field of engineering concerned with the development, design, construction, testing, and operation of aircraft and space vehicles. Aeronautical engineering traces its roots back to balloon flight, gliders, and airships. But the real expansion of activity came with the first mechanically powered and controlled flight of the Wright brothers' Flyer in December 1903 at Kitty Hawk in North Carolina. During the 1960s the concept of aeronautical engineering was broadened to include all vehicles that operate above the surface of the Earth, in outer space as well as in the atmosphere. The term aerospace engineering thus came to denote this broadened discipline. In addition to space vehicles, all types of hovercraft are included in this field of engineering. The principal technologies encompassed by aerospace engineering are those of aerodynamics, propulsion, structures and stability, and control. The aerospace-engineering process begins in academic, industrial, and government research centres. Industrial designers, using the latest technological developments, propose an initial vehicle design calculated to satisfy the particular requirements specified. This initial design is followed by a long process, lasting months and sometimes years, in which the design and development of the many vehicle components are carried out by aerospace engineers. The design process precedes the construction and testing of one or more prototype vehicles. Satisfactory completion of flight testing of prototypes is followed by quantity production and operation. Aerospace engineers participate in all steps of these processes. The history of aerospace engineering has been prone to revolutionary leaps in technology, coupled with the slower but continual evolutionary development of basic processes. The metal monocoque fuselage, the cantilevered monoplane wing, the jet engine, supersonic flight, and space flight are such examples. In fact, the post-World War II period was one of rapid change in aerospace engineering, as new knowledge in aerodynamics, structures, propulsion, stability, and control developed at increasing rates. Low-speed aerodynamics gave way to transonic, supersonic, and hypersonic aerodynamics; frame structures were replaced by thin, metallic shells that required the development of new aluminum, magnesium, titanium, and steel alloys; internal combustion engines were replaced by rocket and turbojet engines; and manual control developed into automatic control. The practice of aerospace engineering rests upon principles fundamental to all flight vehicles-a propulsion system with high thermodynamic and propulsive efficiencies, a structure of minimum weight and maximum strength, an external shape that is stable in flight with maximum aerodynamic efficiency, a precision control and guidance system, and a suitable design compromise among all these elements that allows the vehicle to achieve the required performance. An understanding of these principles depends upon knowledge of the engineering sciences: materials science, solid and structural mechanics, thermodynamics, fluid mechanics, and electrical science. In turn, the engineering sciences rest upon the basic sciences of physics, chemistry, and mathematics. To create a successful aircraft, the aerospace designer must blend the sciences of fluid mechanics and aerodynamics with the most advanced engineering techniques available. The aircraft's wing is perhaps the most difficult part of an aircraft to design because of the compromise that must be achieved between the air loads the wing must carry and the shape that it must have in order to produce lift and minimize drag. The location of an aircraft's power plants is also an important consideration for the designer, since the power plant must create sufficient thrust for the craft while itself producing minimal amounts of drag through the airstream. Stability, or the ability of an aircraft disturbed from its equilibrium to create forces and moments which tend to restore that equilibrium, is also important and is determined by the configuration and shape of the power plants, wings, fuselage, tail, and flaps. Structural considerations in aircraft design are dominated by the need to create airplane frames of minimum weight and maximum strength and rigidity. The largest employers of aerospace engineers are the aircraft and aerospace industries and the supporting subcontractors associated with those industries. Aerospace engineers employed in such activities are engaged in a wide variety of duties ranging from basic research on fundamental principles to hardware design and production. The second largest employer in most countries is the government. Here the engineer's duties lie principally in research, development, and procurement. Aerospace engineers are also employed to a limited extent by universities and by commercial airlines. Important engineering functions must be carried out by the airlines in acquiring new equipment and in the maintenance and operation of equipment. Additional reading C. Hart, The Prehistory of Flight (1985), covers early concepts of the nature of flight and early attempts to construct flying machines. Charles H. Gibbs-Smith, Flight Through the Ages (1974), surveys aeronautics from its early period to the age of space exploration. Tom D. Crouch, A Dream of Wings (1981), traces the history of U.S. aeronautics. P.A. Hanle, Bringing Aerodynamics to America (1982), focuses on the European influences that led to the establishment of the science of flight as an exact science in the United States. Roger E. Bilstein, Orders of Magnitude: A History of the NACA and NASA, 1915-1990, rev. ed. (1989), chronicles the growth of the National Advisory Committee for Aeronautics and the National Aeronautics and Space Administration. Jerome Lederer, "Highlights in the Development of Civilian Aircraft," Automotive Engineering, 88(12):33-43 (December 1980), is a review that dwells on the prominent technical concepts and development of civil air transportation. John D. Anderson, Jr., Introduction to Flight, 3rd ed. (1989), deals with theoretical questions of aerodynamics and describes the design and construction of airplanes. Other useful works include J.H. Hughes, Jr., and J.S. Priamos, Aerospace (1977); Barnes W. McCormick, Aerodynamics, Aeronautics, and Flight Mechanics (1979); Leland M. Nicolai, Fundamentals of Aircraft Design, rev. ed. (1984); and Richard S. Shevell, Fundamentals of Flight, 2nd ed. (1989). Kaydon Al Stanzione The Editors of the Encyclopdia Britannica

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