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Tom
I am in complete agreement with you. I am
currently flying with a muffler design that is:
1. Designed to break up the sonic/transonic
shock wave that is so shattering to the ears
2. Minimize impediment to the lower velocity gas
flow.
My initial result was inconclusive because it
was complicated by the fact that the discs I had inserted into the muffler
to accomplish this task decided to act like turbine wheels. One of the
local airport bums had mentioned to me after my first test flight that
on take off the exhaust sounded just like a turbine - yeah! Yeah! the
poor mans turbine (rotary) and though no more about it until my next flight -
which was to Florida. But, in any case, the discs spun so fast they
caused the stainless steel metal to deform/flow. I initially had them
locked to a 5/16 SS thread bar with jam nuts on each side. They even
caused the jam nuts to form a flange due to heat and force. All the thread on
the rod has been worn off where the discs were located. The inside of the 3" muffler clearly showed where the tips of
the discs were rubbing on the walls.
But while they did decrease the noise level
significantly - they also reduce the gas flow due to the "windmilling propeller"
effect. My exhaust temp in the one muffler (have two) where this was
happening reflected that by increasing from a nominal 1600F to 1750F. Also
the back pressure was considerable and my engine could not get above 6000 rpm (I
have had it up to 6800 rpm).
Well, I was on my way to Lakeland for an RV Flyin
in Jan when I discovered the extent of the problem. At Tracy Crooks we
found this out when I pulled the mufflers apart. I removed 3 of the 5
discs and Tracy welded a couple of the surviving discs to the 5/16" shaft and I
have flow that way since.
I intend to revisit the design with a more robust
way of securing the discs (probably welding) and add the three discs back in to
see what difference it makes.
So if you have any ideas you want to discuss
off-line as I am certain most are tired of hearing about the FAW Muffler
{:>)
Ed Anderson
----- Original Message -----
Sent: Tuesday, March 08, 2005 6:58
PM
Subject: [FlyRotary] Re: Anechoic
Muffler
Just to stir things up... It seems that with
exhaust systems, the exhaust consists of two parts which should be handled
differently. Part 1 is the exhaust gas flow which we want
to flow out with little restriction. Part 2 is the exhaust
pulse which we try to attenuate, breakup,
etc. These two are like the difference between
wind and sound-waves. In the past 24
hours or so, I've been wondering about using anechoic chamber
principles to attenuate the pulse. I have a
specific layout in mind which should tend to attenuate the pulses while
not interfering with exhaust gas flow. Anybody hear
of such a thing?
Tom (looking for project sponsors or a job)
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