As Clive alluded to, resonance in the opposed 4 banger exhaust is an issue as
well
as intake. The thin fiberglass footwell directly under the feet of the pilot
or passenger, especially in the Classic with the exhaust pipe exiting directly
aft under the pilots feet, resonates something fierce and sounds just like
the carb inlet. Creighton Smith's 96EG underwent a surgery of the heavy Classic
Exhaust and the aft lobe was removed, and a straight pipe added. What a
racket that made initially. We changed the tuning length and put in an
expansion
pipe (nothing sophisticated, just cut the pipe and put a wider pipe on the
end to change the note). Creighton was a motorcycle racer, and he did an
excellent
job softening the sound. What a difference. Still louder than my 914
but it didn't bring the airport to a stop on ground runs any more.
Prop pressure pulses across the aircraft windscreen in the Europa are not that
bad, so I have not been concerned with that as in other light aircraft.
However,
any looseness in the doors hinges, latches and the D panel in the back are
very large drum skins and the low frequency drone is annoying enough and
fatiguing,
but the rattle is irritating beyond description. Prop power pulses as
I call them, is normally not bad on a three blade that is tapered. The two
blade
wide chord blades can definitely be felt and heard as even the XS nose tends
to transmit some of that back to the cockpit.
Personally, having a 914 and leather interior makes most of my aircraft
remarkably
quiet on the inside. The 912S and 912 versions I tend to prefer a rework
of the inlet air geometry to break up the intake noise and as far as the exhaust
note, I leave it to Robin at CKT Engineering for the 912S exhaust note. It
is amazing what a bad baffle in the exhaust sounds like. Many don't realize
they have a bad silencer baffle. CKT has done a nice, but expensive, Rotax 912
down pipe exhaust and side exit that makes the little fart can engine sound
very quiet. My opinion for what that is worth.
Noise is fatiguing. ANR helps the ears, but the vibration of the various noises
hitting the body is fatiguing. The Europa has that phenolic type firewall that
is very thick and I do not do any heat or soundproofing on it. I do add a
thin stainless steel plate some 4-6mm proud of the pilots footwell on some of
the 914s as this cuts the heat on the feet. Proper air venting is needed down
here in the South. I will not do a painted only interior because it is loud
and sound bangs around all through the cockpit with nothing to absorb it. I
do not do any firewall sound proofing on a trigear because I build in a firewall
aft of the nose gear covered with firewall 2000 (excellent fire and sound
proofing).
The mono is a different animal. I find the metal firewall an excellent
sound transporter and amplifier. The airflow through the slots is also a
bugger. I have tried the soft and hard Lord mounts and frankly didn't see any
change in apparent vibration (purely measured by feel) Props make a difference
as does exhaust plumbing and support. Nothing worse than an exhaust system
in contact or firmly attached to the frame on a 912S. The 914, you don't have
a choice on the mounting. But in its 15-20 years it has had a few turbo support
cracks repaired.
One of the reasons I went with the stock kit. Experimenting to fix issues is
time
consuming/expensive and well, an experiment, sometimes it works, sometimes
it doesn't and hopefully, it doesn't add weight.
Keep up the good work.
Bud Yerly
-----Original Message-----
From: owner-europa-list-server@matronics.com
<owner-europa-list-server@matronics.com>
On Behalf Of Area-51
Sent: Saturday, March 18, 2023 6:45 PM
Subject: Europa-List: Re: the Obsidian Files - So Much Noise!!!
Oh woww!! Excellent... I totally agree with everything you have imparted... The
job is yours, you're hired; report back in month's time
Where can we liberate this said test equipment from???? We need to know where to
put the Helmoltz resonator!!
Flew again today; the results are very consistent.. next stage is an internal
baffle
for the air box... an extended forward running induction tube was considered
however this would end with the inlet port facing forward instead of upward;
so any noise emissions would be directed out front like an air horn as apposed
to an upwards direction away from the ground below. However so far i am totally
satisfied with the result as is, but will take it further with the internal
baffle and hear what happens
Any technical comments toward the "shut that noise up" project is helpful for
Europans..
Read this topic online here:
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