Cierva Air Horse
The Cierva Air Horse W. 11 was a transport helicopter of the British manufacturer Cierva from the 1940s. She was in her time the largest helicopter in the world and is unique in that it had three main rotors, a design never used before and after.
This 3 rotors rotate all the same direction do not overlap and are for the purpose of compensating yaw moment around tilted slightly.
History
The origins of the Air Horse go back to the late 1930s, as the G. & J. Weir Ltd.. in Glasgow under the chief engineer C. G. Pullin their helicopter W.5 and W.6 developed. The interpretation of these constructions with two adjacent rotors and an aircraft- tail proved then to be very successful. Following the acquisition of relevant Weir - Cierva employees by the technical design of new structures reflected the Weir - heritage, even the numbering was continued in the W- series.
Since the number of parts is the same for small and large machines, in essence, Cierva was of the view that only very large helicopter designs with payloads over 1.25 t be economical to operate. The first helicopter was configured according to these provisos was the W.10 with three rotors that were powered by two converted to water cooling 475 hp Armstrong Siddeley Cheetah engines. From then the scaled- W.11 was derived, while the W.10 was abandoned. Their name later took a five-seat Einrotor helicopter.
On August 1, 1945 Cierva was granted to the three - rotor design patent number 19758. In July 1946, the Ministry of Civil Aviation, the Tender Specification E.19/46 issued, which was specifically aimed at the interpretation of the W.11 out. Cierva was also commissioned to build a prototype with military ID VZ724. The design called for two rotors side by side, complemented by a rotor over the nose of the machine. When driving the civilian Rolls -Royce Merlin 24 was provided.
Early in 1947 a second prototype was then ordered ( identifier WA 555 ). The first prototype was presented at the SBAC exhibition in August 1948 in Farnborough. When the aircraft performed its first flight on unfettered December 8, 1948, she presented with a takeoff weight of 6600 kg ( 14,600 lb) at the same time set a world record for rotorcraft.
However, the aircraft crashed on June 13, 1950 during test flights due to material fatigue of a mechanical part from, the three pilots were killed. At this time, the prototype had a total of 69 hours in the air.
Because after this accident, the British government lost interest in a procurement, the project was discontinued and Saunders -Roe took over 1951 plants of Cierva. Thereafter, the second prototype led some tethered flights through and was used as a test machine for various purposes, it was scrapped in 1960.
One project was the variant W.11T (later referred to as W.12 ) with two 1435 bhp engines of the type Rolls -Royce Merlin 502 which should transport 36 passengers.
Construction
The hull with a rectangular cross-section semi-monocoque construction was metallbeplankt and largely windowless. The freight or passenger cabin was located behind the centrally located machine area, separated by a fire wall. The engine was installed forwardly directed at an angle of 7.5 °.
Only one engine was used, which transferred power through a transfer case to the three driveshafts. At the end of each arm there was another gear, which made for a speed reduction and the force return to the rotors.
The torque balance which is always necessary in rotary wing aircraft with an odd number of main rotors, took place, as well as other designs with three rotors, by gently tilting the vertical axes of the rotors.
The end of the fuselage had two side hinged doors. Unusually, the tailplane was attached to the two end plates on the doors and was swung away with this.