It is a great pleasure and honour to accept the Royal Aeronautical Society's invitation to deliver the Eleventh Cierva Memorial Lecture. I remember Cierva from a number of meetings and conversations. He was one of the great pioneers without whose work the autogyro would have been developed only far later, or possibly not at all. His significant contributions included the following:

He created a completely new concept, the autogyro.
He perfected the flexible, rotating-wing which was later used by the helicopter.
He demonstrated autorotation. Before Cierva many doubted that autorotation was possible in case of engine failure.