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Date: Thu, 12 Jan 2006 13:14:41 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Cool Tube Muffler Sound Readings
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Ernest Christley wrote:

> Bob White wrote:
>
>> I guess after that it's just a matter of whether I'm happy with
>> the noise level in the cockpit.
>>
>> Bob W.
>>
> And do we really care what the people we leave on the ground think!?
>
> 8*)  Well, I guess that would depend on if we want to come back, but 
> your point is insightful.  Taking readings at the wing tips and such 
> is interesting, the cockpit is the crucial area.  There's some 
> correlation between the sound at the wing and the sound in the 
> cockpit, but I'm sure that various configurations will direct the 
> sound in different directions.  If I can direct that sound energy at 
> the wing instead of the cockpit...well, the guys in the hangar will 
> just have to stop talking for a second while I leave. Right?
>
> Once in the air (so the ground isn't reflecting), are straight pipes 
> pointed down better for the pilot than ones that are angled back?
>
Pipes pointed down (any direction perpendicular to airflow) will 
increase drag significantly.

Bob,

3000 rpm implies about the power level needed for a fast taxi. I'd 
guesstimate that 104-105dB is at least 10dB louder than a small Lyc at 
taxi power. (That's a *big* difference.)

Simplified info about weighting scales on dB meters (from 20 year old 
memory):
 
The A scale on a dB meter is designed to approximate the human ear's 
frequency responce curve *at low volume*. Any time you see a company 
hyping their product's noise level & quotes levels based on the A curve, 
they are hiding the true noise level of the product. At high noise 
levels, your ear is no respector of weighting curves & the frequency 
extremes that are filtered by the meter's A weighing still damage  your ear.

Charlie