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