Steve, I don’t see anything in your muffler that muffles … it
looks like an expansion chamber?
Jeff
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of sboese
Sent: Friday, January 16, 2009 12:57 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] another Muffler
The following muffler description is provided purely as another
data point in the muffler discussion. I would suspect that not many of
you would be interested in it due to its large size and external
mounting. I have had good service from it so far and it fits somewhat
into my loosely interpreted Navy F6F Hellcat inverted paint scheme as a bomb.
The materials of construction are 0.032” thick 304 SS and the
design is based on data in NACA Report 1192. The weight is 9.6 lb and the
diameter is 6.25 inches. A SS heat shield is also installed between the
muffler and the fuselage belly. I have about 100 hours on this installation
with no signs of deterioration of the muffler. The engine is NA with
exhaust splitters and is operated normally at density altitudes above 7000 ft
which limits max power, although several hours of max power operation at DA
lower than 5000 ft have not damaged this muffler so far.
I have been told that from the ground, the primary source of noise
for my plane is the propeller. I have landed with a C172 following me in
the pattern and observers told me that they did not know I was there until I
taxied in since they only heard the C172. I have no quantitative data on
the noise characteristics of my muffler system. Inside the cockpit, the
noise level goes from reasonable to unbearable if the muffler is removed.
This is purely subjective, of course.
Not shown in the “muffler parts” image are three 1” x 1” angles
made from the same material as the shell that connect the rear of the internal
center tube to the front of the rear cone section. The round flange in
the center of the internal tube is a push fit in the shell and is not fastened
directly to the shell. A down turn also has been added to the outlet of
the rear cone section.
From data in the “muffler test chart” image, the speed penalty of
the muffler is about 3 kt.
The “muffler in flight” photo may be of interest in that it shows
the heat distribution in the muffler with the dark areas being hotter.
This image is not current since the lower cowling has been modified and the
engine cooling air outlet is now much smaller than shown in this photo.
Steve Boese
RV6A, 1986 13B NA, EC2, RD1A