Tangential mufflers vs. tuned headers and flow-through

Discussion in 'Mazda Rotary' started by Peterson, Jul 6, 2014.

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  1. Jul 6, 2014 #1

    Peterson

    Peterson

    Peterson

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    Rotaryeng.net has some drawings of a tangential muffler. The basic idea is that the exhaust pulses enter the side of the muffler body and swirl around colliding out of phase with eachother thus reducing the volume and exit out the end. There are no internal parts to burn or melt and the design is simple, compact, and light weight.

    Has anyone tried this design? How well does it reduce noise? How would power output compare to tuned header pipes and a traditional flow through muffler such as a glass pack? With the high EGTs of a rotary, I can see a glass pack needing to be replaced periodically, but tuned headers and a proven and affordable muffler seem like they would work better while the compact size and the weight savings of the tangential design are very appealing.
     
  2. Jul 7, 2014 #2

    TFF

    TFF

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    Airplane mufflers dont have packing because it can come loose and clog. Bad enough when the stainless breaks out. For sure you have to have something for a rotary; too noisy without. Most homebuilt piston just go straight pipes, but not all. Most piston mufflers are just a chamber; some have partitions.
     
  3. Jul 7, 2014 #3

    Will Aldridge

    Will Aldridge

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    I take it you are not subscribed to Paul Lamar's newsletter. If you have been for any length of time you would have seen this. In his words its "the best thing since sliced bread". According to him it's by far the best way to quiet the rotary enough to be neighbor friendly. It surprises me that he hasn't posted this on his website. I don't know how to go back and look through the archives of his newsletter but you'll find all this plus several sound files that are recordings of different mufflers. I personally don't like it from an aesthetics point of view and drag as well since there is not place in my design to put it except hanging under the fuselage which is where it usually goes since most aircraft don't have a tunnel designed into the underside of the fuselage. And btw he doesn't think any of the mufflers currently listed on his site reduce the noise adequately.


    coax-muff-side-v-dims.jpg coax-muff-side-v-.jpg coaxial-muffler.jpg

    I was also planning on using the tangenetal muffler in my design but there was no room for the motor mount so in order to try and come up with a compromise for my design I came up with a semicircular augmentor with both exhaust pipes feeding into it one above the other instead of a 2 into one like pictured above, then I added a fishtail onto the end of each header and cut the swiss cheese holes in it. Although Mr. Lamar said it was an ingenious idea he didn't think it would be long enough to get the decibel level down to an acceptable level.

    Below is the augmentor. It is in three colors, the green is the intake and transition, then the dark grey and the light grey are the augmentor. I have been fairly worried about the rotary's high exhaust temps and this seemed like a good idea to get some cooling air directly to the exhaust system and help carry it out of the cowling a little quicker.

    augmentor.jpg

    In this screen cap below I have removed the augmentor so you can see the headers. Knowing that my setup was several feet shorter than Mr Lamars design I added the fish tail to the end of each header, and although not shown they will also have the "swiss cheese" holes drilled in them between where they enter the augmentor and the fish tail.


    header.jpg

    And below you can see that I had to cut a recess in the side of the fuselage to accomodate the whole setup. As noted Mr Lamar doubts that it will be adequate and suggested that I extend it aft of the cockpit. That quite simply is not going to happen.


    aft quarter.jpg

    So I came up with these fishtail fins as I call them. No idea if they'll actually work, but they will be easy to add if the setup is inadequate.
    fish tail fins.jpg
     
  4. Jul 7, 2014 #4

    Peterson

    Peterson

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    ^^coming out of the cowling on the side like that looks kind of like the exhaust of a Pratt and Whitney PT6! I had thought of using the tangential muffler design and a stainless U bend with the muffler exit forward and the U bend coming out the side of the cowling rearwards to resemble a turboprop. Paul's newsletter mainly goes straight to my spam folder but I would like to hear some sound clips of the tangential design.
     
