FLIGHT CONTROLS
AIRPLANE
OPERATIONS
MANUAL
2-13-20
Page
2
Code
01
REVISION 27
RUDDER CONTROL SYSTEM
Directional control about the yaw axis is provided by two in-tandem
rudders. Forward rudder is driven by the control system, while the aft
rudder is linked to the forward rudder and deflected as a function of
forward rudder deflection. Either set of rudder pedals will position the
rudder through a Power Control Unit (PCU). The mechanical control is
fully duplicated, consisting of cables running from the pedals in the
cockpit to the rear fuselage, where the PCU is commanded to position
the forward rudder. The rudder can also be commanded through the
autopilot.
The rudder PCU is a dual hydraulic unit, simultaneously powered by
both hydraulic systems. Each PCU hydraulic circuit controls the
hydraulic power to one respective rudder actuator. Therefore, the
rudder system is divided into Rudder System 1 and Rudder System 2.
The PCU also incorporates an artificial feel device that provides the
pedals with an artificial feel of the aerodynamic load imposed on the
rudder.
Rudder System 1 and/or Rudder System 2 may be either manually or
automatically shut off. The manual shut off operation is provided
through the Rudder Shutoff Buttons, located on the Overhead Panel.
The automatic shut off operation is provided through the speed switch
and through the hardover protection function.
When operating under mechanical mode the aerodynamic loads on the
rudder are directly transmitted to the pedals and, therefore, to the
pilots. Since no rudder hydraulics control is available, artificial feel and
trim functions will also not be available. Some characteristics can be
observed:
− greater control forces
− sluggish response of rudder to pedals inputs
− backlash of rudder pedals around neutral position when changing the
force application from one to the other pedal.
If either or both rudder systems are inoperative, caution messages are
presented on the EICAS.
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