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