A little bit of engineering (562404), страница 20
Текст из файла (страница 20)
Introduced in 1933, Boeing’s Model 247 was considered the first truly modern airliner. It was an all-metal, low-wing monoplane, with retractable landing gear, an insulated cabin, and room for ten passengers. An order from United Air Lines for 60 planes of this type tied up Boeing’s production line and led indirectly to the development of perhaps the most successful propeller airliner in history, the Douglas DC-3. Trans World Airlines, not willing to wait for Boeing to finish the order from United, approached airplane manufacturer Donald Douglas in Long Beach, California, for an alternative, which became, in quick succession, the DC-1, the DC-2, and the DC-3.
The DC-3 carried 21 passengers, used powerful, 1,000-horsepower engines, and could travel across the country in less than 24 hours of travel time, although it had to stop many times for fuel. The DC-3 quickly came to dominate commercial aviation in the late 1930s, and some DC-3s are still in service today.
Boeing provided the next major breakthrough with its Model 307 Stratoliner, a pressurized derivative of the famous B-17 bomber, entering service in 1940. With its regulated cabin air pressure, the Stratoliner could carry 33 passengers at altitudes up to 6,100 m (20,000 ft) and at speeds of 322 km/h (200 mph).
| F | Aircraft Developments of World War II |
It was not until after World War II (1939-1945), when comfortable, pressurized air transports became available in large numbers, that the airline industry really prospered. When the United States entered World War II in 1941, there were fewer than 300 planes in airline service. Airplane production concentrated mainly on fighters and bombers, and reached a rate of nearly 50,000 a year by the end of the war. A large number of sophisticated new transports, used in wartime for troop and cargo carriage, became available to commercial operators after the war ended. Pressurized propeller planes such as the Douglas DC-6 and Lockheed Constellation, early versions of which carried troops and VIPs during the war, now carried paying passengers on transcontinental and transatlantic flights.
Wartime technology efforts also brought to aviation critical new developments, such as the jet engine. Jet transportation in the commercial-aviation arena arrived in 1952 with Britain’s DeHavilland Comet, an 885-km/h (550-mph), four-engine jet. The Comet quickly suffered two fatal crashes due to structural problems and was grounded. This complication gave American manufacturers Boeing and Douglas time to bring the 707 and DC-8 to the market. Pan American World Airways inaugurated Boeing 707 jet service in October of 1958, and air travel changed dramatically almost overnight. Transatlantic jet service enabled travelers to fly from New York City to London, England, in less than eight hours, half the propeller-airplane time. Boeing’s new 707 carried 112 passengers at high speed and quickly brought an end to the propeller era for large commercial airplanes.
After the big, four-engine 707s and DC-8s had established themselves, airlines clamored for smaller, shorter-range jets, and Boeing and Douglas delivered. Douglas produced the DC-9 and Boeing both the 737 and the trijet 727.
| G | The Jumbo Jet Era |
The next frontier, pioneered in the late 1960s, was the age of the jumbo jet. Boeing, McDonnell Douglas, and Lockheed all produced wide-body airliners, sometimes called jumbo jets. Boeing developed and still builds the 747. McDonnell Douglas built a somewhat smaller, three-engine jet called the DC-10, produced later in an updated version known as the MD-11. Lockheed built the L-1011 Tristar, a trijet that competed with the DC-10. The L-1011 is no longer in production, and Lockheed-Martin does not build commercial airliners anymore.
In the 1980s McDonnell Douglas introduced the twin-engine MD-80 family, and Boeing brought online the narrow-body 757 and wide-body 767 twin jets. Airbus had developed the A300 wide-body twin during the 1970s. During the 1980s and 1990s Airbus expanded its family of aircraft by introducing the slightly smaller A310 twin jet and the narrow-body A320 twin, a unique, so-called fly-by-wire aircraft with sidestick controllers for the pilots rather than conventional control columns and wheels. Airbus also introduced the larger A330 twin and the A340, a four-engine airplane for longer routes, on which passenger loads are somewhat lighter. In 2000 the company launched production of the A380, a superjumbo jet that will seat 555 passengers on two decks, both of which extend the entire length of the fuselage. Scheduled to enter service in 2006, the jet will be the world’s largest passenger airliner.
