The Early Years
The Lynx was the first completely new major British helicopter since the Saunders-Roe Scout and the Bristol Belvedere of the late 1950s. While the licence production of Sikorsky designs had been a money-spinner for many years, Westland's future in a collaborative Europe benefited from starting out with a fresh sheet of paper. The association of Westland and Aerospatiale in the form of Heli-Europe Industries owed its formation at least partly to this initiative. This joint organisation had behind it the technical and commercial resources of Europe's two largest helicopter industries, Aerospatiale with 8,100 people and Westland with 6,900.
The military requirements for the Lynx were sufficiently stringent to keep the two design teams stretched, but at the same time allowed a completely orthodox layout to be chosen. Actually the idea of the Lynx goes back to the early 1960s when, after the amalgamation of the British helicopter industry under the Westland banner, a long range plan was made to reduce the number of types of helicopters then in production. Up to that time the rotary winged needs of the British armed services had been met by no fewer than six basic types: Skeeter, Sycamore, Scout/Wasp, Whirlwind, Wessex and Belvedere (the Wessex itself going into several versions). The gradually tightening purse-strings particularly for non-combat aircraft made some form of rationalisation desirable, and Westland planned a range of four helicopters to meet all the needs then foreseen, though not necessarily formally stated.
The largest of the proposed helicopters, the WG.1, was a Belvedere replacement weighing 35,000lb (15,875kgs). Next down in size was the WG.4, a Wessex successor and at 17,000Ib (7,711kgs) half the weight of the WG.l. Third in the series, the WG.3 was planned as an 8,000lb (3,628kgs) squad-carrier for the British Army, while the smallest of the family was the 2,500lb (1,133kgs) WG.l2 LOH, a light observation helicopter.
Except for the largest helicopter, this scheme carried through quite well, despite inevitable changes in the political climate. Britain still had no 35,000lb (15,875kgs) helicopter, though the RAF had made two unsuccessful attempts to buy a 50,000lb medium-lift helicopter. The largest rotorcraft built in Britain was the 21,500lb (9,752kgs) Sea King and its land based derivative the Mk 4 Commando and these equated to the WG.4. The 8,000lb Anglo-French Lynx exactly followed the WG.3 as the WG.l3, while the WG.12 LOH became the Gazelle and provided the eyes for the armies of the two countries.
The Lynx was in fact was a direct replacement, in terms of gross weight and role, for the RAF's Whirlwind and the Navy's Wasp (role-wise). After studying the histories of a number of helicopters, particularly the Whirlwind, Westland felt that improvements could be achieved in maintenance, reliability, speed (the specification called for a sustained maximum of 160kt), ease of ground handling and minimum re-assembly time after ferrying by air. These substantially affected the design in many important areas. For example, the choice of two 720 shp Pratt & Whitney Canada (formerly UACL) PT6 engines driving a modified Whirlwind gearbox appeared to offer the cheapest and most reliable powerplant installation. The Bristol Belvedere rear rotor, with a slightly modified hub to improve the control power appeared promising. However, it was argued that the time and money spent in the maintenance of a conventional, articulated rotor could be greatly diminished by dispensing with mechanical hinges and allowing the natural elasticity of the hub and rotor to provide the flap and drag movement needed. Accordingly a flexible hinge rotor system was, in the early stages, adopted as the design goal and developed in parallel with the articulated rotor, which was pursued as a back-up scheme.
The WG.3A, as the helicopter was called, was shown to the Services in 1960. The main adverse comments concerned what they regarded as the inadequacy of the 3,000lb (1.360kgs) slung payload proposed and there were strong views that this should be increased to 4,000lb in order to carry a Land Rover. The scaled-up design to accommodate the extra load emerged at 11,000lb (4,989kgs) gross weight, and brought about powerplant difficulties. There was no 800 shp engine in existence or proposed and the choice of a coupled Gnome installation (1,200 shp each) was over-powerful and uneconomic. As time went by still more increases in payload were called for, however, and as the design was beginning to approach the WG.4 Wessex replacement in size, a return was made to the original WG.3 design. To "peg" the new proposal it was redesignated WGl3.
The convenience of an 8,000lb helicopter was gaining favour in the British Army, and in 1964 a draft specification defined the requirements of such a vehicle for reconnaissance, command post, liaison, troop deployment, supply-carrying and casualty evacuation duties, coupled with the carriage of offensive and defensive armament.
