Humans have always envied birds for their ability to fly. The mythologies of many ancient peoples spoke of gods who flew and of humans who tried to fly but failed. In the 18th and 19th centuries humans flew in lighter-than-air ships such as balloons, but not until 1903 did people build the first heavier-than-air craft—the airplane. The term airplane, which is often shortened to plane, usually refers to any type of power-driven aircraft that has fixed wings and is heavier than air. An airplane propels itself through the air and supports itself with its wings. The wings are shaped in a particular way so that air travels over them and gives them lift. By contrast, balloons and airships are lifted by gases that are lighter than air, helicopters are lifted by spinning rotors, and gliders have wings but are not powered. Types of airplanesAirplanes can be grouped into many different categories. One way of classifying them is by the number of wings. Many early airplanes, including the first one built by the Wright brothers, were biplanes with two pairs of wings, one above the other. Triplanes were also built in the early days of aviation. Today most airplanes are monoplanes, with one pair of wings. Single wings create less drag, or wind resistance. Wings come in different shapes and sizes to create different effects when flying. Airplanes can also be classified according to whether they use dry land or water for takeoffs and landings. Most planes are landplanes, which are supported on the ground by wheeled landing gear. Seaplanes are supported in the water by small, airtight floats. If a seaplane has a body that rests upon the water, it is called a flying boat. An amphibian is a plane that can take off from land or water. Airplanes can also be classified by the purposes for which they are used. Military aircraft include the entire range of airplanes used by the armed forces, including fighters, bombers, spy planes, troop transports, and tankers that refuel other military planes while in flight. The familiar airliners that carry large numbers of people from city to city are classified as civil aircraft. Other kinds of civil aircraft carry cargo. Still others are flown by their owners as a hobby. Crews on airplanesOn an airliner, the pilot, or captain, is in charge of operating the plane and reaching the destination safely. Airline pilots must pass health tests and have hundreds of hours of flying experience. They get their training in military service or in flying schools. The copilot, or first officer, assists the captain. After serving some time as copilot, a person may become a captain. The flight engineer, or second officer, constantly monitors the mechanical performance of the airplane. Some international flights, especially those that cross an ocean, also have a navigator who keeps track of the airplane's position. Flight attendants are responsible for the comfort and safety of the passengers. Military airplanes carry crews of various sizes to operate the plane and its weapons. A B-52 bomber carries a crew of five, while some jet fighters carry only the pilot. Parts of an airplaneTo understand how an airplane can fly, it is first necessary to know its different parts. The major parts are the airframe, the power system, and flight controls and instruments. AirframeThe airframe includes the fuselage, wings, tail assembly, engine mounts, and landing gear. The fuselage is the body of the aircraft. It consists of a rigid frame and a covering of aluminum, magnesium, or molded plastic or fiberglass. The wings of a small airplane may be supported by means of wires or struts attached to the fuselage. Larger airplanes have wings that are supported from the inside. Some smaller planes might have wings made of wood, but aluminum is more common. The wings of modern airplanes have several moving parts. Ailerons are hinged to the wings to control the way the fuselage rolls. Flaps are hinges at the rear of a wing that increase lift or drag, thus allowing for shorter takeoffs and slower landings. Other pieces of the wing include spoilers, which increase drag and decrease lift, and slots, which are narrow openings that improve airflow over the wing. In the rear of the plane is the tail assembly. The fixed horizontal stabilizer is a part of the tail assembly that often looks like a small wing. It prevents the aircraft from pitching, or bucking up and down. The elevator, connected to the horizontal stabilizer, raises or lowers the airplane's nose. The fixed vertical stabilizer often looks like a fin. It prevents the aircraft from yawing, or moving from side to side. The rudder, which is connected to the vertical stabilizer, controls movement to the left or right. The landing gear consists of rubber tires and a shock-absorbing mechanism. Most planes have two main wheels or sets of wheels and another wheel to support the tail. Some planes have wheels that fold up to reduce drag when the plane is in the air. Power systemA plane's power system includes an engine, sometimes one or more propellers, and fuel and oil tanks and lines. The two main types of engines on planes today are reciprocating engines and jet