YAW DAMPERS
GENERAL
A single yaw damper is installed on model 23
and 24 airplanes, dual yaw dampers on model 25
airplanes. The system(s) provides full-time yaw
damping in flight by applying rudder against
transient motion in the yaw axis. Yaw deviation,
sensed by rate gyros and lateral accelerometers,
results in damper servos positioning the rudder
as required. The damper servos are reversible
DC motors in the cable control system to the
rudder. They can be overridden by the pilot at
any time, if necessary, by the application of suf-
ficient force of the rudder pedals.
The yaw damper should be disengaged while
trimming the rudder, then reengaged.
SINGLE YAW DAMPER SYSTEM
Operation
Model 23 and 24 airplanes are equipped with a
single (primary) yaw damper system. A rate
gyro and a lateral accelerometer provide yaw
signals to the computer-amplifier, which trans-
mits the necessary drive commands to the yaw
damper servo. Airplanes SNs 23-003 through
24-129 have two rate gyros with a selector
switch on the center instrument panel.
The system is engaged by turning on the
AUTOPILOT MASTER switch and the YAW
DAMPER switch on the subpanel on model 23
airplanes or by depressing the YAW DAMPER
ON button on the autopilot controller (Figure
15-11) on model 24 airplanes.
On model 23 airplanes, the yaw damper is inter-
rupted while the control wheel master switch is
depressed and held. On all other airplanes,
depressing the wheel master completely disen-
gages the yaw damper and a warning tone
sounds. Turning off the AUTOPILOT MASTER
switch or the YAW DAMPER switch on the
pilot’s subpanel or depressing the YAW
DAMPER OFF button on the autopilot con-
troller disengages the yaw damper.
DUAL YAW DAMPER SYSTEM
All 25 series airplanes are equipped with dual
(primary and secondary) yaw damper systems.
Each system is completely independent with its
own rate gyro, lateral accelerometer, computer/
amplifier, and damper servo. Yaw deviation sig-
nals from the rate gyro and lateral accelerometer
are processed by the computer/amplifier, and
drive signals are transmitted to the applicable
damper servo for rudder deflection.
Prior to engagement of either the primary or
secondary damper, the respective force indica-
tors should be centered. The primary damper
force indicator is on the autopilot force indica-
tor panel on the pilot’s instrument panel. The
secondary damper force indicator is located on
the yaw damper panel on the center pedestal
(Figure 15-11).
To engage the primary yaw damper, position the
selector switch on the yaw damper panel to PRI
YAW DAMPER, then depress the YAW
DAMPER ON button on the autopilot flight con-
troller. Disengage the primary damper by
depressing the YAW DAMPER OFF button, by
depressing the wheel master switch on either
control wheel, or by selecting the secondary
yaw damper.
To engage the secondary yaw damper, position
the selector switch to SEC YAW DAMPER, then
position the SEC YAW DAMPER switch to
ENGAGE. Disconnect the damper by moving
the SEC YAW DAMPER switch out of the
ENGAGE position, by depressing the wheel
master switch on either control wheel, or by
selecting the primary yaw damper.
On SNs 25-363 and subsequent, the yaw damper
is automatically disengaged by the squat switch-
es at touchdown.
Only one yaw damper can be engaged at a time.
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
15-16
FOR TRAINING PURPOSES ONLY
