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securing the roller into the uplock hook. A hydraulically actuated pushrod then
rotates the uplock hook upward to provide positive nose gear latching.
Two symmetrical nose wheel doors, hinged on the outside of the forward nose
wheel well and mechanically linked together, operate in conjunction with the nose
gear. Timing valves integrated into the extension/retraction cycle operate the
hydraulic door actuating cylinder in the correct sequence. When the nose gear is
retracted and seated in the uplock hook, the doors close to cover the forward
wheel well, with the fairing panel attached to the rear of the nose gear drag brace
enclosing the aft portion of the wheel well.
Indication of landing gear position is provided to the flight crew through lights on
the landing gear control panel, an aural warning horn/klaxon, and by messages on
the Crew Alerting System (CAS) in the event of malfunction.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-32-00
Page 5
January 31/02
Revision 6
2. Description of Subsystems, Units and Components
A. Landing Gear Doors
The landing gear doors are shaped to conform to the surrounding fuselage
areas, providing an aerodynamically smooth covering of the wheel well
areas when closed. The main landing gear wheel well is enclosed by a
single door in conjunction with a fairing panel attached to the outside of the
gear strut. The nose gear wheel well is enclosed by two symmetrical
curved doors and a fairing panel attached to the aft side of the nose gear.
When the landing gear is fully extended, the gear doors close to reduce
drag and air noise. All gear door movement is sequenced by mechanical
linkages operating hydraulic actuators to coordinate actuation with landing
gear extension and retraction.
Procedures exist to open and close the doors on the ground in order to
accomplish maintenance tasks. Hydraulic power from the Auxiliary system
and operation of a ground service valve, located adjacent to the nose
wheel well, allow movement of the gear doors by pressurizing the landing
gear on the ground. The ground service valve is shown in Figure 5.
B. Shock Struts
Standard oleo-pneumatic (gaseous nitrogen and hydraulic fluid) shock
struts are incorporated into each gear assembly. The shock struts consist
of a movable stainless steel piston within a cylinder containing hydraulic
fluid pressurized with gaseous nitrogen. O-ring seals maintain strut
pressure and allow the movement of the steel piston. The struts absorb the
shock of landing, and provide damping during taxi, takeoff and landing
rollout. An air/oil filler valve is provided at the top of each strut for servicing.
During normal operations, approximately three to five inches of inner
cylinder chrome is exposed at the bottom of each main landing gear strut,
depending on aircraft gross weight and outside air temperature. A placard
attached to upper portion of the landing gear strut indicates the correct
extension for ambient conditions.
C. Extension / Downlock Mechanisms
(1) Main Landing Gear Sidebrace Actuator / Downlock Mechanism
The sidebrace hydraulic piston and actuator arm extends the main
landing gear outboard and down from the wheel well and locks the
landing gear in the down position using internal locking keys located
in the lower end of actuator cylinder. The keys slide into annular
slots when the sidebrace actuator reaches full extension. A lock ram
positioned by down hydraulic pressure and a spring maintain the
keys in the slots preventing any further actuator movement. Spring
pressure is necessary to maintain the keys in the locked position in
the event of hydraulic pressure failure. The movement of the keys
into the slots also provides the input for the downlock microswitch
that provides the cockpit indication that the gear is down and locked.
When the gear is selected up, hydraulic pressure is ported to the
other side of the lock ram, displacing the keys from the slots and
overriding spring pressure, allowing the actuator to move in the
retract direction.
The sidebrace actuators have provisions for inserting ground lock
pins to maintain the main landing gear in the extended position
OPERATING MANUAL
2A-32-00 PRODUCTION AIRCRAFT SYSTEMS
Page 6
January 31/02
Revision 6
during ground operations. See the illustration in Figure 6.
(2) Nose Landing Gear Extend / Retract Actuator
Unlike the main landing gear sidebrace actuator that pushes the
main gear into the extended position, the nose gear actuator pulls
the nose gear aft and down to the extended position. One end of the
actuator is attached to the aft structural wall of the nose wheel well.
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