12. Stabilizer Position Fuselage Markings
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A. The fuselage markings at the stabilizer leading edge coincide with the upper and lower manual control limits and the stabilizer neutral position as rigged. These markings may not coincide directly with the EICAS displays, and should not be used in control or rigging.
13. Operation
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A. Functional Description
(1) Stabilizer operation can be commanded in any of the three electrical modes. The electrical modes provide for manual-electric, speed trim, and autopilot operation. The autopilot modes are auto flight system functions (Ref 22-14-00/001). In all modes, the stabilizer is hydraulically driven. No. 2 and No. 3 hydraulic systems normally supply the right and left STCM respectively.
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MAINTENANCE MANUAL
14-3/4 UNIT AIRPLANE NOSE UP
STABILIZER TRIM UNITS
MANUAL - ALTERNATE ELECTRIC NOTE: TOLERANCE ON INDICATED OPERATIONAL LIMIT SETTING IS | 1/4 UNIT
MAIN ELECTRIC - LANDING ONE UNIT OF STABILIZER TRIM IS GEAR DOWN, LE FLAPS DOWN, EQUIVALENT TO 1 DEGREE OF OR SPEED TRIM MODE - MAX STABILIZER ANGLE. STABILIZER OPERATIONAL LIMIT ANGLE IS MEASURED FROM A
REFERENCE NEUTRAL POSITIONMAIN ELECTRIC - LANDING WHICH CORRESPONDS TO 3 UNITSGEAR UP, LE FLAPS UP, AND OF STABILIZER TRIM. THEREFORE,NOT SPEED TRIM MODE - MAX 0 UNITS OF TRIM EQUALS +3 DEGREES;OPERATIONAL LIMIT
15 UNITS OF TRIM EQUALS -12 DEGREES. MAIN ELECTRIC -OPERATIONAL LIMIT
MAIN ELECTRIC -AUTO PILOT INPUT -OPERATIONAL LIMIT
HORIZONTAL TAIL FUELING LIMIT
Stabilizer Trim Limits
Figure 4
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MAINTENANCE MANUAL
Stabilizer Trim Hydraulic System Schematic
Figure 5
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(2)
The stabilizer trim system requires simultaneous application of hydraulic power from No. 2 and No. 3 hydraulic systems to achieve the normal trim rate. Stabilizer trim rate has two positions which are calculated by the SRMs, using calculated airspeed from the digital air data computer (DADC). The SRMs then position a rate control solenoid valve located on the STCM to provide the required trim rate. With both systems operative, the trim rates are 0.5 degree per second and 0.2 degree per second; with only one system operative, the trim rates are 0.25 degree per second and 0.1 degree per second. The rate control system is controlled by the SRMs, and it is not a linear change, but a step change between the rates mentioned above. The SRM uses the DADC inputs (Vc). Each SRM is capable of controlling both left and right STCM rates. Defaults to slow speed, thus eliminating trim oversensitivity at high speeds.
(3)
In the manual-electric mode, the STAB TRIM dual thumb switches on the captain's and first officer's control columns command operation of the STCMs. Each switch controls both STCMs simultaneously. Selection of either switch to the nose up or nose down position energizes a pair of solenoids in each STCM; an arming solenoid and a control solenoid. Both solenoids must be energized to initiate stabilizer operation. All solenoids are dual wound, with one winding for manual-electric, speed trim and auto flight system operation. The other is for alternate electric trim operation. The STCMs function identically in all electrical modes.
(4)
With trim selected in either direction, hydraulic fluid enters each package through integral check valves and passes through a filter and a normally open shutoff valve to the trim rate controller. The controller regulates the fluid flow rate in proportion to aircraft speed and flow continues through the arming and control service ducts as directed by the arming and control up or down solenoid.
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