The Prototype.

In summer 1922 the well-known inventor of the microphone, Emile Berliner, and his son Henry A. Berliner made the first successful flight in a helicopter. It attained an altitude of only fifteen to twenty feet and flew at just 20 MPH. The significance of the flight was that the machine rose vertically from the ground and proceeded to fly horizontally. Other experimental craft at the time were able to rise vertically and set down vertically, but they were incapable of horizontal movement.

Sikorsky.

Russian American Igor Sikorsky, who directed his efforts solely to fixed-wing aircraft during the 1920s, had built two prototype helicopters before he emigrated from the Soviet Union in 1919, but neither the helicopter he built in Kiev in 1909 nor his 1910 model would fly. Having decided that the helicopter needed to wait for "better engines, lighter materials, and experienced mechanics," Sikorsky returned to work...