777 AMM 飞机维护手册 飞行操纵 Flight Controls 2(12)

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The elevator neutral position moves from 0 to 4 degrees trailing edge up in proportion to the stabilizer movement from 2 degrees leading-edge-up to 2 degrees leading-edge-down. When the stabilizer is from 2 to 11 degrees leading-edge-down, the elevator neutral position stays at 4 degrees trailing-edge-up.
The control column does not move as a result of the elevator rig position function.
EFFECTIVITY BEJ ALL
Elevator Command Limiting Function
The elevator command limiting function receives the command signals from the summing point. The function limits the rate of elevator movement. It also limits the position of the elevator for structural protection.
Force Fight Equalization
The elevator commands go to the force fight equalization function. The PFCs use elevator PCU differential pressure data from the ACEs to equalize all the elevator PCU commands before transmission to the ACEs and the EHSV of each elevator PCU. This function minimizes elevator PCU force fight.
Elevator Feel Logic
The elevator feel logic monitors the CAS. The logic sends a signal to the ACE for the elevator feel actuators. As the airspeed increases and decreases, the feel logic commands the actuators to extend and retract respectively.
When one of the two elevator feel actuators is defective, the elevator feel logic sends a much larger command to the good actuator to compensate for the defective one.
If the airplane approaches a stall condition, the stall protection sends a signal to the elevator feel logic to increase the elevator feel force if the pilot pulls the column. The signal does not change the feel force if the pilot pushes the column.
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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE

Elevator Offload Function
The elevator offload function operates only in the air.

It uses the elevator commands to determine when the elevator is not at the neutral position for more than two seconds minimum. The function then commands the horizontal stabilizer to move as a function of airspeed. The movement of the horizontal stabilizer then causes the elevator to move to the neutral position.
The function is inhibited during these times:
*
During flare

*
During stabilizer commands

*
During alternate trim lever use

*
When roll or pitch attitude is more than 30 degrees.

 

See the horizontal stabilizer control section for more information (SECTION 27-41).
Autopilot Pitch Commands

During autopilot operation, the PFCs use the autopilot pitch commands to calculate the elevator commands. They also calculate the backdrive actuator commands which go the AFDCs. This causes the backdrive actuators to move the control columns in the same relationship to the autopilot commands. When the pilots move a control column while the autopilot is engaged, the autopilot disengages. The backdrive actuators then stop the movement of the control column.
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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -NORMAL MODE

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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -SECONDARY MODE

General

In secondary mode operation of the PFCS, the PFCs calculate elevator commands based on this data:
*
Elevator control schedule

*
Pitch rate

*
Elevator command limiting function

*
Force fight equalization

*
Elevator feel logic.

Elevator Control Schedule

The PFC calculates the elevator commands as a function of the column position transducers and the flaps and slats position. The commands from the elevator control schedule are higher when the flaps and slats are not retracted.
Pitch Rate

The pitch rate sensor in each ACE supplies a feedback signal to the elevator command for pitch damping.
Elevator Command Limiting Function

The elevator command limiting function limits the rate of the elevator movement and the position of the elevator for structural protection.
Force Fight Equalization
The force fight equalization function uses elevator PCU differential pressure data from the ACEs to equalize all the elevator PCU commands. This function minimizes elevator PCU force fight.
Elevator Feel Logic
The elevator feel logic operates on the basis of the flaps and slats position. When the flaps and slats are retracted, the logic supplies a high feel signal to the feel actuators. When the flaps and slats are not retracted, the signal is for low feel.

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