Hi Paul,
I hope the Oshkosh experience was very good. The TTC project is
very impressive.
I’m gradually working through my radiator and oil cooler
issues, and
also building an exhaust header / tangential muffler. I have a
couple of questions on the latter.
Please see the attached, although very crude, drawing.
I am using the Racing Beat SS header, with short 2.5”x 1.75”
OD .065
304 SS tubes welded in place. These will slip into 0.65”
1.88” tubes
that will in turn be welded into a 6” 304 SS .065
cylinder/muffler.
On the front, a 90 degree 1.88” tube is used to reduce the
length of
the 6” tube and significant weight.
Due to space and other constraints, I need to bring the 3”
tailpipe
(also .065” 304 SS) out of the
*rear* of the muffler and up. This
gives me at least 3 options: 1. A straight 3” pipe welded to
the rear
of the muffler. 2. Squeeze the 3” tailpipe into a fish mouth (your
previous drawings showed an area about 1/2 of that of the
tailpipe).
Or weld up a larger fish mouth. 3. Or, allow a short section
of the
3” tailpipe to remain inside of the muffler, which could be closed
off and drilled with (e.g. 0.5”) holes to arrive at the same exit
area as the fish mouth design. I am wondering if this might be a
more conventional muffler design and possibly allow better sound
reduction?
The prior concerns regarding the longevity of any metal living
“inside” the muffler have been noted. However, with a Renesis
engine
having exhaust ports coming through the iron housings, as well
as a
cooling tube, both giving lower exhaust temps, do you think
this is a
concern for .065" 304?
Thanks for your input,
Scott Gettings
You are on the leading edge Scott. Nothing like this has been
built
yet. The RX8 side port exhaust is a little cooler so it
should work
all right. If it burns through opposite the exhaust ports you can
weld on doubler patches.
Paul Lamar
Scott, Suggest that you investigate 321 S/s as 304 is a very low
grade Stainless. Remember the exhaust temp will get up to 1800
degrees which is rather warm. Your design is similar to what
I made
and is still alive, but I have not the cooling tube. Neil Unger
Nice work Neil.
Paul Lamar
Typically 309 & 310 are used for high heat applications, 309
is good
for 2000F and 310 2100F. Be sure to use the correct filler rod the
material you are working with or you will be wasting your time
using
these more expensive grades. I would not call 304 a low grade
steel,
they all have their place in the appropriate application. Andrew
Campbell.
Paul, do you recommend having slip joints on the pipes just after
the SS flange like Scott has, or is it ok to put these further
downstream. Reason is ask is that I wanted to duct some
cooling air
around that area in flight and my concern is when going from high
power straight to a power off, high rate of descent leading to
possible uneven temps around the exhaust due to cooling air
distribution.
I want to try and minimize the risk of possible cracking. With the
space I have to duct cooling air I have to duct it from front to
rear so the front (if sitting in the cockpit) exhaust header pipe
gets the coolest shot and the rear header pipe gets the air
warmed by
the other 2 further in front.
Any issues you can see using thick wall stainless tubing bends
Alex Molteno
The thicker the wall the better. There is a weight draw back of
course, .109 wall 304 and it hardly shows any problems at all. One
can buy 304 SS hand rails from
http://www.wagnercompanies.com/products-services/railing-systems-and-components/railing-components/elbows-and-wall-returns/
<http://www.wagnercompanies.com/products-services/railing-systems-and-components/railing-components/elbows-and-wall-returns/>
<
http://www.wagnercompanies.com/products-services/railing-systems-and-components/railing-components/elbows-and-wall-returns/
<http://www.wagnercompanies.com/products-services/railing-systems-and-components/railing-components/elbows-and-wall-returns/>>
rfq@mailwagner.com <mailto:rfq@mailwagner.com>
<
mailto:rfq@mailwagner.com <mailto:rfq@mailwagner.com>>
<
mailto:rfq@mailwagner.com <mailto:rfq@mailwagner.com>
<
mailto:rfq@mailwagner.com <mailto:rfq@mailwagner.com>>
You can then use the exhaust plumbing for motor mounts :-)
Joking of
course. It is only the first 18 inches of a p-port or so and
by that
time it has cooled. The slip joint can go there. Scott has a
problem
in that it is a pusher so he has way less room in the cowl to work
with. If you can avoid it keep the muffler out of the cowl and
use a
coax muffler.
