Steve,
That "sounds" great. I hope the packing holds up. Can it be
repacked easily? The Austin bunch is going through Hushpower II resonators
pretty fast. I'm on my second one and it's starting to sound different. I think
Dennis H is down to just a can without any internals. But his RV7 is still
very quiet. I don't have any issues when keying the mic with my
Lightspeed. I only have one flight with my new Zulu and it works great.
Better than my 20XL that's gone missing.
Bobby Hughes
RV10 Super Renesis
Well, I just made a guess and measured it at 100 ft. I'll
measure cockpit noise later, when I've got some flight time in. Here is my
story:
I have a Glasair Super II RG with a Mistral 2 rotor engine. I've had
it in the air once, and landed immediately as there was an oil temp problem that
turned out to be a measurement problem. However, what I did find that was
particularly annoying was the noise. My LightSpeed Zulu handled the noise
fine until I keyed the mic. Man, what a blast of noise! I could
barely hear the tower.
The muffler that I was using was a 2 1/2 inlet/outlet and 3 1/2" diameter
Burns Stainless device that I purchased many moons ago. It was made up
with stainless scrubble innards. So, I decided to replace it with another
Burns Stainless muffler, but a 2 1/2" inlet/outlet, 6 1/4" diameter, dual stage
muffler. See:
Although this one has a 3" inlet/outlet, they made one for me with the 2
1/2". What a difference!!!! Here are the measurements I took from
100 feet, off the wing tip and about 30º aft. They also put in a stainless
cloth material instead of the stainless scrubble. They claim that it works
great for the rotary.
idle: 57-60 DB
1500 RPM: 78 DB
2000 RPM: 87DB
By RPM, I mean prop at 2.85-1 reduction ratio. I was fearful that
going any higher would put my prop too close to the ground as the nose gear
compressed down with power. I suppose you math-types can extrapolate
different distances.
I'll be hitting the air tomorrow. While I had one short flight
already, this will be much longer, hopefully and I can see what the plane will
do.
The only real disadvantage of the muffler is that it hangs underneath the
belly and looks ugly. But it, so far, works terrific. I hope the
drag penalty is not too great.
BTW, the rest of my exhaust consists of 2" headers into a collector with a
2 1/2" outlet made with .065 321 SS.
Best Regards,
Steve Thomas
_______________________________________________________
Steve,
Typically the measurement for cars and motorcycles is at 50 feet away at
90 degrees to the directin of the exhaust flow. Any in-cabin measurements
wouldn't need orientation, just put the pick up about where your head
is.
Bill Jepson
-----Original
Message-----
From: Steve Thomas <
glasair2@me.com>
To: Rotary motors in
aircraft <
flyrotary@lancaironline.net>
Sent:
Thu, Jul 29, 2010 9:31 am
Subject: [FlyRotary] Noise Measurements
I want to take some noise measurements today with a new muffler I just
installed. What is a reasonable distance from the aircraft to be taking these
measurements? Right next to the airplane seems to be somewhat unreasonable, and
distance makes a big difference.
Best Regards,
Steve Thomas
_______________________________________________________
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