landing gear control circuit of a patrol type
This prevents accidental release of wing station
aircraft.
external stores when the weight of the aircraft has
compressed the shock strut oleo.
CIRCUIT OPERATION. --The landing gear
A solenoid mechanically prevents movement
circuit includes an electrical, solenoid-operated
of the landing gear control lever from the
selector valve to control hydraulic actuation of
wheels down position when the aircraft weight is
the landing gear. Current goes to the landing gear
on the gear. When the weight of the aircraft is
selector valve through two single-pole, double-
on the landing gear, this solenoid de-energizes,
throw (SPDT) switches. These switches operate
allowing the solenoid armature pin to protrude
by a cam on the landing gear control lever,
outboard. This solenoid armature pin position
permitting current to flow to either the up or down
mechanically prevents movement of the landing
coil of the valve. Coil selection depends on control
gear control lever from the wheels down position.
lever position. The landing gear control circuit
Depressing the solenoid armature pin allows
also includes electrical control for emergency
control lever movement for emergency or test
extension of the nose gear with emergency
procedures.
hydraulic system power. A center-off switch
(SPDT type) provides control of a double
solenoid-actuated hydraulic selector valve. The
Arresting Gear System
center-off position of the switch is the normal
position during operation of the landing gear with
The arresting gear system stops the aircraft
the main hydraulic system. The down position
during carrier landings and emergency field
selects emergency hydraulic system power for nose
arrestments. The primary component of the
gear extension. The bypass position is for use only
system is the arresting hook on the underside of
during retraction of the nose gear with main
the aft fuselage. The hook is pivoted at the
hydraulic power after extension by emergency
forward end allowing up, down, and sideways
hydraulic power. The bypass also allows for
motion. The hook engages a runway or cross deck
release of emergency system hydraulic pressure
pendant when in the down position. A lever in
any time you desire.
the cockpit controls raising and lowering of the
hook (fig. 4-16). The lever electrically energizes
ADDITIONAL CIRCUITS. --In some air-
a hydraulically actuated vertical damper cylinder
craft, the landing gear control circuit also controls
for hook retraction and trips an uplatch
the supply of power to the propeller-reversing
mechanism through mechanical linkage for
lowering the hook. Two horizontal dampers and
circuit (through left and right main torque-link
switches) and to the stores release circuit (through
one vertical damper dampen hook motion from
left main torque-link switch). The left main gear
deck impact forces. Two centering spring
torque-link switch supplies power to energize the
assemblies maintain the hook in the center
landing gear lever locking solenoid. The weight
position.
of the aircraft must be off the landing gear shock
EXTENSION. --You extend the arresting
strut before you move the landing gear control
lever from the wheels down position. The solenoid
hook by moving the control handle in the
will be de-energized by the up sense switch of the
cockpit from the up to the down position.
left main gear after the gear retracts. This switch
This removes tension from the cable and allows
energizes a relay, whose normally closed contacts
the uplatch mechanism to deflect to the opposite
are in series with the solenoid circuit. The left and
extreme of travel (aft). The arresting hook
right main gear torque-link switches (parallel
is then free to extend by action of the vertical
connected) are in series with the power to the
damper cylinder and its own weight. At the
same time, a switch in the control handle actuates,
throttle lever-locking solenoid to prevent the
de-energizing both the arresting hook relay and
throttles from being placed in reverse propeller
the selector valve solenoid. This action permits
range. When one of the torque-link switches
fluid from the vertical damper cylinder to return.
actuates (by aircraft weight compressing one or
The surge damper prevents return line high-
both main landing gear strut oleos), the throttle
pressure surges, caused by hook extension, from
levers come into the reverse pitch range. The left
damaging other subsystems by reducing the
main landing gear torque-link switches (series
surge.
connected) also open the stores release circuit.
