Flight Controls and the Longitudinal Axis
The longitudinal axis of the airplane runs through the middle of the airplane, from nose to tail, passing through the center of gravity. Movement around this axis is known as roll, and control around this axis is called lateral control. Movement around this axis is controlled by the ailerons, and on jet transport airplanes, it is aided by surfaces on the wing known as spoilers.
The ailerons move as a result of the pilot rotating the control wheel to the left or to the right, much the same as turning the steering wheel on an automobile. [Figure 3-68] When a pilot turns the control wheel to the left, the airplane is being asked to turn or bank to the left. Turning the control wheel to the left causes the trailing edge of the aileron on the left wing to rise up into the airstream, and the aileron on the right wing lowers down into the airstream. This increases the lift on the right wing and decreases the lift on the left wing, causing the right wing to move up and the airplane to bank to the left.
In Figure 3-69, an Air Force F-15 can be seen doing an aileron roll. Notice that the left aileron is up and the right aileron is down, which would cause the airplane to roll around the longitudinal axis in a counterclockwise direction.
Flight Controls and the Vertical Axis
The vertical axis of an airplane runs from top to bottom through the middle of the airplane, passing through the center of gravity. Movement around this axis is known as yaw, and control around this axis is called directional control. Movement around this axis is controlled by the rudder, or in the case of the Beechcraft Bonanza in Figure 3-67, by the ruddervators.
The feet of the pilot are on the rudder pedals, and pushing on the left or right rudder pedal makes the rudder move left or right. When the right rudder pedal is pushed, the trailing edge of the rudder moves to the right, and the nose of the airplane yaws to the right. The rudder pedals of a Cessna 182 can be seen in Figure 3-68.
Even though the rudder of the airplane will make the nose yaw to the left or the right, the rudder is not what turns the airplane. For what is called a coordinated turn to occur, both the ailerons and rudder come into play. Letís say we want to turn the airplane to the right. We start by turning the control wheel to the right, which raises the right aileron and lowers the left aileron and initiates the banking turn. The increased lift on the left wing also increases the induced drag on the left wing, which tries to make the nose of the airplane yaw to the left. To counteract this, when the control wheel is moved to the right, a small amount of right rudder is used to keep the nose of the airplane from yawing to the left. Once the nose of the airplane is pointing in the right direction, pressure on the rudder is no longer needed. The rudder of a Piper Cherokee Arrow can be seen in Figure 3-70.
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