Secondary flight controls include those controls not designated as primary controls. The secondary controls supplement the primary controls by aiding the pilot in controlling the aircraft. Various types are used on naval aircraft, but only the most common are discussed here.

TRIM TABS. -Trim tabs are small airfoils recessed in the trailing edge of a primary control surface. Their purpose is to enable the pilot to neutralize any unbalanced condition that might exist during flight, without exerting any pressure on the control stick or rudder pedals. Each trim tab is hinged to its parent control surface, but is operated independently by a separate control. 

The pilot moves the trim tab by using cockpit controls. The tab on the control surface moves in a direction opposite that of the desired control surface movement. The airflow striking the trim tab causes the larger surface to move to a position that will correct the unbalanced condition of the aircraft. For example, to trim a nose-heavy condition, the pilot sets the elevator trim tab in the "down" position. This causes the elevator to be moved and held in the "up" position, which, in turn, causes the tail of the aircraft to be lowered. Without the use of the trim tab, the pilot would have to hold the elevator in the up position by exerting constant pressure on the control stick or wheel.

Construction of trim tabs is similar to that of the other control surfaces, although greater use is being made of plastic materials to fill the tab completely. Filling the tab improves stiffness. Tabs may also be honeycomb filled. Tabs are covered with either metal or reinforced plastic. Trim tabs are actuated either electrically or manually.

WING FLAPS. -Wing flaps are used to give the aircraft extra lift. Their purpose is to reduce the landing speed, thereby shortening the length of the landing

rollout. They are also used to assist in landing in small or obstructed areas by permitting the gliding angle to be increased without greatly increasing the approach speed. In addition, the use of flaps during takeoff serves to reduce the length of the takeoff run.

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 1-9. 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 the wing skin, In the extended position, the spoiler is pivoted up and forward approximately 60 degrees above the hinge point. The spoilers disturb the smooth flow of air over the wing so that burbling takes place. The lift is

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 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 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.