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in straight-and-level flight it remains on its course heading even though the pilot takes his or her hands and feet off the controls. If an aircraft recovers automatically from a skid, it has been well designed for directional balance. The vertical stabilizer is the primary surface that controls directional stability. Directional stability can be designed into an aircraft, where appropriate, by using a large dorsal fin, a long fuselage, and sweptback wings. 

## Lateral Stability 

Motion about the aircraft’s longitudinal (fore and aft) axis is a lateral, or rolling, motion. The tendency to return to the original attitude from such motion is called lateral stability. 

## Dutch Roll 

A Dutch Roll is an aircraft motion consisting of an out-of- phase combination of yaw and roll. Dutch roll stability can be artificially increased by the installation of a yaw damper. 

## Primary Flight Controls 

The primary controls are the ailerons, elevator, and the rudder, which provide the aerodynamic force to make the aircraft follow a desired flightpath. [Figure 2-10] The flight control surfaces are hinged or movable airfoils designed to change the attitude of the aircraft by changing the airflow over the aircraft’s surface during flight. These surfaces are used for moving the aircraft about its three axes. 

Typically, the ailerons and elevators are operated from the flight deck by means of a control stick, a wheel, and yoke assembly and on some of the newer design aircraft, a joy- 

stick. The rudder is normally operated by foot pedals on most aircraft. Lateral control is the banking movement or roll of an aircraft that is controlled by the ailerons. Longitudinal control is the climb and dive movement or pitch of an aircraft that is controlled by the elevator. Directional control is the left and right movement or yaw of an aircraft that is controlled by the rudder. 

## Trim Controls 

Included in the trim controls are the trim tabs, servo tabs, balance tabs, and spring tabs. Trim tabs are small airfoils recessed into the trailing edges of the primary control surfaces. [Figure 2-12] Trim tabs can be used to correct any tendency of the aircraft to move toward an undesirable flight 

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