Re: Jet Engines above the wing

From:         Steve Lacker <slacker@arlut.utexas.edu>
Organization: applied research laboratories
Date:         20 May 96 10:13:18 
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Don Stokes <Don.Stokes@vuw.ac.nz> wrote:
>kls@ohare.Chicago.COM writes:
>>sources of noise reduction, MD also notes that the aft-mounted engines
>>use the wing as a partial noise shield.
>
>Um, how?  Most of the noise comes from just behind the tailpipe, where
>there is a "tearing" effect between the core flow and the bypass flow.
>Take a line from that area through the wing, and you find that for the
>most part you have to go through the engine nacelle first.


Actually, a great deal of engine noise does come from the intake side, and
especially at lower thrust settings. Not quite as much with the IAE engines as
with JT8D's (which have inlet guide vanes in front of the fan- one of the most
effective hush-kitting procedures for pre-200 series JT8d's involves re-spacing
these guide vanes) but still a non-trivial amount.

FWIW- I've now ridden DC-9-90's (MD-90's) about half a dozen times. I hate them
just as much as I hate all other DC-9's, but I must admit that they are
extraordinarily quiet. IMO, they're even quieter inside than a 757. Still, the
5-across seating and low ceilings decrease my comfort more than the quiet
enhances it.

--
Steve Lacker	/	Applied Research Laboratories, The University of Texas
512-835-3286	/	PO Box 8029, Austin TX 78713-8029
slacker@arlut.utexas.edu