Figure 1-12.—Shock strut showing internal construction.
When the strut has made a stroke to absorb the energy
of the impact, the air or nitrogen at the top expands and
forces the fluid back into the lower chamber. The slow
metering of the fluid acts as a snubber to prevent
rebounds. Instructions for the servicing of shock struts
with hydraulic fluid and compressed air or nitrogen are
contained on an instruction plate attached to the strut, as
well as in the maintenance instruction manual (MIM)
for the type of aircraft involved. The shock absorbing
qualities of a shock strut depends on the proper servicing
of the shock strut with compressed or nitrogen and the
proper amount of fluid.
RETRACTING MECHANISMS.—Some aircraft
have electrically actuated landing gear, but most are
hydraulically actuated. Figure 1-11 shows a retracting
mechanism that is hydraulically actuated. The landing
gear control handle in the cockpit allows the landing
gear to be retracted or extended by directing hydraulic
fluid under pressure to the actuating cylinder. The locks
hold the gear in the desired position, and the safety
switch prevents accidental retracting of the gear when
the aircraft is resting on its wheels.
A position indicator on the instrument panel
indicates the position of the landing gear to the pilot. The
position indicator is operated by the position-indicating
switches mounted on the UP and DOWN locks of each
landing gear.
EMERGENCY EXTENSION.—Methods of
extending the landing gear in the event of normal system
failure vary with different models of aircraft. Most
aircraft use an emergency hydraulic system. Some
aircraft use pneumatic (compressed air or nitrogen),
mechanical, or gravity systems, or a combination of
these systems.
1-13
