U. S. Army's McDonnell XV-1 Convertiplane. - This revolutionary aircraft, shown as it made the world's first helicopter-to-airplane conversion, combines the vertical flight characteristics of the helicopter with the speed and range of a conventional fixed-wing airplane. For forward flight, the forn-place aircraft uses a pusher propeller in the rear plus 20 percent forward lift from the overhead rotor. December 22, 1955. (Photo by United States Information Center).