Between 1920 - 23 Cierva progressively developed autorotation in the C.1, C.2 and C.3. The original model did not fly, but after various trials and modifications, such as the addition of ailerons on outriggers, the C.4 flew. Cierva stated that the first flight of his C.4 Autogiro was on January 9, 1923 at Getafe airfield outside Madrid when (Calvary) Lieutenant Alejandro Gomez Spencer guided the craft in taxi tests during which the craft became airborne. But most historians maintain that the first observed (and filmed) flight of C.4 took place on January 17, 1923 when Gomez Spencer flew 600 ft at a steady height of 13 ft across the field. The autogyro was moved to Cuatro Ventros aerodrome, also in the Madrid neighbourhood, and at the end of the same month performed a closed circuit flight of 4 kilometres in 4 minutes at a height of about 30 metres. The four blades of this prototype were articulated at the root and were thus able to flap vertically. Hinged, articulated blades thus proved the answer to the difficulties encountered in the previous types.