The first of three compound-helicopter prototypes, called the Gyrodyne, had its maiden flight on December 7, 1947. Powered by a single 520-hp Alvis Leonides radial engine, it set a helicopter world speed record of 124.3 mph on June 28, 1948. Unfortunately, it was destroyed 10 months later when its rotor head disintegrated in midair, killing the pilot and flight observer.

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As a result of that tragic accident, Fairey completely revised its compound helicopter project. Four years elapsed before the second prototype, known as the Jet Gyrodyne, appeared. That aircraft was characterized by an entirely new transmission system that was intended to simplify and strengthen the rotor. Contrary to its name, the Jet Gyrodyne was actually powered by the same type of reciprocating engine as that installed in the original prototype. Instead of transmitting its power through a mechanical gearbox, however, pressurized air was pumped into miniature jet nozzles located in the tips of the rotor blades, by means of a pair of compressors. The compressors, modified from surplus Supermarine Spitfire superchargers, were driven by the engine. Fuel was delivered by centrifugal force to jet burners at the tips of each rotor. Power for level flight, and for yaw control in the helicopter mode, was provided by a pair of controllable pitch pusher propellers mounted in the wingtips.

Flown for the first time in January 1954, the Jet Gyrodyne proved to be somewhat underpowered and could only carry enough fuel for a 15-minute flight, but it served as the experimental model for a larger and more ambitious project that was being developed concurrently–the Fairey Rotodyne.

Outwardly, the Rotodyne looked like a cross between a helicopter and an airliner–which, for all intents and purposes, was exactly what it was. The aircraft had a wingspan of 48 feet 6 inches and an overall length of 58 feet 8 inches. The production version was intended to carry 57 passengers.

The Rotodyne was powered by a pair of 2,800-hp Napier Eland turboprop engines mounted in nacelles slung underneath the wings. The engines drove a pair of four-bladed, controllable-pitch, tractor propellers that, as in the Jet Gyrodyne, doubled as yaw stabilizers when the aircraft was operated as a helicopter. A 90-foot-diameter rotor was mounted atop a tall fuselage pylon. The rotor was powered by jets installed at the tips of its four blades, similar to the arrangement used on the Jet Gyrodyne. Each engine provided compressed air for a pair of tip jets on opposite sides of the rotor.

Most of the power from the Rotodyne’s turboprop engines was diverted to nine-stage axial compressors located behind them for vertical takeoff. The compressed air produced was then ducted to the jet nozzles in the rotor tips, where it was combined with fuel and ignited. A small amount of residual power was made available to the propellers for yaw control. Once the aircraft had gained sufficient altitude and speed, the compressors were disconnected by means of hydraulic clutches and all engine power was then diverted to the propellers.

Once the Rotodyne was in forward flight, about half of its lift was generated by the autorotating rotor, and the remainder by its wings. Landing could be accomplished in autorotation, or by engaging the compressor’s clutches and relighting the tip jets for a conventional helicopter landing. The flight crew could accomplish, with practice, the transition between helicopter and autogiro modes in approximately 30 seconds.

The future of the Rotodyne seemed assured in the mid-1950s. Britain’s regional carrier, British European Airways (BEA), had issued a specification for just such a short-haul/medium-haul aerial ‘bus’ in December 1953. Other commercial operators were also showing interest. Development was slow, however. It was not until November 6, 1957, that the prototype was finally flown, and then only in the helicopter mode. Transition between helicopter and autogiro flight was not achieved until April 10, 1958.

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