engines. A reciprocating (or piston) engine is similar to the engine found in an automobile. In this type of engine, the burning of fuel inside a chamber starts a chain of events that ultimately turns a propeller. Reciprocating engines are usually found on smaller airplanes. Jet engines are common on large commercial planes and military aircraft. This type of engine burns fuel but propels a plane forward with a jet of exhaust gas that shoots out behind the plane. One type of jet engine, the turboprop, is used to turn a propeller. Military aircraft have experimented with rocket engines. Flight controls and instrumentsFlight controls help a pilot to regulate the movement and position of an airplane. The control wheel or stick is used to raise or lower the plane's nose. Foot pedals allow the pilot to control the rudder, which turns the plane to the right or left. A throttle controls the engine power. The pilot can also control flaps on the wing to slow the airplane for landings. Flight instruments are used for navigation, checking engine performance, and monitoring other equipment. The airspeed indicator tells the pilot the speed of air flowing past the airplane. The altimeter shows how high an airplane is. The vertical-speed indicator shows the plane's rate of climb. The turn-and-bank indicator shows the direction and rate of turning. A magnetic compass shows the direction in which the plane is heading. Radar is used for navigation, and radio is used for communicating with the ground. An instrument called the automatic pilot can be used to keep a plane on course without the pilot's help. In addition to these instruments, there are a variety of indicators that monitor the engines and other parts of the plane's mechanical and electrical systems. How airplanes flyThe science of flight is called aerodynamics. Four main aerodynamic forces act upon an airplane in flight. They are called drag, thrust, gravity (or weight), and lift. As an airplane moves through the air, the air tends to slow it down. This effect is called drag. To overcome drag, forward thrust must be applied. The thrust is produced by the plane's engines. An airplane is heavier than air. It will fall to the ground under the influence of gravity unless lift is applied. The plane's wings are able to produce the necessary lift because of their shape. The upper surface is curved, while the lower surface is flatter. To get past the curved surface, the air that flows over the wing has to go farther—and therefore faster—than the air that flows under it. This creates a difference in air pressure between the upper and lower surfaces as the plane moves forward. The air underneath is under greater pressure and therefore pushes the wing up. The faster the air flows past the wings, the greater the lift. For this reason, an airplane takes off most easily when it faces the wind. Lowering the flaps on the wing increases the curved surface of the wing, which provides even more lift. Slots also increase lift by allowing air to flow more smoothly over the wing. When flaps are raised, lift is reduced and the plane descends. HistoryMany ancient civilizations told stories of gods, humans, and even horses that could fly. The Greek myth of Daedalus is about an inventor who builds wings made of feathers and wax. His son Icarus is killed when he flies too close to the sun, causing the wings to melt. The ancient Chinese invented the kite, and early Australians created the boomerang—a throwing stick that sails in the air. But human flight remained a dream. In 1250 an English scientist named Roger Bacon proposed a vehicle that would use flapping wings to fly. Such an aircraft is now referred to as an ornithopter, meaning “bird-winged aircraft.” In 1490 the great Renaissance artist and scientist Leonardo da Vinci drew sketches of various types of flying machines, including Bacon's ornithopter and a machine resembling a modern helicopter. Suitable power sources and materials did not exist in Leonardo's time, however, and his machine never flew. Before humans took to the air in airplanes, they flew in lighter-than-air craft. In 1783 two French brothers, Joseph-Michel and Jacques-Étienne Montgolfier, filled a paper balloon with hot air and saw it rise to a height of 6,000 feet (1,800 meters). Their first passengers were a rooster, a duck, and a sheep, but later that year they sent two people aloft. The 19th century saw much experimentation in both lighter-than-air and heavier-than-air craft. Work with gliders, which are heavier than air, established principles of airplane design. Otto Lilienthal of Germany made more than 2,000 glider flights. Octave Chanute of the United States built several gliders and wrote extensively on flight. Another U.S. inventor, Samuel P. Langley, experimented with aircraft powered by steam and gasoline and achieved powered flight in 1896. Early aviationOn December 17, 1903, in Kitty Hawk, North Carolina, Orville and Wilbur Wright conducted the first sustained, controlled, powered flight. The Wright brothers had experimented with gliders, and they chose the North Carolina coast for their testing because the strong winds there helped to