1 / 20

Which of the following are an aircraft's secondary flight controls?

  • A

    Elevator, rudder, aileron.

  • B

    All movable parts on the aircraft which aid in controlling the aircraft.

  • C

    Elevator, rudder, aileron, trim tabs, high-lift wing devices, power controls.

  • D

    Wing flaps, leading edge devices, spoilers or speedbrakes, trim systems.

Primary Flight Controls

Aircraft control systems are carefully designed to provide adequate responsiveness to control inputs while allowing a natural feel. At low airspeeds, the controls usually feel soft and sluggish, and the aircraft responds slowly to control applications. At higher airspeeds, the controls become increasingly firm and aircraft response is more rapid.

Movement of any of the three primary flight control surfaces (ailerons, elevator or stabilator, rudder), changes the airflow and pressure distribution over and around the airfoil. These changes affect the lift and drag produced by the airfoil/ control surface combination, and allow a pilot to control the aircraft about its three axes of rotation.

Design features limit the amount of deflection of flight control surfaces. For example, control-stop mechanisms may be incorporated into the flight control linkages, or movement of the control column and/or rudder pedals may be limited. The purpose of these design limits is to prevent the pilot from inadvertently overcontrolling and overstressing the aircraft during normal manoeuvres.

A properly designed aircraft is stable and easily controlled during normal manoeuvring. Control surface inputs cause movement about the three axes of rotation. The types of stability an aircraft exhibits also relate to the three axes of rotation.


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.

Spoilers

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.

Trim Systems

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.

Designed to help minimise a pilot’s workload, trim systems aerodynamically assist movement and position of the flight control surface to which they are attached. 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.

Your Notes (not visible to others)



This question has appeared on the real examination, you can find the related countries below.

  • Austro Control