All of us know the history of the helicopter, but certain facets of this history need to be repeated in the framework of the development of the rigid rotor helicopter. It was in 1919, I believe, that Juan de la Cierva, shocked from the death of his brother in a spin accident, reasoned that the best way to build an aeroplane was to build one that made use of the spin as a fundamental. He put a bearing between the spinning wings and the fuselage so that the wings could spin without spinning the fuselage. This was a great advance in the state of the art and created an aeroplane with some rather good low-speed characteristics.