[NSRCA-discussion] YS170 at 96dB

[Troy Newman]

7600-7800rpm passes 94db

 

If your model is not "loud" meaning composite drummy type fuse then some
foam in the cowl helps...Hollow fuse and hollow wings and such will act
like a megaphone. Seal any belly pan connections so they are not banging
together, rubbing, and such. Any holes on the right side of the model
stuff with foam. Totally enclosed header and pipe is quieter.

 

 

The 18" dia makes noise above these rpms. Take the 18.1-11 and remove
about 3/16" from each tip and reshape. Clean up the L.E. of the prop and
make sure it doesn't have nicks in it.

 

Use a velocity stack it will also help the noise. The last little carb
opening creates very little power for the amount noise gained. SO set it
all up and detune the top end with ATV until the noise meter is happy.

 

A good solid wood model will yield about 76-7800 and make noise. A
composite model will be less RPM because the noise drum affect inside
the fuse.  This is where  dampen it with foam from the Engine box.
Exhaust deflectors will also have an effect.

 

If you are trying to make AMA noise limits its 96Db....and the
microphone set is 30mm off the surface. Mic is off the right hand side
of the model 3meters away and downwind. Point the mic directly inline at
the prop, then turn it 70degs toward the right...meaning the microphone
is 70degs   away from the nose of the model. This is where readings are
taken in AMA classes. The limit is 96db(A) use slow response and "A"
weighting on the meter.

 

F3A measurements are totally different. First off the model points into
the wind. The meter is set off the right side directly inline and
pointing at the prop meaning pointed at the prop right inline with
it....but the meter is 90degs to the wind. Readings are taken here and
the limit is 94db(A)

 

Penalty for AMA class is a raw score % deduction for 96-98db(A), in F3A
it is ZERO for the flight over 94db(A)

 

I have done extensive testing on the 170's and the noise meter....tons
and tons of props and played with all kinds of ideas to make things
quiet.  There are lots of things that help. Nothing is  a secret bullet
that gives 1-2db other than the RPM and the vel stack. The type of fuse
is so huge its not even funny. 

 

Troy Newman

 

 

 

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of colin
chariandy
Sent: Tuesday, August 04, 2009 6:58 PM
To: NSRCA Mailing List
Subject: [NSRCA-discussion] YS170 at 96dB

 

Does anybody know what rpm will pass a noise test for a YS170 turning
18.1X11? 

 

Colin.

 

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