
Mat,
As usual I have no idea. I
made all 3 slip joints and to date no grief in
that area. I am coming around to the stock
manifold in some way. Yes it is heavy, but
appears to muffle the noise as well. Know of 2
installations that use the stock manifold with a
simple muffler after and both claim "acceptable"
noise. It appears that the stock manifold has a
big influence on noise?? Would prefer a DB
reading, but if not available it is what it is.
All is compromise, weight, cost, time, but at the
end of the day it has to work.
Still working on the turbo even though the world
is on holidays. All to save my hearing. So far
the rotary is definitely "unique" as far as a
turbo is concerned. The heat generated exceeds
all else. Two things to date -- special exhaust
wheel and water cooled bearing body =, all for
heat. Have modified the stock front plate on the
renesis to take an electric water pump. That is
the simple bit.
Neil.
okay I
found a good company called SPD Exhaust. They
have everything you need in 321ss.
With the engine being an RX8, we have three
exhaust ports. Should I weld the front and back
solid to the muffler, and make the middle one a
slip fit for expansion? Or vice-vesa?
- Matt Boiteau
On
2019-12-28 11:03:42 AM, Finn Lassen finn.lassen@verizon.net
<flyrotary@lancaironline.net>
wrote:
I did something
similar with my RV-3 13B decades ago. It
split open at the welds around one of the
pipes from the manifold into the the big
outer tube. True, it did use individual
manifold base plates, not the connected
factory manifold and the big tube was only
0.035.
Still, I would recommend slip joints on
two of the three pipes, like I added on
one of the pipes (cut through and a
surrounding bigger pipe -- missing in
picture).
Can't remember why I went from the above
to individual runners into a perforated
pipe under the fuselage. Probably got
lured by promise of increased power by
tuned lengths and still uncomfortable by
the muffler being inside the cowling.
Finn
On 12/28/2019 12:10 AM, Matt Boiteau mattboiteau@gmail.com
wrote:
This is what I'm
going to try in a few weeks.
" Exhaust valve opens and a pulse
of hot gas puffs out through a short
pipe, then tangentially into a cylindrical canister.
Being tangential, the pulse flattens
out and travels helically (rather than bouncing and
reverberating around) along the inside
curved wall of the can, spiraling
toward the exit, where it comes out
more uniform in flow and so pretty
quiet."
Outer pipe = 321 ss 0.050 thick.
Flat plate bent to a 5" tube
Inner pipe = 321 ss 0.036 thick.
2.5" diameter
(I might use
302ss 0.065 since I already have it)
From my understanding, the area
of the holes should be double the
area of the inner pipe.
- Matt Boiteau
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