Mailing List flyrotary@lancaironline.net Message #65510
From: Neil Unger 12348ung@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Mufflers
Date: Mon, 20 Jan 2020 07:51:16 +1100
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

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.

            

On 1/19/2020 9:29 AM, 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)

I found a company that makes flex bellows in 321. I'm just not sure if I should have it vertical on the downpipe or close to the muffler horizontal before the first 90degree bend downwards.
https://www.aceraceparts.com/products/3-000-flex-bellow-assembly-321-stainless?variant=11067135556


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.

On 1/4/2020 5:37 AM, Matt Boiteau mattboiteau@gmail.com wrote:
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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