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The Fairey Rotodyne - an Opportunity Missed

The opening title sequence to the film Coogan's Bluff1 shows the title character flying in a twin-rotor passenger helicopter into the centre of New York. The helicopter lands on the rooftop of the Pan-Am skyscraper2 in Manhattan and our hero, deputy sheriff Walt Coogan, disembarks. He is only an elevator ride from the streets of the metropolis where he will be free to wreak his own brand of havoc. Although this is all part of a fictional story, it was filmed using a real helicopter service which existed at the time to transport passengers from New York's outlying international airports to the city centre. These film sequences give an indication of the convenience of speedy air travel between city centres to busy business executives.

The cessation of hostilities at the end of World War II left the British aviation industry as one of the world’s major producers of aeroplanes, and arguably second only to the US. The British aviation industry was a hotbed of innovation as new ideas and designs leapt from manufacturers’ drawing boards seemingly on a daily basis. Many aviation constructors vied with one another for lucrative contracts to supply military and commercial hardware. It was inevitable, though, that changes in the nature of the aeroplanes and the industry itself were on the horizon, as the sector turned from a war footing to a time of peace.

Concept

One idea that had its roots in the immediate post-war days was foreseeing the need for the quick and efficient transportation of the business community between British and continental cities. Established in the 1950s, the state-owned British European Airways (BEA) provided air travel between major European cities using conventional passenger aeroplanes. These had the disadvantage of being limited to established airports on the outskirts of these conurbations. BEA wanted to provide an air-bus service between the city centres, cutting out the time wasted in transferring between airport and city centre - which could double the overall journey time.

How much faster it would be for a businessman to disembark from an aeroplane only a block or two from their office? For one manufacturer the answer was VTOL (vertical take-off and landing): taking off from a small patch or heliport in the heart of a city, making the transition to horizontal flight with the speed of a conventional aeroplane, followed by a vertical landing at the destination. That, the Fairey Aviation Company believed, would come in the form of the Fairey Rotodyne.

The story of the Rotodyne is one of brilliant design and innovation being ostensibly killed off by noise pollution, which, although it played a part, was not the real cause. The reality was that, although the Rotodyne was ahead of its time, it was stalled by lack of foresight and brought to naught through under-investment and the politics of an interfering government.

For 1950, the Rotodyne had a futuristic look that would not have looked out of place in the skies decades later. Indeed, had it realised the commercial success its potential promised, it may well have been as common a sight in modern skies as the conventional helicopter is today. The Rotodyne was intended to be sold for civilian and military use, for both of which it was well-suited.

Design

Designed by Dr JAJ Bennett and captain A Graham Forsyth, the Rotodyne was technically classed as a compound helicopter. It combined the advantages of a helicopter's vertical take-off and landing with the speed of a conventional aeroplane in horizontal flight.

The vehicle was based on the autogyro that was designed in the inter-war years by Juan Cervia. This was simply an aircraft powered by a single tractor engine, but, instead of using conventional wings, lift was generated by a helicopter-like, four-blade rotor mounted on a pylon high above the fuselage. As the machine moved forward, air passing through the rotor caused it to auto-rotate, generating lift.

The autogyro was unable to take off vertically because it required the forward motion of the whole aeroplane to generate the necessary air current through the rotor. Conventional helicopters have an engine to power the rotor which provides vertical lift-off. The helicopter’s speed is also limited by the inherent drag caused by the need for the rotor to be tilted forward to provide forward thrust.

The helicopter's Achilles heel is the inherent associated forces of torque reaction from the fuselage-mounted engine which makes the fuselage want to rotate in the opposite direction to the rotor. To counteract this torque, it is necessary to provide a complicated mechanism to drive a small tail rotor to keep the fuselage from spinning. The failure of this mechanism is almost always disastrous.

The beauty of the Rotodyne concept was that it combined the best concepts of the autogyro, the helicopter and the conventional aeroplane, while avoiding their complications. The power to the main rotor was provided by small jets mounted at the end of each of the four blades. Power was applied by these jets to spin up the rotor to take-off speed and lift the whole weight of the aircraft vertically. Once height had been gained, forward motion was provided by conventional forward-pointing engines as the Rotodyne carried out a transition from vertical to horizontal flight.

