Page 50 - 2006 DT 12 Issues

Stealth wing absorb the remaining frequencies limits the number of take-offs and
above 2,000 hertz, enabling a noise- landings allowed. A recent proposal
s the sun drops behind the less approach. These unique stealth to shift departure paths to increase fuel
Spring Mountains, twilight adaptations make nocturnal owls the efficiency, reduce waiting time on the
Aquickly fades to darkness. quietest flying bird and completely runway and enable more flights per
This is the moment night stalkers have silent to their prey. day has become a contentious issue for
been waiting for, none more eagerly As if stealth weren’t enough of an some Las Vegas residents because the
than owls. They rule the night with advantage, Mother Nature has given change in flight path means potentially
swift and deadly silence. owls superb night vision, as well. But more noise.
For most birds, including day- another weapon in the owls’ arsenal Many noise reduction techniques
active owls, flight involves noise as can sometimes be a greater asset than are already in use on various parts
air passing over their wings creates sharp eyes in locating prey—an acute of an aircraft, including the engines.
a swooshing turbulence most prey sense of hearing. Because one ear is Some ideas for applying owl-feather
can hear. Not so for nocturnal owls, positioned higher and more forward technology might include a retractable
however, whose particular gifts in- than the other and each has a dif- brush-like fringe to mimic trailing
clude a unique set of wing feathers. ferent shape, owls hear sounds a bit edge feathers and a velvety coating on
The “primary feathers” the landing gear. The critical hurdle is
on the leading edge not to increase drag on the aircraft once
are serrated, like the it reaches cruising altitude and speed.
teeth of a comb. The NASA’s highly ambitious goal
trailing feathers on the for QAT is noise reduction in sub-sonic
back edge resemble aircraft by 50% in 10 years and 75% in
the tattered fringe of 25 years, using 1997 levels as a base-
a shawl. line. Mimicking the stealth world of
The leading edge silent wings is a worthy, but daunting,
feathers contribute goal. After all, the owls have been at it
more to stability than sound -damp- differently in each ear, helping them for at least 20 million years. 
ing. But the fringe-like trailing edge pinpoint the direction the sound is
produces “a very large noise reduction coming from. With sound-damping General Meeting
at the speed owls fly,” says Geoffrey feathers, owls can take full advantage and Election, August 12
Lilley, professor emeritus of aeronau- of their hearing abilities.
tics and astronautics at the University Nature’s engineering has in- et ready for our favorite
of Southampton in England. Lilley creasingly become a model for high meeting of the year! Lovely
has pioneered in studying owls’ technology. In the world of aircraft GRed Springs will be a perfect
silent flight for the Quiet Air- design, noise reduction research is a backdrop for late summer evening
craft Technology (QAT) project at priority at every major airport in the na- breezes and early twilight. Sign-in is
NASA’s Langley Research Center in tion, second only to fuel efficiency. at 4:30 p.m., with the meeting starting
Hampton, Virginia. The trailing edge David Lockard, a NASA research at 5:00. Our after-meeting dinner will
fringed feathers help to break up the scientist and colleague of Lilley’s, be catered, once again, by John Mull’s
sound waves produced when air is believes that lessons learned from the Road-Kill-Grill. Bring your own cool-
forced over the top of the wing and study of owl feathers have the potential ers with beer/and or wine if you’d like.
forms downstream wakes. The uneven to increase where and how often planes Check the August Desert Trumpet for
feathers change the angle of the air can take off and land. Busy airports, a complete agenda.
flow, reducing the amount of noise like McCarran Airport in Las Vegas, At this all-important meeting,
generated by the wakes. Down feath- have a limit on the amount of noise the 2006-07 Proposed Budget will
ers on the legs and other parts of the per day a carrier can generate. This be presented for your review and ap-
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