RETRACTING MECHANISMS

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