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(2)
The TUA and TDA signals are sent through the SRMs internal stab trim limit switches to limit stabilizer travel authority; under certain conditions, changes to these limits are desirable. The SRM will change the limit values for the following cases. FRAT mode will change the nose up limit. Landing gear position, Flap position or Speed Trim mode will change the nose down limit.
(3)
The normal nose up limit is 11.6 units of trim; the limit is switched to 13.5 units during FRAT mode. The nose down limit changes from 0.8 unit for landing gear down to 1.8 units for landing gear up.
0.3
STABILIZER
TRIM RATE 0.2
(DEG/SEC)
0.1
AIRSPEED (KNOTS)
NOTE: LSTR = 0.10 DEG/SEC HSTR = 0.25 DEG/SEC
Stabilizer Trim Rate Schedule
Figure 5
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D. Stab Trim Rate Control
(1)
At power up, one SRM is randomly selected to implement the stab trim rate control function for both stab trim channels. At high airspeeds, the SRM provides low stab trim rate (LSTR) ouput; at low airspeeds, the SRM commands high stab trim rate (HSTR). This is accomplished by changing the output to the rate control solenoids on the STCMs.
(2)
To produce HSTR, the SRMs rate control output is 28 volts dc. For LSTR, the SRMs rate control output is open circuited. The SRM in control receives airspeed data from the DADC. If in HSTR mode (low airspeed) and airspeed increases above 230 knots, the SRM output changes from 28 volts dc to OPEN, thereby switching from HSTR to LSTR (see figure 5 for trim rate schedule). Similarly, if in LSTR mode (high airspeed) and airspeed decreases below 220 knots, the SRM output changes from OPEN to 28 volts dc, thereby switching from LSTR to HSTR.
SINGLE CHNL BOTH CHNL
(1 MOTOR) (2 MOTORS)
LSTR 0.1 DEG/SEC 0.2 DEG/SEC
HSTR 0.25 DEG/SEC 0.5 DEG/SEC
NOTE: 1 DEG = 1 UNIT ON STABILIZER POSITION INDICATOR
Stabilizer Trim Rates
Figure 6
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RATE CONTROL ARMING VALVE VALVE SOLENOID SOLENOIDS
Stabilizer Trim Control Module (STCM) Function
Figure 7
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7. Stabilizer Trim Control Module (STCM) (Figure 7)
_____________________________________
A. The two STCMs provide directional and rate control to the STDM. The SRM provides signals to the following components on the STCM: two control valve solenoids, one for nose up and one for nose down; two arming valve solenoids, one for nose up and one for nose down; a rate control valve solenoid; and a motor operated valve (MOV).
B. The solenoid valves provide spool valve control by switching between two states: when deenergized, the pressure port (P) is connected to the cylinder port (C); when energized, the return port (R) is connected to (C). If the SRM provides an open to the solenoid, (C) is pressurized; if it provides 28 volts dc, (C) is depressurized. Each solenoid has two separate sets of coils, one set for manual electric or autopilot trim and one set for alternate electric trim. Two arming valve solenoids are controlled by the TUA and TDA commands; similarly, two control valve solenoids are controlled by the TUC and TDC commands from the SRM. For example, to provide hydraulic pressure to the APL Nose Down output port, both the arming and control spools must slide left. For this to occur, TDA and TDC commands must be high and TUA and TUC commands must be low. In other words, (C) is depressurized for the nose down solenoids and pressurized for the nose up solenoids. The difference in pressure slides both of the spools left and allows pressure to the APL Nose Down port and reflief pressure to the APL Nose Up port.
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