Rotation about the longitudinal axis is called roll and is controlled by the outboard movable portions of each wing: the ailerons. The term "aileron" is the French word for "little wing." Ailerons are located on the trailing (rear) edge of each wing near the outer tips. When deflected up or down, they in effect change the wing's camber (curvature) and its angle of attack. This changes the wing's lift and drag characteristics.
Their primary use is to bank (roll) the airplane around its longitudinal axis. The banking of the wings results in the airplane turning in the direction of the bank, i.e., toward the direction of the low wing.
The ailerons are interconnected in the control system to operate simultaneously in opposite directions of each other. As the aileron on one wing is deflected downward, the aileron on the opposite wing is deflected upward.
The ailerons are controlled by turning the control yoke.
secondary effect of aileron actuation
The ailerons primarily control bank. However because the air underneath a wing is denser than that above it, the lowering aileron causes more drag on its side than the rising aileron. Using ailerons causes a small amount of yaw to occur. This is more pronounced for light aircraft with long wings, such as gliders. It is usually counteracted by the pilot with the rudder. Another most import consideration is that the stall speed of the aircraft increases with the angle of roll. Large angles of bank at slow speed may very well result in a stall and spin.
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Vertical (yaw) axis -- an imaginary line extending vertically through the intersection of the lateral and longitudinal axes
Rotation about the vertical axis is called yaw and is controlled by the rudder. This rotation is referred to as directional control or directional stability.
The rotation is similar to a weather vane, in which the post holding the vane is the vertical axis but the rotation is directional.
The rudder is attached to the vertical stabilizer. Controlled by the rudder pedals, the rudder is used by the pilot to control the direction (left or right) of yaw about the airplane's vertical axis for minor adjustments. It is NOT used to make the airplane turn, as is often erroneously believed. Banking the airplane makes it turn.
When the foot pressure on the left rudder pedal moves the rudder to the left, causing the nose of the airplane to move to the left.
When the foot pressure on the right rudder pedal moves the rudder to the right, causing the nose of the airplane to move to the right.
secondary effect of rudder actuation
Using the rudder causes one wing to move forward faster than the other. Increased speed means increased lift, and hence rudder use causes a small roll effect. For this reason ailerons and rudder are generally used together on light aircraft.
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The application of power will increase the aircraft speed with a secondary effect of climb. A reduction in power will reduce speed with a secondary effect of descent.
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