SMART MATERIALS—MATERIALS THAT ADAPT TO CHANGING CONDITIONS - Chemistry: Notable Research and Discoveries - page 124

Compare the wing shape of a soaring bird (left) with a diving bird
(right).
Although modern airplanes have features such as fl aps and rudders that
provide control and some degree of adaptability, the change in shape
of the wings is modest compared to the ability of peregrine falcons and
other birds. Th e fi gure above compares the shape of a falcon's wings
when soaring and diving. Adaptations as eff ective as these shape-chang-
ing wings are main goals of smart airplane technology.
Th e U.S. Air Force is particularly interested in developing this tech-
nology. Air Force planes must accomplish a variety of diff erent tasks,
from ground support to high-altitude bombing. Since airplanes are not
very adaptable, each type must be optimized for a single task, which re-
quires specifi c geometrical and structural properties. Th e Air Force has
heavy bombers to drop high-explosive weapons, maneuverable fi ghters
to engage enemy aircraft , and soaring reconnaissance airplanes to scout
enemy positions. Procuring and maintaining a fl eet of all these diff erent
airplanes is a tremendously expensive job. Any one of these sophisticated
airplanes requires millions or even billions of dollars to design and test,
and they can be equally costly to build—a B-2 Spirit, for example, has a
price tag of more than $2 billion.