Cierva C.40

Development of the ‘Jumping’ Autogyro

The Cierva C.40 was a reconnaissance autogyro developed by the Spanish-born engineer Juan de la Cierva. This autogyro was Cierva’s last realized project, as he had been working on a vertical take-off system since 1934, later patented as “Autodynamic.” The rotor blades could now change their angle of attack, a significant innovation.

Before take-off, the main rotor was spun up to high RPMs by the engine with the blades in a horizontal position. Then, a mechanism simultaneously rotated all blades relative to the hub, setting them to the required angle of attack. This allowed the autogyro to perform a “jump” five to six meters upwards, which led to machines of this design being called “jumpers.”

In 1936, the “Autodynamic” type hub was tested on a modified C.30 prototype and then on the C.30A, sometimes referred to as the C.30R. The new rotor initially suffered from vibrations and required extensive refinement over time.

C.40 Design Innovations

An improved and lighter version of the new rotor hub was implemented in the production C.40 autogyro. Externally, it was similar to the C.30A, but several significant modifications were made: the two crew members sat side-by-side, the fairing at the top of the pylon was extended downwards, and the space between the struts was glazed, creating a semi-enclosed cockpit.

The main landing gear struts were substantially redesigned. The horizontal empennage lost its transverse V-shape, and the vertical empennage incorporated a quite large rudder. The autogyro was powered by a French Salmson 9Ng radial engine producing 175 hp, driving a two-bladed wooden propeller in a tractor configuration.

Cierva was only involved in the initial stages of the C.40’s design. Tragically, he died in December 1936 in an aviation accident – not during the testing of one of his autogyros, but as a passenger on a regular “Douglas” airliner. The C.40 prototype began flight tests in the spring of 1938, piloted by R. Briar. Tests showed that its flight performance had significantly improved compared to the C.30A, with near-vertical take-offs and landings.

Service with the Royal Air Force

Serial production of the C.40 was carried out by the small firm “Oddie, Bradbury and Cull” in Eastleigh, while the final assembly of the aircraft was handled by the “British Aircraft Manufacturing Company” in Hanworth. However, only nine C.40s were ever built.

Of these, seven machines were ordered in 1937 for the Royal Air Force. Military requirements were considered from the outset in the C.40’s design, as specified in requirement 2/36, prepared by the Air Staff for a prospective autogyro. It was anticipated that the C.40 would replace “Rota” autogyros.

Five C.40s were delivered to the military in the first half of 1939 (two in January and three in May), with two more following by the end of the year. During the war, these autogyros were used as liaison aircraft by the Fighter and Coastal Command headquarters of the RAF, as well as for training. Occasionally, they were also involved in radar calibration.

One autogyro was written off after an accident in January 1941, and two were dismantled for spare parts in the autumn of the same year. The last two C.40s survived until 1944, finally being decommissioned in September as “obsolete.” However, the actual reason for their retirement was a lack of spare parts, due to the very limited production run.

Technical Specifications

Modification	C.40
Main rotor diameter, m	11.60
Length, m	6.10
Height, m	3.50
Empty weight	586
Normal takeoff weight	885
Engine type	1 Piston engine Salmson 9Ng
Power, hp	1 x 175
Maximum speed, km/h	193
Cruising speed, km/h	171
Practical range, km	510
Practical ceiling, m	3400
Crew, crew	2

Image and diagram gallery of the Cierva C.40

C.40	C.40
C.40	C.40