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Mystery of Aer Lingus Flight 712 British Missile Strike & Commercial Cover-up in 1968?
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Aircraft Structure
The present-day conventional aeroplane may be divided into four components: fuselage, wings, tail assembly, and landing gear, or undercarriage. Fuselage In the early days of aviation, the fuselage was merely an open framework to support the other components of the plane; the bottom of the airframe served as the landing gear. Subsequently, the need for greater strength and better performance resulted in the development of enclosed, box-like "strut-and-wire" fuselages that decreased drag, and also provided protection for pilot and passenger, as well as space for the payload. This "truss" structure was gradually superseded by the monocoque (literally, single shell) fuselage. The loads imposed on such a structure are carried primarily by the skin, rather than by an internal framework, as in the trussed structure. It is the most common fuselage presently in use. The outer shell also confers the possibility of pressurizing the internal volume for high-altitude flight. Wings Although the single-winged plane, known as the monoplane, made its appearance in the first decade of powered flight, early aeroplane construction favoured the use of two wings (the biplane), and occasionally even three or four. Multiple-wing planes have the advantage of superior lift and relatively stronger construction, but the monoplane has lower drag. Once the cantilever principle of wing construction was developed, the dominance of the monoplane was assured, although it did not become the design of choice until the 1930s. Cantilever wings obtain their entire strength from internal structural elements. Cantilever construction is employed in most present-day aircraft, and external bracing is used only for some small, light planes.The structure of a typical wing consists of a spar-and-rib framework enclosed by a thin covering of metal sheet. Treated fabric, or, infrequently, bonded plywood or resin-impregnated glass fibre are used for some small aircraft and sailplanes. The spar, or beam, extends from the fuselage to the wing-tip. One or more spars may be used in the wing, but the two-spar design is most common. The ribs, normally at right angles to the spars, give the wing its external shape. If the covering is of metal sheet, it contributes its own share of strength to the wing. This "stressed-skin" type of wing is used in all large planes, although there is an increasing use of high-strength reinforced plastic skins and structure. The size and shape of wings vary widely, depending on specific aerodynamic considerations. Wings of many supersonic planes have a high degree of sweepback (arrowhead tapering from the nose of the plane) and are as thin as possible, with a knife-like leading edge. Such a shape helps to reduce the shock of compression when the plane approaches the speed of sound. The structural importance of the wing is dramatically demonstrated by the development of the so-called "flying wing", a craft in which fuselage and tail are almost entirely eliminated. Tail Assembly The conventional type of tail assembly consists of two basic surfaces, horizontal and vertical, each of which has movable sections contributing to control of the craft and fixed sections to provide stability. The leading section of the horizontal surface is known as the horizontal stabilizer, and the rear movable section is known as the elevator. Sometimes the whole surface can move and the elevator is eliminated. The stationary section of the vertical surface is called the fin, and the movable section, the rudder. Two vertical surfaces are used in some aircraft; in that case, a double rudder is used. The V-shaped tail combines the rudder and elevator functions in a single device. Tails vary in size according to the type of aircraft. In some supersonic aircraft the horizontal tail is replaced by a foreplane, or "canard", located near the nose of the plane. Landing Gear Present-day landing gear is one of the most intricate of all aeronautical mechanisms. Its components include the shock strut, a hydraulic leg connecting the wheel with the wing or fuselage to absorb the shock of landing; the retracting mechanism, which raises and lowers the gear; the wheels; and the wheel brakes. There are a number of types of undercarriage, but two are most commonly employed: the older two-wheel gear and the nose or tricycle gear, which is now usual. The former consists of two large wheels located forward of the centre of gravity of the plane with a small wheel at the tail. A tricycle gear consists of two large wheels or wheelgroups behind the centre of gravity and a third wheel, called the nosewheel, in front of the two main wheels. Landing is easier with the tricycle gear because braking and manoeuvring are improved and the danger of nosing over is diminished. Some large aircraft have more than two rear wheel groups. Other forms of landing gear include a caterpillar tread for handling heavy loads on poor landing fields, a swivelling gear for landing in crosswinds, and a combination ski-wheel gear for use on ice and snow. |