Re: Phase III Engine

Date:         05 Nov 97 23:41:55 
From:         David Lednicer <>
Organization: Analytical Methods, Inc.
References:   1 2 3
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Marc Schaeffer wrote:
> I wonder if there is a hushkit which converts the original JT3D's to
> stage 3. I am pretty sure that there is none but the Cargo Lion DC8's
> (LX-TLA and B) have a stage 3 writing on their JT3D engines. The noise > however doesn't seem that low, so is this just marketing ?

	There are several hushkits available that take JT3D powered aircraft
from Stage I to Stage III.  There is a 707 hushkit certified
(by QNC) that will make a 707 Stage III compliant.  Several companies
have work is underway on certifying hushkits to make 707s and DC-8s
Stage III compliant.

	Hushkits can take many forms.  Most involve inlet treatment, bypass
duct treatment and a exhaust mixer.  Some involve changes to the
aircraft operating procedures that place the aircraft higher over the
microphones during approach or departure, along with changing the thrust
in use at these times.  Some hushkits, such as the Valsan/Rohr 727
package and the 7Q7 program, involve wholesale reengining with modern,
quieter engines.

	Just because an aircraft is Stage III compliant doesn't mean that it
will necessarily sound quiet.  The means by which noise is measured
doesn't necessarily match your ear's perception of the noise.  This is
because noise is produced at many different frequencies.  The weighting
of the frequencies to produce a Effective Percieved Noise (EPNdB) rating
attempts to match human perception, but is not foolproof.

David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:
2133 152nd Ave NE          |   tel:     (206) 643-9090
Redmond, WA  98052  USA    |   fax:     (206) 746-1299