WIPLINE MODEL 8000 SERVICE MANUAL
Page 18 of 62
1002554 • Rev H
5.0 MAIN AND NOSE GEAR OPERATION, REMOVAL AND SERVICE
5.1 DESCRIPTION AND OPERATION
Retraction and extension of the main and nose landing gear is effected by a hydraulic
actuation system shown schematically in figure 5.3.
The gear system is hydraulically actuated and driven by two hydraulic pumps
located in the Aft fuselage.
A pressure of between 500 and 1000 psi is maintained in the supply line. When
the pressure falls below 500 psi, the pressure switch activates the pump solenoid,
providing power to the pump. When the pressure reaches 1000 psi, the pressure
switch deactivates the solenoid and the pump motor stops. Figure 5.2 shows the
electrical schematic of the system. A check valve on the output side of the pump
retains pressure in the system while the pump is off. The pump has an internal relief
valve, which directs oil back to the pump reservoir when the line pressure exceeds
1200 psi. The system also has an internal relief valve to protect against thermal
expansion when line pressure exceeds 1900 psi.
A cockpit mounted control valve accomplishes the selection of gear up or gear
down. Each float gear has individual indicator lights on the control valve allowing the
pilot to confirm that each gear has fully retracted or extended.
An emergency hand pump is provided, in case of total electric pump failure, or loss of
fluid. The reservoir has additional hydraulic fluid, available only to the hand pump.
The main gear is mechanically locked in both up and down positions. Locking and
unlocking is done utilizing a small amount of lost motion of the actuator rod. Retraction
takes place when pressure is exerted on the actuator piston driving the collar along the
slide tube. The lock is tripped when the follower slides up the contoured track in the
actuator as shown in figure 5.3. A reverse process affects extension. Gear position
light proximity switches are closed when the appropriate hook (containing the magnetic
material) nests over the locking bar.
Shock absorption for the main landing gear is provided by a hydraulically dampened air
spring. Figure 5.4 shows the main components. The oil and air share a common
chamber. When the oleo is collapsed, the oil is forced through the main orifice,
compressing the air in the upper cylinder. Extension reverses this process. The
extended oleo is initially set at the factory to 210 psi no load. In-field adjustment of air
pressure and oil volume is described in this section.
The nose gear has an over-center down lock. Retraction occurs when pressure is
applied to the forward face of the actuator piston and the carriage is drawn along the
tracks in the nose box as shown in figure 5.6. Gear position light proximity switches
