Tonight we commemorate the achievements of Juan de la Cierva, the great pioneer of rotary aviation. His development of the autogyro stimulated the development of the early rotor theories and paved the way for the modern helicopter. In turning the autogyro into a practical aircraft, Cierva proved to be an innovator prepared to take an unconventional approach. He was at the same time pragmatic in that he really wanted to build a helicopter but realised that the required technology was not yet mature, and settled on the autogyro as representing what was an achievable concept. His concept was thus unconventional, dramatic and achievable — an admirable combination. However, in his first attempts to fly an autogyro he rapidly came up against the problem that faces all rotory wing designers — which is that the advancing blade has a much greater lifting potential than the retreating blade, due to the difference in dynamic head. This led him to introduce the flapping hinge that allowed the rotor to achieve roll balance as well as providing the backward tilt of the rotor that is necessary for autorotation. Having made this step forward, he realised that the introduction of blade camber would allow the retreating blade to achieve higher angles of incidence before stalling, but in so doing he built in a potentially dangerous control characteristic.