First flight of a rotorcraft with an articulated/flapping blade (Cierva C.4)
Wednesday, January 10, 1923
This was the key to over-coming most of the problems that had prevented successful flight of earlier rotary wing aircraft. The aircraft did not fly successfully done to uncompensated torque reaction from the propeller but the basic problems of uncontrolled rolling moment from the rotor appeared to have been solved.
The flight was carried out by a Cierva C.4 Autogiro. The first controlled flights subsequently took place on January 17, 1923.
Source: The "autogiro", Moreno-Caracciolo, M, NACA-TM-218, Jul 01 1923, Page 6