The Cierva W.5 was a

helicopter A helicopter is a type of rotorcraft in which Lift (force), lift and thrust are supplied by horizontally spinning Helicopter rotor, rotors. This allows the helicopter to VTOL, take off and land vertically, to hover (helicopter), hover, and ...

developed by the

Cierva Autogiro Company The Cierva Autogiro Company was a British firm established in 1926 to develop the autogyro. The company was set up to further the designs of Juan de la Cierva, a Spanish engineer and pilot, with the financial backing of James George Weir, a Scot ...

in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

. It was a single seater twin rotor helicopter- the rotors were mounted side-by-side on outriggers- with a wooden frame. It was powered by a 50 hp 4-cylinder air-cooled Weir engine. Its first flight was at Dalrymple, Ayrshire, on 7 June 1938, and it is considered to have been the world's second fully practical helicopter. Pitch and Yaw control was achieved by tilting the rotor disks, roll control by differential pitch input to the rotors. Rotor thrust was controlled directly by the motor speed, which damped the response heavily.Book: Principles of Helicopter Aerodynamics Ch 1.1 The first successes/ By J. Gordon Leishman (2edn, 2006, ) Cambridge Aerospace Series

References

Reference to the W.5 in the history of British research and developments in the Helicopter field on the website by Vic Flintham
British helicopters Aircraft first flown in 1938 Transverse rotor helicopters Single-engined piston helicopters Cierva aircraft 1930s British helicopters {{Aero-1930s-stub