The Airbus A320 series aircraft on the wings can increase lift at different phases of flight and this is possible with the use of Flaps at the aft of the wing and Slats at the front of the wing.
The devices allow the wing profile to change – the physical wing of course cannot move or change, we use devices on the wing to aid control, such as the Ailerons for roll control and the spoilers to assist roll control, operate as speed brakes, and dump lift.
The slats and flaps however are there to change the lift characteristics and are commonly called “high lift devices”. They can allow us to create more lift in certain conditions such different angles of attack and reduce the take-off roll distance.
For the A320 the slats and flaps are electrically controlled and hydraulically operated. Two Slat Flap Control Computers (SFCCs) ensure control and monitoring.
The slat and flap systems are similar.
A Power Control Unit (PCU) drives each system with two hydraulic motors coupled to a differential gearbox. Torque shafts and gearboxes transmit the mechanical power to the actuators, which drive the surfaces.
Each motor is powered by a different hydraulic system and has its own valve block and Pressure Off Brake (POB). Valve blocks control the direction of rotation and the speed of their related PCU output shaft. The POB locks the transmission when the slat and flap surfaces have reached the selected position or if hydraulic power fails.
Wing Tip Brakes (WTBs) are provided to stop and lock the system when major failures are detected. They are hydraulically activated and can only be reset on ground.
Position Pick-Off Units (PPUs) send slat and flap position feedback.
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