The Fairey Rotodyne was a 1950s British compound gyroplane designed and built by Fairey Aviation and intended for commercial and military uses. A development of the earlier Fairey Jet Gyrodyne, which had established a world helicopter speed record, the Rotodyne featured a tip-jet-powered rotor that burned a mixture of fuel and compressed air bled from two wing-mounted Napier Eland turboprops. The rotor was driven for vertical takeoffs, landings and hovering, as well as low-speed translational flight, but autorotated during cruise flight with all engine power applied to two propellers.
One prototype was built. Although the Rotodyne was promising in concept and successful in trials, the programme was eventually cancelled. The termination has been attributed to the type failing to attract any commercial orders; this was in part due to concerns over the high levels of rotor tip jet noise generated in flight. Politics had also played a role in the lack of orders (the project was government-funded) which ultimately doomed the project.
Development Background
From the late 1930s onwards, considerable progress was made on an entirely new field of aeronautics in the form of rotary-wing aircraft. While some progress in Britain had been made prior to the outbreak of the Second World War, wartime priorities placed upon the aviation industry meant that British programmes to develop rotorcraft and helicopters were marginalised at best. In the immediate post-war climate, the Royal Air Force (RAF) and Royal Navy elected to procure American-developed helicopters in the form of the Sikorsky R-4 and Sikorsky R-6, known locally as the Hoverfly I and Hoverfly II respectively. Experience from the operation of these rotorcraft, along with the extensive examination that was conducted upon captured German helicopter prototypes, stimulated considerable interest within the armed services and industry alike in developing Britain's own advanced rotorcraft.
Fairey Aviation was one such company that was intrigued by the potential of rotary-wing aircraft, and proceeded to develop the Fairey FB-1 Gyrodyne in accordance with Specification E.16/47. The Gyrodyne was a unique aircraft in its own right that defined a third type of rotorcraft, including autogyro and helicopter. Having little in common with the later Rotodyne, it was characterised by its inventor, Dr JAJ Bennett, formerly chief technical officer of the pre-Second World War Cierva Autogiro Company as an intermediate aircraft designed to combine the safety and simplicity of the autogyro with hovering performance. Its rotor was driven in all phases of flight with collective pitch being an automatic function of shaft torque, with a side-mounted propeller providing both thrust for forward flight and rotor torque correction. On 28 June 1948, the FB-1 proved its potential during test flights when it achieved a world airspeed record, having attaining a recorded speed of . The programme was not trouble-free however, a fatal accident involving one of the prototypes occurring in April 1949 due to poor machining of a rotor blade flapping link retaining nut. The second FB-1 was modified to investigate a tip-jet driven rotor with propulsion provided by propellers mounted at the tip of each stub wing, being renamed the Jet Gyrodyne.
During 1951 and 1952, British European Airways (BEA) internally formulated its own requirement for a passenger-carrying rotorcraft, commonly referred to the Bealine-Bus or BEA Bus. This was to be a multi-engined rotorcraft capable of serving as a short-haul airliner, BEA envisioned the type as being typically flown between major cities and carrying a minimum of 30 passengers in order to be economical; keen to support the initiative, the Ministry of Supply proceeded to sponsor a series of design studies to be conducted in support of the BEA requirement. Both civil and government bodies had predicted the requirement for such rotorcraft, and viewed it as being only a matter of time before they would become commonplace in Britain's transport network.
The BEA Bus requirement was met with a variety of futuristic proposals; both practical and seemingly impractical submissions were made by a number of manufacturers. Amongst these, Fairey had also chosen to submit its designs and to participate to meet the requirement; according to aviation author Derek Wood: "one design, particularly, seemed to show promise and this was the Fairey Rotordyne". Fairey had produced multiple arrangements and configurations for the aircraft, typically varying in the powerplants used and the internal capacity; the firm made its first submission to the Ministry on 26 January 1949. Within two months, Fairey had produced a further three alternative submissions, centring on the use of engines such as the Rolls-Royce Dart and Armstrong Siddeley Mamba. In October 1950, an initial contract for the development of a , four-bladed rotorcraft was awarded. The Fairey design, which was considerably revised over the years, received government funding to support its development.
Early on in development, Fairey found that securing access to engines to power its design proved to be difficult. In November 1950, Rolls-Royce chairman Lord Hives protested that the design resources of his company were being stretched too thinly across multiple projects; accordingly, the initially selected Dart engine was switched to the Mamba engine of rival firm Armstrong Siddeley. By July 1951, Fairey had re-submitted proposals using the Mamba engine in two and three-engine layouts, supporting all-up weights of respectively; the adopted configuration of pairing the Mamba engine to auxiliary compressors was known as the Cobra. Due to complaints by Armstrong Siddeley that it too was lacking resources, Fairey also proposed the alternative use of engines such as the de Havilland Goblin and the Rolls-Royce Derwent turbojet to drive the forward propellers.
