A little bit of engineering (Несколько текстов для зачёта), страница 16

The rate of airplane manufacture in Europe and the United States skyrocketed during the war. Britain turned out more than 55,000 airplanes from 1914 to 1918, and Germany produced 40,000 airplanes during the same period. The fledgling American industry also rallied behind the war effort, turning out 14,000 planes in 1918 alone. By the end of the war, the American aerospace industry had grown to 200,000 workers.

In the years following World War I, the frenzied pace of airplane production slowed, and the aircraft industry turned its attention to improvements to aircraft design. American and British firms, encouraged by NACA in the United States and the Royal Aircraft Establishment in Britain, investigated a broad range of design innovations. Progressive techniques of design, engineering, and construction also came from graduates of newly established professional aeronautical engineering schools, first introduced during the 1920s. These innovation efforts resulted in dramatic changes to aircraft. Wooden airframes gave way to lightweight metal structures, while improvements in engine technology and fuels yielded greater speed and engine reliability.

These and other advances opened up new uses for airplanes. In 1921 the U.S. Post Office began regular transcontinental airmail service between New York City and San Francisco, California. Boeing developed its first commercial aircraft, the Model 40, in 1927 after winning a contract to fly mail for the U.S. Postal Service between Chicago, Illinois, and San Francisco.

In 1933 Boeing introduced the twin-engine Model 247 airplane, an all-metal, low-wing monoplane with retractable landing gear and room for ten passengers. The Model 247 revolutionized commercial aircraft design but was soon displaced by the larger, faster DC-3 designed and built by the Douglas Aircraft Company. The DC-3 carried 21 passengers and could travel across the country in less than 24 hours, though it had to stop many times for fuel. The DC-3 quickly came to dominate commercial aviation in the late 1930s and helped establish the United States as the leading producer of global airline equipment.

In 1939 World War II broke out in Europe. Airplane manufacturers in Britain and France, already overburdened with orders for military aircraft, placed massive orders for planes and equipment with American manufacturers. In response, the American aeronautics industry significantly expanded its production capabilities. By the time the United States entered the war in December 1941, the nation’s aerospace industry was prepared to meet the increased demand for aircraft and produced more than 300,000 aircraft before the war was over.

During the war the geographic centers of U.S. aircraft production, traditionally concentrated on the coasts, became more diversified. Wartime planners moved production inland to improve security against foreign attack and to satisfy the skyrocketing demand for workers. In Wichita, Kansas, formerly center of the light plane industry, manufacturers produced thousands of training aircraft and larger combat planes. New facilities in Atlanta, Georgia, built B-29 bombers, and new plants in the Dallas-Fort Worth region of Texas turned out B-24 Liberator bombers, P-51 Mustang fighters, and AT-6 trainers.

World War II military research also produced technological innovations that forever changed aviation. Rocket scientists in Germany developed missile prototypes that later served as the foundation for space exploration. The most important of these prototypes was the world’s first large-scale rocket, the A-4 (later renamed the V-2).

Wartime efforts also resulted in the use of jet propulsion in military aircraft. In the late 1930s British aeronautical engineer Frank Whittle made the first successful tests of the turbojet engine. The Germans, French, and Italians made subsequent improvements to jet engine design during the war. The British shared their engine technology with the United States, and by the end of World War II in 1945, Germany, Britain, and the United States had built jet-powered fighter planes.

After the war, most airplane manufacturers shifted their efforts back to passenger airplanes. They incorporated technology developed for troop transports during the war, such as pressurized cabins. This innovation enabled pilots to fly at higher altitudes, above turbulent weather, increasing passenger comfort. Lockheed began commercial production of the Constellation, one of the first commercial airplanes with a pressurized cabin. The Constellation joined the Douglas DC-3 and the newer DC-6 in transcontinental and transatlantic service. Together these large, comfortable airliners posed a significant threat to railway travel and ocean liners as the principal modes of long-distance transportation.

Following World War II, the United States and the Union of Soviet Socialist Republics (USSR) engaged in a long struggle that came to be known as the Cold War. The defense budgets of both countries escalated during this period as each tried to stay ahead of the other’s military technology. Assisted by NACA research and generous federal funding for aeronautical research and development, American firms such as General Electric and Pratt & Whitney developed powerful jet engines. These new engines powered subsequent generations of military aircraft, such as the North American F-86 Sabre fighter and the Boeing B-47 Stratojet bomber. American manufacturers reaped additional profits during the Cold War by selling helicopters, fighters, and transport aircraft to friendly foreign powers.

In 1957 the USSR put Sputnik, the world’s first artificial satellite, into orbit. In response, the United States revamped its aerospace efforts. In 1958 it restructured NACA and dubbed the new organization the National Aeronautics and Space Administration (NASA). NASA devoted all of its resources to catching up with—and beating—the Soviet space program. The United States also announced its intention to be the first nation to put a human on the moon. This led to the Apollo program, a multibillion-dollar space exploration effort that eventually sent 12 American astronauts to the surface of the moon.

British aerospace engineers revolutionized the air transport industry when they incorporated the jet engine, previously used only in military aircraft, into a commercial plane. The de Havilland Comet, introduced in 1952, was celebrated as the first commercial airplane powered by jet engines. Unforeseen structural weaknesses in the Comet caused a series of crashes, two of them fatal. The Comet was grounded for investigation for several years, giving American manufacturers the opportunity to catch up to their British counterparts. In the late 1950s Boeing and Douglas introduced the jet-powered 707 and DC-8. Pan American World Airways inaugurated Boeing 707 jet service in October 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 time a propeller airplane took to fly that distance. Boeing’s 707 carried 112 passengers at high speed and quickly completed the displacement of ocean liners and railroads as the principal form of long-distance transportation.

