It would be right to state that, with the successful flight of the XR-4 in the summer of 1942, the helicopter became a reality in the United States.
Igor SikorskyThis machine was a failure to the extent that it could not fly. In other respects it was a very important and necessary stepping stone.
Igor SikorskySupersonic airplanes have carried men at more than 2,000 miles per hour and there are reasons to believe that this speed will be doubled by 1960 or so.
Igor Sikorsky