HELICOPTER

aircraft with one or more power-driven horizontal propellers or rotors that enable it to take off and land vertically, to move in any direction, or to remain stationary in the air. Other vertical-flight craft include autogiros, convertiplanes, and V/STOL aircraft of a number of configurations. The idea of taking off vertically, making the transition to horizontal flight to the destination, and landing vertically has been for centuries the dream of inventors. It is the most logical form of flight, dispensing as it does with large landing fields located far from city centres and the inevitable intervening modes of travel-automobile, subway, bus-that flight in conventional aircraft usually requires. But vertical flight is also the most demanding challenge in flying, requiring more sophistication in structure, power, and control than conventional fixed-wing aircraft. These difficulties, solved over time by determined engineers and inventors, made the progress of vertical flight seem slow compared to that of conventional flight, for the first useful helicopters did not appear until the early 1940s. U.S. Army CH-137 helicopter lifting tank aircraft with one or more power-driven horizontal propellers or rotors that enable it to take off and land vertically, to move in any direction, or to remain stationary in the air. The helicopter is often described as a rotary-wing aircraft, in contrast to a conventional fixed-wing airplane. It does not require a runway but can land on and take off from small areas that are inaccessible to most fixed-wing aircraft. It can land in a small clearing in the jungle, on the deck of a ship, or on suitable flat roofs. Its ability to hover motionless over a given area enables it to deliver or take on personnel or cargo without actually landing. Because of its versatility, the helicopter is used extensively by the armed forces for transportation of troops into otherwise inaccessible areas; for rescue and medical evacuation; and for communication, surveillance, and search at sea and on land. It proved its military value during the Korean War (1950-53), when it was used to evacuate thousands of wounded men from the front lines. Its commercial uses include short-haul transportation between city centres and outlying airports, transportation into undeveloped or inaccessible areas, crop dusting, surveying, and exploration. The helicopter also gained widespread publicity as a result of its lifesaving activities in civil emergencies, particularly those resulting from floods and earthquakes. The helicopter was one of the earliest ideas for flying. For many years Leonardo da Vinci was credited with the original idea, but it is now known that the Chinese and the Renaissance Europeans made helicopter toys before Leonardo's time. Various experimenters before 1900 failed with helicopters because they lacked an engine powerful enough to produce the vertical thrust required to raise its own weight and some useful load from the ground. Thus, these early designers never became aware of the difficult in-flight control problems that would perplex later experimenters. In 1907 the first manned helicopter, built by the Frenchman Paul Cornu, made a brief vertical flight. Controlled vertical and forward flight by a helicopter was finally attained in 1930, and in 1939 Igor Sikorsky in the United States established the practical single-rotor helicopter with record-breaking flights of his VS-300. In 1923 the Spaniard Juan de la Cierva had successfully flown an autogiro (q.v.) for the first time. It was the technical innovations introduced by Cierva that paved the way for Sikorsky's first successful prototype of 1939. Once the basic principles of helicopter design had been established, development was rapid on both sides of the Atlantic. Additional reading Basic Helicopter Handbook, rev. ed. (1978), prepared by the U.S. Federal Aviation Administration, is a well-illustrated primer on the principles of helicopter flight and structure. Larry Collier, How to Fly Helicopters, 2nd ed., rev. by Kas Thomas (1986), describes basic operations with excellent illustrations. Walter J. Boyne and Donald S. Lopez (eds.), Vertical Flight: The Age of the Helicopter (1984), surveys the history and technology of helicopters and other aircraft designed for vertical flight. Mike Rogers, VTOL Military Research Aircraft (1989), describes basic types of research and production vertical-takeoff aircraft. Andrew C. Marshall, Composite Basics, 2nd ed. (1989), covers in detail the use of composite materials in aircraft construction. Walter James Boyne