Cierva W.11

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Cierva W.11 Air Horse
Cierva W.11.jpg
Type: Heavy-duty transport helicopter
Design country:
Manufacturer:

Cierva Autogiro

First flight:

December 8, 1948

Commissioning:

-

Production time:

-

Number of pieces:

2

The Cierva W. 11 Air Horse was a transport helicopter made by the British manufacturer Cierva Autogiro in the 1940s. It was the largest helicopter in the world in its day and unique in that it had three main rotors , a design that was never used again before or after.

These three rotors all turn in the same direction, do not overlap and are tilted slightly all around to compensate for the yaw moment.

history

The origins of Air Horse go back to the late 1930s when G. & J. Weir Ltd. developed their W.5 and W.6 helicopters in Glasgow under chief designer CG Pullin. The design of these constructions with two rotors lying next to one another and an airplane-like tail unit proved to be very successful at the time. After Cierva took over key Weir employees, the technical design of the new constructions also reflected the Weir legacy; even the numbering was continued in the W series.

Since the number of parts for small and large machines is essentially the same, Cierva was of the opinion that only very large helicopter designs with payloads over 1.25 t could be operated economically. The first helicopter that was designed according to these specifications was the W.10 with three rotors, which were driven by two 475 hp Armstrong Siddeley Cheetah engines that had been converted to water cooling . The scaled-up W.11 was derived from this, while the W.10 was abandoned. Their name was later adopted by a five-seater single-rotor helicopter.

On August 1, 1945, Cierva was granted patent no. 19758 for the three-rotor design. In July 1946, the Ministry of Civil Aviation issued Specification E.19 / 46 , which was specifically geared towards the design of the W.11. Cierva also received an order to build a prototype with the RAF serial number VZ724. The design provided for two rotors lying next to each other, supplemented by a rotor above the nose of the machine. The civilian Rolls-Royce Merlin 24 was intended as the drive .

A second prototype was then ordered at the beginning of 1947 (identification WA 555). The first prototype was presented at the SBAC exhibition in Farnborough in August 1948. When the machine made its first untethered flight on December 8, 1948, it also set a world record for rotary wing aircraft with a takeoff weight of 6600 kg (14,600 lb) .

The machine crashed on June 13, 1950 during test flights due to material fatigue in part of the mechanics, killing the three pilots. At this point the prototype had been in the air for a total of 69 hours.
As the British government lost interest in procurement after this accident, the project was discontinued and Saunders-Roe took over the Cierva plant in 1951. After that, the second prototype made a few more tied flights and was used as a test machine for various purposes before being scrapped in 1960.

One project was the W.11T variant (later referred to as W.12) with two 1435 hp Rolls-Royce Merlin 502 engines that were supposed to transport 36 passengers.

construction

The fuselage with a rectangular cross-section in half-shell construction was metal-clad and largely windowless. The cargo or passenger cabin was located behind the centrally arranged machine area, separated by a fire bulkhead . The engine was installed facing forward at an angle of 7.5 °.

Only one motor was used, which transferred its power to the three drive shafts via a transfer case . At the end of each boom there was another gearbox that reduced the speed and diverted power to the rotors.

The torque compensation, which is always necessary for rotary wing aircraft with an uneven number of main rotors, was carried out, as in other designs with three rotors, by slightly tilting the vertical axes of the rotors.

At the end of the fuselage there were two hinged doors. It was unusual that the tailplane was attached to the doors with the two end plates and swiveled away with them.

Technical specifications

Parameter Data
crew 2
Passengers 24
Length (over the rotor tips) 27.00 m (88 ft 7 in)
Span (over the rotor tips) 28.96 m (95 ft)
Rotor diameter 14.33 m (47 ft)
Rotor circle distances from each other 0.30 m (1 ft)
height 5.41 m (17 ft 9 in)
Empty mass 5507 kg (12140 lb)
Max. Takeoff weight 7940 kg (17500 lb)
Cruising speed 153 km / h
Top speed 225 km / h
Service ceiling 8540 m or 28000 ft
Range 531 km
Engines 1 × Rolls-Royce Merlin 24 with 1210 kW (1645 PS)

See also

literature

  • Elfan Ap Rees: Cierva's Triple Rotor Chopper. Airplane Monthly, January 1978.

Web links