Helicopter
The first helicopter can be traced back hundreds of years. In the early fourteenth century, the Chinese made toy flying tops that consisted of four rotor blades attached to a spindle. String was wound on the spindle, and, when pulled, sent the rotors spinning upward. In the sixteenth century, Leonardo da Vinci drew sketches of a flying machine with a twisting screw-like wing and an on-board power source. In 1784, two Frenchmen, Launoy and Bienvenu, gained widespread attention with a twin-rotor helicopter model operated by a spring -bow mechanism. Inventors experimented with helicopter designs throughout the nineteenth century but were unable to come up with an engine that was light-weight yet powerful enough to lift a full-size helicopter off the ground.
In the early 1900s, with the invention of the gasoline engine, new possibilities opened up for helicopter flight. In 1907, French inventor Louis Bréguet (1880-1955) achieved the first manned helicopter flight, lifting his four-rotor helicopter two feet off the ground for approximately one minute.
The foundations of the modern helicopter can be seen in the design of the autogyro, sometimes called the gyroplane. Developed in 1923 by a Spanish engineer, Juan de la Cierva (1895-1936), the autogyro was an attempt to solve the problem of torque that helicopter designers faced: when a power-driven rotor swung overhead, it caused the fuselage to spin in the opposite direction. This forced designers to employ much complicated machinery to counteract the torque. Cierva's autogyro had a traditional engine at the front giving the craft its power, and it added an unpowered, free-rotating rotor tilted up at a slight angle so that air met the rotor blades from below and caused the blades to spin. Control in flight was handled by conventional airplane devices (ailerons, elevators, and rudder) on the autogyro's short fixed wings and tail assembly. This autorotating rotor was torqueless, so there was no need of complex machinery like other helicopter designers were forced to use. In addition, Cierva made each rotor blade hinged, allowing the blade to flap freely up or down to find its own best angle.
The autogyro was a commercial success throughout the 1920s until the Great Depression caused sales to plummet. Its limited speed, range, and cargo capacity prevented it from being used for military purposed and by the beginning of World War II, the autogyro had all but faded from the scene. Its innovative construction, however, paved the way for future helicopter designers. In the 1930s the prototypes of traditional helicopters were being built with varying results. The French had a design in 1936 with two rotors, one above the other, rotating in opposite directions to cancel out torque. This helicopter had set an altitude record of 500 feet (152.5 m) and could reach a speed of 65 miles per hour (104 kph). The Germans designed another configuration in which two rotors, again spinning opposite directions from each other, were mounted side by side on outriggers. This machine set a speed record of 76 miles per hour (122 kph), an endurance record of 1 hour and 20 minutes, and an altitude record of 10,000 feet (3050 m).
At this time Igor Sikorsky made a breakthrough that greatly advanced the helicopter industry. In 1909 he had built helicopters with two rotors, one above the other like the French design, but they were failures. His new idea was to use a small vertical rotor at the end of a long tail boom. This rotor would produce lateral thrust that would counteract the torque of a single main lifting rotor on top of the helicopter. Thus, he solved the problem of complex machinery used in the past to offset the torque problem. This new system, which he first tested in 1940, proved so successful that it is still the most popular configuration for all types of helicopters. United States military officers were so impressed with Sikorsky's helicopter design that they rushed it into production to be used in World War II.
Several advances in helicopter design took place after the war. The turbine engine solved a major overheating problem that occurred when the helicopter hovered, unable to use moving air to cool the engine. The turbine engine also had more power, an advantage for lifting or rescue operations. Helicopters soon appeared that could transport large weights, and they therefore played crucial roles in the Korean and Vietnam wars. Their ability to take off and land vertically made them preferable to fixed-wing aircraft in the often localized and geographically remote battles of these conflicts. Today, helicopters are widely employed for commercial aviation, by news organizations (e.g., as the familiar "eye-in-the-sky" traffic spotters) and for rescue and emergency transport (most medium or large modern hospitals are equipped with a helipad).
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