signals to the amplifier are equal. The amplifier
of a potentiometer that attaches to and is driven
now signals the servo valve to a neutral position.
by the drive arm on the nose gear spindle. As the
When the servo valve goes to a neutral position
nose gear moves in response to the pilot's
command, the feedback potentiometer feeds back
(with the steering system energized and hydraulic
pressure available), it blocks off both pressure and
a signal to the steering amplifier. When the
return passages to the steering actuator. Thus, the
feedback potentiometer signal matches the
command potentiometer signal, the amplifier
actuator is hydraulically locked in position. The
steering actuator will remain locked in position
output causes the servo valve to neutralize and
until the servo valve receives a signal to turn the
stop movement of the nosewheel. The feedback
wheel or hydraulic and/or electrical power is
potentiometer assembly contains a swivel dis-
removed from the system. When the steering
connect switch, which opens when the nosewheel
turns 750 to 800 either side of straight ahead. This
system is not in use, the steer-damper unit
action electrically de-energizes the circuit to
performs the functions of a shimmy damper. The
prevent reverse steering or damage to the aircraft.
system accomplishes shimmy damping by trapping
hydraulic fluid on both sides of the steering
AMPLIFIER. --The steering amplifier is a
actuator piston and forcing this fluid from one
small transistorized differential amplifier. The
side of the actuator to the other side through the
restrictor.
amplifier detects the differential positions of the
command potentiometer and the steering feed-
back potentiometer. Any difference in signals
Catapulting System
received results in a signal going to the servo valve
to port hydraulic pressure to the steering actuator.
The catapulting system (fig. 4-18) provides
This causes the nosewheel to turn and the steering
feedback potentiometer to move. When the
catapult handling and attachment capabilities for
carrier operations. The system consists of a
feedback potentiometer signal matches the
catapult launch bar, a launch bar actuating
command potentiometer signal, the nosewheel
cylinder and gimbal, swivel joints, a cockpit-
stops turning. In addition, the amplifier contains
controlled selector valve, leaf centering spring,
a circuit that provides a centering signal, which
leaf retracting springs, and a catapult tension bar
holds the nosewheel in the straight-ahead position
socket. The launch bar is swivel mounted on the
during arrested landings.
nose gear outer cylinder and can extend and
retract during taxi operations. The launch bar
OPERATION. --When the nosewheel steering
automatically retracts after catapulting. A launch
switch button is depressed, power goes to the
electrical control system and the solenoid-operated
bar warning light comes on during any of the
following conditions:
shutoff valve. As the valve opens, hydraulic
pressure flows to the servo valve on the steer-
damper unit. Signals go to the amplifier from the
The launch bar control switch is in
EXTEND.
command potentiometer and from the feedback
potentiometer on the steering linkage. If these
The selector valve is in bar extend position
signals are equal, the amplifier signals the servo
valve to stay in the neutral position. When the
(solenoid A energized).
nosewheel (and consequently the feedback
The launch bar is not up and locked with
potentiometer) does not correspond to rudder
weight off the landing gear.
pedal position (and command potentiometer), the
signals going to the amplifier are different. This
The launch bar control switch is in
causes the amplifier to send a signal to the servo
valve.
RETRACT and the launch bar actuator is
The signal sent to the servo valve causes the
not up and locked.
valve to port pressure to the steering actuator in
Accessories for the catapulting system include
the steer-damper unit. The hydraulic pressure
a tension bar and a catapult holdback bar. The
causes the actuator to move the nosewheel (and
catapult tension bar socket mounts on the nose
the feedback potentiometer) to a position
corresponding to rudder pedal position (command
gear axle beam and provides for attachment of
the tension bar for tensioning the aircraft before
potentiometer). When the nosewheel reaches a
catapulting.
position corresponding to the pedal position, the