Boeing introduced the 777, a wide-body jumbo jet that can hold up to 400 passengers, in 1995. In 1997 Boeing acquired longtime rival McDonnell Douglas, and a year the company later announced its intention to halt production of the passenger workhorses MD-11, MD-80, and MD-90. The company ceded the superjumbo jet market to Airbus and instead focused its efforts on developing a midsize passenger airplane, called the Sonic Cruiser, that would travel at 95 percent of the speed of sound or faster, significantly reducing flight times on transcontinental and transoceanic trips.
Engineering
| I | INTRODUCTION |
Engineering, term applied to the profession in which a knowledge of the mathematical and natural sciences, gained by study, experience, and practice, is applied to the efficient use of the materials and forces of nature. The term engineer properly denotes a person who has received professional training in pure and applied science, but is often loosely used to describe the operator of an engine, as in the terms locomotive engineer, marine engineer, or stationary engineer. In modern terminology these latter occupations are known as crafts or trades. Between the professional engineer and the craftsperson or tradesperson, however, are those individuals known as subprofessionals or paraprofessionals, who apply scientific and engineering skills to technical problems; typical of these are engineering aides, technicians, inspectors, draftsmen, and the like.
Before the middle of the 18th century, large-scale construction work was usually placed in the hands of military engineers. Military engineering involved such work as the preparation of topographical maps, the location, design, and construction of roads and bridges; and the building of forts and docks; see Military Engineering below. In the 18th century, however, the term civil engineering came into use to describe engineering work that was performed by civilians for nonmilitary purposes. With the increasing use of machinery in the 19th century, mechanical engineering was recognized as a separate branch of engineering, and later mining engineering was similarly recognized.
The technical advances of the 19th century greatly broadened the field of engineering and introduced a large number of engineering specialties, and the rapidly changing demands of the socioeconomic environment in the 20th century have widened the scope even further.
| II | FIELDS OF ENGINEERING |
The main branches of engineering are discussed below in alphabetical order. The engineer who works in any of these fields usually requires a basic knowledge of the other engineering fields, because most engineering problems are complex and interrelated. Thus a chemical engineer designing a plant for the electrolytic refining of metal ores must deal with the design of structures, machinery, and electrical devices, as well as with purely chemical problems.
Besides the principal branches discussed below, engineering includes many more specialties than can be described here, such as acoustical engineering (see Acoustics), architectural engineering (see Architecture: Construction), automotive engineering, ceramic engineering, transportation engineering, and textile engineering.
| A | Aeronautical and Aerospace Engineering |
Aeronautics deals with the whole field of design, manufacture, maintenance, testing, and use of aircraft for both civilian and military purposes. It involves the knowledge of aerodynamics, structural design, propulsion engines, navigation, communication, and other related areas. See Airplane; Aviation.
Aerospace engineering is closely allied to aeronautics, but is concerned with the flight of vehicles in space, beyond the earth's atmosphere, and includes the study and development of rocket engines, artificial satellites, and spacecraft for the exploration of outer space. See Space Exploration.
| B | Chemical Engineering |
This branch of engineering is concerned with the design, construction, and management of factories in which the essential processes consist of chemical reactions. Because of the diversity of the materials dealt with, the practice, for more than 50 years, has been to analyze chemical engineering problems in terms of fundamental unit operations or unit processes such as the grinding or pulverizing of solids. It is the task of the chemical engineer to select and specify the design that will best meet the particular requirements of production and the most appropriate equipment for the new applications.
