General Description and Operation of the Yaw
Damper System
An electro-hydraulic yaw damper in each rudder PCU is used to
dampen aircraft oscillations or (dutch roll) about the vertical axis.
The series yaw damper signals for the rudder actuators is fully active
for takeoff, cruise and landing. With this system, the rudder pedals
are not displaced. The system includes two computers, inboard and
outboard flaps UP limit switches, two rudder power control units, the
pilot and copilot attitude director indicators, the flight control surface
position indicator and the yaw damper control and test switches.
Turn Coordination
The 747 yaw damper also provides turn coordination. It operates the
rudders proportional to the Aircraft roll rate, sensed by the Yaw Rate
Gyros in the Yaw Damper Computers, to improve roll control
response when flaps are extended on the 747–200/300 Aircraft. On
the 747SP Aircraft the Turn Coordination function is active at all
times (No Flap input) and controlled by the Aircraft Airspeed (ADC
Input), and Aileron CCA output transducers.
Computers
Two computers are located in the main equipment centre. Each
computer contains a rate gyro and electronics to monitor and correct
aircraft oscillations or dutch roll.