Subject: [Tweeters] Speaking of Birds in the News -- Studying the Owl for
Date: Feb 12 09:45:53 2007
From: Desilvis, Denis J - denis.j.desilvis at boeing.com


4th para -- djd
Commercial Aircraft Have Silent Potential
Aviation Week & Space Technology 02/12/2007
Author: James Ott
Researchers from England's Cambridge University and the Massachusetts
Institute of Technology, who have taken a clean- sheet approach to
designing a quiet aircraft, draw the conclusion that a virtually silent
commercial airplane is achievable, although there are caveats.

The conceptual design for the SAX-40 would generate noise at the
equivalent of the background levels at the perimeter of an urban
airport, the goal of the Silent Aircraft Initiative (AW&ST July 17,
2006, p. 138). The proposed configuration would hush aircraft sounds,
particularly those most annoying to the human ear and merge them into
the normal racket of the surrounding community.

The key enabling design is a reshaped airframe center body. "To reduce
the aircraft noise below the background sound level of a well-populated
area, it is clear that the airframe and the propulsion system must be
highly integrated and that the airframe design must consider aircraft
operations for slow and steep climbouts and approaches to the airfield,"
writes James I. Hileman, a partner in the MIT-Cambridge team.
Furthermore, the undercarriage [landing gear system] must be simple and
faired, and high-lift and drag must be generated quietly."

The researchers borrowed from studies of the owl's unique soft plumage
on its wings' trailing edge that reduces flow noise, as reported by
Geoffrey M. Lilley, a professor at Southampton University. "The airframe
trailing edges are acoustically treated by deploying brushes to reduce
the airfoil self-noise," Hileman writes. A 4-dB. reduction has been
demonstrated using trailing edge brushes on a scale model aircraft wing.

Etc.

May all your birds be identified,

Denis DeSilvis
Seattle, WA
mailto:denis.j.desilvis at boeing.com