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.
Ed
------ Original Message ------
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.
Charlie
On 11/24/2019 11:48 AM, eanderson@carolina.rr.com 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.
Ed
------ Original Message ------
Sent: 11/23/2019 10:35:27 PM
Subject: [FlyRotary] Re: Mufflers
Ed,
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.
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
Ed
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