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  • Post category:Structure
  • Post last modified:August 26, 2021

For an aircraft to reach its destination, the forces of flight have to be precisely manipulated. To do this, aircraft have control surfaces that can direct airflow in very specific ways.

Flight control surfaces are hinged (movable) airfoils designed to change the attitude of the aircraft during flight. These surfaces are divided into three groups – primary, secondary, and auxiliary.

There are three axes on which an aircraft can turn: the lateral axis, the longitudinal axis, and the vertical axis.

Primary Flight Control Surfaces

The movement of any primary flight control surface causes the aircraft to rotate around the axis of rotation associated with the control surface.

Primary Control SurfaceAircraft MovementAxis of RotationType of Stability
AileronRollLongitudinalLateral
Elevator/StabilatorPitchLateralLongitudinal
RudderYawVerticalDirectional

Secondary/Auxiliary Flight Control Surfaces

An aircraft may possess none, one, or a combination of these control surfaces.

NameLocationFunction
FlapsInboard trailing edge of wingsExtends the camber of the wing for greater lift and slower flight.
Allows control at low speeds for short field takeoffs and landings.
Leading-edge flapInboard leading edge of the wingExtends the camber of the wing for greater lift and slower flight.
Allows control at low speeds for short field takeoffs and landings.
SlatsMid to outboard leading edge of the wingExtends the camber of the wing for greater lift and slower flight.
Allows control at low speeds for short field takeoffs and landings.
SlotsThe outer leading edge of wing forward of aileronsDirects air over the upper surface of the wing during a high angle of attack.
Lowers stall speed and provides control during slow flight.
SpoilersUpper and/or trailing edge of the wingDecreases (spoils) lift.
Can augment the aileron function.
Trim tabsThe trailing edge of primary flight control surfacesReduces the force needed to move a primary control surface.
Balance tabsThe trailing edge of primary flight control surfacesReduces the force needed to move a primary control surface.
Anti-balance tabsThe trailing edge of primary flight control surfacesIncreases feel and effectiveness of primary control surface.
Servo tabsThe trailing edge of primary flight control surfacesAssists or provides the force for moving a primary flight control.

Flight Control Tabs

TypeDirection of motion in relation to control surfaceActivationEffect
Trim tabOpposite directionSet by the pilot from the cockpit. Uses independent linkage.Statically balances the aircraft in flight. Allows “hands-off” maintenance of flight conditions.
Balance tabOpposite directionMoves when the pilot moves control surface. Coupled to control surface linkage.Aids pilot in overcoming the force needed to move the control surface.
Servo tabOpposite directionDirectly linked to flight control input device. Can be primary or backup means of control.Aerodynamically positions control surfaces that require too much force to move manually.
Anti-balance or Anti-servo tabSame directionDirectly linked to flight control input device.Increases force needed by the pilot to change flight control position. De-sensitizes flight controls.
Spring tabOpposite directionLocated in line of direct linkage to servo tab. Spring assists when control forces become too high in high-speed flight.Enables moving control surface when forces are high. Inactive during slow flight.

AH Team

Our team at AviationHunt is a group of aviation experts and enthusiasts. We aim to provide the best aircraft maintenance practices, technology, and aviation safety tips.

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