With the advance of technology, the number of unit operations increases, but of continuing importance are distillation, crystallization, dissolution, filtration, and extraction. In each unit operation, engineers are concerned with four fundamentals: (1) the conservation of matter; (2) the conservation of energy; (3) the principles of chemical equilibrium; (4) the principles of chemical reactivity. In addition, chemical engineers must organize the unit operations in their correct sequence, and they must consider the economic cost of the overall process. Because a continuous, or assembly-line, operation is more economical than a batch process, and is frequently amenable to automatic control, chemical engineers were among the first to incorporate automatic controls into their designs.
| C | Civil Engineering |
Civil engineering is perhaps the broadest of the engineering fields, for it deals with the creation, improvement, and protection of the communal environment, providing facilities for living, industry and transportation, including large buildings, roads, bridges, canals, railroad lines, airports, water-supply systems, dams, irrigation, harbors, docks, aqueducts, tunnels, and other engineered constructions. The civil engineer must have a thorough knowledge of all types of surveying, of the properties and mechanics of construction materials, the mechanics of structures and soils, and of hydraulics and fluid mechanics. Among the important subdivisions of the field are construction engineering, irrigation engineering, transportation engineering, soils and foundation engineering, geodetic engineering, hydraulic engineering, and coastal and ocean engineering.
| D | Electrical and Electronics Engineering |
The largest and most diverse field of engineering, it is concerned with the development and design, application, and manufacture of systems and devices that use electric power and signals. Among the most important subjects in the field in the late 1980s are electric power and machinery, electronic circuits, control systems, computer design, superconductors, solid-state electronics, medical imaging systems, robotics, lasers, radar, consumer electronics, and fiber optics.
Despite its diversity, electrical engineering can be divided into four main branches: electric power and machinery, electronics, communications and control, and computers.
| D1 | Electric Power and Machinery |
The field of electric power is concerned with the design and operation of systems for generating, transmitting, and distributing electric power. Engineers in this field have brought about several important developments since the late 1970s. One of these is the ability to transmit power at extremely high voltages in both the direct current (DC) and alternating current (AC) modes, reducing power losses proportionately. Another is the real-time control of power generation, transmission, and distribution, using computers to analyze the data fed back from the power system to a central station and thereby optimizing the efficiency of the system while it is in operation.
A significant advance in the engineering of electric machinery has been the introduction of electronic controls that enable AC motors to run at variable speeds by adjusting the frequency of the current fed into them. DC motors have also been made to run more efficiently this way. See also Electric Motors and Generators; Electric Power Systems.
| D2 | Electronics |
Electronic engineering deals with the research, design, integration, and application of circuits and devices used in the transmission and processing of information. Information is now generated, transmitted, received, and stored electronically on a scale unprecedented in history, and there is every indication that the explosive rate of growth in this field will continue unabated.
Electronic engineers design circuits to perform specific tasks, such as amplifying electronic signals, adding binary numbers, and demodulating radio signals to recover the information they carry. Circuits are also used to generate waveforms useful for synchronization and timing, as in television, and for correcting errors in digital information, as in telecommunications. See also Electronics.
Prior to the 1960s, circuits consisted of separate electronic devices—resistors, capacitors, inductors, and vacuum tubes—assembled on a chassis and connected by wires to form a bulky package. Since then, there has been a revolutionary trend toward integrating electronic devices on a single tiny chip of silicon or some other semiconductive material. The complex task of manufacturing these chips uses the most advanced technology, including computers, electron-beam lithography, micro-manipulators, ion-beam implantation, and ultraclean environments. Much of the research in electronics is directed toward creating even smaller chips, faster switching of components, and three-dimensional integrated circuits.
| D3 | Communications and Control |
Engineers in this field are concerned with all aspects of electrical communications, from fundamental questions such as “What is information?” to the highly practical, such as design of telephone systems. In designing communication systems, engineers rely heavily on various branches of advanced mathematics, such as Fourier analysis, linear systems theory, linear algebra, complex variables, differential equations, and probability theory. See also Mathematics; Matrix Theory and Linear Algebra; Probability.
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