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  5. Oct 18, 2016 #5

    Billrsv4

    Billrsv4

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    Will,
    LOOKS nice but I expect the fins would only last a few days. The problem is the sonic pulse hitting any flat surface. If you made them really robust they might hold up. By robust I mean close to .100 inches thick! On the rotary fishtails just blow up. some lasting only a few hours. One muffler concept that was designed for the rotary was the Supertrapp. It got Moller enough money when he sold it to help finance his flying car idea a little longer. I don't know if that was before or after the S.E.C. investigation.
    Bill
     
  6. Oct 19, 2016 #6

    rv7charlie

    rv7charlie

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    Hi Will,

    Bill is correct. That setup, as shown in the drawings, will disintegrate very quickly; likely before you finish ground tests (if you're lucky). Are on on the Flyrotary email list? There are guys on that list who have actual rotary *flying* experience, who could have told you about it. ;-)

    BTW, most exhaust augmenters I'm familiar with actually amplify the noise from the exhaust; not lower it. They are typically used to help extract cooling air at low airspeeds; not reduce noise.

    Edit: Is that a separate air inlet that just feeds the augmentor? If so, that will be a *lot* of extra drag to duct that much extra air through the cowl.

    I do love the look of the plane, though. Beautiful!

    Charlie
     
    Last edited: Oct 19, 2016
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  7. Mar 16, 2017 #7

    Billrsv4

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    Will, Charlie,
    The tangential muffler does reduce noise it isn't very efficient. While testing our small port 2 rotor the muffler we built using proper header pipes worked better than a tangential muffler. We also used a small can flowmaster with all the guts replaced with stainless and thicker about .100" thick. That holds up fairly well. Louder than the custom built muffler, but freer flowing. Made good power too. We were getting 195 HP at 6500 RPM with 1-5/16" inlet peripheral ports. We try the 1-3/4" ports soon.
    Bill
     
  8. Mar 16, 2017 #8

    pictsidhe

    pictsidhe

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    An exhaust ejector can increase thrust. Not much good for silencing, though. Expansion chamber and the longest tailpipe you can fit. Won't be great in a feasible size, but a definite improvement on straight pipes.
     
  9. Mar 16, 2017 #9

    Will Aldridge

    Will Aldridge

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    I've started redrawing the fwf to accommodate the new gear box(the offset prop shaft requires the engine to be raised 2.5 inches) and looking at different configurations for exhaust systems. Raising the engine allows me to mount a radiator vertically under the engine and would allow a muffler to also go under the engine. I'm also thinking of keeping it in the same place and sending the headers into wild contortions to add a little length before they dump into the muffler. We'll see how things turn out. Going to have to make decision on this before I can resume building the fuselage as I would have to add our subtract cutouts I the forward fuselage.
     
  10. Mar 17, 2017 #10

    pictsidhe

    pictsidhe

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    For sound reduction, you want a long pipe between muffler and atmosphere
     
  11. Mar 17, 2017 #11

    Will Aldridge

    Will Aldridge

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    Based on Terry Crooks conversion manual I'm fairly confident the sound issue is under control, I need the extras length in the headers for performance.
     
  12. Mar 18, 2017 #12

    deskpilot

    deskpilot

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    In years long passed, I worked for Tenneco's exhaust division under the name of Walker Australia. At some time since forgotten, it came to light that our parent company in the States was working on a "noise celling system" that did what you describe but in a very different way. They produced a system, initially for use on buses, that worked by having a microphone near the exhaust manifold, fed the signal through an inverter, and played it back through a pair of special speakers that fed the out of phase sound directly into the muffler. Apparently it worked well but the speakers didn't last long enough for it to be a viable exercise. Unless you can instantaneously produce a negative sound or power pulse, you can't reduce sound to zero.
     
