Control Surfaces PDF

**CONTROL SURFACES** The movements of the aircraft in flight are produced and controlled by the control surfaces. Then, these surfaces will be examined under their functional aspect, that is, how they work. An airplane may turn about three **axes**. They intersect at the center of gravity of the a...

**CONTROL SURFACES** The movements of the aircraft in flight are produced and controlled by the control surfaces. Then, these surfaces will be examined under their functional aspect, that is, how they work. An airplane may turn about three **axes**. They intersect at the center of gravity of the airplane and each one is perpendicular to the other two. **Longitudinal Axis**. The imaginary line which extends **lengthwise**, from nose to tail, is the longitudinal axis. The motion about the longitudinal axis is **roll** and is produced by the movement of the ailerons located at the trailing edges of the wings. **Lateral Axis.** The imaginary line which extends **crosswise**, wing tip to wing tip, is the lateral axis. The motion about the lateral axis is **pitch** and is produced by the movement of the elevators at the rear of the horizontal tail unit. **Vertical Axis**. The imaginary line which passes **vertically** through the center of gravity is the vertical axis. The motion about the vertical axis is **yaw** and is produced by the movement of the rudder located at the rear of the vertical tail unit. **Ailerons**. The two ailerons, one at the outer trailing edge of each wing, are movable surfaces that control the movement of the airplane about the longitudinal axis (roll). Lowering the aileron on one wing raises the aileron on the other. For example, when the left aileron goes down, the right aileron goes up, rolling the airplane to the right. The wing with the lowered aileron goes up because of its increased lift -- the wing camber is increased; the wing with the raised aileron goes down because of its decreased lift -- the wing camber is decreased. **Elevators**. The elevators control the movement of the airplane about its lateral axis (pitch). The elevators form the rear part of the horizontal tail unit and are free to swing up and down. They are hinged to a fixed surface -- the horizontal stabilizer. Together, the horizontal stabilizer and the elevators form a single airfoil.A change in position of the elevators modifies the camber of the airfoil which increases or decreases lift. When the elevators move downwards, the lift produced by the horizontal tail surfaces is increased. The increased lift forces the tail upwards, causing the nose to drop. Conversely, when the elevators move upwards, the lift produced by the horizontal tail surfaces is decreased. The tail is forced downwards and the nose up. The elevators control the angle of attack of the wings. When the tail lowers, the nose rises, increasing the angle of attack. Conversely, when the tail rises, the nose lowers, decreasing the angle of attack. **Rudder**. The rudder controls the movement of the airplane about its vertical axis (yaw). Like the other primary control surfaces, the rudder is a movable surface hinged to a fixed surface which, in this case, is the vertical stabilizer, or fin. Its action is very much like that of the elevators, except that it swings in a different plane -- from side to side instead of up and down. Control cables connect ailerons and elevators to the control stick (or control wheel) and the rudder to the rudder pedals in the cockpit.