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Summary

Aluminum alloys in the form of shells are most generally used in making the fuselage, nacelles, wings, and empennage. The basic fuselage constructions are the truss and monocoque. The truss is a rigid construction; and the monocoque is shell-like and gets its shape from formers, frame assemblies, and bulkheads. Maintaining strength while keeping weight down is the main problem in monocoque construction. The semimonocoque and reinforced shell are the most widely used fuselage constructions in present-day aircraft.

Formers, frame assemblies, and bulkheads are the structural members that give cross-sectional shape and strength to the construction. Frame assemblies used to separate areas are reinforced, disc-shaped, equipped with doors or access plates, and known as bulkheads. Channel members, hat-shaped sections, and built-up assemblies give the structure additional strength. Stringers and longerons are the principal lengthwise fuselage structural members. These joined to the formers, bulkheads, and assemblies make a rigid fuselage framework.

Nacelles are used primarily to house engines on multiengine aircraft. Generally, on twin-engine Army planes they house the main landing gear. Their repair fundamentals are essentially the same as for a fuselage. Nacelles must be kept within weight limits, built to withstand compression and shear loads, and aerodynamically suited for their location. Wings on military airplanes are generally without external bracing, and the skin is part of the wing structure, carrying some of the wing stresses. Monospar, multispar, and box-beam are the basic wing-construction designs. Monospar means that one main longitudinal member is used. The monospar wing is not in common use. Multispar wings have more than one main longitudinal member, and box-beam wings have two with connecting bulkheads for additional strength. Spars, ribs, bulkheads, and stringers are riveted or welded together. Spars run from the wing's base to its tip. Webs are deep wall plates and with their attached capstrips form the foundation for attaching the skin. Ribs are a wing's crosspieces, running from the leading edge to the trailing edge. They give the wing its shape and transmit the load from the skin to the spars. Ribs are also used in ailerons, elevators, fins, and stabilizers. Lightening holes in former ribs lessen their weight without decreasing their strength. Reinforced and truss ribs are heavier than former ribs and are only used at points where the greatest stress is imposed.

The empennage, the aft end of the fuselage, consists of the rudder, elevators, stabilizers, and trim tabs. These empennage components are usually of all-metal construction and cantilever design. In general, their construction features are the same as those of wings. The vertical stabilizer helps maintain directional stability in flight and supports the rudder. The horizontal stabilizer helps maintain stability about the airplane's lateral axis, and it is the base for the elevators.

Airframe structure for helicopters is generally the same as that for airplanes. The typical single-rotor helicopter has two major sections: the cabin and tail cone. Basically, the cabin structure is semimonocoque with strengthened high-stress areas. The tail cone supports the tail rotor, tail-rotor drive shafting, and stabilizers. The stabilizers give lateral and longitudinal stability to the aircraft during flight, and they are of semimocoque construction.

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