Cierva’s Autogyros

When the famous Spanish inventor, Juan de la Cierva, was only fifteen he designed and built his first glider. Three years later, in the summer of 1918, he was able to develop a three-engined aircraft. The goal of his experiments was to achieve the creation of an air platform that could sustain lift and land safely after an engine failure. With the development of helicopters still a thing more of the imagination rather than a practical concept, Cierva turned his attention to the idea of an airplane that utilized an unpowered rotor system for lift and a conventional propeller mechanism for propulsion. Does the concept sound familiar?

The term ‘autogyro’ was conceived by Cierva to describe his new aircraft idea, which featured a freewheeling main rotor providing lift for vertical flight. His idea would revolutionize the air industry thus paving the way for the full development of the helicopter. The main operational system of the autogyro was the articulated rotor hub. Its drag and flapping hinges allowed the individual rotor blades to rise and fall, and so even-out the plane’s lift. After a two year development program, Cierva’s first autogyro took to the air on a cool January morning in 1923. Called the C.4, the first unit flew a distance of 3 miles. By September 1928, Cierva’s C.81 design, powered by a 149kw (200hp) Lynx engine and based on an Avro 504 airframe, performed the always dangerous 25 mile crossing of the English Channel, bound for Paris.

Avro-built Cierva C.30P G-ACIN. (photo, via author)
Avro-built Cierva C.30P G-ACIN. (photo, via author)

After experimenting with a few ideas and systems, Cierva refined his autogyro concept into what would become the technology setter platform of C design and development: version number 19. Version 19 introduced a dedicated fuselage to the series. Prior Cierva models utilized existing aircraft fuselages. After the 19, all other versions were purpose-built. Sixty six 19s were licensed built by AV Roe and Co. Ltd. with headquarters in Manchester, England. France also got into the act. The famous Liore-et-Oliver produced twenty five units designated LeO C130. Even the German Focke-Wulf Corporation managed to built 19s (40 units are believed to have been produced by the venerable aviation company).

If version 19 was a leap forward in rotary wing development, then version 30 was the pinnacle of it. The C.30 was a two seat airplane that featured the pilot occupying the rear, open cockpit. The pilot was able to unlock and tilt the main rotor mechanism using the control column attached to the rotary head. The 30’s airframe structure was of Duralumin tubing with a fabric skin cover. The next evolution of the series, the C.40, was designed around a wooden skin cover over a metal internal frame. A seven cylinder, Armstrong Siddeley Genet Major I-a radial (139hp) engine gave power to the 40. The other main feature introduced in the 30 was folding rotor blades for easier hangar handling. It also possessed a reverse aerofoil section on the port tailplane in order to counter the anticipated rotor torque.

At the beginning, autogyro flying was deemed too dangerous for combat operations, thus not many air forces in the world were interested in Cierva’s revolutionary work. Early flying tests were plagued by accidents. In fact, the first three C designs failed to become airborne. It is worth remembering that the initial C.1, utilized a French Deperdussin fuselage that did not provide the aircraft with enough lifting area which impeded its ability to takeoff. It was number four in the series, C.4, which eventually broke that barrier and got airborne. Following the experiments of the C.1, Cierva went on to produce several other unreliable machines, including the C.4, until he designed the unit 6. With subsidies from the Spanish government, the ingenious Cierva developed the C.6 series utilizing an Avro 504K airframe. The new fuselage would give the series and its inventor a big boost with its lift-drag ratio and overall airframe performance. All other versions of the Autogyros will incorporate the same, basic layout of the 504K airframe.

By the mid 1930s, Cierva and his team were able to stabilize vertical takeoff to the point that air forces felt comfortable enough to invest heavily in the concept. Unfortunately, Juan de la Cierva died in an airline crash at Croydon in December 1936. By that time his ideas were more than accepted, it was becoming the ‘law of the land’ in rotary flying. At the time of his death, Cierva had formed his own aircraft company based in Great Britain. His design was being manufactured in England, France and Germany. The C.30 saw service in the Second World War, most of them with the British Royal Air Force (RAF). There were a commercial version of the C.30, chief among them the de Havilland’s C.24 developed in 1931, but the unit did not meet with much success. Nevertheless, the original Cierva concept would go on to become today’s helicopters platforms. Quiet the achievement for this distinguished Spanish inventor.

Specification for Cierva C.40
Powerplant: One 104kw (140hp) Armstrong Siddeley Genet Major I-A radial engine
Maximum Weight: 816kg
Main Rotor Diameter: 11.28m
Length: 6.01m
Height: 3.38m
Total Rotor Area: 99.89 m square
Top Speed: 117km/h
Operational Range: 459km
Service Ceiling: 5800m

– Raul Colon

 

More information:
The Encyclopedia of Modern Military Aircraft, Editor Paul Eden, Amber Books 2007
The men, machines and ideas that revolutionized war, from Kitty Hawk to Gulf War II, Stephen Budiansky, Penguin Books 2004
Concept Machines, Carl Thomas, Ispring Group 1972

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