Fairey did not enjoy a positive relationship with de Havilland however, so instead they chose to use D. Napier & Son and its Eland turboshaft engine in April 1953. Following the selection of the Eland, the basic design of the rotorcraft, known as the Rotodyne Y, soon emerged; it was powered by a pair of Eland N.El.3 engines furnished with auxiliary compressors and a large-section four-blade main rotor, with a projected all-up weight of . At the same time, a projected enlarged version, designated as the Rotodyne Z, outfitted with more powerful Eland N.El.7 engines and an all-up weight of , was proposed as well.
Contract
In April 1953, the Ministry of Supply contracted for the building of a single prototype of the Rotodyne Y, powered by the Eland engine, later designated with the serial number XE521, for research purposes. As contracted, the Rotodyne would have been the largest transport helicopter of its day, seating a maximum of 40 to 50 passengers, while possessing a cruise speed of and a range of . At the time of the award, Fairey had estimated that £710,000 would cover the costs of producing the airframe. With a view to an aircraft that would meet regulatory approval in the shortest time, Fairey's designers worked to meet the Civil Airworthiness Requirements for both helicopters and similar-sized twin-engined aircraft. A one-sixth scale rotorless model was extensively wind tunnel tested for fixed-wing performance. A smaller (1/15th-scale) model with a powered rotor was used for downwash investigations.
While the prototype was being built, funding for the programme reached a crisis. Cuts in defence spending led the Ministry of Defence to withdraw its support, pushing the burden of the costs onto any possible civilian customer. The government agreed to maintain funding for the project only if, among other qualifications, Fairey and Napier (through their parent English Electric) contributed to development costs of the Rotodyne and the Eland engine respectively. As a result of disagreements with Fairey on matters of policy, Dr Bennett left the firm to join Hiller Helicopters in California; responsibility for the Rotodyne's development was assumed by Dr George S Hislop, who became the firm's chief engineer.
The manufacturing of the prototype's fuselage, wings, and rotor assembly was conducted at Fairey's facility in Hayes, Hillingdon, West London, while construction of the tail assembly was performed at the firm's factory in Stockport, Greater Manchester and final assembly was performed at White Waltham Airfield, Maidenhead. In addition, a full-scale static test rig was produced at RAF Boscombe Down to support the programme; the static rig featured a fully operational rotor and powerplant arrangement which was demonstrated on multiple occasions, including a 25-hour approval testing for the Ministry.
While construction of the first prototype was underway, prospects for the Rotodyne appeared positive; according to Wood, there was interest in the type from both civil and military quarters. BEA was monitoring the progress of the programme with interest; it was outwardly expected that the airline would place an order shortly after the issuing of an order for a militarised version of the rotorcraft. The American company Kaman Helicopters also showed strong interest in the project, and was known to have studied it closely as the firm considered the potential for licensed production of the Rotodyne for both civil and military customers.
Due to army and RAF interest, development of the Rotodyne had been funded out of the defence budget for a time. During 1956, the Defence Research Policy Committee had declared that there was no military interest in the type, which quickly led to the Rotodyne becoming solely reliant upon civil budgets as a research/civil prototype aircraft instead.Wood 1975, pp. 119-120. After a series of political arguments, proposals, and bargaining; in December 1956, HM Treasury authorised work on both the Rotodyne and Eland engine to be continued until the end of September 1957. Amongst the demands exerted by the Treasury were that the aircraft had to be both a technical success and would need to acquire a firm order from BEA; both Fairey and English Electric (Napier's parent company) also had to take on a portion of the costs for its development as well.
Testing and evaluation
On 6 November 1957, the prototype performed its maiden flight, piloted by chief helicopter test pilot Squadron Leader W. Ron Gellatly and assistant chief helicopter test pilot Lieutenant Commander John G.P. Morton as second pilot. The first flight had originally been projected to take place in 1956; however, delay was viewed as inevitable with an entirely new concept such as used by the Rotodyne.
On 10 April 1958, the Rotodyne achieved its first successful transition from vertical to horizontal and then back into vertical flight. On 5 January 1959, the Rotodyne set a world speed record in the convertiplane category, at , over a closed circuit. As well as being fast, the rotorcraft had a safety feature: it could hover with one engine shut down with its propeller feathered, and the prototype demonstrated several landings as an autogyro. The prototype was demonstrated several times at the Farnborough and Paris air shows, regularly amazing onlookers. In one instance, it even lifted a 100 ft girder bridge.
The Rotodyne's tip drive and unloaded rotor made its performance far better when compared to pure helicopters and other forms of "convertiplanes." The aircraft could be flown at and pulled into a steep climbing turn without demonstrating any adverse handling characteristics.