provide lift. They were bicycle mechanics by trade, but they were able to build a gasoline engine powerful enough to propel their 750-pound (340-kilogram) flying machine. Its first flight, with Orville piloting, lasted 12 seconds and covered 120 feet (37 meters). By 1905 the Wright brothers had improved their machine to the point that it could fly 24 miles (39 kilometers) in 38 minutes. During World War I the availability of airplanes began to change the nature of war. Planes were first used for aerial observation, but eventually nations discovered they could use them for dropping bombs on targets. Anthony Fokker, a Dutch airplane designer, found a way to control the fire of a forward-facing machine gun so it would not shoot away the plane's own propeller. Soon the skies became a battlefield with pilots firing on one another. During the war Army pilots in the United States began to deliver the mail to Washington, D.C., and New York City by way of Philadelphia. After the war airmail delivery was transferred to private carriers. This helped to expand commercial aviation in the 1920s and 1930s. The period between the world wars was an era of stunt flying and aviation firsts. The British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown made the first nonstop flight across the Atlantic Ocean, from Newfoundland to Ireland, in 1919. A U.S. airmail pilot named Charles Lindbergh became famous in 1927 for making the first solo flight over the Atlantic. By 1931 pilots were able to fly around the world with several stops. Amelia Earhart, the best-known female aviator of the time, flew solo across the Atlantic in 1932. On a later flight, in 1937, she and her navigator disappeared over the Pacific. They were never found. Many airlines were established in the 1920s and 1930s, but early passenger planes saw only limited service because they could not fly over high mountains and had to stop frequently for refueling. The twin-engined DC-3, first flown in 1936, was the first successful commercial airliner. World War II demonstrated the importance of air superiority in waging war. The German air force initiated the blitzkrieg, or “lightning war,” in attacks on Great Britain and France. In the Pacific, Japanese bombers destroyed much of a U.S. naval base at Hawaii's Pearl Harbor, which led the United States to enter the war. The jet ageWhen Frank Whittle of Great Britain invented the jet engine, he had airplane propulsion specifically in mind. Whittle's engine was first used in a plane in 1941, but jet-powered aircraft did not come into wide use until after World War II. At first most jet planes were made for military uses. Rocket propulsion brought even faster speeds. In 1947 a U.S. Air Force pilot named Chuck Yeager took an early rocket plane called the Bell X-1 on the first flight faster than the speed of sound. This speed is called Mach 1, and faster speeds are measured as multiples of this speed. Mach 2 is twice the speed of sound. The actual speed varies depending on the altitude. Yeager's flight on the X-1 took place at about 40,000 feet (12,000 meters), where the speed of sound is approximately 662 miles (1,066 kilometers) per hour. Rockets can exceed the speed of sound many times over. In recent years they have been used for space travel rather than air travel. The first jet used for civilian (nonmilitary) transportation, the British De Havilland Comet, flew in 1949. Regular jet services across the Atlantic were started in 1958 with the Comet 4 and the American Boeing 707. The first commercial jet to travel faster than the speed of sound was the Concorde. Developed by Great Britain and France, the Concorde began service between Europe and North America in 1976. The Concorde was not used for flights over land, however, because of the sonic booms that result when an aircraft flies faster than sound. In 1986 the U.S. pilots Dick Rutan and Jeana Yeager flew an experimental light airplane called Voyager for nine days without landing. It was the first nonstop around-the-world flight. Air travel safetyAirline safety became an important issue in the second half of the 20th century. In the United States, a government agency called the Federal Aviation Administration (FAA) was created in 1958 to monitor aircraft and to investigate crashes. The FAA also operates the air traffic control system. Air traffic controllers use radar to keep airplanes out of each other's way. Even with these precautions, however, crashes sometimes do occur. Not all air disasters are accidental. An airliner can be hijacked by terrorists or destroyed by a bomb planted on board. A series of hijackings in the 1970s caused some concern over airline safety and additional security at airports. Security was expanded greatly following a terrorist attack on the United States in September 2001 in which airplanes themselves were used as weapons. Hijackers flew airplanes into the World Trade Center in New York City and the Pentagon in Washington, D.C., killing thousands of people. Despite these events, and despite several airline crashes over the decades, flying remains a far safer method of travel than most other modes of transportation. |