On 4 December 1947, the first of the two prototypes of the Gyrodyne — a compact and streamlined helicopter weighing just over 2000kg — took off from White Waltham airport. With a 525hp Alvis Leonides radial engine, the power from which could be transmitted in variable ratios to a three-blade rotor just over 15m in diameter and to the anti-torque propeller on the starboard tip of the stub wing, the Gyrodyne behaved like a helicopter, but the same propeller also provided the necessary thrust for fast flight, when the aircraft looked almost like an autogyro. The British compound aircraft set a world speed record by flying at 200km/h on 28 June 1948. An extensively modified second prototype, renamed Jet Gyrodyne, flew in January 1954; it had two blade-tip jets, fed with air from two compressors driven by the usual Alvis Leonides radial.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
In April 1946 Fairey announced a private-venture project for a rotary-wing aircraft, to be built to a new concept originated by Dr J. A. J. Bennett who had joined the company the previous year. Dr Bennett had assumed control of the Cierva Autogyro Company in 1936, following the death of Juan de la Cierva, and Bennett's ideas were based on the combination of a lifting rotor plus an asymmetric propeller mounted on a stub wing, which would counteract yaw and provide thrust, lessening the loading on the rotor.
A government contract to Specification E.4/46 was awarded for two prototypes, and the first Fairey Gyrodyne was exhibited almost complete at White Waltham on 7 December 1946, and continued to build up flying time until March 1948 when it was dismantled for a thorough examination. The second prototype, basically similar to the first but with more comfortable interior furnish- . ings befitting its role as a passenger demonstrator, was flying by the time of the next SBAC Display, in September 1948, at Farnborough.
The first Gyrodyne was re-assembled and, following further test flying, it was decided to make an attempt on the world's helicopter speed record in a straight line. On 28 June 1948, flown by test pilot Basil Arkell, the Gyrodyne made two flights in each direction over a 3km course at White Waltham, achieving 200km/h, enough to secure the record. An attempt was to be made in April 1949 to set a 100km closed-circuit record, but two days before the date selected a rotor head fatigue failure resulted in the crash of the aircraft at Ufton, near Reading, killing the pilot, F. H. Dixon, and his observer. The subsequent grounding of the second Gyrodyne for an investigation was only to be expected, and the aircraft did not appear again until 1953; by then it had been completely redesigned to provide data on Fairey's big project, the Rotodyne.
D.Donald "The Complete Encyclopedia of World Aircraft", 1997
The story of the compound, or convertible, helicopter endeavours of the Fairey company should really be told as a continuing 15-year saga of experimental development, testing, successes and failures. The Gyrodyne, Jet Gyrodyne and Rotodyne stemmed from some fairly fundamental re-thinking about helicopter/autogyro principles and somewhat similar philosophies lay behind each. For simplicity, and so as to retain the near-chronological pattern of other sections, the three aircraft and the Ultra-light Helicopter — in which use was made of much of the experience gained during developments leading to the Jet Gyrodyne and Rotodyne — are separately dealt with.
At the risk of irritating the initiated by over-simplification, it is necessary, by way of a start, to look quickly at the principles behind the two basic types of rotary-wing aircraft which had already demonstrated some practical success before the 1945—46 period, when the details of the Gyrodyne were being worked out. In the autogyro, a freely revolving rotor provided lift in autorotation down to very low airspeeds; propulsion was by engine-driven propeller. During later development, means of short-period vertical ascent and descent were provided by a power-drive to spin up the rotor and/or by using the kinetic energy of the rotor to provide direct lift. In the helicopter, the rotor was continuously power-driven, providing both lift and, when tilted forward, the means of propulsion. Control in yaw was maintained by altering the pitch of a powered lateral-thrust propeller in the tail — hence the still-familiar 'penny-farthing' configuration of many helicopters a quarter of a century later.
In simplest terms the Gyrodyne (= gyratory aerodyne) was designed to take advantage of the favourable features of the autogyro and the helicopter while avoiding some of their respective limitations. The aim was to obtain greater operating efficiency while reducing the loads on transmission and rotor systems which were then considered by many technicians to be severely, if not dangerously, stressed throughout each flight. By using a propeller for normal propulsion, as well as for control in yaw at low speeds, the 'balance of power' was reversed so that rotor and transmission loads were greatly reduced during most of the time while airborne. The fact that the rotor was not being used for propulsion meant that this would be operating for long periods within or near the autorotative pitch-range and with a lower disc loading.
