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747-400 MAINTENANCE MANUAL
 ELEVATOR CONTROL SYSTEM - DESCRIPTION AND OPERATION
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 1.  General (Fig. 1)_______
 A.  The elevator control system provides primary control of the airplane about its pitch axis. Hydraulic power drives the elevators in response to control column inputs. Two elevators are provided on each side of the airplane. The elevators are attached by hinges to the stabilizer aft torque boxes.
 B.  Fore and aft movement of the captain's and first officer's control columns activates the elevator control system. A torque tube rigidly interconnects the control columns. Crank arms on the torque tube transmit movement to pushrods. The left pushrod connects to a forward quadrant; the right pushrod connects to a crank. The forward quadrant and the crank are connected by cables to quadrants on a torque tube (referred to as common aft quadrant), which delivers control input to the inboard elevator power control packages (PCPs) through crank arms and pushrods. The PCPs are attached between the stabilizer rear spar and the elevator front spars. Activation of the inboard elevator PCPs, which can be accomplished manually or by the autopilot, causes deflection of the associated inboard elevators. Input to each outboard PCP is conducted through a slave linkage system from an input control rod mounted on the front spar of the adjacent inboard elevator.
 C.  The PCPs respond to control system inputs to deflect the elevators. They also limit elevator overtravel and provide snubbing action on the ground to protect the elevators from wind gust damage.

OUTBOARD ELEVATOR
CONTROL
COLUMNS

INBOARD ELEVATOR
ELEVATOR FEEL COMPUTER
FLIGHT CONTROL COMPUTERS (3) INBOARD ELEVATOR
OUTBOARD ELEVATOR
Elevator Control System Figure 1
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 D.  Elevator feel is provided by an elevator feel unit. A feel computer directs modulated hydraulic pressure to the feel unit, which then applies a resistance force in the feel unit actuator and through the common rear quadrant to simulate elevator aerodynamic centering forces. The metered feel pressure is controlled by stabilizer position and airplane pitot system pressure.
 E.  Hydraulic power is supplied to the elevator control system from airplane hydraulic systems No. 1, 2, 3, and 4 at a pressure of 3000 psi. Figure 3 shows the elevator hydraulic system. Left outboard elevator uses No. 1 system. Left inboard elevator uses No. 1 and 2 systems. Right inboard elevator uses No. 3 and 4 systems. Right outboard elevator uses No. 4 system. For autopilot operation, hydraulic systems No. 1, 2, and 3 supply the three elevator autopilot servo modules mounted on the stabilizer hinge bulkhead, and hydraulic systems No. 2 and 3 supply the feel computer and centering system. The elevator system hydraulic power is controlled by independent switches for each hydraulic system. These switches are common to the elevator and rudder hydraulic supply systems.
 F.  A position transmitter attached to each inboard and outboard elevator transmits electrical signals to the aft surface digitizer circuit card in the E8 aft electrical equipment rack to provide control surface position. This is then routed to the EICAS display screens on the flight deck (Ref 27-38-00/001).
 2.  Outboard Elevators (Fig. 3)
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 A.  Each outboard elevator consists of a conventional spar and rib frame supporting honeycomb sandwich skins. The frame members are of aluminum alloy. The front spar and ribs are built up from extruded upper and lower flange members with alclad sheet webs supported by stiffeners. The skin panels consist of fiberglass honeycomb core material contained between two 5-ply bonded surfaces of fiberglass fabric reinforced epoxy plastic. A trailing edge, also of fiberglass honeycomb bonded construction with reinforced plastic surfaces, is riveted to the rear spar. A leading edge, consisting of aluminum alloy skins supported by ribs, projects forward of the front spar. The leading edge structure supports mass balance weights.
 B.  Each outboard elevator attaches to the horizontal stabilizer trailing edge at six points. The major attachment is at the actuator reaction structure, where the hinge bearing is carried by support structure in the horizontal stabilizer trailing edge. At each of the remaining attachment points, which are of lighter construction, the hinge bearing is contained in a machined hinge fitting bolted to the elevator front spar. Balance weight installations (Fig. 3) project forward of the hinge line. Each supports a tungsten balance weight. The three inboard installations also provide fittings for additional adjustment weights. Eleven panels in the lower skin provide access to the interior of the elevator.
　
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