  13. Jun 5, 2018 #13

    Billrsv4

    Billrsv4

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    Hopping back into this thread,
    The rotary is particularly difficult to muffle due to some supersonic pulses at the port. I am attaching a patent from no less than Francisco Iannetti the guy that makes the ceramic rotary apex seals. He has built versions of this dispersion type muffler that works but he only would lease them to the race teams! This patent isn't exactly like those pipes, but is very similar. Note this, all the materials MUST be best materials, also any fillers used MUST tolerate 1500°F temperature. (No fiberglass packing, since even if you have some that will tolerate the temp the sonic pulses will destroy it!) Some of the fillers that have been successful are ceramic beads, stainless steel scrabble or shavings. Check out the patent. Also all welds must be excellent.
    TOB The other Bill View attachment 1498380186941948695-05962821.pdf
     
  14. Jun 5, 2018 #14

    Marc Bourget

    Marc Bourget

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    Peterson said: "Rotaryeng.net has some drawings of a tangential muffler. The basic idea is that the exhaust pulses enter the side of the muffler body and swirl around colliding out of phase with eachother thus reducing the volume and exit out the end"

    It seems (almost) that the essential point being missed is the need for attenuation of the pulse. John Thorp published an article on Exhaust Extractors in a 1960's Sport Aviation Article. Readers might benefit from review of his considerations. The phrase "colliding out of phase" is close as it breaks up the pulse by "destructive interference." There are lots of ways of attenutating pulses and a Heimholtz Cavity or Resonator works well as it doesn't require energy input.

    If you could break up a single exhaust pulse into smaller pulses of different frequencies, you would end up with "white noise" which is more tolerable than an open header from the cylinder. The problem with my exposure to Heimholtz Resonators (from my Formula Atlantic racing days) is that the unit I had worked very well, but was large in cross section. Iannetti's approach, above, appears to lasso the same benefit from a different approach.

    FWIW
     
    Last edited: Jun 5, 2018
  15. Jun 6, 2018 #15

    dino

    dino

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    A turbine wheel does good work breaking up exhaust pulses.
     
  16. Jun 6, 2018 #16

    pictsidhe

    pictsidhe

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    I've heard them called 'rotary mufflers'. Waste gates can spoil the effect somewhat, though.
     
  17. Jun 16, 2018 #17

    Pale Bear

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    Too, .. there's something called the "Swiss muffler" which resembles the tangential muffler mentioned above.

    http://www.piteraq.dk/flight/muffler.html

    The problem would be in the length of this, though .. even, if it would work well.
     
  18. Jun 30, 2018 #18

    rv7charlie

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    The tangental for a rotary looks more like that Cessna muffler in that link, than a Swiss muffler.

    A friend, Ed Anderson (rotary RV-6A; again, with actual building & flying experience), ran some numbers and built a prototype muffler that's a long tube, like the Swiss, but very different inside. The 'guts' were basically a series of discs with radial slits cut in them, and then twisted, somewhat like crude fans. The discs were spaced at varying distances within the tube, and the 'fans' had roughly the same open area as the tube. The principle behind the design is that high frequencies have a really hard time turning corners. (It's the higher frequency harmonics that make a rotary (and 2 strokes) sound so nasty. I didn't get to hear it in person, but his airport neighbors said it was very quiet; better than a typical Lyc. Unfortunately, the prototype was fairly crudely built (it was only a proof of concept piece), and the discs, which were assembled on a piece of all-thread with nuts, quickly worked themselves loose and spun themselves into a short stack. Ed has always kept a lot of irons in the fire (he's also the designer/builder of the EI Commander http://www.eicommander.com/), and he never finished the project. He recently sent me his notes on the muffler with permission to share, if anyone's interested. They're in a zip file, so I doubt I can upload them here, but I can forward the file or unzip & forward the individual files, if that's preferred.

    I'd prefer that Bill make his tuned box design 'open source', as it packages better. But for a belly mount, Ed's design has real potential.

    Charlie
     
  19. Jun 30, 2018 #19

    plncraze

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    Could you upload the zipfile here or is it too big?
     
  20. Jun 30, 2018 #20

    rv7charlie

    rv7charlie

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