The engine situation remained a major difficulty. Although the 720 shp PT6 was known to have plenty of stretch built into it, P&W (UACL) was unable to guarantee the required growth to meet the timescale. Single Rolls Royce Gnome and Gazelle engine installations were insufficiently powerful, while twin arrangements - as mentioned earlier - gave too much power. At the same time Westland was becoming convinced of the superiority of twin engined installations from the vulnerability and reliability aspects. A stretched Astazou (as fitted to the Aerospatiale Gazelle) was considered, but again would have delayed the programme. Also, Westland and the Ministry of Aviation committees undoubtedly felt that the only acceptable choice laid between a British, or at least part-British engine and an American powerplant which would guarantee very wide international acceptance and which could form the basis of a commercial or technical agreement. Continental had a powerplant, the T72, which had been proposed in coupled form for the Bell UH-l. The scheme had fallen through and, in the absence of any other application, the engine had been shelved. However, with 770shp, a 60lb saving over the PT6 and a slightly better specific fuel consumption, the US powerplant appeared promising. In September 1966 Rolls-Royce therefore discussed with Continental the supply of T72s and also investigated the possibility of uprating it. However, the pressures for a completely new British engine tailored to the Lynx were intensified by an increasing realisation of the changes needed to adapt the American engine. Also the substantially larger market offered by the Anglo-French helicopter alliance now on the horizon could now justify a new powerplant, and so the 900 shp BS.360 project (later named the Gem) by Rolls-Royce was adopted, despite some reservations by Westland about the risks of embarking on a completely new engine at such a relatively late stage.
In 1966 discussions began with the Royal Navy about a replacement for the Wasp. This little 5,500lb (2.500kgs) ASW helicopter had already been in service for three years and the Naval staff was impressed with the potential of small shipboard helicopters for this purpose. They felt, however, that a larger helicopter would considerably extend the performance. The RN pioneered small ship borne helicopter techniques and to this day has accumulated most of the world's operating experience with them. The Lynx generally suited the Navy's requirement except that the rotor diameter - 49ft, set by the Army's maximum allowable engine-out vertical descent speed was too large to allow acceptable clearance from the ship's structure while landing. The Navy called for a maximum rotor diameter of 36ft, which was not only incompatible with the Army requirements, but would have needed a considerable power increase to drive. A 44ft rotor was eventually selected when the Army's relaxed hover-failure requirement was matched by the Royal Navy's acceptance of reduced clearances. The Navy at that time were not thinking ahead to new larger classes of warship that could have accommodated the larger rotor diameter. This reduction in rotor diameter obviously reduced some capability and capped future growth until the advent of the ‘BERP’ blades in the early 90s.
In parallel with the British exercise, France was investigating a similarly sized helicopter for its Army and Navy. The requirements were much the same as Britain's except that the French rotor size was limited to 42ft, which once again raised the question of engine suitability, while their three-seat armed reconnaissance helicopter looked like calling for a modified airframe. The Anglo-French helicopter agreement of July 1967 formalised the requirements for five versions of the WG.13 (three for the British armed services and two for the French Army and Navy), together with those of the Puma and the SA.340 (now the SA.341 Gazelle) LOH as common equipment for the two countries. Britain was nominated leader of the WG.13, France of the Puma and Gazelle. At that time the service introduction of a utility WG.13 for the British Army was envisaged for late 1972, with that of the French aircraft following a year later. Tentative schemes for the British Army gunship variant had already been dropped and plans for the French attack helicopter with an extensively modified airframe also came to nought. Ironically, Agusta; a licensee with Westland, utilised a lot of the development work for the tandem seat attack helicopter and produced the A-129 Mangusta (albeit in a simpler form than the original WG-13 Gunship). The delays that followed reflected the changing requirements (with their inevitable effect on the flight development programme and the number of aircraft taking part in it) and the increased time needed to bring a substantially more advanced aircraft and engine into being. As is usually the case, developing a complex platform that has to fit several very different roles for different customers proves nigh on impossible and a compromise is the result. This compromise blunts the original individual requirement but generally costs a lot more than procuring individual specific platforms in the long run. This is due to highly modifying each platform later in its life when those specific requirements are called for. On the one hand, the Royal Navy wanted a dedicated Anti Submarine Warfare helicopter and the British Army wanted a Battlefield Utility Helicopter as well as a dedicated Attack Helicopter (from lessons learned by US Forces in the ongoing Vietnam war).
The main requirements for the WG.13, both before and after the liaison with France, remained the same. They were, in order: reliability and robustness, ease of maintenance, compactness and strategic mobility, performance, all-weather and night capability, versatility, ease of concealment (i.e. good ground handling), and crew and component protection.
Three of these; reliability, ease of maintenance and performance (the aircraft was required to be "fast and manoeuvrable") were very largely responsible for the decision to settle for the hingeless rotor, but one which was "soft" enough not to depart radically from the well known behaviour of articulated rotors and which therefore did not constitute an unreasonable technical risk. To achieve great torsional stiffness the blade was designed around a rectangular section stainless-steel spar, with leading and trailing edges bonded to it. The dynamic behaviour of the hub dictated that the weight of the blades be concentrated towards the root-end, calling for a certain "weight taper" over the blade. This was realised by tapering the chord of the spar and its thickness/chord ratio (though the blade itself was of constant chord). To stretch-form the stainless-steel sections a special machine was ordered from America and was installed at Yeovil. The production of reliable bonds took a long time, but eventually a process used by Bell for its helicopter blades was adopted. The specification called for a blade life of 2,500 hrs and a transmission life of 1,200hr.
