Mailing List Message #65400
From: <>
Subject: Re: [FlyRotary] Re: Mufflers
Date: Tue, 26 Nov 2019 15:23:58 +0000
To: Rotary motors in aircraft <>
Interesting idea about the diagonal placement of the discs, Charlie.  When a disc did break loose from the jam nuts and spung, it really restricted gas flow, so I think welding the disc in place is likely the best solution.

  I think your idea about diagonl slots would be worth trying.  It may be that simply cutting say 1/4 - 1/3 of the disc off for gas flow and then alternating the side of the tube with the slot in it would still cause the shock wave to see a solid wall  bounce back and forth between disc (mostly) and still permit good gas flow.  

Apparently the reduction of the shock wave in the several sections did not result in the loss you mention due to refledted shock wave.  

You and Tupper have a great Thanksgiving. 


------ Original Message ------
To: "Rotary motors in aircraft" <>
Sent: 11/24/2019 2:48:50 PM
Subject: [FlyRotary] Re: Mufflers

Ed, I really wish I'd had a chance to hear those mufflers; I've been fascinated by the idea since you first mentioned it many years ago. Do you remember what you were running before, and how much takeoff rpm you gained when you made the switch?

With only 5 washers, I wonder if the same effect could be achieved using half-discs slid into diagonal slots cut in the tube and then welded around the cut. Cuts could be staggered in rotation around the tube as you move down the tube. Would likely need to 'break' the straight edge of the half-disc to resist fatigue. Small hole at the edge of the cut would allow the 'break' to slide into the gap.

I would have expected at least some power loss on a 13B because of the detuning effect of a mis-timed reflected shock wave; good to hear that it didn't. With a Renesis and no intake/exhaust overlap, it shouldn't make much if any difference to power as long as back pressure is managed with a large pipe.


On 11/24/2019 11:48 AM, wrote:
Sorry, Neil,

Been a while, it was two exhaust pipes, one for each exhaust port.  Mistyped, error on the drawing the disc were 2 1/2" dia inside a 2 1/2" dia pipe.  The discs fit snugg enough that when one broke loose and spun on the rod,  it scored the inside of the exhaust tube.  I got the discs from McMaster Carr.  Try oversize SS washers.   The tubes were actually glass pack mufflers which had 2" dia inlet/outlet.  I cut the front off and then after inserting the discs use wide metal clamps to put the tube back together (welding would of course have been better).

I do not believe that any of the dimensions are critical except the discs should fit touching the inside of the tube if possible.  I called them discs but they were actually oversize SS washers with a hole in the center for the rod.  I ended up with 5 discs inside each tube.  I used the spacing for the shorter 36" long tube.  The idea was to have a large portion of the shock wave dissipated inside each segment of the tube while keep the gas flowing freely.  

It was truly quite and like I mentioned I could get 6000 rpm with my 13B on take off.  Large diameter tube/discs would likely permit more/easier gas flow, but since I can not weld, just finally gave up and went on to other things.



------ Original Message ------
To: "Rotary motors in aircraft" <>
Sent: 11/23/2019 10:35:27 PM
Subject: [FlyRotary] Re: Mufflers


                  On rereading your post, am I correct in believing that you had one pipe per exhaust?  A total of 2 pipes?  How many discs were in each pipe?  I may have misunderstood, but you say you had a 2.5 inch disc fitted inside a 2 .125" exhaust pipe.  If correct measurement how did you manage to force 2.5 " inside  2.125" pipe?  perhaps the other way around measurement wise? 

Thanks,  Neil.

On 11/21/2019 3:08 AM, wrote:
Given the recent interest in mufflers, I thought I would throw in my experience with home made muffer.  I could hit 6000 rpm on take off with my  13B with the 2.18:1 Gear ratio.  You could stand within a wing width with the engine idling and bearly hear it.  At 6000 rpm it was about 1/2 as loud as an unmufflered lycoming.  

The basic idea was to break up the shock wave while minimizing gas flow impedeance.  I used 1/8" thick 2"1 /2 Dia stainless steel disc inside of a 2 1/8" dia stainless steel tube.  The disc has slits cut from the outer edge approx 1/2" toward the center in 8 regions as shown in the diagram.  Then each "tab" was twised 45 deg from the plane of the disc.  If you looked at the disc front on it look almost as a solid disc with just a small slot area showing through.  The idea was that the shock wave would basically see a "solid or mostly solid" disc where as the gas could still flow through the slots around the tabs.  I had a threaded rod extending the length of the tube with jam nuts on each side to hold the disc in place.
The reason for the rod and nuts was not being a welder-  I used jam nuts - welding it turns out would have been much better as the nuts eventually became loose.  That was not good, when one of the disc came lose it started to spin and greatly  impeded the gas flow.   Although folks told me it sound cool - like a turbin winding up.

In any case, I decided that not being a welder there was no way I could remedy the defects.  I think if there were some way to "spot weld" the outer part of the tabs to the tube and perhas to a rod in the center the muffler would have extend it useful time.  I flew approx 12 hours 
including one trip to Tracy Crook (first extended flight with muffler) by the time I got there at least one disc had broken loose and was spinning.  Tracy was kind enough to use his welding skills to weld the discs to the rod on one of the mufflers (had two one for each exhaust), but within another 6 hours or so disc in the other muffler started to spin.  Also I found that the shock wave pounding eventual would break off a tab or two since they were not anchored and could flex.

Just thought I would throw the idea out there in case it has any merit.

Best Regards


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