Fairey Rotodyne

The Fairey Rotodyne was a 1950s British compound gyroplane designed and built by Fairey Aviation and intended for commercial and military applications. 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.

Fairey Rotodyne
Fairey Rotodyne

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.

Below is a promotional film produced by Fairey, extolling the benefits of this revolutionary aircraft

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.

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?’

via Fairey Rotodyne – Wikipedia, the free encyclopaedia. and 

and

via Fairey Rotodyne – an Opportunity Missed

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s