A little bit of engineering (562404), страница 15

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Narrow-body jets seat fewer passengers. Boeing and Airbus build large narrow-body jets that carry between 100 and 200 passengers. For commuter flights, airlines use smaller jets, called regional jets, some seating as few as six passengers. The majority of these planes are built by Canadian airplane manufacturer Bombardier and Brazilian manufacturer Empresa Brasileira de Aeronautica (Embraer).

Aerospace manufacturers produce more than 30 types of general aviation aircraft, a category that encompasses corporate aircraft, recreational airplanes, planes used to spray agricultural crops, and helicopters for police, ambulance, and patrol service. Corporate aircraft are usually powered by jet engines and carry up to 40 passengers. Major manufacturers in the corporate jet market include the Cessna Aircraft Company, Gulfstream Aerospace Corporation, and Raytheon in the United States, Bombardier in Canada, and Dassault Aviation in France. Recreational pilots commonly fly single-seat or twin-seat planes designed and manufactured by several companies, including Cessna and The New Piper (formerly Piper Aircraft Corporation).

Other aerospace firms specialize in designing and building the engines that power aircraft. The three most common types of jet engines are the turbojet, the turboprop, and the turbofan (see Jet Propulsion). In turbojet engines, energy produced by burning fuel spins a turbine that compresses the air entering the engine and directs it into a combustion chamber, where it is mixed with fuel vapor and burned. Turboprop engines are driven almost entirely by a propeller mounted in front of the engine. Turbofans combine air passing through the engine, hot engine exhaust, and air from a fan.

Production of large jet engines for airliners is dominated by American jet engine manufacturers General Electric Company and Pratt & Whitney, and Rolls-Royce of Britain. These companies also produce engines for jet fighters, bombers, and transports. Several manufacturers produce smaller gas turbines for corporate jets and helicopters. AlliedSignal Engines, part of Honeywell International in the United States, supplies a wide range of engines for regional airliners, corporate jets, helicopters, and military aircraft.

Aerospace firms design and build a wide variety of missiles for military use. These range in size from large guided missiles that carry nuclear warheads to small portable rockets carried and launched by foot soldiers. Modern missiles incorporate their own propulsion systems and sophisticated guidance systems.

Surface-fired missiles launch from the ground or the sea. There are two chief types of surface-fired missiles: those fired at targets on Earth’s surface or in its oceans, and those fired at targets in the air. The largest surface-to-surface missiles are intercontinental ballistic missiles (ICBMs), which are capable of carrying nuclear warheads to targets as far as 15,000 km (9,200 mi) away. Soldiers use smaller surface-to-surface missiles against enemy tanks or troops. Still other missiles dive deep into the ocean to search out and destroy enemy submarines. Surface-to-air missiles are used against airborne targets, such as airplanes or other missiles. This category includes the U.S. Army’s Patriot missile system, a large missile and launcher that intercepts and destroys enemy missiles before they strike. The Patriot missile system was developed for the U.S. military by Raytheon and Lockheed Martin. Patriots are also used by Germany, Israel, Japan, and a number of other countries.

Air-launched missiles are launched from fighter aircraft. Missiles in this category tend to be short-range. Air-to-air missiles, such as the U.S. Sidewinder missile built by Raytheon and other companies, usually rely on infrared heat-seeking devices to track their targets. These sophisticated missiles follow and destroy enemy aircraft and can change course when their targets do. Air-to-surface missiles commonly incorporate global positioning and inertial guidance systems, or miniature television homing systems.

Aerospace contractors design and build spacecraft for military and commercial purposes, and for use in space exploration. Products in this category include unmanned spacecraft, such as satellites and space probes, and piloted spacecraft. Other aerospace contractors design and build the rockets used to propel spacecraft out of Earth’s atmosphere and into space.

Telecommunications companies contract with aerospace manufactures to design and build communications satellites. These Earth-orbiting satellites transmit radio signals from cellular telephones, television broadcasting, and a number of other wireless communications. Military networks of defense-system satellites detect missile and satellite launches in other countries. Surveillance satellites provide a way to monitor activity in other countries, making it possible to detect terrorist actions or other illegal activities. The U.S. military also maintains 24 satellites as part of the global positioning system (GPS), an electronic satellite navigation system. Research satellites gather scientific information. The National Aeronautics and Space Administration (NASA) uses research satellites to observe Earth, other planets and their moons, comets, stars, and galaxies. The Hubble Space Telescope orbits about 610 km (about 380 mi) above Earth’s surface, photographing objects as far as 15 billion light-years away.

