the wing skin. In the extended position, the spoiler is
The pilot moves the trim tab by using cockpit
pivoted up and forward approximately 60 degrees
controls. The tab on the control surface moves in a
above the hinge point. The spoilers disturb the smooth
direction opposite that of the desired control surface
flow of air over the wing so that burbling takes place.
movement. The airflow striking the trim tab causes the
The lift is consequently reduced, and considerable drag
larger surface to move to a position that will correct the
is added to the wing.
unbalanced condition of the aircraft. For example, to
trim a nose-heavy condition, the pilot sets the elevator
Another type of spoiler in common use is a long,
trim tab in the "down" position. This causes the elevator
slender, curved and perforated baffle that is raised
to be moved and held in the "up" position, which, in
edgewise through the upper surface of the wing forward
turn, causes the tail of the aircraft to be lowered.
of the aileron. It also disrupts the flow of air over the
Without the use of the trim tab, the pilot would have to
airfoil and destroys lift. These spoilers are actuated
hold the elevator in the up position by exerting constant
through the same linkage that actuates the ailerons.
pressure on the control stick or wheel.
This arrangement makes movement of the spoiler
dependent upon movement of the aileron. The linkage
Construction of trim tabs is similar to that of the
to the aileron is devised so that the spoiler is extended
other control surfaces, although greater use is being
only when the aileron is raised. In other words, when
made of plastic materials to fill the tab completely.
the aileron moves downward, no deflection of the
Filling the tab improves stiffness. Tabs may also be
spoiler takes place.
honeycomb filled. Tabs are covered with either metal or
reinforced plastic. Trim tabs are actuated either
SPEED BRAKES.--Speed brakes are hinged,
electrically or manually.
movable control surfaces used for reducing the speed of
WING FLAPS.--Wing flaps are used to give the
aircraft. Some manufacturers refer to them as dive
aircraft extra lift. Their purpose is to reduce the landing
brakes or dive flaps. They are hinged to the sides or
speed, thereby shortening the length of the landing
bottom of the fuselage or to the wings. Regardless of
rollout. They are also used to assist in landing in small
their location, speed brakes serve the same purpose on
or obstructed areas by permitting the gliding angle to be
all aircraft. Their primary purpose is to keep aircraft
increased without greatly increasing the approach
from building up excessive speed during dives. They
speed. In addition, the use of flaps during takeoff serves
are also used in slowing down the speed of the aircraft
to reduce the length of the takeoff run.
prior to landing. Speed brakes are operated
hydraulically or electrically.
Most flaps are hinged to the lower trailing edges of
the wings inboard of the ailerons, however, leading
edge flaps are in use on some Navy aircraft. Four types
of flaps are shown in figure 2-9. The PLAIN flap forms
the trailing edge of the airfoil when the flap is in the up
position. In the SPLIT flap, the trailing edge of the
airfoil is split, and the bottom half is so hinged that it
can be lowered to form the flap. The FOWLER flap
operates on rollers and tracks. This causes the lower
surface of the wing to roll out and then extend
downward. The LEADING EDGE flap operates
similarly to the plain flap. It is hinged on the bottom
side and, when actuated, the leading edge of the wing
actually extends in a downward direction to increase
the camber of the wing. Leading edge flaps are used in
conjunction with other types of flaps.
SPOILERS.--Spoilers are used for decreasing
wing lift; however, their specific design, function, and
use vary with different aircraft.
The spoilers on some aircraft are long, narrow
surfaces hinged at their leading edge to the upper wing
skin. In the retracted position, the spoiler is flush with
Figure 2-9.--Types of flaps.