Figure 1-10.—Typical landing gear system.
consequently reduced, and considerable drag is added
to the wing.
Another type of spoiler in common use is a long,
slender, curved and perforated baffle that is raised
edgewise through the upper surface of the wing forward
of the aileron. It also disrupts the flow of air over the
airfoil and destroys lift. These spoilers are actuated
through the same linkage that actuates the ailerons. This
arrangement makes movement of the spoiler dependent
upon movement of the aileron. The linkage to the aileron
is devised so that the spoiler is extended only when the
aileron is raised. In other words, when the aileron moves
downward, no deflection of the spoiler takes place.
SPEED BRAKES.—Speed brakes are hinged,
movable control surfaces used for reducing the speed of
aircraft. Some manufacturers refer to them as dive
brakes or dive flaps. They are hinged to the sides or
bottom of the fuselage or to the wings. Regardless of
their location, speed brakes serve the same purpose on
all aircraft. Their primary purpose is to keep aircraft
from building up excessive speed during dives. They are
also used in slowing down the speed of the aircraft prior
to landing. Speed brakes are operated hydraulically or
electrically.
SLATS. -Slats are movable control surfaces
attached to the leading edge of the wing. When the slat
is retracted, it forms the leading edge of the wing. At
low airspeed, the slat improves the lateral
control-handling characteristics and allows the aircraft
to be controlled at airspeeds below the normal landing
speed. When the slat is opened (extended forward), a
slot is created between the slat and the leading edge of
the wing. The slot allows high-energy air to be
introduced into the air layer moving over the top of the
wing. This is known as boundary layer control.
Boundary layer control is primarily used during
operations from carriers; that is, for catapult takeoffs
and arrested landings. Boundary layer control can also
be accomplished by a method of directing high-pressure
engine bleed air through a series of narrow orifices
located just forward of the wing flap leading edge.
AILERON DROOP.—The ailerons are also
sometimes used to supplement the flaps. This is called
an aileron droop feature. When the flaps are lowered,
both ailerons can be partially deflected downward into
the airstream. The partial deflection aIlows them to act
as flaps as well as to serve the function of ailerons.
LANDING GEAR
The landing gear of the earliest aircraft consisted
merely of protective skids attached to the lower surfaces
of the wings and fuselage. As aircraft developed, skids
became impractical and were replaced by a pair of
wheels placed side by side ahead of the center of gravity
with a tail skid supporting the aft section of the aircraft.
The tail skid was later replaced by a swiveling tail wheel.
This arrangement was standard on all land-based
aircraft for so many years that it became known as the
conventional landing gear. As the speed of aircraft
increased, the elimination of drag became increasingly
important. This led to the development of retractable
landing gear.
Just before World War II, aircraft were designed
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
gear. See figure 1-10. It was a big improvement over the
1-11
