Learjet 20 Series Pilot Training Manual page 300

RUDDER
The rudder is manually positioned with either set
of rudder pedals or by a yaw damper servo. The
yaw damper can be overridden through a
mechanical slip clutch in the event of a malfunc-
tion. The yaw damper can be interrupted on
model 23 airplanes by depressing and holding
either wheel master switch. The wheel master
switch completely disengages the yaw damper
on airplanes with the two-speed trim system.
Figure 15-6 shows the rudder control system.
Rudder Trim Tab
A trim tab, mounted on the bottom trailing edge
of the rudder, is controlled by a trim switch on
the aft end of the center pedestal. Trim position
is indicated by the rudder trim indicator.
TRIM SYSTEMS
GENERAL
The airplane is trimmed in the pitch axis by
changing the angle of attack of the movable hori-
zontal stabilizer. A dual-motor (normal and
emergency) actuator moves the leading edge of
the horizontal stabilizer up or down in response
to pitch trim inputs. Controls and indicators for
the trim systems are shown in Figure 15-7.
The trim position indicators for pitch, roll, and
yaw are all DC powered through the TAB &
FLAP PN circuit breaker.
RUDDER TRIM
Control
Rudder trim is controlled by the YAW TRIM
rudder switch on the aft end of the center
pedestal, spring-loaded to the OFF position.
The switch is split into an upper and a lower
half. Both halves must be pressed simultaneously
to initiate rudder trim tab motion. Model 23 air-
planes and SNs 24-100 through 24-169 may
LEARJET 20 SERIES PILOT TRAINING MANUAL
FOR TRAINING PURPOSES ONLY
have a single toggle or a rocker switch for rudder
trim. The rudder trim system is DC powered
through the YAW circuit breaker.
AILERON TRIM
Control
Aileron (roll) trim is controlled with either con-
trol wheel trim switch located on the outboard
horn of each control wheel (Figure 15-7). Each
control wheel trim switch is a dual-function (trim
and trim arming) switch which controls roll and
normal pitch trim. Each switch has four posi-
tions—LWD, RWD, NOSE UP, and NOSE
DOWN—and is spring-loaded to the neutral
position. The arming button on top of the switch
must be depressed and held while simultaneous-
ly moving the trim switch in the direction of
desired trim action. Actuation of either control
wheel trim switch to LWD or RWD (with arming
button depressed) will signal the trim tab actua-
tor motor in the left aileron to move the trim tab
in the appropriate direction. Actuation of the
pilot's trim switch will override actuation of the
copilot's switch.
The aileron trim motor is DC powered through
the ROLL circuit breaker.
Aileron Trim Indicator
Aileron trim tab position indication is provided
by the AIL trim indicator (Figure 15-7).
PITCH TRIM
General
Pitch trim is accomplished by repositioning the
horizontal stabilizer to the desired trim setting
with a dual-motor (normal and emergency) actu-
ator that operates in three modes:
1. Normal pitch trim mode—Normal trim
motor
2. Emergency pitch trim mode—Emergency
trim motor
3. Autopilot pitch trim mode—Emergency
trim motor
FlightSafety
international
15-9