In order for an aircraft to maneuver and maintain its stability, this required for aircraft to have control surfaces. Mainly, the aircraft are divided into two main control surfaces which are the primary flight control and the secondary flight control. The primary flight control is a basic control surfaces used to maneuver such as rolling, pitching and yawing. Meanwhile, secondary flight control surfaces are designed to augment stability, assist pilot control and ease the work-load. Some of the aircraft does not necessarily to have the secondary flight control, but for a jumbo and high performance jet it is very crucial to have the secondary flight control surfaces. Secondary flight control surfaces are often works mechanically or via computer programming by sensing the correction have to make in order to maintain the aircraft stability. Older aircraft does not have as many secondary flight control surfaces compared to the latest jet design. This is because, over the time the engineer working hard enough to increase the aircraft ability, performance and capability. Nowadays, all the latest aircraft design are fitted with sophisticated devices to increase its performance and reliability.
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Boeing 747-400 Flight Control Surfaces
This aircraft consists of primary flight control surfaces and secondary flight control surfaces. The primary flight control surfaces are aileron, elevator and rudder. This aircraft uses spoilers, trailing edge flaps, leading edge flaps, and an adjustable horizontal stabilizer for its secondary flight control surfaces. Secondary Flight Control Surfaces
1. Wing Flaps
It is devices used to improve the lift characteristics and are mounted on the trailing edges of the wings. It also can be used to reduce the speed at which the aircraft can be safely flown and to increase the angle of descent for landing. A. Flaps during take-off
Flaps are extended at a specific value in accordance to the manual. Flap at this configuration are used to trade runway distance for climb rate. B. Flaps during landing
Flaps may be fully extended for landing to give the aircraft a lower stall speed so the approach to landing can be flown more slowly, which also allows the aircraft to land in a shorter distance.
C. Types of flap
This aircraft consist of 2 triple slotted trailing edge flaps and 14 leading edge flaps on each wing. The three inboard leading edge flaps on each wing are krueger flaps with a folding nose which extends as the flaps are extended. The remaining eleven leading edge flaps on each wing are variable camber flaps with camber which is changed by mechanical linkages as the flaps are extended.
2. Wing Spoilers
Spoilers are hydraulically powered. When used for lateral control, the spoilers are controlled by a mechanical output from the aileron control system. When used as speed brakes, the spoilers are controlled from the speed brake lever on the pilots’ control stand. There are 6 spoiler panels on each wing where 2 are ground spoilers ant the rest are flight spoilers.
A. The lateral control system
The lateral control system is trimmed by shifting the neutral position of the aileron control system with an electric motor-driven aileron trim actuator. The actuator is controlled by switches on the pilots’ control stand. B. The directional control system
The directional control system is trimmed by shifting the neutral position of the rudder control system with an electric trim actuator controlled by the rudder trim knob on the pilots ‘control stand. C. Pitch trim control system
Pitch trim of the airplane is set by the position of the horizontal stabilizer. The horizontal stabilizer is positioned to provide pitch trim. Stabilizer trim is set by a hydraulically powered drive mechanism.
Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower speeds, or take off and land in shorter distances. They are usually used while landing or performing maneuvers which take the aircraft close to the stall, but are usually retracted in normal flight to minimize drag.
For the conclusion, the secondary flight control surfaces in Boeing 747-400 are almost the same as the other aircraft. The secondary flight control surface plays very important role for a large aircraft. It’s used to maintain stability and assist the pilot control. Without this flight control surface the aircraft would be much difficult to be operated.