Page 86 - Understanding Flight

CH03_Anderson 7/25/01 8:56 AM Page 73

Wings 73

During the early days of flight the Wright brothers advocated a
design in which the airplane was slightly unstable.They felt that
this forced the pilot to pay attention and continually fly the
airplane. Meanwhile, competitors built airplanes that were
inherently stable. Eventually, the Wright brothers could not
compete with these stable designs.This is one factor that has
led to the eventual loss of the Wright name in any airplane
company today.

For completeness we should mention another stabilizing effect of
all wings. Consider an airplane that is rotating because of a gust of air
or a sudden short movement of the ailerons. After the gust of air is
over or the ailerons are back to neutral, the lift on both wings would
seem to be the same, though the inertia keeps the airplane rotating.
But, while the airplane is in rotational motion, the wing going up sees
the relative wind with a reduced angle of attack, and the lower wing
sees an increased angle of attack. This causes a force opposite to the
rotation and tends to bring the rotation to a stop. When the rotation
stops, the counterrotational force also ceases.
Some military aircraft, such as the F-104 (Figure 3.15), have
anhedral wings. Anhedral is negative dihedral; in other words the
wings slope down as seen in the picture. Just as dihedral is stabilizing,
anhedral is destabilizing. As mentioned earlier, stability reduces
maneuverability, so by making the airplane less stable it becomes
more maneuverable. Anhedral is found only on military fighters and
aerobatic airplanes.

High Wings vs. Low Wings

The wing designer must also decide where to put the wing on the air-
plane. Should it be a low wing, high wing, or midwing? What are the
benefits of wing position? The effects of wing position on stability are
fairly minor. A high wing has a little more stability than a low
wing, but the change in stability is small when compared to Howard Hugh’s infamous Spruce
the effects of sweeping the wing and adding dihedral. So, the Goose was actually made mostly
choice of wing position is based on much more practical mat- of birch.
ters. Private pilots frequently argue this point in hangar talks.