A320 flight control

General
The two pilots use sidestick to control the Airbus A320 aircraft in pitch and roll. The computers receive pilot input and move the flight control surface. There is no direct mechanical link between the sidestick and the flight control surfaces. When in normal law, the computers will prevent excessive maneuvers in pitch and roll.
Flight Control
The two sidestick controllers are not coupled mechanically, and they send separate sets of signals to the flight control computers.
Two pairs of pedals, which are rigidly interconnected, give the pilot mechanical control of the rudder. As on conventional aircrafts, there is no flight enveloppe protection for the rudder. A single switch on the center pedestal enables to set the rudder trim.
The speed brakes are controlled with a lever on the center pedestal.
Two mechanically interconnected handwheels on each side of the center pedestal enable to control the trimmable horizontale stabilizer.
Pitch control
Two elevators and the Trimmable Horizontal Stabilizer (THS) control the aircraft pitch. The maximum elevator deflection is 30 degree nose up and 17 degree nose down. The maximum THS deflection is 13.5 degree nose up and 4 degree nose down.
The elevators and the THS are controlled by the computer. Mechanical control of the THS is available from the pitch trim wheel at any time. It has priority over electrical control.
Roll control
Rotation around the roll axis is controlled by one aileron and four spoilers on each wing. The maximum deflection of the ailerons is 25 deg. The ailerons extend 5 degree down when the flaps are extended (aileron droop). The maximum deflection of the spoilers is 35 deg.
Speedbrakes and spoilers control
The speedbrakes are controlled by the speed brake lever. The speedbrakes are actually spoilers 2,3 and 4.
The maximum speedbrake deflection in manual flight is 40 deg for spoilers 3 and 4, and 20 deg for spoiler 2. The maximum speedbrake deflection with the autopilot engaged is 25 deg for spoilers 3 and 4, and 12.5 deg for spoilers 2.
The spoilers 2, 3 and 4 perform both roll and speedbrake functions; the roll function has priority. When the sum of a roll order and a simultaneous speedbrake order on one surface is greater than the maximum deflection available in flight, the same surface on the other wing is retracted until the difference between the two surfaces is equal to the roll order.
Ground spoiler control
The ground spoilers are spoilers 1 to 5. The pilot arms the ground spoilers by pulling the speedbrake controler lever up in the armed position. The ground spoilers then automatically extend at landing when both main landing gears have touched down. They retract after landing when the ground spoilers are disarmed, or during a touch and go,
when at least one thrust lever is advanced above 20 deg.
Yaw Control
Yaw is controlled by the rudder surface. Yaw order is calculated by the computer to achieve turn coordination and to damp yaw oscillations. The pilots can use conventional rudder pedals to control the rudder.
The deflection of the rudder is limited as a function of speed: 25 deg from speed 0 to 160 knots, decreasing to 3.4 deg at speed 380 and constant after.
In manual flight, the pilot can apply rudder trim with the rotary RUD TRIM switch on the pedestal.
Normal Law
Pitch Control
Ground mode: there is direct relationship between sidestick deflection and elevator deflection. The THS is automatically set at 0. During take-off, when the speed reaches 70 knots, maximum elevator deflection is reduced from 30 deg to 20 deg. Take-off is performed in direct law. After take-off the system blends to flight mode
Flight mode: the sidestick determines the elevator and THS position in order to maintain a load factor proportional to sidestick deflection. In normal turn (up to 33 deg), the pilot does not have to make any pitch corrections.
Flare mode: below 50 feet before landing, the aircraft switches to flare mode. The pitch attitude at this point becomes the reference for pitch attitude control.
Lateral Control
Ground mode: the sidestick commands the aileron and spoiler deflection. For a given sidestick deflection, the amount of aileron and spoiler deflection depends on speed.
Flight mode: the roll rate is proportional to sidestick deflection, with a maximum rate of 15 deg per seconds.
Flare mode: same as flight mode.
Protections
Load factor limitation: the load factor is automatically limited from +2.5 g to -1 g.
Pitch attitude limitation: 30 deg nose up in flap configuration 0 to 3, 25 deg nose up in flap configuration Full, 15 deg nose down.
High angle of attack protection: when the angle of attack becomes higher than αprot, the system switches to a mode in which the angle of attack is proportional to sidestick deflection, up to αmax. For neutral sidestick the system comes back to αprot. To desactivate the angle of attack protection, the pilot must push the stick more than 8 deg forward, or more than 0.5 deg forward for at least 0.5 second, when the angle of attack α is < αprot.
Bank angle protection: the bank angle cannot go beyond 67 deg. If the pilot releases the sidestick above 33 deg bank angle, the aircraft goes back to 33 deg. If the angle of attack protection or high speed protection is active, the bank angle limit goes from 67 deg to 45 deg. For high speed protection and neutral sidestick, the aircraft goes back to 0 deg bank angle.
Flaps and slats
Each wing has 2 flaps and 5 slats to increase sustentation. They are controlled by the flap lever on the central pedestal.
The flap lever has 5 positions: 0, 1, 2, 3 and FULL.
Alpha/speed lock function: slat retraction from position 1 to position 0 is inhibited if angle of attack exceeds 8.6 deg or speed falls below 148 knots. The inhibition is removed when angle of attack falls below 7.6 deg or speed exceeds 154 knots. This function is not active if aircraft is on the ground with speed less than 60 knots.

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