Do you have an RX8 engine? Things are a lot easier and quieter as
the exhaust is a couple hundred degrees F cooler with the side
exhaust.
Paul Lamar
OK thanks Paul, good to know for the parts source to use tubing
handrail. I've added a bit of extra weight already during the
build
so a few extra lbs of exhaust weight will be OK for extra
insurance
against cracking
Alex Molteno
Paul,
While studying the best configuration for the tailpipe on a
tangential muffler, I came across another idea that might further
reduce the noise:
If the combination of the Renesis exhaust being around 1600
degrees
and a cooling tube might reasonably allow 304 metal to survive, do
you think it might work to place the cooling tube INSIDE the
tailpipe
and let the exhaust augment the cooling tube air? This would
allow a
lot more area for holes to be used in the “muffler” section of the
tailpipe. The inside of the cooling tube only gets fresh air and
does not mix with the exhaust air until after exit.
In the attached drawing both the exhaust and cooling tube go
straight back, but would ideally need to exit vertically or at
least
at a 45 degree upward angle. I assume to have any
augmentation the
cooling tube would need to extend past the exhaust exit flow.
If this is not still too far on the bleeding edge to make an
educated
guess, any suggestions are appreciated.
Thanks
Scott Gettings
Hard to say with out spending a lot of money on
instrumentation and
data recording.
Paul Lamar
What is the purpose of the cooling tube?
James Whitehurst
Alex; With regard to your thoughts on using slip joints to prevent
cracking, I need to relate about Detroit Diesel exhaust manifold
issues on the Series 60 engines. Due to heat expansion on a long
manifold they went to a three piece manifold. I do not know
why for
certain because they had used a one piece manifold on 6 71 and
12 71
engines for years with no troubles.
Anyway, the Series 60 had joints that one slipped inside the
other.
With time and repeated heat and cooling cycles the joints
would gaul
and start to leak exhaust. I proposed we try cutting a groove
for a
small piston ring seal on the outside of the parts that slipped
inside the other. Worked real well to keep leaking down but
the next
time the manifold had to be removed as one piece as the piston
rings
wore grooves in the other part and they could not be
separated. Using
an antisieze compound helps the gauling but only for a short time
until it is gone. Expansion joints allow for the expansion and
contraction without leaks.
Dale Davies
Interesting. There are certainly lots of options for flexible
joints. My 45-year-old Cessna has multiple slip joints in its exhaust
system and they have never had a problem. Some of them have a clamp with
an alignment button. I have had several failures in welds in areas that
have expansion and contraction.
Scott Gettings.
One advantage with aircraft is a more constant exhaust temperature.
You start and warm the engine. Then for about 5 minutes during takeoff
and climbout you are at maximum power and exhaust temp. Then you ease
out of the throttle a bit and set for ROP or LOP. The manifold cools a
bit but you are still at 75% load so the exhaust is still hot. Then when
you want to land you ease off the power to slow down and descend. The
manifold cools slowly. Once on the ground and parked the manifold
returns to ambient.
With a heavy truck the manifold temp is changing continually. Stop
at lights and it cools. Then accelerate to road speed probably under ful
power. Manifold gets red hot. Cruise on the highway is only about 225 to
275HP depending on the load. When you come to a hill you are full power
and red hot again. Then coming down the other side of the hill you
injevt no fuel and Jacobs Engine Brake or exhaust retarder on. Exhaust
drops to about 500°F. Continual expansion and contraction.
Worse situation than AC but principals are the same. Best to
engineer and design for worst case and prevent troubles later. You do
not want to find a carbon monoxide situation in mid flight or get at
least a major headache from it. If you loose coherent thought during mid
flight bad things happen.
Dale Davies
OK thanks Steve, noted on the seamless bends. Dale, very good points,
I'll sit and think it out some more before I commit, I only want to
build this exhaust once if possible, I can't weld got to pay someone.
It's a Renesis so some relief there on exhaust temps Paul,
Alex Molteno
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