Mike,
The length of the cylindrical section is 24 inches. The
conical section is 9 inches long.
The dome was made from a Kmart mixing bowl. Some of it is
less than 0.032 inches thick but has held up so far.
The cylindrical section was made by a local sheet metal shop
with a stove pipe joint that also has been tack welded in a few places.
I made the conical section, inside parts, heat shield, and mount
from the same sheet material as the cylindrical section. The joint in the
conical section is similar to the stove pipe joint and is also tack welded.
Steve Boese
N613BX, RV6A, 1986 13B NA, EC2, RD1A
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills
Sent: Saturday, January 17, 2009 9:13 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: another Muffler
Quite
the opposite Steve. I think the 3 Kt loss and looks (it actually looks better
than most) is a fair price to payfor a relatively light, easy to construct
muffler that works. My current "muffler" isnt a lot smaller and
weighs about the same.
2)
Source for the dome and cone used in the construction?
-----
Original Message -----
Sent: Friday, January 16,
2009 9:57 AM
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
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