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Okay so after 2 full days of having our welder out, finally brought the CAD design to life. Except both days were all nighters, so I was too tired and busy to take 'in progerss' pictures. Was tricky to build, which made the hourly welding cost sky high, more then the engine itself. Hopefully that means I can save money in the future on hearing aids.Thanks Charlie for the tip on the spectrum analyzer. I didn't get any before numbers, but it's all low Hz now. That harsh high pitch is gone. Db's are still there, but I'd say with just the muffler design, it's comparable to typical lycoming. I can start to hear the prop noise over the engine noise. I measured back pressure around 3.5psi @ 2200rpm prop.
I ran out of time to flight test the long pipe under the airplane. I quickly held it up with my hands and the exhaust pretty much disappeared with the prop taking over the noise. Before flying, I want to add backpressure gauge to that part and drill holes to find a balance between backpressure and noise.
SO the "header" muffler should make quite like any other plane, and the "under belly" pipe will make you standout in silence.
- Matt Boiteau
On 2020-01-18 5:29:51 PM, Matt Boiteau <mattboiteau@gmail.com> wrote:
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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