Forces Acting on an Airplane
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The increased lift forces the tail upward, causing the nose to drop. Conversely, when back pressure is applied on the wheel, the elevators move upward, decreasing the lift produced by the horizontal tail surfaces, or maybe even producing a downward force. The tail is forced downward and the nose up.
The elevators control the angle of attack of the wings. When back pressure is applied on the control wheel, the tail lowers and the nose raises, increasing the angle of attack. Conversely, when forward pressure is applied, the tail raises and the nose lowers, decreasing the angle of attack.
Rudder: The rudder controls movement of the airplane about its vertical axis. This motion is 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 the rudder to the rudder pedals. Trim Tabs: A trim tab is a small, adjustable hinged surface on the trailing edge of the aileron, rudder, or elevator control surfaces.
Trim tabs are labor saving devices that enable the pilot to release manual pressure on the primary controls. Some airplanes have trim tabs on all three control surfaces that are adjustable from the cockpit; others have them only on the elevator and rudder; and some have them only on the elevator. Some trim tabs are the ground-adjustable type only.
The tab is moved in the direction opposite that of the primary control surface, to relieve pressure on the control wheel or rudder control. For example, consider the situation in which we wish to adjust the elevator trim for level flight. ("Level flight" is the attitude of the airplane that will maintain a constant altitude.
) Assume that back pressure is required on the control wheel to maintain .Скачать