Fairey Rotodyne

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Rotodyne
SFF 002-1055526 Fairey Rotodyne.jpg
The Fairey Rotodyne prototype circa 1959.[1]
RoleCompound gyroplane
National originUnited Kingdom
ManufacturerFairey Aviation
First flight6 November 1957
StatusCancelled 1962
Number builtOne
Developed fromFairey Jet Gyrodyne
 
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Rotodyne
SFF 002-1055526 Fairey Rotodyne.jpg
The Fairey Rotodyne prototype circa 1959.[1]
RoleCompound gyroplane
National originUnited Kingdom
ManufacturerFairey Aviation
First flight6 November 1957
StatusCancelled 1962
Number builtOne
Developed fromFairey Jet Gyrodyne

The Fairey Rotodyne was a 1950s British compound gyroplane designed and built by Fairey Aviation and intended for commercial and military applications.[2] A development of the earlier 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, and autorotated during cruise flight with all engine power applied to two propellers. Although promising in concept and successful in trials, the Rotodyne program was eventually cancelled when a combination of politics and lack of commercial orders arising from concerns over high levels of rotor tip-jet noise doomed the project.

Design and development[edit]

Fairey developed the Fairey FB-1 Gyrodyne, 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. J.A.J. 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. The FB-1 set a world airspeed record in 1948, but a fatal accident due to poor machining of a rotor blade flapping link retaining nut 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 was renamed the Jet Gyrodyne, which despite its name, was a compound autogyro.

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 number XE521).

A wind tunnel model of the Fairey Rotodyne.

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.[3]

The Rotodyne had a large, four-bladed 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. The air was produced by compressors driven through a clutch off the main engines. This was fed through ducting in the leading edge of the wings and up to the rotor head. Each engine supplied air for a pair of opposite rotors; the compressed air was mixed with fuel and burned.[4] As a torqueless rotor system, no anti-torque correction system was required, though 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 cockpit controls included a cyclic and collective pitch lever, as in a conventional helicopter.[5]

The transition from helicopter to autogiro took place around 60 mph by extinguishing the tip-jets, and up to half the lift was provided by the wings, enabling higher speed.[6]

The rotor blades were a symmetrical aerofoil around a load-bearing spar. The aerofoil was made of steel and light alloy because of centre of gravity concerns. Equally the spar was formed from a thick machined steel block to the fore and a lighter thinner section formed from folded and rivetted steel to the rear. The compressed air was channeled through three steel tubes within the blade.[7] The tip-jet combustion chambers were made from Nimonic 80 with liners made from Nimonic 75.

While the prototype was being built, funding for the programme reached a crisis. Cuts in defence spending led the Ministry of Defence to withdraw support, pushing the burden of the costs onto any possible civilian customer. The Government agreed to 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.

Operational history[edit]

Testing and evaluation[edit]

CG image of a Rotodyne in flight.

Although J.A.J. Bennett had left Fairey to join Hiller Helicopters in California, the prototype, its development assumed by Dr. George S. Hislop, made its first flight on 6 November 1957 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 successful transition from vertical to horizontal and back to vertical flight was achieved on 10 April 1958.[8] The Rotodyne performed to expectations and set a world speed record in the convertiplane category, at 190.9 mph (307.2 km/h) on 5 January 1959, over a 60 mi (100 km) closed circuit.[9][10] As well as being fast, the craft 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. It even lifted a 100 ft girder bridge.[11]

External images
Rotodyne lifting a 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 175 kn (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. 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 propellers 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 kn (280 km/h) to another city, e.g., London to Paris, where the rotor tip-jet system would be restarted for landing vertically in the city centre. When the Rotodyne landed and the rotor stopped moving, its blades drooped downward from the hub. To avoid striking the vertical stabilizers on startup, the tips of these fins were angled down to the horizontal. They were raised once the rotor had spun up.

British European Airways (BEA) announced that it was interested in the purchase of six aircraft, with a possibility of up to 20. The Royal Air Force ordered 12 military transport versions. New York Airways signed a letter of intent for the purchase of five at $2m each with an option of 15 more albeit with qualifications, after calculating that a larger Rotodyne could operate at half the seat mile cost of helicopters,[12] however unit costs were deemed too high for very short hauls of 10 to 50 miles, and the Civil Aeronautics Board was opposed to rotorcraft competing with fixed-wing on longer routes.[13] Japan Air Lines said they would experiment with Rotodyne between Tokyo airport and the city itself.[14] The U.S. Army was interested in buying 200 of the Type Y Rotodyne to be manufactured by Fairey's U.S. licensee, Kaman Helicopters in Bloomfield, Connecticut. 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, and that importance made Fairey develop 40 different noise suppressors by 1955.[15]

Cancellation[edit]

One of the few surviving parts of the dismantled prototype.

