Elevator Trim Control - Maintenance Practices; Trim Tab Actuator Removal/Installation; Trim Tab Actuator Disassembly/Assembly; General - Cessna 172 Series 1996 Maintenance Manual

CESSNA AIRCRAFT COMPANY
MODEL 172
MAINTENANCE MANUAL
ELEVATOR TRIM CONTROL - MAINTENANCE PRACTICES
1. General
A.
The elevator trim tab, located on the right elevator, is controlled by a trim wheel mounted in the
pedestal. Power to operate the tab is transmitted from the trim control wheel by means of chains,
cables and an actuator. A mechanical pointer, adjacent to the trim wheel indicates tab position. A
nose up setting results in a tab down position. For an illustration of tab system components, refer to
Figure 201.
2. Trim Tab Actuator Removal/Installation
A.
Remove Trim Tab Actuator (Refer to Figure 201 and Figure 202).
(1) Remove baggage compartment aft wall for access to elevator trim control cable stop blocks.
Refer to Chapter 25, Interior Upholstery - Maintenance Practices.
CAUTION:
POSITION A SUPPORT STAND UNDER TAIL TIE-DOWN RING TO PREVENT
TAILCONE FROM DROPPING WHILE PERSON IS WORKING INSIDE.
(2) Remove safety wire and relieve cable tension at turnbuckle.
(3) At the elevator hinge gap, disconnect push-pull channel from actuator.
(4) Remove access plate 320AB. Refer to Chapter 6, Access/Inspection Plates - Description and
Operation.
(5) Remove chain guard.
(6) Remove chain from actuator sprocket.
(7) Remove screws attaching actuator clamps to bracket, and carefully work actuator out through
access opening.
B. Install Trim Tab Actuator (Refer to Figure 201 and Figure 202).
(1) Place actuator in position and attach actuator clamps to bracket using screws.
(2) Install chain to actuator sprocket.
(3) Install chain guard.
(4) Install access plate 320AB. Refer to Chapter 6, Access/Inspection Plates - Description and
Operation.
(5) At the elevator hinge gap, connect push-pull channel to actuator.
(6) Rig trim system. Refer to Trim Tab Control Adjustment/Test.
3. Trim Tab Actuator Disassembly/Assembly
A. Disassemble Trim Tab Actuator (Refer to Figure 203).
(1) Remove trim tab actuator. Refer to Tim Tab Actuator Removal/Installation.
(2) Using suitable punch and hammer, remove groove pins securing sprocket to screw and remove
sprocket.
(3) Unscrew threaded rod end and remove rod end from actuator.
(4) Remove groove pins securing bearings at the housing ends.
(5) Lightly tap screw toward the sprocket end of housing, remove forward bearing and collar.
(6) Lightly tap screw in the opposite direction from sprocket end, remove aft bearing, O-ring and
collar.
NOTE:
It is not necessary to remove retaining rings.
B. Assemble Trim Tab Actuator (Refer to Figure 203).
NOTE:
Discard groove pins, O-rings and nuts removed in disassembly, and install new parts during
reassembly.
NOTE: During reassembly lubricate collars, screw and threaded rod end.
(1) Install collar and forward bearing on screw.
(2) Press sprocket into the end of screw and align groove pin holes and install new groove pins.
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Page 201
Aug 18/2001