Secondary Flight Controls

data computer to generate wing sweep commands consistent with the aircraft’s speed, altitude, and configuration of the flaps and slats. If the automatic mode is used to apply the commands, the wings are positioned at a rate of 7.5 degrees per second. Mechanical Control.—When wing sweep is in the mechanical control mode, the wing sweep handle uses the wing sweep/flap and slat control box to position the wings. Because minimum wing sweep limiting is not available in the mechanical control mode, the wings can be swept to an adverse position that could cause damage to the wings. Mechanical control is used for emergency wing sweep and wing oversweep. Secondary Flight Controls 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 Figure 1 -9.—Types of flaps. 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 1-10