by Bruce Bagnell
A bird that moves silently through the air has sent engineers back to the drawing board.
What horror movie would be
complete without a night scene using an owl or two
hooting in the woods?
NASA flight engineers are especially interested in these night owls
, for they may hold the secret _(1)_ silent
aircraft.
Ornithologists, or bird experts, have long known about the great difference _(2)_ day-flying and night-flying owls. Like all other birds, day-flying owls create sound as they fly, while their _(3)_
cousins do not. A close examination of
the latter explains why. Their
primary feathers are
jagged, much like the teeth of a comb. Their
trailing feathers on the back ends of the wings, _(4)_, are
fringed, much like the ends of a
scarf. Furthermore, the rest of the wings and the legs of the owl are _(5)_ in soft, small feathers. The fringe on owls' trailing feathers helps reduce noise, and the soft, small feathers actually _(6)_ sound. The
combined effects of the feathers
make for silent flights.
As everyone knows, aircraft _(7)_ are extremely noisy. Most airports around the world have strict noise pollution
standards, which means that during a 24-hour period, only a certain amount of _(8)_ noise can be produced. If aircraft can be _(9)_ to be
soundless or nearly silent, airports may be open for business 24 hours a day. The number of
take-offs and
landings could _(10)_, which would be good for business and more convenient for travelers. Flight engineers from
commercial airlines to NASA are excited about the possibility of designing the first silent aircraft as they continue their studies of the world's only silent flying bird.
(A) designed (B) to (C) covered (D) increase (E) in flight (F) in contrast (G) absorb (H) nocturnal (I) measurable (J) between