During the past sixty years since their first successful flights, helicopters have matured from unstable, vibrating contraptions that could barely lift the pilot off the ground, into sophisticated machines of extraordinary flying capability. They are able to hover, fly forward, backward and sideward, and perform other desirable maneuvers.
Igor Sikorsky lived long enough to have the satisfaction of seeing his vision of a flying machine "that could lift itself vertically from the ground and hover motionless in the air" come true in many more ways than he could have initially imagined. At the beginning of the new Millennium, there were in excess of 40,000 helicopters flying worldwide. Its civilian roles encompass air ambulance, sea and mountain rescue, crop dusting, fire fighting, police surveillance, corporate services, and oil-rig servicing. Military roles of the helicopter are extensive, including troop transport, mine-sweeping, battlefield surveillance, assault and anti-tank missions. In various air-ground and air-sea rescue operations, the helicopter has saved the lives of over a million people.
Over the last forty years, sustained scientific research and development in many different aeronautical disciplines has allowed for large increases in helicopter performance, lifting capability of the main rotor, high speed cruise efficiencies, and mechanical reliability. Continuous aerodynamic improvements to the efficiency of the rotor have allowed the helicopter to lift more than its empty weight and to fly in level flight at speeds in excess of 200 kts (370 km/h; 229 mi/h). Since the 1980s, there has been an accelerating scientific effort to understand and overcome some of the most difficult technical problems associated with helicopter flight, particularly in regard to aerodynamic limitations imposed by the main rotor. The improved design of the helicopter and the increasing viability of other vertical lift aircraft such as the tilt-rotor continue to advance as a result of the revolution in computer-aided design and manufacturing and the advent of new lightweight composite materials. The helicopter today is a safe, versatile, and reliable aircraft, that plays a unique role in modern aviation provided by no other aircraft.
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Compared to airplanes, the development of which can be clearly traced to Otto Lilienthal, Samuel Langley, and the first fully controlled flight of a piloted powered aircraft by Orville and Wilbur Wright in 1903, the origins of successful helicopter flight are considerably less clear. A pure helicopter can be defined as any flying machine using rotating wings (i.e., a rotor with blades that spin about a shaft) to provide lift, propulsion, and control forces that enable the aircraft to hover relative to the ground without forward flight speed to generate these forces. In addition, to be practical, the machine must also be able to fly forward, climb, cruise at speed, and then descend and come back into a hover for landing. This is the dream of true flight, a feat only achieved in nature by the hummingbird or dragonfly. Nature has inspired humankind for literally hundreds of years before the vertical flight machine we now know as a helicopter became a practical reality.