Secondary Flight Controls: Wing flaps, leading edge devices, spoilers, and trim systems constitute the secondary control system.

Flaps increase the Camber, Angle of Attack (AoA) and sometimes the area of the wing. When increasing the Camber and AOA of the wing, also increase the amount of lift the wing can produce. With Flaps down, the wing can produce more lift at slower speeds. But also produce drag, as we refer previously. This drag isn’t always a bad thing, especially when you’re trying to reduce speed for landing. But during takeoff, it could make your aircraft work harder to get into the air.

Leading-edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading-edge slot is a spanwise gap in each wing, allowing air to flow from below the wing to its upper surface. In this manner they allow flight at higher Angles of Attack and thus reduce the stall speed by producing less drag.

Found on some fixed-wing aircraft, high drag devices called spoilers are deployed from the wings to spoil the smooth airflow, reducing lift and increasing drag. On gliders, spoilers are most often used to control rate of descent for accurate landings. On other aircraft, spoilers are often used for roll control, an advantage of which is the elimination of “Adverse Yaw”. To turn right, for example, the spoiler on the right wing is raised, destroying some of the lift and creating more drag on the right. The right wing drops, and the aircraft banks and yaws to the right. Deploying spoilers on both wings at the same time allows the aircraft to descend without gaining speed. Spoilers are also deployed to help reduce ground roll after landing. By destroying lift, they transfer weight to the wheels, improving braking effectiveness.

Although an aircraft can be operated throughout a wide range of attitudes, airspeeds, and power settings, it can be designed to fly hands-off within only a very limited combination of these variables. Trim systems are used to relieve the pilot of the need to maintain constant pressure on the flight controls, and usually consist of flight deck controls and small hinged devices attached to the trailing edge of one or more of the primary flight control surfaces. Common types of trim systems include trim tabs, balance tabs, antiservo tabs, ground adjustable tabs, and an adjustable stabiliser.

Wing flaps, leading edge devices, spoilers, and trim systems constitute the secondary control system and improve the performance characteristics of the aeroplane or relieve the pilot of excessive control forces.