is installed under each wing. Because aircraft are different in size, shape, and construction, every landing gear is specially designed. Although main landing gears are designed differently, all main gear struts are attached to strong members of the wings or fuselage so that the landing shock is distributed throughout the main body of the structure. The main gears are also equipped with brakes that are used to shorten the landing roll of the aircraft and to guide the aircraft during taxiing. Nose Landing Gear On aircraft with tricycle landing gear, the nose gear is retracted either rearward or forward into the aircraft fuselage. Generally, the nose gear consists of a single shock strut with one or two wheels attached. On most aircraft the nose gear has a steering mechanism for taxiing the aircraft. The mechanism also acts as a shimmy damper to prevent oscillation or shimmy of the nosewheel. Since the nosewheel must be centered before it can be retracted into the wheel well, a centering device aligns the strut and wheel when the weight of the aircraft is off the gear. Damping, steering, and centering devices are discussed later in this chapter. ROTARY-WING AIRCRAFT The landing gear systems on rotary-wing aircraft come in several different designs. A helicopter may have a nonretractable landing gear, such as that found on the H-46 and H-60 helicopters, or it may have a retractable type landing gear like that incorporated on the H-3 and H-53 helicopters. Some helicopters have a nose landing gear while others have a tail landing gear. The H-53 has a retractable nose landing gear, but the H-46 has the nonretractable type of nose landing gear. The H-3 and H-60 helicopters use tail landing gears. The tail landing gear on both these helicopters is nonretractable. While both these helicopters have tail landing gear, the H-3 can retract its main landing gear while the H-60 has a nonretractable main landing gear. As you can see, helicopter landing gear systems come in several different configurations. The landing gear systems on most of the helicopters used in the Navy use wheel and brake assemblies. The components used in the landing gear system of a helicopter are very similar to those used in a fixed-wing aircraft landing gear system. In helicopters that use retractable landing gear systems, the components and means of actuation are also similar in design to fixed-wing aircraft. For discussion purposes, we will use the landing also system of the H-60 helicopter. This helicopter uses a nonretractable main and tail landing gear. Main Landing Gear The main landing gear system of the H-60 helicopter consists of nonretractable left and right single wheel landing gear assemblies and the weight- on-wheels system. Each main landing gear assembly is composed of a shock strut, drag beam, axle, wheel, tire, and wheel brake. The left main landing gear assembly also includes a weight-on-wheels sensing switch, The main landing gear supports the helicopter when it is on the ground, and cushions the helicopter from shock during landing. The weight-on-wheels switch provides helicopter ground or for various helicopter systems. Tail Landing Gear flight status indications The H-60 tail landing gear system consists of a dual- wheel landing gear, tail wheel lock system, and tail bumper. The tail landing gear is a cantilever type with an integral shock strut. The gear is capable of swiveling 360 degrees. It can be locked in the trail position by the tail wheel lock system. A tail recovery assist, secure, and traverse (RAST) probe is mounted on the tail gear. LANDING GEAR SYSTEMS OPERATION Learning Objective: Identify the operational and troubleshooting procedures for landing gear systems. Landing gear systems on naval aircraft, as stated earlier, are similar in design. Most aircraft equipped with the tricycle-type, retractable landing gear have two systems of operation, normal and emergency. NORMAL SYSTEM The normal system of a “typical” landing gear system is described because many components used in different landing gear systems are similar. Figure 12-2 is a schematic that shows the fluid flow in the nose gear up cycle. This system contains a selector valve, flow regulators, priority valves, check valve, actuating cylinders, and the necessary hydraulic tubing that routes hydraulic fluid to and from the required components. 12-2