Yaw alternate and Dutch Roll:
Here some 'food for thought' considering Yaw alternate law and dutch roll dampening, extracted from AMM.
AMM 27-90 - ELECTRICAL FLIGHT CONTROL SYSTEM (EFCS)
(1) Normal configuration
----
----
(2) Reconfigurations
(a) Laws and associated functions
1 If the normal control laws are lost:
When the conditions required for keeping the normal control laws are no longer fulfilled, the control laws are reconfigured.
The various degraded law states that are possible are (in flight or upon flare):
// Roll and yaw:
Yaw alternate law
// Pitch:
Nz law (with limited pitch rate and gains)
Vc PROT law (ALPHA 2)
VMO2 law
Pitch direct law
The "Alternate" laws are engaged when the protections related
to the normal laws (ALPHA 1, VM01) are lost.
The "Direct" laws are engaged when the Nz law is lost.
The associated functions available are :
----
----
sideslip estimation (except in alternate 2 law or direct law)
if yaw alternate law, sideslip estimation is changed in Ny body lateral accelerometer.
----
----
2 Yaw alternate law
This FCPC and FCSC law is engaged if the lateral normal law is lost.
Its characteristics are:
- The roll control is direct, an order on the side stick directly commands a deflection, according to a kinematic calculation.
- The yaw control is achieved by the summation of two terms:
. pedal orders
. Dutch roll damping orders (from yaw rate)
In the event of loss of the inertial data from the ADIRUs, the yaw rate data for Dutch roll damping is provided to the FCPC via the rate gyro unit.
If the three FCPCs are lost, the FCSC1 ensures Dutch roll damping, using yaw rate data from the rate gyro unit.
(6) Turbulence Damping Function
(a) General
The purpose of the Turbulence Damping Function implemented in the Electrical Flight Control System is to damp the structural modes induced by atmospheric turbulence.
(b) Architecture
The Turbulence Damping Function consists of two lanes:
1 Longitudinal lane
The longitudinal Turbulence Damping command is computed by the FCPC1 (FCPC2 as a redundancy) as a function of the Nz accelerometer information.
It is added to the normal law command and transmitted to the associated elevator servo-controls.
2 Rear lateral lane
The rear lateral Turbulence Damping command is computed by the FCPC1 (FCPC2 and FCPC3 as a redundancy) as a function of the information of a specific Ny accelerometer located at the rear bulkhead level.
It is added to the normal law command and transmitted to the associated rudder servocontrols.
(c) Specific equipment
- the TURB. DAMP pushbutton switch
- the Ny rear accelerometer.
----
----
(11) Sideslip estimation and Beta target computation
(a) Sideslip estimation
This function is elaborated in the FCPCs in the flight and flare phases. The estimated sideslip is used as an input parameter for the lateral normal law. It is fed to the FMGECs and sent to the DMCs by the FCDCs for display on the PFD.
~o~
Here's a simplified schematic for the 'mechanical' rudder:
