MAIN ROTOR ASSEMBLY

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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Figure 1-17.—Rotary-wing blade. A typical Navy helicopter, the H-3, is shown in figure 1-16. A flying boat-type hull provides this helicopter with water-operational capabilities for emergencies only. The fuselage consists of the entire airframe, sometimes known as the body group. The body group is of all-metal semimonocoque construction, consisting of an aluminum and titanium skin over a reinforced aluminum frame. LANDING GEAR GROUP The landing gear group includes all the equipment necessary to support the helicopter when it is not in flight. Conventional landing gear consists of a main landing gear and a nonretractable tail landing gear plus sponsons. See figure 1-16. The sponsons house the main landing gear during flight. They also aid in stabilizing the aircraft during emergency operation on the water when the aircraft is floating. Main Landing Gear Each main landing gear is composed of a shock strut assembly, dual wheels, a retracting cylinder, an uplock cylinder, and upper and lower drag braces. The wheels retract into a well, recessed into the underside of the sponsons. The dual wheels, equipped with tubeless tires and hydraulic brakes, are mounted on axles. They are part of the lower end of the shock strut piston. The main landing gear is extended hydraulically. In case of hydraulic failure, an emergency system of compressed air lowers the gear. Should the air system fail, the pilot actuates a valve to allow the gear to fall by its own weight. Retractable landing gear is not a feature common to all helicopters or even a majority of them. The H-3 is discussed here because it is one of the Navy’s latest helicopter designs. The H-3 has emergency water-operational capability. Tail Landing Gear The H-3 tail landing gear is nonretracting and full swiveling. It serves as an aft touchdown point for ship/land-based operations only. An air-oil type of shock absorber cushions the landing shock. MAIN ROTOR ASSEMBLY The main rotor (rotary wing) and the rotor head are discussed under the rotor head section because their functions are closely related. Neither has a function without the other. Rotary Wing The main rotor or rotary wing on the H-3 has five identical wing blades. Other helicopters may have two, three, or four blades. A typical wing blade is shown in figure 1-17. The rotary-wing blade is made of aluminum alloy, except the steel cuff by which the blade attaches to the rotor hub. The main supporting member of the blade is a hollow, aluminum alloy extruded spar, which forms the leading edge. The steel cuff is bolted to the root end of the spar. Twenty-three individual pockets constructed of aluminum ribs, aluminum channels, and aluminum skin covering are bonded to the aft edge of the spar. The tip 1-17

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