Airframe Introduction
The airframe of a fixed wing aircraft is generally considered to consist of five principle units, the fuselage, wings, stabilizers, flight control surfaces and landing gear. Helicopter airframe consists of the fuselage, main rotor and related gearbox, tail rotor and the landing gear. The airframe components are constructed from a wide variety of materials and are joined by rivets, bolts, screws and welding or adhesives. The aircraft components are composed of various parts called structural members. Aircraft structural members are designed to carry a load or to resist stress. A single member of the structure may be subjected to a combination of stresses. In most cases the structural members are designed to carry loads rather than side loads, that is to be subjected to tension or compression rather than bending. Strength may be the principle requirement in certain structures, while others need entirely different qualities. For example, cowling, fairing and similar parts usually are not required to carry the stresses imposed by flight or landing loads. However these parts must have such properties as neat appearance and streamline shape.
Fuselage
The fuselage is the main structure or body of the aircraft. It provides space or cargo, controls , accessories, passengers and other equipment. In a single aircraft it also houses the powerplant. In multi engine aircraft the engines may either be in the fuselage, attached to the fuselage or suspended from the wing structure. They vary principle in size and arrangement of the different compartments. These are two general types of fuselage construction, the truss type and the monocoque type. A truss is a rigid frame work made up of members such as beams, struts and bars to resist deformation by applied loads. The truss framed fuselage is generally covered with fabric.
Wing Structure
The wings of an aircraft are surfaces which are designed to produce lift when moved rapidly through the air. The particular design for any given aircraft depends on a number of factors such as size, weight, use of the aircraft, desired speed in flight and at landing and desired rate of climb. The wings of a fixed wing aircraft are designated left and right, corresponding to the left and right sides of the operator when seated in cockpit. The wings of some aircraft are cantilever design, that is they are built so that no external bracing is needed. The skin is part of the wing structure and carries part of the wing stresses. Other aircraft wings use external bracing to assist in supporting the wing and carrying the aerodynamic landing loads. Both aluminum alloy and magnesium alloy are used with the construction..
Nacelles or Pods
Nacelles or pods are streamlined enclosures used on multi engine aircraft primarily to house the engines. They are round or spherical in shape and are usually located above, below or at the leading edge of the wing on multi engine aircraft. If an aircraft has only one engine, it is usually mounted at the forward end of the fuselage, and the nacelle is the streamlined extension of the fuselage. An engine nacelle or pod consist of skin, cowling, structural members, a firewall and engine mounts. Skin and cowling cover the outside of the nacelle. Both are usually made of sheet aluminum alloy, stainless steel, magnesium or titanium. Regardless of the material used the skin is usually attached to the framework by rivets.
Empennage
The empennage is also called the tail section and most aircraft designs consists of tail cone, fixed surfaces and movable surfaces. The tail cone serves to close and streamline the aft end of most fuselages. The cone is made up of structural members like those of the fuselage. However cones are usually lighter construction since they receive less stress than the fuselage.
Landing Gear
The landing gear is the assembly that supports the aircraft during landing or while it is resting or moving about on the ground. The landing gear has shock struts to absorb the shock of landing and taxing. By means of gear retraction mechanism, the landing gear attaches to the aircraft structure and enable the gear to extend and retract. The landing gear arrangement either has a tailwheel or a nosewheel. Landing gear arrangements having a nosewheel are usually equipped for nosewheel steering. Nosewheel aircraft are protected at the fuselage tail section with a tail skid or a bumper. By means of wheels and tires, the landing gear forms a stabilizing contact with the ground during landing and taxing. Brakes installed in the wheel enable the aircraft to be slowed or stopped during movement on the ground.
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