Pilots use flight control systems to control the forces of flight and the aircraft’s direction and altitude. Flight control systems and characteristics can vary greatly depending on the type of aircraft you’re flying. The most basic flight control system designs are mechanical and date back to the earliest aircraft. Flight control systems are subdivided into primary and secondary flight controls. In this article, we’ll take a birds eye’s view of flight controls to give you some insights into the general principles and terminology.
Flight Control General Principles
For steady flight, an airplane must be in a state of balance and the controls enable this to happen in all positions. Here are the basic rotation controls around 3 axises:
- Longitudinal axis: Rotation around the longitudinal axis is rolling and is controlled by ailerons, spoilers, or a combination of the two.
- Lateral axis: Rotation around the lateral axis is pitching and is controlled by elevators or by a moving tailplane.
- Normal axis: Rotation around the normal axis is yawning and is controlled by the rudder.
Primary Flight Controls
Primary flight controls are required to safely control an aircraft during flight. They consist of three areas:
- Aileron –controls movement about the longitudinal axis of an aircraft. This movement is referred to as “roll.” Ailerons are attached to the outboard trailing edge of each wing and move in the opposite direction from each other.
- Elevator – controls movement about the lateral axis of an aircraft. The movement is referred to as “pitch.” Most aircraft have two elevators, one mounted on the trailing edge of each half of the horizontal stabilizer.
- Rudder – controls rotation about the vertical axis of an aircraft. This motion is called yaw. The rudder is a moveable surfaced hinged to the vertical stabilizer or fin. The rudder is controlled by the left and right rudder pedals.
Secondary Flight Controls
- Flaps –used during takeoff and landing phases of flight. They help to improve aircraft performance. Flaps increase the airfoil camber, resulting in a significant increase in the coefficient of lift.
- Leading Edge Devices –instruments used to increase the critical angle of attack and delay stalls. The most common type of leading edge high lift devices are fixed slots, movable slats, leading edge flaps, and cuffs.
- Spoilers –are devices intended to reduce the lift component of an airfoil in a controlled way. Typically, spoilers are plates on the top surface of a wing that can be extended upward into the airflow. Sometimes they are called lift spoilers or lift dumpers.
- Trim Systems – used to relieve a pilot of the need to maintain constant pressure on the flight controls and usually consist of light deck controls and small hinged devices attached to the trailing edge of one or more of the primary flight control surfaces.