The first manned helicopter flight was achieved by the Frenchman Paul Cornu who lifted his twin-rotor craft off the ground fortwenty seconds in 1907; his machine unfortunately broke up on landing. In 1909 Igor Sikorsky (1889-1972) built two helicopters but these could lift very little more than their own weight. The first practical helicopter was the German Focke-Wulf FW 61, which flew in 1936. By 1939 the British had built the two-seater Weir W.6, which was powered by a pair of rotors mounted independently, one on each side of the fuselage. The Weir W.6's prototype was the first helicopter in the world to carry three occupants.
Many control problems had to be solved, the main ones being unsymmetrical lift, which caused the craft to flip over on takeoff, and the fact that the body's natural tendency was to spin in the opposite direction to the rotors. However, one big advance was the realization that changing the angle at which the rotor blades were set was much more effective for stabilizing the helicopter in flight than trying to change the rate at which the rotors rotated.
The real breakthrough came with Sikorsky's VS-300 in 1939. As well as the horizontal main rotor the prototype had two smaller tail rotors, one ensuring horizontal stability and the other acting like a rudder and controlling the direction of flight. This was followed in the United States in 1945 by the highly successful mass-produced Bell 47.
Today there are more helicopters in military service than in civilian operations. The vision of city-center "vertiports" speeding passengers to local airports and between nearby airports is still to be realized.