When powered, the main rotor provided all of the lift necessary for vertical take-off. After transition to horizontal flight, and with the tip-jets shut off, the freewheeling rotor supported 65 per cent of the aeroplane's weight as the airstream passed through the disc of the rotor blades in the same manner as the autogyro. The remaining lift requirement was provided by a stubby, shoulder-mounted wing, in the same way as a conventional aeroplane.

The 46ft span wing supported two Napier Eland turboprop3 engines slung underneath. A three-point retractable undercarriage provided the landing gear. The two rear undercarriage legs and wheels retracted rearwards into the engine nacelles, and a front-mounted nose wheel retracted into the front part of the fuselage just behind the pilot's position. At low forward speeds, the direction of the Rotodyne was controlled by increasing or decreasing the amount of thrust at the propeller blades. At higher speeds, the roll and the pitch of the aircraft was controlled by the amount of tilt applied to the rotor.

To provide power for the rotor, the two turboprop engines drove additional compressors to feed air through ducting in the wings and pylon and out along each rotor blade to jets at their tips. Fuel was supplied to the rotor and fed to the tip-jets by centrifugal force. It was then mixed with the compressed air and ignited. With the power being generated within the rotor itself, this overcame the need for a tail rotor to counteract the torque generated by a fuselage-mounted engine.

A square sectioned, but elegantly designed, fuselage was topped at its mid-section by a triangular pylon on which was mounted the main 90ft diameter, four-bladed rotor. The fuselage provided seating for up to 50 passengers, and the rear end of the fuselage opened with twin clamshell doors for cargo access. The cockpit was fully glazed to provide all-round visibility.

A conventional horizontal stabiliser at the rear of the fuselage was tipped by twin vertical fins and rudders. The lower half of the fins was fixed, while the upper half folded down to increase clearance of the main rotor blades when the drooping tips were in danger of fouling the fins upon first starting up.

Development

The Fairey FB-1 Gyrodyne was Fairey's first compound helicopter design. It was powered by an Alvis Leonides radial engine that drove the main rotor, and also a controllable pitch propeller which provided yaw4 control and forward thrust after transition to horizontal flight. It first flew on 7 December, 1947 and set a new speed record in June 1948 of 124.3mph. Unfortunately, the rotor head suffered a metal fatigue failure and disintegrated in mid-air, killing the pilot and observer. Fairey spent the next four years in research and development revising the design.

Fairey's envisaged concept design for a large transport compound helicopter capable of carrying 20 passengers was submitted to the British government in January 1949. Three alternative designs submitted in March that year specified differing combinations of engines and methods of powering the main rotor. Fairey's preferred choice of engine was either the Armstrong-Whitworth Mamba or the Rolls-Royce Dart turboprop engines. But each design was to ultimately incorporate a rotor powered by tip-jets.

The government awarded an initial development design contract for a 20-passenger aircraft powered by Rolls-Royce Dart turboprop engines. However, a complaint by Lord Hives, head of experimental development at Rolls-Royce, that its design facility was being overstretched was upheld and the specification requirement changed to the Armstrong-Whitworth Mamba combination. This met with a similar response from Armstrong-Whitworth, which was already developing the 'Double Mamba' engine for Fairey's 'Gannet' anti-submarine aircraft.

Meanwhile, Fairey was modifying the design to meet BEA’s requirements for a ten- to 12-seat passenger helicopter for use between European cities. A further shift in the specification to De Havilland engines came to nothing when they were unable to reach an agreement, and resulted in a complaint by Fairey to the government that it was being neglected.

Politics had already raised its head when in 1949, as the original proposal was being submitted, the government's head of engine research publicly objected to supporting the Rotodyne project. The writing was already on the wall, but no one at Fairey had read it. The firm pressed on with its design and it was eventually agreed that the engines would be supplied by Napier, a subsidiary of English Electric.

In July 1953, the government's Ministry of Supply agreed funding for the Napier-powered Rotodyne. The design was now specifying 40 - 50 passengers, a 250-mile range and a cruising speed of 150mph. It was to be designated the Rotodyne Y. Following this, in December 1954, BEA entered discussions with Fairey, anticipating a London to Paris city centre service with a projected 88-minute fly-time. Fairey was also proposing a larger aircraft, the Rotodyne Z, capable of transporting small military vehicles and fully armed troop detachments.

