Stability and Controls

Basic Controls

page 1

The primary controls the pilot uses are the ailerons, the elevators and the rudder. The elevators are the horizontal flaps on the tail assembly. Elevators in buildings go up or down. Elevators on the tail assembly cause the nose of the airplane to point up or down. The rudder is the vertical flap on the tail assembly. It helps the airplane turn. The ailerons are the flaps on the trailing edge of the wing. The ailerons help in banking or turning the aircraft. These are shown clearly in the figure below.

To make a turn, the pilot will move a control device in the cockpit. This is usually either a stick in a fighter-type aircraft or a yoke in most others (the yoke looks similar to a car steering wheel). In making a turn, one aileron goes up and lift decreases. At the same time the other aileron goes down, lift increases. The airplane will roll (turn) with the high lift wing up and lower lift wing down. If a pilot wishes to turn right, he or she will raise the right aileron and lower the left aileron (by moving the stick or yoke to the right). The right wing will dip as the left wing rotates upward. Rolling the airplane is considered a lateral (sideways) motion, so the ailerons are called lateral controls.

The pilot uses the elevators on the tail to pitch the airplane. This means that if the pilot pulls back on the stick or yoke the elevators move up. The lift on the tail surfaces decreases, causing the nose to pitch up (the opposite happens if the stick or yoke is pushed forward). At the nose pitches up (and the wings too) the airflow will increase the overall lift on the plane. The plane will begin to climb. The pitching motion is longitudinal (over the length of the airplane), and so the elevators are known as longitudinal controls.

To start a yawing (turning) motion, the pilot will use the rudder. Almost all rudders are controled by pedals operated by the feet of the pilot. If the pilot steps on the right rudder pedal, the rudder moves to the pilot's right. The pressures on the right side of the rudder are now higher. The plane begins to rotate in a clockwise direction, or to the right! The rudder is called a directional control, since yawing is considered a directional motion.

Rolling and yawing of the airplane are related; it is very hard to do one without the other. For example, during a right turn, when the lift is increased on the left wing, drag is also increased on that same wing. This causes the airplane to be pushed slightly to the left. To overcome this, the pilot will push the right rudder pedal. So, in most cases he or she will use both the ailerons and the rudder to turn the aircraft.

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Last modified: Wed Aug 19 20:50:57 PDT 1998

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