Cierva C.30 Autogyro
The Cierva C.30 was an autogyro designed by Juan de la Cierva and built under licence from the Cierva Autogiro Company in Britain, France and Germany. It introduced direct control to production autogyros, the pilot steering by tilting the rotor head itself, and it became the most numerous autogyro of the pre-war years, with 143 production aircraft built. Britain's twelve military machines served the RAF as the Avro Rota, and wartime examples found lasting work calibrating coastal radar stations; survivors are now displayed in museums in several countries.
Why It Mattered
The C.30 was the machine that turned the autogyro from an experiment into a practical aircraft, because it changed how the pilot controlled the rotor. Earlier autogyros had been steered like aeroplanes, by surfaces working in the airflow; at the very low speeds an autogyro flies at, particularly when landing, those controls became ineffective. The C.30 replaced them with direct control — a tilting rotor hub worked from the cockpit — and History of War calls the result a significant improvement in autogyro design. The type was forgiving as well: it was designed to be almost impossible to stall, and a machine flown too slowly simply lost height gently instead of dropping. Licence production in Britain, France and Germany made it by far the most numerous autogyro of the pre-war years, and Cierva spent his last years developing its ideas further on a C.30A test aircraft.
Design Notes
Direct control came from the experimental C.19 Mk V, whose tilting rotor hub, worked by a hanging stick from the cockpit, let the pilot change the plane of the rotor directly. Fantasy of Flight, which keeps a 1934 C.30A, describes a control column extending down to the cockpit, letting the pilot steer by tilting the rotor head; the museum judges this gave far more control than earlier versions. Yaw, though, was still handled in the fixed-wing way, with foot pedals working a rudder at the rear. The production C.30A carried a three-blade, 37 ft (11.3 m) rotor above a fabric-covered fuselage with two cockpits. A tall fin would have fouled the rotor sagging at rest, so the fin was long and low, stretching well back behind the tailplane. Power came from an Armstrong Siddeley Genet Major radial: 105 hp in the first C.30, and the 140 hp Genet Major IA in the production C.30A. Before take-off the engine could be coupled to the rotor to spin it up — earlier autogyros had needed ropes for that — while in flight the rotor turned freely, driven only by the airflow.
Operational History
Avro obtained its British licence in 1934 and built 78 aircraft, the first production C.30A being delivered that July. France and Germany built the type under licence too: Lioré-et-Olivier produced 25 as the LeO C.301 with Salmson radial engines, and Focke-Wulf 40 as the Fw 30 Heuschrecke with a Siemens radial. With the five development machines, 148 C.30s were built in all, 143 of them production aircraft. Most of Avro's output was civil: 66 of its aircraft were non-RAF machines, flown by wealthy enthusiasts and by flying clubs that offered autogyro training, and Avro exported 26 directly. Cierva himself showed what the type could do in 1934, landing a Spanish Navy C.30 on the seaplane tender Dédalo in Valencia harbour and taking off again from the anchored ship. The RAF's twelve machines entered service as the Avro 671 Rota Mk I with the School of Army Co-operation at Old Sarum, deliveries running from August 1934 to May 1935. They were never used in that intended role: their very low minimum speed made them ideal for calibrating coastal radar, and the RAF Museum credits the Rota with an important part in the Dowding System during the Battle of Britain, calibrating its radar stations. History of War traces the calibration work through No. 81 Squadron in 1939–40 and No. 1448 Flight to No. 529 Squadron, and surviving civil machines were taken into RAF service in 1939 and 1940 as well. When the squadron disbanded in October 1945, its twelve surviving aircraft were sold on to civilian owners.
Afterlife
Most of the Rotas sold back to civilians in 1945 did not last long, although one ex-RAF machine stayed airworthy until an accident in 1958. One civil machine outlived nearly all the rest: G-ACUU, impressed as HM580 in 1942 and flown by 529 Squadron, returned to civil use afterwards and was not withdrawn until 1960. It is now the Imperial War Museum's exhibit at Duxford. Other survivors are spread widely: the RAF Museum in London displays Rota K4232 and the Science Museum another C.30A, Sydney's Powerhouse Museum holds a third, and Fantasy of Flight in Florida keeps a 1934 C.30A of its own. In Spain, a C.30 that had undergone years of work at the Maestranza Aérea de Albacete was flown again in January 1998; after an accident in 2000 it passed to the Museum of Aeronautics and Astronautics at Cuatro Vientos, Madrid.