Meanwhile, Fairey's research had resulted in a second Gyrodyne with a redesigned and strengthened rotor head, and incorporating a jet-powered rotor. It was to become known as the Jet Gyrodyne. This retained the Leonides engine to drive two ex-Supermarine Spitfire superchargers and force compressed air to the jet tips. The engine also powered two pusher propellers mounted at the ends of a short wing, to provided yaw control and forward thrust.

The Jet Gyrodyne's first transition flight took place successfully on 24 March, 1955. It proved to be under-powered with heavy fuel consumption, limiting flight duration to 15 minutes. But it showed that the concept worked.

Up until this point, government funding for the Rotodyne had been through the defence budget. But in 1956 the Ministry of Defence declared that the funding would be cut, as neither the Air Force nor the Army had any further interest in it. This effectively meant that all further development costs would have to be met by the private sector.

Discussions continued with the MoD through 1956, until it finally conceded funding until the end of the year, providing three conditions were met. These were that the Rotodyne proved to be technically successful, that Fairey and English Electric fund a substantial proportion of the development costs of the airframe and engine adaptation, and, most crucially, the securing of firm orders from BEA and others. It was this last proviso that was to ultimately prove the death knell for the Rotodyne. Fairey had little option but to agree, confident that once the prototype was flying substantial orders would come in.

Bearing a military serial number XE521, the prototype Rotodyne's first flight took place on 6 November, 1957, from White Waltham airfield - in the hands of Fairey's chief test pilot Ron Gellatly. It carried out its first transition to horizontal flight on 10 April, 1958.

Right from the start, the Rotodyne proved to be everything it had been hoped it would be. The sheer elegance of what was the largest helicopter of its time wowed the crowds at the 1958 SBAC 5 show at Farnborough. Gellatly put on a stunning show of vertical take-off under power of the tip-jets, translating to level flight with only the quiet whine of the Eland engines as he demonstrated its manoeuvrability; then reigniting the tip-jets to finish off with a near-vertical landing approach.

This resulted in an order for a single Rotodyne, with options for two more by Okanagan Helicopters of Vancouver Canada for use on a triangular route between Vancouver, Victoria and Seattle. Interest and negotiations also followed with New York Airways for the purchase of five Rotodynes to operate between the Pan-Am building in Manhattan, New York and its outlying airports. New York Airways had calculated that the larger 65-seat Rotodyne Z could reduce its operating costs by 50 per cent compared with the existing conventional helicopters it was using.

The Rotodyne established a new world speed record for convertiplanes - of 191mph - in January 1959, exceeding the previous record by more than 30mph. It followed this up later that year with another acclaimed display at the Paris Air Show. The Rotodyne demonstrated its heavy lift capability by picking up a 100ft prefabricated bridge and carefully placing it to span a river. At the SBAC airshow in September that year, the Rotodyne flew in and deposited 40 uniformed nurses onto the grass beside Farnborough's runway.

The only source of criticism was the noise produced by the tip-jets when lit. This was clearly unacceptable when taking off or landing under power in built-up areas of a city. Indeed, several prospective buyers had commented adversely on the noise. BEA had made it a pre-condition that it be reduced to acceptable levels before it placed an order.

Fairey had worked on this problem from the start and managed to reduce the decibel level by modifying the jets. On two occasions, the company had flown the Rotodyne from London's new Battersea heliport on the Thames, and it had made several flights over London suburbs without any complaints being raised by the surrounding population. If fact, the only call that was recorded was a query asking '...was that really the Rotodyne?'.

Politics

Having proved its technical viability, the Rotodyne's commercial success clearly depended on the development of the larger Rotodyne Z, which would be able to attract orders from the military as well as the commercial sector. But the development of a new aeroplane was, and still is, an expensive business. Fairey estimated that development of the larger Rotodyne was going to require a further £10 million and returned to the British government to ask for additional funding. With the successful demonstrations of the prototype Rotodyne, Fairey had a good case. But the funding was not forthcoming without restrictions, among which was the requirement of a firm order from BEA.

Meanwhile, Duncan Sandys, minister of aviation, was seeking to consolidate the multitude of British aeroplane manufacturers, all of which were vying for the same contracts while being financed by government money. By selectively withholding government subsidies and support, he was able to force companies to sell off selective parts or merge with other firms. The Rotodyne was something of a one-off development in the rotary wing aircraft industry where the conventional helicopter was the norm. The major manufacturer of rotary wing aircraft was Westland Helicopters, which produced them under licence using engines and technology developed by US firm Sikorsky.

