(b) Pitch
The aircraft pitch control is achieved from the side sticks and in certain cases, from the pitch trim control wheels, which act on the elevators and on the THS, depending on the different laws.
1 Nz law
This law, elaborated in the FCPCs, is the normal pitch law engaged in the flight phase.
Through a pitch action on the side stick, the pilot commands a load factor ; the Nz law achieves this command, depending on the aircraft feedbacks, so that:
- The short-term orders are achieved by the elevator servo controls.
- The long-term orders are achieved by the THS actuator (autotrim function).
The gains depend on the Vc, on the flap and slat position and on the CG location.
In addition, the Nz law permits to achieve:
- A load factor limitation, depending on the flap and slat position.
- A bank angle compensation, for bank angles lower than 33°.
- A deflection limitation of the THS in the nose-up direction in the event of the activation of the high angle-of-attack protection, the excessive load factor and the excessive bank angle exceeding.
The Nz law is such that the aircraft response is quasi independent of the aircraft speed, weight, and CG location.
If both ADIRUs are failed, the Nz law is kept, but with limited pitch rate and gains. A consolidation of the vertical acceleration and pitch attitude rate is then performed via the two accelerometer units.
2 Flare law
This law, elaborated in the FCPCs, is engaged at landing, during the flare phase.
It elaborates an elevator control order from a pitch command on a side stick and the aircraft inertial feedbacks.
The purpose of this law is to make the pilot regain the behavior of a conventional aircraft near the ground.
3 Pitch derotation law for landing
This law, elaborated in the FCPCs, is engaged when the aircraft has touched the ground until pitch angle is less than 0.5°
A pitch demand depending on pitch rate and side stick position is added to the ground law orders.
The purpose of this law is to avoid hard nose wheel impact.
4 Pitch direct law
This law, elaborated in the FCPCs and FCSCs, is engaged on the ground or upon loss of the Nz law.
A pitch order on the side stick directly controls an elevator deflection as per a kinematic.
In flight, the maximum up and down deflections are function of the CG location (in FCPC only) and slat and flap position so that:
- The load factor is limited at high speed
- A minimum maneuverability is obtained at low speed.
On the ground, the pitch direct law is such that the pilot can control maximum authority of the elevators.
The THS actuator control is performed from the trim control wheel by means of a mechanical linkage.
5 High angle of attack protection (ALPHA 1)
This law, elaborated in the FCPCs, can be engaged in the flight and flare phases.
It replaces the Nz law when the aircraft angle of attack exceeds the protection angle of attack (called ALPHA PROT).
A pitch order on the side stick then controls an angle of attack proportional to the side stick position.
The maximum angle of attack commanded with the stick in full nose-up position (called ALPHA MAX) is lower than the stall angle of attack.
The gains of this law depend on the Vc, flap and slat position and CG location.
The purpose of this law is to provide:
- A protection against stalls during maneuvers or in case of wind gusts.
- An improved resistance to windshear.
6 Vc PROT law
This law, elaborated in the FCPCs, can be engaged in the flight and flare phases, in the event of loss of the ALPHA1 law.
It replaces the Nz law when the aircraft speed becomes less than a threshold (Vc PROT).
A pitch order on the side stick then directly commands an elevator deflection order to which a stability order with limited authority is added.
The gains of the Vc PROT law depend on the slat and flap position.
The purpose is to provide stall protection through enhanced static stability at very low speed , while being still overrideable by the pilot.
7 High Speed protection
This law, elaborated in the FCPCs, can be only engaged in the flight law.
It permits, while staying in the Nz law, to add to the pilot's orders a positive load factor when the aircraft speed or Mach number exceeds VMO or MMO plus a certain threshold.
In normal conditions (VMO1 law), the pilot's authority is reduced in the nose down direction in order to make this protection not overrideable.
In degraded conditions (VMO2 law), the pilot's authority is not reduced.
The purpose of the high speed protection is to limit speed or Mach excursions beyond VMO or MMO, by adding a positive static stability.
8 Pitch attitude protection
This law, elaborated in the FCPCs, is available in the flight phase and is an integral part of the Nz law.
it serves to reduce the pilot's authority when the aircraft pitch attitude exceeds a threshold. This is to not exceed, in the nose down or nose up direction, a pre-defined pitch attitude.
9 Alpha floor detection
The purpose of this function is to enhance windshear survivability.
The alpha floor detection is performed in the FCPCs when the alpha floor condition is activated, the FCPCs send a signal to the FMGECs (Autothrust Function) which control the Take Off/Go Around (TO/GA) engine thrust whatever the throttle control lever position.
The activation conditions are:
- Alpha filtered (3s) greater than a threshold depending on the aircraft configuration, the ground speed variation and the difference between the ground speed and airspeed.
or
- Side stick nose up demand < -14° and theta > 25°.
or
- Side stick nose up demand < -14° and alpha protection.
Alpha floor is inhibited when Mach is above 0.53. Additional inhibitions, function of engine failure are performed in the FMGEC.
10 Low energy awareness
The purpose of this function is to warn the crew that the energy of the aircraft is too low.
The low energy function is performed in the FCPC in normal law. When the condition is activated, the FCPCs send a signal to the FWC (via the FCDC) which trig the aural warning "SPEED SPEED SPEED".
