ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -SECONDARY MODE

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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -DIRECT MODE

General

In direct mode operation of the PFCS, the ACEs calculate pitch control commands based on:
*
Elevator control schedule

*
Pitch rate sensor

*
Elevator feel logic

*
Failure monitor.

Elevator Control Schedule

The ACEs calculate the pitch commands from the column position transducers and the position of the flaps and slats. The commands changes per fixed gain schedules for flaps and slats retracted or not retracted.
The elevator displacement is larger with the flaps and slats not retracted and smaller with the flaps and slats retracted. The elevator command goes directly to the EHSV of the elevator PCU.
Pitch Rate Sensor

As in the secondary mode, the pitch rate sensor in each ACE supplies a feedback signal to the elevator command for pitch damping.
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.
Failure Monitor
When the ACE failure monitor finds a PCU electrical failure, it removes power from the bypass solenoid, the pressure reducer solenoid and/or the blocking solenoid of the applicable PCU.
If the failure monitor detects a first failure, the ACE de-energizes the bypass solenoid of the on-side PCU. It also de-energizes the pressure reducer solenoid of the adjacent PCU.
The blocking solenoids are dual-coil solenoids. When the ACE detects the first failure, one of the coils is de-energized on both the on-side and the adjacent PCUs.
If a second failure occurs, the second coil on both PCUs is de-energized when the elevator is less than two degrees from neutral with flaps retracted or less than five degrees from neutral with flaps extended.
The failure monitor operates in the normal, secondary, and direct modes. The failure monitor can find faults in the ACE, the PCUs, column position transducers and interface wiring.

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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -DIRECT MODE

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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -ELEVATOR FEEL

General

The PFCS controls the elevator feel actuators and works with the elevator feel unit to supply resistance to the movement of the control column.
The PFCs control elevator feel in the normal and secondary modes and the L2 and C ACEs control it in the direct mode.
Elevator Feel Actuator

The elevator feel actuator contains a brushless 28v dc reversible motor, and a 7v RVDT to supply an actuator position signal.
Normal Mode

In the normal mode, the PFC calculates elevator feel commands as a function of airspeed. As airspeed increases, it commands the actuator to extend. As airspeed decreases, the PFC commands the actuator to retract. This results in more or less resistance (feel) to movement of the control column. The command goes to the feel actuator through the ACE.
During takeoff, the feel actuators disengage above 40 knots. The feel actuators engage to provide variable feel 5 seconds after the ground-to-air transition. On the ground with airspeed below 40 knots, the feel actuators engage to permit the flight crew to do a check of the feel forces during the freedom of controls check.
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Secondary Mode
In the secondary PFCS mode, the PFC calculates feel commands as a function of flaps and slats position. The FSEUs supply through the ACEs a discrete flaps and slats retracted signal. When the flaps and slats are not retracted, a low feel command is made. When the flaps and slats are retracted, a high feel command is made.
Direct Mode
The ACE uses the FSEU discrete flaps and slats retracted signal to calculate feel actuator commands in the direct mode. When the flaps and slats are not retracted, it makes a low feel command. When the flaps and slats are retracted, it makes a high feel command.
Failure Monitor
In normal mode, if the PFC detects a difference between the output and the feed back signals from one of the feel actuators, it shuts off the signal to that actuator. The failed actuator is spring loaded to a zero force input.
The PFC then commands the other actuator with a doubled signal that compensates for the failed actuator. Because of this, the feel force at the control columns remains the same.
　
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