SERVICE MANUAL & ICA
8750 AMPHIBIAN/SEAPLANE FLOATS ON CESSNA 208/208B
Revision IR
Page 47 of 104
P/N 1005723 Doc. No. W8750-24-01
4.1 MAIN GEAR RETRACTION
DESCRIPTION
Refer to Figures 4-1, 4-2, 4-3, 4-4A, 4-4B, 4-5
and 4-6 for visual reference.
Retraction and extension of the main gear is
accomplished with a hydraulic rack and pinion
type actuator. The actuator consists of two
opposing pistons connected by a geared rack,
with a rotating pinion gear in the middle.
Hydraulic fluid is transferred from one piston to
the other using an electrically reversible
hydraulic pump located in the empennage of the
aircraft. The differential pressure build up
causes the piston to move, pushing the rack and
rotating the pinion gear and its attached drive
shaft.
Attached to each end of the drive shaft are
actuating arms that drive separate rod linkages
with adjustable rod ends. The drive shaft and
actuating arms have a keyway to prevent
slippage on the rotating drive shaft. The rod
linkages push and pull on the Main Gear Top
Arm Assembly causing it to pivot around a
fixed point. Also attached to the actuators drive
shaft is a visual gear position indicator.
This indicator consists of colored bands that
rotate with the drive shaft allowing the pilot to
visually determine the position of the main
landing gear by looking at a placard on the deck
of the float.
Since the actuator rotates through approximately
193 degrees, the rod linkages and the actuating
arm pass an over center point, preventing
reverse driving of the rack and pinion actuator
in both the fully extended and fully retracted
positions. The actuator rotation is adjusted by
setscrews that determine the length of travel of
the actuator pistons. Providing an over center
up-lock prevents inadvertent main gear
extension in the case of a hydraulic failure.
As a secondary safety to ensure the geometry
remains over center with a hydraulic failure, a
spring is installed on the actuating arm
preventing motion of the rack and pinion
actuator. Since the retraction mechanism is over
center, the weight of the landing gear and oleo,
when retracted, also prevent the retraction
mechanism from rotating past the over center
point.
