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1. 08:01 AM - Re: muffler (Bud Yerly)
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Rick,
I=92ve cc=92d the Europa list also.
I must admit that the end cut of the pipe didn=92t affect me much as I alwa
ys terminated it close to the duct exit and only the angle to miss the tire
on the mono, and the support for each was my concern. The engine pipes di
ameters are so small I never thought about anything but support and augment
ation effects were not going to be a factor on such a small displacement en
gine.
I support any pipe on an aircraft if longer than 12 inches due to harmonics
. The problem I see is the exhaust on the Jab is not supported except at t
he head. Not good. There is no strap or support on the muffler to the eng
ine, so it seemed logical to support the end of the pipe to save the head b
olts, muffler, and pipes somewhat. On Joe Likes, and John Kershner=92s Jab
irus, I terminated the pipes at the end of the cowl and support each with a
n exhaust rubber clamp hanger with a bolt and spacer into a nutplate in the
footwell. Supporting just the pipe ends has its issues, the engine will
move a bit on its mounts so the pipes need to be supported vertically and
not restrict side to side movement or you will have more problems with dama
ge. So far It has worked, but their engines are low time. Time will tell
and these planes aren=92t getting any.
I believe most exhaust problems come from lack of proper support. The man
ifolds on aircraft are light pipe with thin flanges and small bolts holding
them unlike that in an auto engine. The 912S Rotax hangs straight down an
d failure is with the springs and vibration breaking them as the force is b
asically vertical with a slight horizontal shake. The Jabiru exhaust hangs
going aft quite a ways, so leaks occur at the heads and the muffler inlet
due to bending and weld failures. I hate supporting only the pipe on the J
abiru as the muffler needs support also in my opinion. Finding a suitable
place to mount a support from the exhaust to the engine means engine bolt m
odification, labor to fab a support and then test. I am loath to attach a
clamp or support to the intake manifold as that is a small bolt. That leav
es modifying the through bolt studs and or hang the muffler from the case b
olts which means potential case leaks and is expensive in time and material
. Then only time will tell if the mod was worth it.
The Jab seems to have a typical 100 hrs until at least one cylinder change
then an overhaul around 500 hours even if properly maintained. This makes
it hard to recommend these really expensive exhaust replacement/repairs for
exhaust components and testing for harmonics. Welding the muffler up and
patching properly is more cost effective than a grand for a new exhaust whi
ch is still not supported. Use good quality springs on the exhaust, safety
wire it also and a hangar on the airframe is all I can suggest. Proper pr
op balancing and support for engine accessories is really necessary on thes
e opposed engines as the exhaust really dances around under the engine.
Best Regards,
Bud Yerly
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________________________________
From: Rick Stockton <aireupora@sbcglobal.net>
Sent: Tuesday, May 29, 2018 10:09:06 AM
Subject: muffler
Thanks Bud for the note.
I took the muffler to a welding shop and they thought it would be to expens
ive to repair and told me to buy a new one, so I priced one out. $895.45
I think I can make a lot of straight pipe for that amount of money.
Anyway I then took the muffler to a local muffler shop and he said he could
repair it good as new. That was Friday and he called me late Friday, but
I was heading to the ball game with my family. I told him I'd pick in up o
n Tuesday morning, so one of my first stops this morning is his shop. It i
s nice having an experiential airplane. If not, I'd have to go through a c
ertificated repair shop or buy the new one.
I was going to drop a line to you as you might have some knowledge as to th
e shape and length of the tube coming out of the muffler.
The way this pipe cracked out I'm thinking that I had it to long and the 10
0+ kts wind was pushing it backwards all the time. So maybe I need a short
pipe coming out of the cowl. I've seen a lot of pipes and think that most
only come out an inch or two. I believe mine was about four inches from t
he bottom of the cowl.
What do you know about the end cut. I've seen 45 degrees facing back and f
orward. Slight cut up etc..
Rick Stockton
Europa N120EJ
Jabiru 3300 189 hours
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