During 1959 and 1960, Westland took over the rotary wing divisions of Saunders-Roe and Bristol Aircraft, leaving only Fairey to operate independently. Sandys withheld further contracts from Fairey and made it plain that future funding for the Rotodyne would only be forthcoming if it merged its aircraft division with Westland. With the prospect of no further military contracts, including those for fixed-wing aircraft, Fairey was left with little choice but to comply.

With the merger completed, development costs for the Rotodyne Z were agreed at £5.5 million, but these costs were escalating as fast as the projected size of the aircraft. To make the Rotodyne an economic success and attractive to the military, it would have to capable of carrying 75 passengers or fully equipped troops, and able to lift small military vehicles. To do so, the proposed version was to have a main rotor span of 109ft, 75ft span wings and an all-up weight projected to be 58,500lb.

The Napier Eland engines powering the prototype had never quite delivered their estimated full power, and the larger model was going to require considerably more. Fairey returned to Rolls-Royce with a view to using its new Tyne turboprop engine, which at the time was the most powerful of its type available. Even this, however, would not provide sufficient power, and various remedies were considered, including fitting supplementary engines behind the Tynes to drive compressors for the main rotor. The government still insisted that development costs be shared with the industry, which would mean an investment by Rolls-Royce in excess of £9 million. The company declined the opportunity.

Only part of the projected development costs were guaranteed by the government, and BEA was insisting that all of its previous requirements, including the noise issue, be resolved before it placed a firm order. By 1961, Westland was left in something of a quandary. It faced developing a technology that was far removed from the conventional helicopters which were the mainstay of its business. And it could not finance the complete costs, even though the Rotodyne promised to be a commercial success and would exceed the capabilities of the helicopter.

The noise issue came to the fore again, and has been cited as the reason for the cancellation of the project. Although there was no denying the Rotodyne was noisy, its critics largely ignored the facts. Development had continued throughout, and Fairey had reduced the decibel level to 96 db at a distance of 600ft. At the time of cancellation, further modifications were in hand that would have reduced it further into the 80s db. Coupled with this, techniques were developed, involving vertical take-off and steep approaches during landings, which reduced the noise footprint while the rotor was under power. In fact, once in forward flight, the Rotodyne was quieter than contemporary jet aircraft or helicopters.

The final straw that broke the Rotodyne's back came when the government declined Westland's quoted estimate for the delivery of 12 Rotodynes for the RAF, quoting it as having little need for the aircraft. Funding for the Rotodyne was stopped in February 1962, and the whole project cancelled by Westland a month later.

Fearful of adverse criticism of the amount of money spent on the project, the government ordered the Rotodyne to be broken up and scrapped, and along with it went all the tools and drawings. To this day the only remains are a small section of the fuselage and a couple of examples of the tip-jets. These are preserved at the British Rotorcraft Museum at Weston-Super-Mare. Some of Fairey's promotional films were saved by concerned individuals, but little remains of the record of this fine machine.

Anyone who observed the Rotodyne in flight would have seen an elegant aircraft that could hardly fail to impress. The Rotodyne was ahead of its time and the only commercially viable aeroplane of its type. If different decisions had been made, the unobtrusive whine of the turboprop engine may have been the norm in today's skies, instead of the noisy clatter of the helicopter.

It was truly a missed opportunity.


1 Coogan's Bluff was the precursor to the Dirty Harry series of films. The title character was played by film superstar Clint Eastwood.
2 Now the MetLife Building.
3 Turboprop: a 'turbojet' jet engine that provided thrust through a propeller via a reduction gearbox.
4 Yaw: Movement in the horizontal, left/right directional plane.
5 SBAC, the Society of British Aircraft Constructors.

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Entry Data
Entry ID: A34788667 (Edited)

Written and Researched by:
Deke

Edited by:
Tufty - Squirrel (Un)Extraordinaire


Date: 12   June   2008


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Referenced Guide Entries
Aircraft
Helicopters
The Supermarine Spitfire
Atmospheric Pollution from the Internal Combustion Engine in the Urban Environment


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BBC Science & Nature


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