SLATS.--Slats are movable control surfaces
attached to the leading edge of the wing. When the slat
The landing gear of the earliest aircraft consisted
is retracted, it forms the leading edge of the wing. At
merely of protective skids attached to the lower
low airspeed, the slat improves the lateral
surfaces of the wings and fuselage. As aircraft
control-handling characteristics and allows the aircraft
developed, skids became impractical and were replaced
to be controlled at airspeeds below the normal landing
by a pair of wheels placed side by side ahead of the
speed. When the slat is opened (extended forward), a
center of gravity with a tail skid supporting the aft
slot is created between the slat and the leading edge of
section of the aircraft. The tail skid was later replaced
the wing. The slot allows high-energy air to be
by a swiveling tail wheel. This arrangement was
introduced into the air layer moving over the top of the
standard on all land-based aircraft for so many years
wing. This is known as boundary layer control.
that it became known as the conventional landing gear.
Boundary layer control is primarily used during
As the speed of aircraft increased, the elimination of
operations from carriers; that is, for catapult takeoffs
drag became increasingly important. This led to the
and arrested landings. Boundary layer control can also
development of retractable landing gear.
be accomplished by a method of directing
high-pressure engine bleed air through a series of
Just before World War II, aircraft were designed
narrow orifices located just forward of the wing flap
with the main landing gear located behind the center of
gravity and an auxiliary gear under the nose of the
fuselage. This became known as the tricycle landing
AILERON DROOP.--The ailerons are also
gear. It was a big improvement over the conventional
sometimes used to supplement the flaps. This is
type. The tricycle gear is more stable during ground
called an aileron droop feature. When the flaps are
operations and makes landing easier, especially in
lowered, both ailerons can be partially deflected
crosswinds. It also maintains the fuselage in a level
downward into the airstream. The partial deflection
position that increases the pilot's visibility. Nearly all
allows them to act as flaps as well as to serve the
Navy aircraft are equipped with tricycle landing gear.
function of ailerons.
See figure 2-10 for a typical landing gear system.
Figure 2-10.--Typical landing gear system.