Fairey Rotodyne
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The Fairey Rotodyne was a compound autogyro or gyrodyne. It took off and landed as a helicopter, and cruised as an autogyro with supplemental fixed wings. The Rotodyne had a large, four-blade rotor and two Napier Eland N.E.L.3 turboprops , one mounted under each of the fixed wings. For takeoff and landing the rotor was driven by tip-jets, powered by compressors driven through a clutch by the main engines, and the compressed air produced was mixed with fuel and burned. As a torqueless rotor system, no antitorque correction system was required, though the propeller pitch was controlled by the rudder pedals for low speed yaw control. The propellers provided thrust for translational flight while the rotor autorotated.
The market for the Rotodyne was that of a medium-haul 'flying bus': it would take off vertically from an inner-city heliport, with all lift coming from the tip-jet driven rotor, and then would increase airspeed, eventually with all power from the engines being transferred to the propellors with the rotor autorotating. In this mode, the collective pitch, and hence drag, of the rotor could be reduced, as the wings would be taking as much as half of the craft's weight. The Rotodyne would then cruise at speeds of about 150 knots to another city (say, London to Paris) where the rotor tip-jet system would be restarted for landing vertically in the city centre.
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[edit] Development
Fairey had developed the FB-1 Gyrodyne, a discrete 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 characterized by its inventor, Dr. J.A.J. Bennett, formerly of the 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 proving both thrust for forward flight and rotor torque correction. The FB-1 set a world airspeed record in 1948, but a fatal accident due to poor machining of a rotor blade flapping link terminated development of the pure gyrodyne. 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 - this became known as the Jet Gyrodyne.
Fairey put forward their various designs for the proposed BEA Bus, which were revised over the years, and received government funding. However getting access to engines proved to be difficult with first Rolls Royce then Armstrong Siddeley claiming lack of resources. The Ministry of Supply contracted in 1953 for the building of the prototype (serial XE521). While the prototype was being built funding was reaching a crisis. Cuts in defence spending led the Ministry of Defence to withdraw interest pushing the burden of the costs onto any possible civilian interest. The Government agreed continued funding 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. Although one of Fairey's lead personnel on the project had decamped to the U.S. Hiller company the prototype took its first flight on November 6, 1957 followed by a successful transition from vertical to horizontal and back to vertical flight on April 10 1958. It also performed to expectations. It set a world speed record for a helicopter, at 190.9 mph (307 km/h) on 5 January 1959, over a 100 km closed circuit. As well as being fast, the craft had several safety features: it could hover with one engine shut down and its propellor feathered, and the prototype demonstrated several fully autogyro landings. The prototype was demonstrated several times at the Farnborough and Paris air shows, regularly amazing onlookers. The Rotodyne's tip drive and unloaded rotor made her performance far better when compared to pure helicopters and other forms of 'convertiplanes'. The aircraft could be flown at 175 knots (324 km/h) and pulled into a steep climbing turn without demonstrating any adverse handling characteristics.
Throughout the world, interest was growing in the prospect of direct city-to-city transport.
British European Airways announced that it was interested in the purchase of six craft, with a possibility of up to twenty. The Royal Air Force ordered twelve military transport versions. New York Airways signed a letter of intent for the purchase of five with an option on more albeit with qualifications. There were rumours that the US Army was interested in buying two hundred of the larger design planned. Government funding was secured again on the proviso that firm orders would be gained from BEA. The civilian orders were dependent on the noise issues being satisfactorily met.
In 1959 the British Government, seeking to cut costs, decreed that the number of aircraft firms be lowered and set forth their expectations for mergers in airframe and aero-engine companies. By delaying or withholding access to defence contracts the British firms could be maneuvred into mergers. Fairey, then the helicopter division of Bristol, and Saunders-Roe would be incorporated with Westland. With Westland Aircraft the larger Rotodyne design could be developed to take from 57 to 75 passengers which with the Rolls-Royce Tyne turboprops (5,250 shp) would have a cruising speed of 370 km/h. It would be able to carry nearly 7 tonnes of freight and British Army vehicles would fit into its fuselage. Government funding to the tune of some 5 million pounds was promised. The expected order from the RAF did not appear - they had no particular interest in the design with the issue of nuclear deterrence to the fore at the time. The Tyne engines were starting to appear underpowered for the larger design. Rolls Royce were told that they would have to fund the engine development itself. However the end came when the interest shown by BEA did not provide an order and a request for an order by the military was turned down. The funding for the Rotodyne was cut in early 1962. The Rotodyne which was, after all, government property, was dismantled and largely destroyed in the same way the Bristol Brabazon after it was terminated.
The one great criticism of the Rotodyne was the noise the tip jets made, however, the jets were only run at full power for a matter of minutes during departure and landing and indeed, the test pilot Ron Gelattly made two flights over central London, and several landings and departures at Battersea Heliport with no complaints being registered. There was also a noise-reduction program in process and had managed to get the noise level down to the desired level of 96 dB from 600 feet (180 m) away, less than the noise made by a London Underground train, and at the time of cancellation, silencers were in the pipeline which would have reduced the noise even farther. In the end though it was funding and not noise that killed the Rotodyne
It is only relatively recently that interest has been re-established in direct city-to-city transport, with aircraft such as the Bell/Augusta BA609 and the Carter Copter.
[edit] Particulars
When the Rotodyne landed and the rotor stopped moving, its blades drooped downward from the hub. To avoid striking the vertical stabilizers on start-up, the tips of these fins were angled down to the horizontal. They were raised once the rotor had spun up.
[edit] Specifications (Rotodyne "Y")
General characteristics
- Crew: 3
- Capacity: 40 passengers
- Length: 58 ft 8 in (17.9 m)
- Rotor diameter: 90 ft 0 in (27.4 m)
- Height: 22 ft 2 in (6.76 m)
- Disc area: 6,360 ft² (591 m²)
- Empty weight: lb (kg)
- Loaded weight: 33,000 lb (15,000 kg)
- Max takeoff weight: 38,000 lb (17,000 kg)
- Powerplant: 2× Napier Eland turboprops, 2,800 hp (2,100 kW) each
Performance
- Maximum speed: 213 mph (343 km/h)
- Range: 520 mi (830 km)
- Service ceiling: ft (m)
- Rate of climb: ft/min (m/s)
- Disc loading: 5.2 lb/ft² (25 kg/m²)
- Power/mass: 0.17 hp/lb (280 W/kg)
- Wing loading:
[edit] References
- The Fairey Rotodyne: An Idea Whose Time Has Come – Again? Detailed History
