Re: Jet Engines above the wing

From:         Don Stokes <Don.Stokes@vuw.ac.nz>
Organization: Victoria University of Wellington
Date:         13 May 96 02:08:45 
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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.  The only
exception is on paths that intersect the outer wing, but these leave
only a small shadow at extremely shallow angles to the ground.

That said, a wing mounted high-bypass engine, with the tailpipe well
under the wing, is going to have some of its noise reflected downward.
That give the aft-mounted configuration an advantage due to what isn't
there, rather than what is...

Ironically, the noisy JT8Ds on the 737-100/200 have their tailpipes
well aft of the wing.  (And yes, they're *noisy* inside the cabin!)

--
Don Stokes, Network Manager, Victoria University of Wellington, New Zealand.
don@vuw.ac.nz(work) don@zl2tnm.gen.nz(home) +64 4 495-5052 Fax+64 4 471-5386