In the Gyrodyne the rotor continued to be the sole means of sustentation, apart from the marginal lift provided by the stub wings in cruising flight, and was continuously power-driven, but, except when hovering or in slow-speed flight, the greater part of the available power went to the propeller. So that this could provide propulsive power while retaining its use for anti-torque and slow-speed yaw control, it was moved from the tail to an equivalent azimuthal location at the end of the starboard stub wing, where it was still far enough from the axis of the rotor to absorb minimum power when used for control in yaw. An important incidental advantage of the smaller angles of blade incidence and reduced loading on the non-propulsive rotor was that higher cruising speeds were possible before the onset of the stall for the retreating blade — an inevitable event which limited, and still limits, if only because of vibration, the speed of a conventional helicopter.
In preparation for the move into rotary-wing development, Fairey had built up a strong helicopter team, led by Dr J. A. J. Bennett, who brought the Gyrodyne proposal to the company in August 1945, and with Sqn Ldr Basil H. Arkell, who joined in January 1946, as test pilot. The first official announcement of the project, a private-venture to specification E.4/46, was made on 3 April, 1946, though no information was then given; at that time the Gyrodyne was known as the FB-1 (Fairey-Bennett One).
Although the broad concept was relatively simple, the translation of this concept into working hardware involved a considerable effort in engineering and other ingenuities. An idea of the amount of 'machinery' in the prototype can be gathered from the fact that nearly 50 per cent of the empty weight was contributed by the powerplant and transmission systems. In these there were four primary units: a 520hp Alvis Leonides nine-cylinder radial engine, with its mounting and systems; a main gearbox with first-stage reduction for the rotor and propeller drives, a clutch and freewheel; an upper gearbox with double epicyclic reduction gear, plus the rotor brake; and a gearbox in the starboard wingtip with the reduction-gear and pitch-changing mechanism for the propeller.
The Gyrodyne had an ingenious and comparatively straightforward control system. The rotor articulation was designed so that the collective-pitch changed automatically according to the power being applied. The throttle lever was therefore designed to be similar in length, movement and effect to the collective-pitch control of a conventional helicopter and was pulled up to increase power and lift. Fore-and-aft and lateral control was provided by a form of tilting head; although the rotor-hub axis did not physically tilt, as in the case of most autogyros, a similar effect was produced by tilting the rotor head in relation to the axis. Stick-shake was eliminated, using suitable safeguards, by controlling rotor-tilt through irreversible hydraulic jacks.
Not everyone, it appears, was entirely happy about these logical and ingeniously straightforward methods of control. The Ministry of Supply asked for an alternative rotor-hub arrangement to be designed with overriding collective-pitch and cyclic-pitch blade-angle control so that this could be compared on test with the existing system. This normal helicopter control system was required mainly for trimming purposes at altitude and to provide more positive control when hovering after an autorotative approach.
Yaw control was maintained, as with other helicopters, by altering the pitch of the propeller through conventional pedals. Rudders were fitted for directional control during autorotative flight after power failure. An 'elevator' in the form of a large trim tab, was used to adjust the fuselage attitude when cruising.
By September 1947 the prototype, G-AIKF (provisionally serialled VX591), was complete enough to be exhibited on the ground during the SBAC Display at Radlett in Hertfordshire. After 85 engine-running and 56 rotor-testing hours the first untethered flight was made at White Waltham by Basil Arkell on 7 December. Testing continued, with longer flights at gradually increasing speeds, until March 1948, when the Gyrodyne was dismantled for examination. By then a second prototype, G-AJJP, had been completed.
Following re-assembly and further tests, G-AIKF was prepared for an attempt on the international helicopter (Class G) speed record in a straight line. This had long been held unofficially by the German Focke Achgelis Fa 61 and more recently a Sikorsky R-5 had also been unofficially timed at 185km/h in the USA. Two eastward and two westward flights over a 3km course at White Waltham were made by Arkell on 28 June, 1948, at an average speed, for the best pair of opposing runs, of 200km/h. In addition to being a world record, this was the first British national record for any helicopter. The course was along the London-Reading railway line on the north side of the aerodrome, and, as it happened, was 45 degrees off a fairly strong wind, so the probability is that a speed of 225km/h might have been achieved in calmer conditions.
Some ten months later an attempt to set up a 100km closed-circuit record ended in tragedy. During trials on 17 April, 1949, two days before the attempt was to be made, the first prototype Gyrodyne suffered a fatigue failure in the rotor head and crashed at Ufton, near Reading, killing F. H. Dixon and his flight observer, Derek Garroway. Dixon, who joined Fairey in 1936 and was chief test pilot from 1942 to 1945, had since been involved in less arduous flying and other duties, but had also shared much of the development and demonstration flying of the Gyrodyne with Basil Arkell.
The investigation following the accident led to a protracted period of investigation and fatigue-testing, and development ceased. The second prototype was grounded and was afterwards very much modified to reappear more than four years later as the Jet Gyrodyne, the test vehicle for the Rotodyne.
H.A.Taylor "Fairey Aircraft since 1915", 1974
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