Mailing List flyrotary@lancaironline.net Message #65533
From: Neil Unger 12348ung@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: mufflers
Date: Wed, 22 Jan 2020 07:59:50 +1100
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

Mat,

                  Here again I am just the messenger.  The guru is Kevin Davis from Active Exhaust Systems  (AES). (woolongong Aust)  Yes 28% is the magic number as is the size (dia) of the holes at just over 1/8"(critical apparently).  Packing is Innox  wool which is fine S/S.  Too much and too little, both affect the result. Kev, claims that he weighs the muffler when packing to get the right amount,  says that although not packed precisely even from end to end, it will even out as it works.

The big can has the perforated tube running end to end which is hollow (perforated tube) and the outer can is packed with Innox between the inner perforated tube and the solid outer tube.  The muffler shown, began life as a straight through muffler which was mounted under the RV.  Chris then as usual adapted the muffler by cutting 3 x inlet holes right into the hollow center tube, then welded it to the manifold plate.  The 3 inlets fire directly onto the opposite side of the center tube.  I tried to see what that has done to the "wool"opposite, and it appears to have blasted some away. Hard to tell looking through 1/8" holes, Only way to find out is to disassemble it.  Then to get the noise out, he again simply cut another hole halfway between the back 2 exhaust inlets and welded a 2.5" outlet.  Has done many successful hours Chris says.  Chris cut off the 3" inlet and outlet tube and welded a plate over both ends to seal the whole muffler.  It fitted in the small space available and worked which is what matters

Kev. seems happy with a 2.5" exhaust tube, so is up to you if you chase 2.75".  Here again I have no idea, and I suspect most others have little idea as well.  really a dyno is the only evidence.  Watched many Utube videos of blokes putting different mufflers on their cars to get a lovely "quiet" exhaust.  All terribly successful according to the operators, but IMHO the results ranged from little difference to actually louder.  Perception and fact can be totally different.,  AS they say if your baby cries it is music, if it is someone elses you want to kill it!

Neil.


On 1/22/2020 7:03 AM, Matt Boiteau mattboiteau@gmail.com wrote:
Only 28%. Geesh, I just drilled mine and did about 200%, I guess that is way to much. I guessed the drill area to be double the size of the pipe. Did make design so I can drill out one cap and switch out the inner pipe full of holes to test different back pressure. Neil, can you confirm 28%?  

Is the big can stuffed full of wool, so the primary tubes fire right into it? How does it exit out that bottom pipe?

In RX8, they (car forum) say 2.75" is the best (but hard to find) exhaust size. But since we are taking large harsh pulses and bring them down to a small constant flow, they say you can run smaller size. I did my downpipe as 2.75" and will do the long exhaust underneath plane in 2.5"



- Matt Boiteau

On 2020-01-20 8:24:41 PM, Neil Unger 12348ung@gmail.com <flyrotary@lancaironline.net> wrote:

Second time with 1 photo each to get past the editor!!

Photo of modified straight through muffler to attach directly to the RX8
engine.  The science apparently is to have approx 1/8" holes that amount
to 28% of the area of the through pipe.  This one is 3 inch but the
Manufacturer claims that  2.5" is better. Dia is 5 " and the space
between is packed with fine S/S "wool". THis is the first bloke that can
tell me the science in mufflers as he has made them all his working life.

JUst passing this on as I am totally ignorant as usual.  Still trying to
mount my turbo if I live long enough.

More photos to follw for those interested.  Neil

--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
Subscribe (FEED) Subscribe (DIGEST) Subscribe (INDEX) Unsubscribe Mail to Listmaster