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That's very interesting. Thanks for the info.
From: Mark Steitle <msteitle@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, July 12, 2010 10:58:42 AM
Subject: [FlyRotary] Re: Mufflers
Dwayne,
I added a cone-shaped 3" to 2.5" reducer to the exit of my DNA muffler to try and quiet it down a bit. I think it was Tracy that recommended that. It did work to reduce the noise a little, but at the expense of HP. I left it on until I replaced the whole thing with a tangential muffler.
I looked up the "pre-silencer" muffler on the Mazdatrix web site. Their site is running real slow at the moment, and most pages didn't load at all. I was able to get to their exhaust system information page. It wasn't that much help as it is geared towards automotive applications.
Mark
On Mon, Jul 12, 2010 at 9:00 AM, Dwayne Parkinson <dwayneparkinson@yahoo.com> wrote:
Mark,
If' you're up for more experimenting, try a conical "tail pipe" on whatever muffler you have now. The sound waves will behave just as if you held a cone up to your ear. More sound will be coming out of a smaller hole but due to the shape of the cone I believe some of the sound will run into itself and cancel itself out forming a mildly effective second muffler. I haven't tested this so I don't know if this works. If you have a DB meter (which I don't) you can easily test the theory to see if it's worth your time though. Take a tube from the Christmas wrapping paper, cram a kitchen timer or anything else that makes a constant noise in one end and hold your DB meter just outside the other end and then measure the DB of the noise in a straight pipe. If you want to be really clever, record your rotary engine and replay that sound. Now cut sections out of the last 8 or 10" of the tube and form it into a cone.
See if there's a DB drop. Play around with different shapes of cones and see if it makes a difference.
When I mention this, most people immediately think BACK PRESSURE!!! If you're measuring back-pressure you should see no change. Bernoulli's principle should apply to the exhaust gas and it will merely speed up and exit faster just like it does with the leaf blower attachment on a Shop Vac. There are issues like boundary layers building up and the fact that the muffler pulses aren't a constant pressure, but I believe that shouldn't be an issue based on the fact that there's really no such thing as a true constant pressure and the rotary at any reasonably high RPM will produce a relatively constant flow of exhaust gas.
Good luck. Let me know if you try it and how it goes.
Thanks,
Dwayne
From: Mark Steitle <msteitle@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Fri, July 9, 2010 4:44:19 PM
Subject: [FlyRotary] Re: Mufflers
Steve,
Yes, that would be me, "Mr. Muffler" himself. The Moroso style muffler didn't muffle very well and it kept melting the bolt holding the baffle in place. I finally went with a SS bolt which didn't melt. In an effort to find something that wasn't as noisy, I discarded it for the DNA muffler which wasn't much quieter, but it survived the harsh rotary environment better than anything else I had tried up to that point. I'm now running an inconel 625 tangential muffler, which is the best as for noise attenuation I've used to date. The only problem is that I suspect I'm losing hp due to excess back pressure. But at leaast I can hear to talk on the radio. Its my opinion at this stage of the game that the best muffler is a turbo. At least you achieve a fairly quiet exhaust note, and get some extra hp too.
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