Most of the flap - the vertical motion of the blades takes place within the flat star-shaped titanium hub, while the "in-plane" motion (the movement of the blades with respect to one another in the plane of rotation) is governed by the stiffness of the circular-section titanium extension arms which connect the blades to the hub. Westland was responsible for the basic aerodynamic and structural aspects of the rotor, but the detailed mechanical design and the construction of the hub, were allocated to Aerospatiale.
The technologically advanced gearbox design came about through the necessity to keep the overall height of the aircraft down to ensure it could be fitted in to the back of a C-130 Hercules and keeping to the original requirement of ensuring it could be operational within two hours after being unloaded. The cabin height was a non moveable factor so this left very little room for the designers to play with. At that time, this lead to a major design headache. Considering the twin engine layout (behind the gearbox) and the relatively large loads that would be applied to this small helicopter, the design team came up with a very compact (low in height), strong and ingenious design. To this day, the gearbox design is still considered to be a masterpiece. Evidence of this can be witnessed in the fact that the gearbox (with some modifications) was used in the larger WG-30 (12,800lb/5,806kg) and a development of the original gearbox is used in the 6,000kg AW159 Wildcat.
The first of 12 Lynx prototypes ordered in April 1968 (at one stage during the previous year there were to have been no fewer than 16) flew on March 21, 1971 (XW835) and the batch was completed in June 1974. An additional aircraft (XZ166) was built to take the place of a prototype lost (XX469) during early trials. The first naval prototype crashed on 21 November 1972. This was the first aircraft to have the folding tail design but the coupling unfortunately failed in flight. The first five prototypes were painted in obvious colours for ease of recognition during the early days of the test program,
From the early test flights, there had been two main problems: a shortfall in the performance of the early flight engines and persistent rotor vibration. It was no surprise to find that the first home-designed engine to emerge from Leavesden since the early 1950s would be free from trouble. But the difficulties with low power levels at rated temperatures, excessive oil consumption and compressor surging gradually yielded to rectification action. The resulting delays in the supply of engines during 1971 as the flight development programme got under way spurred the French Government into insisting on a PT6 fallback programme. Low power and excessive oil consumption plagued the Gem engine throughout its operational life and it was only when the LHTEC T800 was fitted to the export Super Lynx 200/300 and AH9A (under an Urgent Operational Requirement for Op HERRIC) did the performance and reliability become realised – albeit some 25 years later for the export Lynx and 37 years later for the British Army. Vibration generated by the rotor still remains but the fitting of a Main Rotor Head Vibration Absorber (‘Bonk’) on top of the rotor head reduces this. Even the brand new AW159 Wildcat (with the same head and Composite Main Rotor Blades) is still fitted with the ‘bonk’. The relatively stiff, hingeless rotor generates quite a sharp resonance in the airframe, accentuated by the unusual transverse trunnion mounting of the main gearbox. A number of schemes for locally stiffening the cabin and tail-rotor pylon were flown on the resonance test aircraft (XW837?) and some vibration absorption was achieved by repositioning of components such as the battery. In simple terms, a conventional articulated head arrangement absorbs a lot of these vibrations so these sharp resonances aren't felt through the airframe. The semi rigid arrangement on the Lynx is akin to a Formula 1 Grand Prix car suspension in that it is very stiff to allow for maximum responsivness and feedback but the byproduct of this is the ride is harsh.
There was considerable emphasis on the naval Lynx, which entered service at an early stage and needed considerably more systems development than the Army versions. Three naval prototypes were flown at Yeovil (XX510 and XX910 with XZ166 replacing the lost XX469 Naval version) and two at Marignane (XX904 and XX911). Weapon trials were done with AS.12 missiles and Mk 46 torpedoes. Westland was very satisfied with the Ferranti Seaspray radar, which worked well though it was slightly susceptible to vibration. Westland realised quite early on that the export market would be predominantly for a naval Lynx. To that end, the naval Lynx has been the most numerous and one of the most successful small ship borne helicopters in the world reaching more than 17 export customers. The story for the skidded Army version is not so successful in the export market. Only one country took delivery of this version; Qatar in 1978. The joint Qatari Police/Air Force purchased three HC Mk 28s but these were returned to Westland in 1990 finding them under powered in the hot Middle East climate. Stories of them being flown in Acc Drive (only one engine driving) cannot be substantiated and probably remains an 'urban myth'.....
Westland also tried unsuccessfully to market the Lynx in the civil sector around 1975. This was to have had a slightly stretched cabin with uprated Gem engines. Westland built a demonstrator and named it the Westland 606 (XW836). However, to stimulate sales in the North American market, Westland dusted off the 1970 PT6 Lynx configuration in the hope that the familiar PT6 powerplant would be more acceptable to potential US customers. The hope was that a US agent could initially reconfigure a military version and push it towards the oil rig and VIP markets. Unsurprisingly, there were no takers for this complex, expensive highly specialised military aircraft.
Total number of Lynx built (all versions) ; 426.
Naval versions; 280.
Army versions; 146 (including 3x HC28s)