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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE
Wheel-Rudder Cross-Tie
The wheel-rudder cross-tie function moves the rudder in response to control wheel inputs. This improves roll and yaw control during one engine-out operation. It also supplies protection against overyaw due to excessive pilot input to the rudder pedals.
The wheel position transducers send data to the wheel-rudder cross-tie function. This data and flap position data are used to calculate rudder commands. The function sends commands to the rudder control summing point.
The wheel-rudder cross-tie operates only when the yaw damper function is available. The PFC limits the wheel-rudder cross-tie to move the rudder to a maximum of 7.8 degrees in both directions. The wheel-rudder cross-tie does not operate above 210 knots or when the angle of attack is above the value that triggers the stall warning plus 5 degrees.
Gust Suppression
The gust suppression function improves the passenger ride quality at the aft section of the fuselage.
The gust suppression differential pressure transducers and the yaw and roll rates are inputs to the gust suppression function. The function sends commands to the rudder control summing point.
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The PFC limits the gust suppression commands as a function of airspeed to a maximum of six degrees of rudder movement in both directions.
Modal Suppression
The modal suppression function improves the passenger ride at the forward and aft sections of the fuselage. The function reduces the body lateral movements due to excitation of the airplane structural modes.
The two modal accelerometers input to the modal suppression function. The function sends commands to the rudder control summing point.
The PFC limits the modal suppression commands to a maximum of 2 degrees of rudder movement in both directions.
Force Fight Equalization
The rudder commands go to the force fight equalization function. The PFCs use rudder PCU differential pressure data from the ACEs to equalize all the rudder PCU commands before transmission to the ACEs and the EHSV of each rudder PCU. This function minimizes rudder PCU force fight.
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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE
Hydraulic Pressure Control
When the airplane is below 500 ft altitude or the flaps are extended, the PFCs de-energize the pressure reducer solenoid of all three PCUs. This causes the PCUs to operate with full hydraulic system pressure.
At altitude above 500 ft and flaps retracted, the PFCs energize the pressure reducer solenoids. This causes the PCUs to operate at the reduced hydraulic pressure of 1910 psi.
Rudder Trim
The rudder trim switches and the TAC function send input signals to the rudder trim to operate the rudder trim actuator.
Autopilot Yaw Commands
During cruise, the autopilot does not provide yaw commands. The rudder pedal backdrive actuators are not engaged and do not control the rudder pedals.
During autoland operation of the autopilot, the PFCs use autopilot yaw commands to move the rudder and calculate backdrive actuator commands. The backdrive actuators move the rudder pedals in relation to the autopilot commands.
If the pilot moves the rudder pedals while the autopilot autoland function is engaged, the autopilot disengages. To override the backdrive actuators, the pilots need to apply more force than the backdrive actuators. The backdrive actuators then cease to move the rudder pedals.
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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE
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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -SECONDARY MODE
General
In secondary mode operation of the PFCS, the PFCs calculate rudder control commands for these functions:
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