The largest manufacturers of satellites include the American companies Hughes Space and Communications Company, Lockheed Martin, and Loral Space & Communications, and the French conglomerate Alcatel. These and other satellite manufacturers develop, build, and sometimes operate satellites for private companies, the military, and governments.

The space shuttle is the only piloted spacecraft produced in the United States. It consists of three main components: an orbiter, propulsion systems—two solid rocket boosters and three main engines—and an external fuel tank. Shuttle orbiters are reusable, designed to withstand 100 missions or more each. Many different aerospace contractors contribute to the shuttle’s design, construction, and maintenance. NASA and the United Space Alliance, a partnership between Boeing and Lockheed Martin, oversee shuttle design and construction.

Some aerospace companies design and build launch vehicles—rockets that propel spacecraft out of Earth’s atmosphere and into space. To escape Earth’s atmosphere, launch vehicles must reach velocities of about 30,000 km/h (about 18,500 mph). To achieve this speed and power, aerospace firms build rockets composed of two or more engines, one atop another. The largest manufacturers of launch vehicles include Lockheed Martin, which makes several versions of its Atlas and Titan rockets, and French rocket manufacturer Arianespace, which builds the Ariane launch vehicle. Boeing also manufacturers rockets for use as launch vehicles. Rockets from Boeing’s Delta family, for example, launched all the GPS satellites.

The fourth and final category encompasses the thousands of different pieces of equipment and equipment systems found on flight vehicles and ground-based flight support facilities. Some firms specialize in flight and engine controls for various flight vehicles. The space shuttle orbiter has more than 2,000 different controls and displays in the crew compartment. Other firms design and build instruments for flight navigation and radar systems, landing gear, flight data recorders, and cabin-pressure control systems. Still others manufacture seats, lights, kitchen equipment, and waste management systems. Companies that specialize in missile technology build state-of-the-art guidance systems, such as infrared heat-seeking devices and computer navigational systems.

Aerospace firms also produce ground-based navigational systems that support flight vehicles. These range from the radar, radio, and computers used in air traffic control at airports to the state-of-the-art command and control systems that track and operate spacecraft millions of miles from Earth. Others produce sophisticated remote controls that enable engineers on the ground to change a spacecraft’s course or to operate telescopes or cameras.

The area of research and development constitutes one of the largest expenditures of the aerospace industry. Development of a new flight vehicle might take a decade or more and involve thousands of people. Such an endeavor requires significant advances in equipment and systems—in some cases it calls for entirely new inventions—and several billion dollars. Because the cost of developing new flight vehicles is so high, most large aerospace companies devote their research and development resources to improving existing products. They may redesign aircraft components to make them lighter and more fuel efficient, for example, or redesign wings or body surfaces to make the craft travel faster (see Aerodynamics).

Much of the design process takes place on supercomputers capable of performing billions of operations per second. Computer-aided design enables engineers to test thousands of design parameters, such as the shape or angle of wings. The designer uses a computer to create a model of the flight vehicle’s basic structure, or airframe, and then to simulate flight in various atmospheric conditions (see Computer-Aided Design/Computer-Aided Manufacturing). In addition to the shape and size of the airframe, engineers must also consider thousands of details. For example, they must consider the weight and placement of the engines, how and where fuel will be stored, the type and layout of instruments in the cockpit, and details of the passenger compartment, such as the number of seats and their dimensions. In designing commercial airplanes, engineers must also plan for entertainment systems, food storage and preparation, and the location and number of lavatories.

After preliminary computer designs are in place, engineers build a scale model of the aircraft and subject it to a series of tests in a wind tunnel. Wind tunnels simulate the conditions encountered by the flight vehicle as it moves through the air. Many research facilities have their own wind tunnels. Manufacturers also have access to government-funded wind tunnels, such as NASA’s Ames Research Center tunnel at Moffett Field, California. This massive wind tunnel can accommodate a full-size aircraft with a wingspan of 22 m (72 ft). Observations made during wind tunnel testing confirm or invalidate design assumptions tested on the computer. Engineers use the results of the wind tunnel tests to refine design as necessary.

