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 8.  Elevator Feel Computer (Fig. 4)
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 A.  The elevator feel computer supplies controlled system A and system B hydraulic pressure to the elevator feel control unit. The feel computer is mounted to structure within the empennage adjacent to the stabilizer front spar. The computer is a dual unit, the housing divided to accommodate identical components for system A as for system B. Internal components for each system include a Q-diaphragm, force balance valve, relief valve, and a stabilizer actuated cam. A feel differential pressure switch is housed within the unit body.
 B.  Inputs to the feel computer are hydraulic system A and hydraulic system B pressure at 3000 psi, pitot pressure, static pressure, and a stabilizer position mechanical input. Pitot pressures are directed to each system from individual pitot tubes on the vertical fin. The outputs from the feel computer are two controlled hydraulic pressures, 200 to 2100 psi, to the feel control unit. The internal feel differential pressure switch turns on an amber light on the overhead panel when an undesirable pressure difference exists between the two feel computer output pressures.
 C.  The two output pressures from the computer are controlled by pitot pressure and stabilizer position. With the feel system pressurized, the force balance valve is hydraulically displaced to limit system pressure. Pitot pressure acting upon the Q-diaphragm meters the flow by displacing the force balance valve until the valve contacts the droop spring and stabilizer actuated cam. As pitot pressure increases, the Q-diaphragm will deflect the droop spring and move the force balance valve to increase pressure to the feel control unit. Changes in stabilizer position will rotate the stabilizer actuated cam and reposition the droop spring. A relief valve provides protection against excessive pressure in the feel system. The valve will relieve at 40% above computer demand pressure.
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 27-31-00
 ALL  ú ú 01 Page 7 ú Jun 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
NEUTRAL SHIFT MACH TRIM

SCHEMATIC

Elevator Feel System
Figure 4 (Sheet 1)

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 27-31-00
 ALL  ú ú 01 Page 8 ú Jul 12/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 9.  Elevator Feel and Centering Unit (Fig. 4)________________________________
 A.  The elevator feel and centering unit provides artificial feel to the pilot and centering for the elevator control system. The feel and centering unit is mounted to structure aft of the stabilizer rear spar and pivots about a lateral axis. The unit consists of a centering cam and roller assembly, centering linkage, and an externally mounted dual feel actuator. The feel and centering unit receives two hydraulic inputs from the feel computer. The inputs act upon pistons within the free-floating dual feel actuator. A rod from one piston attaches to the feel and centering unit body. A rod from the opposing piston attaches, by means of centering linkage, to the feel control centering cam and roller assembly. The feel and centering unit neutral position changes as stabilizer attitude varies. Variations in stabilizer attitude are transmitted through the neutral shift mechanism to rotate the feel and centering unit about the lateral axis. A mach trim actuator is mounted on top of the feel and centering unit. The actuator output rod is linked to the horizontal stabilizer through the neutral shift mechanism. The mach trim actuator and rod function as part of the neutral shift linkage except when the mach tirm system is operating. Mach trim command signals extend or retract the actuator output rod. This action provides a mechanical input to rotate the feel and centering unit and thereby reposition the elevators. If the autopilot system is engaged, a neutral shift sensor driven by movement of the feel and centering unit provides electrical signals to the autopilot system which causes the elevators to be repositoned.
PITOT
PROBE

FEEL COMPUTER
PITOT
LINE

SEE  A
FEEL COMPUTER
PLUG DRAIN  STATIC LINE 
LINE PITOT 
FWD 
Figure 4 (Sheet 2) Elevator Feel System PITOT STATIC SYSTEM  A 
　
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