SERVICE MANUAL & ICA
WIPLINE 4000 FLOATS ON CESSNA A185E, A185F, AND 206 SERIES
Page 22
Revision G
P/N 1002552
Retraction and extension of the main and nose landing gear is effected by a hydraulic actuation system shown
schematically in figure 5-1.
The gear system is hydraulically actuated and driven by one pump located on the engine firewall on a Cessna 185
and in the aft fuselage at Sta. 159.3 on a Cessna 206.
A pressure of between 500 psi 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.
The selection of gear up or gear down is accomplished by a cockpit mounted control valve. 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 effected 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 (see figure 5-3). The lock is tripped when the follower slides up the
contoured track in the actuator as shown in figure 5-4. A reverse process effects extension. Gear position light
proximity switches are closed when the appropriate hook (containing the magnetic material) nests over the locking
bar.
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 5-5. Gear
position light proximity switches are closed when the piston containing the magnetic material has reached either
end of its travel.
5.1 DESCRIPTION AND OPERATION
