The Cierva W.11 Air Horse was a

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

developed by the Cierva Autogiro Company 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 Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

during the mid-1940s. The largest helicopter in the world at the time of its debut, the Air Horse was unusual for using three

rotor Rotor may refer to: Science and technology Engineering * Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator *Helicopter rotor, the rotary wing(s) of a rotorcraft ...

s mounted on outriggers, and driven by a single engine mounted inside the

fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraf ...

Development

The W.11 "Air Horse" heavy lift helicopter was developed by the G & J Weir, Ltd., Aircraft Department, reconstituted in 1943 as the Cierva Autogiro Company. The "W" in the designation is a continuation of the autogiro and helicopter series developed by G & J Weir, Ltd., during the period 1932–1940. The W.11 was a development of the

Weir W.6 A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

dual transverse rotor helicopter. It is the only helicopter of its type ever built and included three lifting rotors all turning in the same direction. The adoption of three rotors was due to concerns over the capability of a single large rotor to generate the required lift. Torque balance was provided by slightly inclining each rotor axis to generate horizontal thrust components to provide anti-torque moments. The three rotor configuration was foreseen by Belgian helicopter experimenter Nicolas Florine in his patent of 1926 which presented the aforementioned means for balancing the reaction on the fuselage of two or more torque driven lifting rotors turning in the same direction. Work on the W.11 commenced in 1945. The original W.11 configuration used two rotors transversely mounted either side at the front of the fuselage and a single rotor mounted on the centerline at the tail. This configuration was tested in 1947 with a scale-model in a wind tunnel at the Royal Aircraft Establishment at Farnborough, and much useful data on its performance was acquired. This determined that a single rotor at the front and the pair at the back of the fuselage was preferred for optimum stability and control. A

Rolls-Royce Merlin The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litres (1,650 cu in) capacity. Rolls-Royce designed the engine and first ran it in 1933 as a private venture. Initially known as the PV-12, it was late ...

piston engine in the fuselage drove three three-blade rotors mounted on outriggers which projected from the fuselage. The blades were constructed from resin-impregnated wood which provided enormous strength, and were manufactured by the Glasgow furniture firm H. Morris & Co., Ltd. The W.11 rotor control system was hydraulically powered. It was the second helicopter ever to fly using such a system, the first being the Cierva W.9. The landing gear had a stroke of to cater for high descent rates in the event of engine failure during low-altitude operations. Roles envisaged for the W.11 included passenger transport,

air ambulance Air medical services is a comprehensive term covering the use of air transportation, aeroplane or helicopter, to move patients to and from healthcare facilities and accident scenes. Personnel provide comprehensive prehospital and emergency and cri ...

, and aerial crane. In September

1945 1945 marked the end of World War II and the fall of Nazi Germany and the Empire of Japan. It is also the only year in which Nuclear weapon, nuclear weapons Atomic bombings of Hiroshima and Nagasaki, have been used in combat. Events Below, ...

the design was modified to meet a requirement from Pest Control, Ltd., for use as a crop sprayer ("Spraying Mantis") in Africa for the

groundnut scheme The Tanganyika groundnut scheme, or East Africa groundnut scheme, was a failed attempt by the British government to cultivate tracts of its African trust territory Tanganyika Territory, Tanganyika (now part of Tanzania) with peanuts. Launched in ...

. Two aircraft were ordered under

Air Ministry Specification This is a partial list of the British Air Ministry (AM) specifications for aircraft. A specification stemmed from an Operational Requirement, abbreviated "OR", describing what the aircraft would be used for. This in turn led to the specification ...

E.19/46 in July 1946. Cunliffe-Owen Aircraft, Ltd. at Eastleigh Airport, Southampton, UK, were contracted to build the two W.11s under the direction of the Cierva Autogiro Company. With a payload of it would have been a very capable sprayer and following the first flights in December 1948 a grant was received from the

Colonial Office The Colonial Office was a government department of the Kingdom of Great Britain and later of the United Kingdom, first created to deal with the colonial affairs of British North America but required also to oversee the increasing number of c ...

to assist in development. However, the exit of Cunliffe-Owen from the aircraft business in 1947 delayed development of the W.11. A proposed enlarged development using two Merlins or two

Rolls-Royce Dart The Rolls-Royce RB.53 Dart is a turboprop engine designed and manufactured by Rolls-Royce Limited. First run in 1946, it powered the Vickers Viscount on its maiden flight in 1948. A flight on July 29 of that year, which carried 14 paying passe ...

turboprops was designated as the W.11T. This was abandoned after the accident with the first W.11. The death of three long-time colleagues in the accident prompted financier James G. Weir to decline to provide additional funds since the Cierva Autogiro Company required ever-increasing investment. As a result, all of the company's development contracts were transferred to

Saunders Roe Saunders-Roe Limited, also known as Saro, was a British aero- and marine-engineering company based at Columbine Works, East Cowes, Isle of Wight. History The name was adopted in 1929 after Alliott Verdon Roe (see Avro) and John Lord took a ...

. Development of the W.11 continued for a short time thereafter but was terminated by the British Government, and the remaining airframe, which had flown for less than 20 hours in total, was scrapped. Saunders-Roe continued development of the smaller Cierva W.14 Skeeter, which was a main/tail rotor configuration helicopter.

Operational history

W.11 ''G-ALCV'' made its first flight on 7 December 1948 and was displayed at the Farnborough Air Show in 1949. ''G-ALCV'' crashed on 13 June 1950, claiming the lives of Sqn Ldr

Alan Marsh Henry Alan Marsh Air Force Cross (United Kingdom), AFC Royal Aeronautical Society, AFRAeS (29 January 1901 – 13 June 1950) was a British rotorcraft instructor and test pilot. Early life Alan Marsh was born in Stratton, Dorset. In 1917, he comp ...

AFC (chief test pilot), Sqn Ldr John "Jeep" Cable, ( Ministry of Supply test pilot), and Joseph K. Unsworth (flight engineer). The cause of the crash was due to fatigue failure of a swashplate carrier driving link in the front rotor hub. Approximately one year later, the second W.11, ''G-ALCW'' was scrapped.

Variants

;W.11 :Prototype three-rotor helicopter powered by a Rolls-Royce Merlin 24 inline piston engine, two built. ;W.11T :Proposal for an enlarged variant powered by two Rolls-Royce Merlin 502 engines, to meet Air Ministry Specification 10/48 for a crop spraying helicopter, requirement was cancelled and the W.11T was not built. ;W.12 :Proposed freighter variant using

turboprops, not built

Specifications (W.11)

References

;Notes

External links