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 forced into mergers. Saunders-Roe and the helicopter division of Bristol were incorporated with Westland, and in May 1960 Fairey Aviation was also taken over by Westland. By this time, the Rotodyne had flown a total of almost 1,000 people for 120 hours in 350 flights and made 230 transitions between helicopter and autogiro — with no accidents.[16] The larger Rotodyne Z design could be developed to take 57 to 75 passengers which with the Rolls-Royce Tyne turboprops (5,250 shp/3,910 kW) would have a cruising speed of 200 kts (370 km/h). It would be able to carry nearly 8 tons (7 tonnes) of freight and British Army vehicles would fit into its fuselage. Government funding of some £5 million 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 themselves.

However, the end came when the interest shown by BEA declined to order the Rotodyne due to tip-jet noise concerns and a request for a military order was also turned down. Funding for the Rotodyne was terminated in early 1962. The corporate management at Westland decided that further Rotodyne development towards production status was not worth the investment required.[5] After the programme was terminated, the Rotodyne, which was, after all, government property, was dismantled and largely destroyed in the same way as the Bristol Brabazon. A single fuselage bay, as pictured, plus rotors and rotorhead mast are on display at The Helicopter Museum, Weston Super Mare.

Analysis[edit]

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 Gellatly made two flights over central London and several landings and departures at Battersea Heliport with no complaints being registered,[6] though John Farley, chief test pilot of the Hawker Siddeley Harrier later commented:

From two miles away it would stop a conversation. I mean, the noise of those little jets on the tips of the rotor was just indescribable. So what have we got? The noisiest hovering vehicle the world has yet come up with and you're going to stick it in the middle of a city?[17]

There was a noise-reduction programme in process which had managed to reduce the noise level from 113dB to the desired level of 96 dB from 600 ft (180 m) away, less than the noise made by a London Underground train, and at the time of cancellation, silencers were under development, which would have reduced the noise even further — with 95 dB at 200 ft "foreseen",[18] the limitation being the noise created by the rotor itself.[19] This effort, however, was insufficient for BEA who, as expressed by Chairman Sholto Douglas, "would not purchase an aircraft that could not be operated due to noise", and the airline refused to order the Rotodyne, which in turn led to the collapse of the project.

It is only relatively recently that interest has been reestablished in direct city-to-city transport, with aircraft such as the AgustaWestland AW609 and the CarterCopter/PAV. The 2010 Eurocopter X3 experimental helicopter shares the general configuration of the Rotodyne, but is much smaller. A number of innovative gyrodyne designs are still being considered for future development.[20]

Specifications (Rotodyne "Y")[edit]

Fairey Rotodyne 3-view
External images
Cutaway drawing of Rotodyne from Flightglobal.com

Data from Fairey Aircraft since 1915[21]

General characteristics

Performance

See also[edit]

Related development
Aircraft of comparable role, configuration and era
Related lists

References[edit]

Notes[edit]

  1. ^ Photo: J Thinesen, SFF photo archive
  2. ^ "Rotodyne, Fairey's Big Convertiplane Nears Completion: A Detailed Description." Flight, 9 August 1957, pp. 191–197.
  3. ^ Flight 9 August 1957, p. 191.
  4. ^ Flight August 1957, p. 197.
  5. ^ a b Winchester 2005, p. 97.
  6. ^ a b Anders, Frank. "The Fairey Rotodyne." Gyrodyne Technology (Groen Brothers Aviation). Retrieved: 17 January 2011.
  7. ^ Flight August 1957. p. 196.
  8. ^ Taylor 1976, p. 97.
  9. ^ "FAI Record ID #13216 - Rotodyne, Speed over a closed circuit of 100 km without payload" Fédération Aéronautique Internationale Record date 5 January 1959. Accessed: 29 November 2013.
  10. ^ Winchester 2005, p. 96.
  11. ^ Promising future
  12. ^ Charnov, p12
  13. ^ "Project Hummingbird - THE HELICOPTER AND OTHER V/STOL AIRCRAFT IN COMMERCIAL TRANSPORT SERVICE" page 913. Federal Aviation Administration, Economics Branch Office of Plans, November 1960. Accessed: 21 November 2013.
  14. ^ JAL and the Rotodyne 13 February 1959 p235
  15. ^ Charnov, p11
  16. ^ Charnov, p14
  17. ^ Hamilton-Paterson, James. "Fighter Jock Heaven". Empire of the Clouds. London: Faber and Faber Limited. p. 314. ISBN 978-0-571-24795-0. 
  18. ^ "Requiem for the Rotodyne - An Account of Unusual Problems Met and Solved." Flight International, 9 August 1962, pp. 200-203, see page 202.
  19. ^ Who believes in Helicopters Flight p380
  20. ^ "Gyrodyne Technology, The GBA Gyrodyne Concept: The Birth of a New Age of Rotary-Wing Aviation." Groen Brothers Aviation. Retrieved: 24 January 2011.
  21. ^ Taylor 1974, p. 426.
  22. ^ Taylor 1961, p. 191.
  23. ^ Flight 9 August 1957, p. 193.
  24. ^ Taylor 1974, p. 407.
  25. ^ Braas, Nico. "Fairey Rotodyne." Let Let Let Warplanes, 15 June 2008. Retrieved: 15 April 2010.
  26. ^ Taylor 1974, p. 419.

Bibliography[edit]

External links[edit]