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 A.  The outboard elevator PCPs receive mechanical inputs via the inboard elevators. Each unit actuates in response to movement of the adjacent inboard elevator. The left PCP is powered by hydraulic system No. 1 and the right PCP by hydraulic system No. 4.
 10. Elevator Feel Computer
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 A.  The feel computer is the controlling element in a hydraulically powered subsystem comprising the computer, a feel actuator and a feel unit. The computer modulates hydraulic pressure inputs to the feel actuator in response to changes in dynamic air pressure (Qc) and horizontal stabilizer position. Airplane hydraulic systems No. 2 and 3 provide the hydraulic pressure inputs from which feel pressure is derived.
 B.  The computer contains two identical groups of components, each of which provides a separate feel pressure input to the feel actuator. A pressure differential sensing actuator in the computer senses the feel pressure output of both groups of components. The actuator closes one of two switches if the output pressure from one group falls to approximately 75 percent of the output from the other group.
 11. Feel Actuator
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 A.  The feel actuator, which is mounted on the elevator feel unit, receives hydraulic pressure inputs from the feel computer. The actuator comprises two rams acting in opposite directions within a free floating cylinder. One ram is connected to the feel unit body, which is attached to the airplane structure, and the other to the feel linkage. The force exerted by the actuator is proportional to the parallel outputs of the feel computer, therefore failure of one output does not effect elevator feel. The feel force is transmitted to the elevator controls through the feel unit.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
 12. Feel Unit_________
 A.  The feel unit transmits the force exerted by the feel actuator to the elevator controls. Feel pressure acts on the feel actuator rams to apply force through a Y linkage attached to a cam mounted on a pivot shaft. A lever mounted on the same shaft connects the feel unit to the elevator aft quadrant. When moving the control column in either direction, the operator must overcome the feel force transmitted through the linkage to rotate the cam. As the cam rotates, a roller in contact with the cam surface moves out of detent, displacing a lever arm against the force exerted by two centering springs. When the pilot releases the control column, the roller exerts pressure to center the cam, acting with feel pressure to return the control column to neutral.
 13. Operation_________
 A.  Functional Description
 (1)  
Airplane hydraulic systems No. 1, 2, 3 and 4 operate the elevators in response to manual or electrical control inputs. The operator applies manual inputs to either control column; the autopilot system applies inputs to the three autopilot servo modules connected to the aft torque tube.

 (2)  
In the manual mode, fore and aft displacement of the control columns transmits motion from the forward control quadrant and crank to the common aft quadrant through two pairs of cables. As the control column is displaced progressively from neutral, the elevator feel unit imparts a progressively increasing centering force to the control system .

 (3)  
The feel force is controlled by the feel computer, and is exerted by the feel actuator acting through the feel unit. In each of the two groups of components in the computer, a Qc-sensing bellows acts through a leaf spring upon a pivot linkage to displace a force balanced slide valve. A cam, connected by linkage to the horizontal stabilizer, acts through another leaf spring in opposition to the Qc-sensing bellows. The sum of these two forces, together with hydraulic return pressure, loads the force balance valve to pressurize the associated chamber of the feel actuator. The force balance valve closes when the force exerted by feel pressure on the opposite end of the valve balances the input forces. The feel pressure acts on the feel actuator rams to apply a force which resists rotation of the feel unit cam. As the cam is connected to the aft quadrant, this resistance plus feel unit centering spring tension resists control column displacement from neutral.

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