In 1970 Boeing introduced the extremely successful 747, a huge, wide-body airliner. The giant aircraft, nicknamed the “jumbo jet,” could carry more than 400 people and several hundred tons of cargo. Douglas and Lockheed soon turned out their own versions of the jumbo jet, the DC-10 and the L-1011.

The Cold War, the space race, and advances in civil aeronautics made the aerospace industry one of the United States’ largest employers and one of the strongest and most robust industries of any kind in the world. By the late 1960s European aerospace industries were seeking ways to reduce their dependence on American manufacturers.

In an effort to usurp American leadership in the production of civil airliners, Britain and France joined forces to develop the Concorde supersonic transport, the first commercial jet to fly faster than the speed of sound (see Aerodynamics: Supersonics). The Concorde, introduced in 1967, set the stage for other multinational European efforts to build and sell airplanes in competition with the big American aerospace companies. In 1970 French, German, British, and Spanish aerospace companies collaborated to form Airbus Industrie (now Airbus). The Airbus A-300 airplane, introduced four years later, inaugurated a family of air transports that by the early 2000s ranked second only to Boeing in worldwide sales. Additional European programs evolved as multinational groups formed to develop fighters, attack aircraft, and helicopters.

In 1989, the collapse of the USSR and the ensuing demise of the Cold War brought fundamental changes to the global aerospace industrial community. Soviet aerospace agencies reorganized as private entities that often collaborated with Asian, European, and American firms—strategic partnering that put them in better positions to obtain contracts. This strategy touched off a wave of mergers in the American aerospace industry. Martin-Marietta acquired the aerospace division from General Electric Company in 1992, then merged with the aerospace giant Lockheed two years later. In 1997 Boeing acquired longtime rival McDonnell Douglas Corporation and in 2000 acquired Hughes Electronics Corporation’s space and communications division, the world's leading manufacturer of communications satellites. Several European firms announced their intention to combine forces to challenge the newly formed American aerospace giants. In 1999 the French, German, and Spanish partners in the Airbus consortium merged to form the European Aeronautic Defense and Space Company, and by 2001 Airbus was a single centralized company.

Airplane

Airplane, engine-driven vehicle that can fly through the air supported by the action of air against its wings. Airplanes are heavier than air, in contrast to vehicles such as balloons and airships, which are lighter than air. Airplanes also differ from other heavier-than-air craft, such as helicopters, because they have rigid wings; control surfaces, movable parts of the wings and tail, which make it possible to guide their flight; and power plants, or special engines that permit level or climbing flight.

Modern airplanes range from ultralight aircraft weighing no more than 46 kg (100 lb) and meant to carry a single pilot, to great jumbo jets, capable of carrying several hundred people, several hundred tons of cargo, and weighing nearly 454 metric tons.

Airplanes are adapted to specialized uses. Today there are land planes (aircraft that take off from and land on the ground), seaplanes (aircraft that take off from and land on water), amphibians (aircraft that can operate on both land and sea), and airplanes that can leave the ground using the jet thrust of their engines or rotors (rotating wings) and then switch to wing-borne flight.

An airplane flies because its wings create lift, the upward force on the plane, as they interact with the flow of air around them. The wings alter the direction of the flow of air as it passes. The exact shape of the surface of a wing is critical to its ability to generate lift. The speed of the airflow and the angle at which the wing meets the oncoming airstream also contribute to the amount of lift generated.

An airplane’s wings push down on the air flowing past them, and in reaction, the air pushes up on the wings. When an airplane is level or rising, the front edges of its wings ride higher than the rear edges. The angle the wings make with the horizontal is called the angle of attack. As the wings move through the air, this angle causes them to push air flowing under them downward. Air flowing over the top of the wing is also deflected downward as it follows the specially-designed shape of the wing. A steeper angle of attack will cause the wings to push more air downward. The third law of motion formulated by English physicist Isaac Newton states that every action produces an equal and opposite reaction (see Mechanics: The Third Law). In this case, the wings pushing air downward is the action, and the air pushing the wings upward is the reaction. This causes lift, the upward force on the plane.

Lift is also often explained using Bernoulli’s principle, which states that, under certain circumstances, a faster moving fluid (such as air) will have a lower pressure than a slower moving fluid. The air on the top of an airplane wing moves faster and is at a lower pressure than the air underneath the wing, and the lift generated by the wing can be modeled using equations derived from Bernoulli’s principle.

Lift is one of the four primary forces acting upon an airplane. The others are weight, thrust, and drag. Weight is the force that offsets lift, because it acts in the opposite direction. The weight of the airplane must be overcome by the lift produced by the wings. If an airplane weighs 4.5 metric tons, then the lift produced by its wings must be greater than 4.5 metric tons in order for the airplane to leave the ground. Designing a wing that is powerful enough to lift an airplane off the ground, and yet efficient enough to fly at high speeds over extremely long distances, is one of the marvels of modern aircraft technology.

Thrust is the force that propels an airplane forward through the air. It is provided by the airplane’s propulsion system; either a propeller or jet engine or combination of the two.