Once the design has been finalized, engineers build one or more full-size prototypes of the flight vehicle and subject them to a barrage of additional tests. Engineers confirm that the structure can withstand the thundering vibrations and heat produced by the jet engines. They use machines to bend, twist, and push the aircraft to verify that it can withstand the stresses it will likely encounter during flight. Engineers also confirm that flight instruments will withstand the pressure and sub-zero temperatures of high altitudes. The engines, landing gear, navigational systems, and other aircraft equipment undergo equally rigorous testing. Finally, pilots take a prototype for a test flight to verify the results of earlier exercises.

The manufacturing process is usually coordinated by a prime contractor that manages a number of subcontractors specializing in particular components of the flight vehicle. Subcontractors build and test their products in their own facilities, then deliver them to the prime contractor’s facility to be integrated into the flight vehicle. The prime contractor oversees the assembly of the flight vehicle, ensures that the project meets schedule and budget requirements, and assumes ultimate responsibility for the safety of the aircraft.

Modern aircraft are often built from parts that come from all over the world. For example, the McDonnell Douglas MD-11 commercial jet, which entered production in the early 1990s, incorporated parts from Italy, Spain, Japan, Brazil, Canada, the United States, and Britain. The exterior panels of the plane’s main body, or fuselage, were produced by the Italian company Aeritalia, which also supplied the plane’s vertical stabilizer and other parts. The Spanish firm CASA made landing-gear doors and the horizontal stabilizer. Japanese companies supplied certain tail parts and movable flaps on the wings called ailerons. Additional ailerons came from Brazil, the nose gear originated in Britain, Canadian firms delivered major wing assemblies, and the engines were built in the United States and Britain. The plane came together at the plant of the prime contractor, McDonnell Douglas, in California.

The earliest aviators made their own wood-framed airplanes by hand. Orville and Wilbur Wright completed their historic 1903 flight in a machine of their own design. While the Wright brothers quietly worked to perfect and patent their flying machine, Brazilian inventor Alberto Santos-Dumont designed and flew a biplane in Paris in 1906. In the following years, fledgling aviation further captured the attention of the public. Wilbur Wright made a triumphal airplane tour of Europe in the summer of 1908. In July 1909 French aviator Louis Blériot flew a plane of his own design across the English channel, completing a highly symbolic journey in the history of flight.

The success of the Wright brothers, Santos-Dumont, and other pioneering aviators created a small demand for flying machines on both sides of the Atlantic Ocean. In Paris, France, the Voisin brothers, who had helped Santos-Dumont build his biplane in 1906, set up the first facility to build airplanes for sale. In the earliest airplane shops, a small number of workers built airplanes from wood and bamboo frameworks covered with fabric. They used modified engines from automobiles and motorcycles or lightweight boat engines to power the planes. They tested new ideas by building the planes to see if they worked.

By 1909 the Voisin brothers had gained a reputation for building reliable airplanes. That year, several competitors arrived with Voisin machines at an aerial exhibition and flying meet held at Rheims, France. Publicity from the exhibition at Rheims brought orders for about 20 more by the end of the year.

In the years leading up to World War I, militaries on both sides of the Atlantic Ocean grew to appreciate the role airplanes could serve in the military. While Wilbur Wright toured Europe to attract the interest of the public, Orville Wright demonstrated their invention before officers of the U.S. Army. Blériot’s successful crossing of the English Channel convinced European militaries of their need for airplanes.

The military saw uses for airplanes in aerial scouting missions and to carry small bombs that were dropped by hand (see Air Warfare). The Nieuport firm, founded in France in 1909, responded to this demand by producing monoplanes for the French army and for military services in Italy, Britain, Russia, and Sweden. Blériot and a number of other manufacturers followed suit, and by the start of World War I in the summer of 1914, Germany, France, Britain, and Russia each had 200 to 300 military planes plus several airships. American manufacturers lagged behind their European counterparts. In 1912 U.S. firms produced just 39 airplanes. In 1915, as the war raged across Europe, the United States Congress formed the National Advisory Committee for Aeronautics (NACA) to fund research and development in the flight industry. Despite this effort, when the United States entered the war in 1917, it had only 16 airplane-building companies, and only 6 of them had built as many as ten airplanes.

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