“Used on the 1950s Fairey Rotodyne, one key concept that DARPA is considering is the use of tipjets to power large-diameter rotors to achieve lift. The technologies have come of age to make an older idea viable … This initiative is complementary to other compound helicopter ideas and has value ranging from combat search and rescue to the heavy lift rotorcraft missions of the future.”
Phillip Hunt, Program Manager Tactical Technology Office, DARPA
The gyrodyne concept and the advantages of autorotative flight have been proven in practice. In the late 1950’s a British gyrodyne, called the Rotodyne, made hundreds of flights and flew hundreds of flight hours in test and demonstration flights. That vertical takeoff aircraft, with a cruise speed of 200mph (when most helicopters were only capable of 100mph or less) and a passenger capacity of 44 people, demonstrated its capacity to transport passengers from the center of London to the center of Paris in less time than any other vehicle. Today, fifty years later, this would still be true even if the aircraft had not been improved through advances in modern aerodynamics. Though a technical success, continued funding for the Rotodyne was canceled by the British government. Its heritage, however, can lead to the realization of the wide range of opportunities envisioned by DARPA.
The Fairey Rotodyne
This article, excerpted from a study produced by Dr. Frank Anders in 1988, and reproduced in part here, relates how the problem of gridlock at major hubs was evaluated, attacked, and solved in 1957.
The Fairey Rotodyne originated from an idea for a large compound helicopter by Dr. J. A. J. Bennett and Capt. A. G. Forsyth of Fairey Aviation, whose original study dates back to 1947. Their concept evolved into the “Eland” Rotodyne prototype, which sucessfully completed its maiden flight in November, 1957. Its four-bladed rotor was powered in helicopter mode by tip jets, driven by compressed air. This compressed air was lit with fuel at tip jet combustion chambers to drive the rotor, removing the necessity for an anti-torque tail rotor. The tip jets were extinguished at about 60 mph after a normal helicopter takeoff, converting the aircraft to an autogiro. In autogiro mode the collective pitch of the rotor blades, and hence rotor lift, was reduced with up to about half the weight taken by the wings, allowing much higher speeds than conventional. When approaching to land the tips were relit, converting the aircraft back to helicopter mode for a normal helicopter hover and landing.
In 1958 the Rotodyne prototype achieved economic cruise speeds of 150 knots. A world record speed of 190.9 mph was set on January 5, 1959 for the 100 km closed circuit. The craft had the remarkable safety feature of being able to convert from autogiro mode to helicopter mode and hover with one engine shut down and its prop feathered. Additionally, it demonstrated safe landings in full autogiro mode.
The greatest criticism of the Rotodyne, in spite of its performance as a VTOL craft, was of the noise generated by the tip jets. The noise attenuation program at the time of cancellation had produced reductions down to the then-desired 96 db. at 600 ft. distance. Noise critics failed to appreciate that the full power tips-lit time in service was only about one minute during takeoff and climb and one minute at landing. In fact, to prove a point, test pilot Ron Gelattly made two flights over downtown London and several takeoffs and landings at Battersea Heliport on a dead calm morning with no complaints raised. At the time of the project’s cancellation the continuing development of silencers had further reduced the noise level by another 16 db. Instrument flying the aircraft was very stable and Gelattly often demonstrated transitions from helicopter to autogiro and back again, in IMC, at less than 500 ft. above the ground!
The Rotodyne’s tip drive and unloaded rotor made a tremendous breakthrough in performance and handling compared to pure helicopters and other forms of convert-a-planes. The aircraft was flown at 175 knots and pulled into a steep climbing high G turn with no adverse handling characteristics. It was demonstrated at the Farnbourgh and Paris Air Shows each year from 1958 to 1962 and always amazed onlookers. From any point of view the Rotodyne was an aircraft ahead of its time.
Throughout Europe and Britain, city-center-to-city-center transport was being touted as taking very little flying time. Kaman Helicopters in the U. S. was proposing a licensesure for civil and military production. Interest was shown from Okanagan Helicopters Ltd. of Vancouver, B.C., New York Airways, Chicago Helicopter Airways and Japan Airlines, who considered the aircraft for its Osaka-Tokyo route.
Nearly 1000 passengers, including a fair portion of the world’s airline chiefs, service chiefs and British Ministers of Parliament, were flown as a demonstration of the enhanced safety of the prototype in order to emphasize faith in the design.
By January of 1959 British European Airways announced that it would write a letter of intent for 6 developed Rotodynes, with the hope of a requirement for up to 20 aircraft for operation on shorter routes. This was in addition to an RAF “order” for 12 military transport version. In March of 1959 New York Airways planned to purchase 5 Rotodynes costing about ten million dollars, with an option for an additional 15 at a later date. The U.S. Army showed considerable interest with a rumored buy of 200 machines. None of this occurred.
Why then, was the project cancelled and the concept not pursued? Why has there not been a logical progression of existing technology dating back 40 years instead of a radical departure from that technology?
In 1959 the British Government, determined to reduce its participation in the aviation industry, reduced the number of helicopter firms. Under the direction of Minister of Aviation Duncan Sandys, the consolidation process was begun. It was done by cutting government funding. Sandys wanted one consolidated helicopter manufacturer centered on Westland aircraft. This meant that Fairey, the helicopter division of Bristol, would have to be taken over by the Westland firm.
In February, 1962, the final axe fell, first with withdrawal by BEA, then the withdrawal of the military order. The world’s first vertical takeoff military/civil transport died.
All of this occured almost 40 years ago. Had the Rotodyne persevered, accentuated with modern low fuel consumption engines and modern electronics for the hydraulic control system, commerical aviation would now have a transport of great potential competing with both fixed and rotary wing machines.
One would think such a remarkable aircraft would be retired to a prestigous position in an elite British museum. In fact, the aircraft was dismantled and destroyed, and all tooling which was used to create the Rotodyne was destroyed. Even in a search of London’s aviation museums and memorabilia, there is no evidence other than the few articles which were written in European and British aviation publications concerning the craft. A few components have been found and brought together at the International Helicopter Museum at Weston-Super-Mare.
The problems with air transport are much the same as they were 40 years ago, more intense. An interesting comment was made in 1989 by Mr. Michael Heatly, author of the Illustrated History of Helicopters, referring to the Rotodyne, “in many ways the Rotodyne was a project decades ahead of its time. Many subsequent projects from the drawing boards of the worlds’ rotocraft manufacturers bore no little relation to this futuristic craft that would seem more at home in the 80’s skys than those of the 50’s. The possibility of a similarly configured VTOL feeder liner achieving success in future decades cannot be ruled out.”