The Aérospatiale Gazelle originated in a French Army requirement for a lightweight observation helicopter intended to replace the Aérospatiale Alouette III; early on in the aircraft's development, the decision was taken to enlarge the helicopter to enable greater versatility and make it more attractive for the export market.
1966, Sud Aviation began working on a light observation helicopter to replace its Alouette II with five-person seating. The prototype SA 340 flew for the first time on 7 April 1967, initially with a conventional tail rotor from the Alouette II.
The second prototype's tail was replaced in early 1968 with the distinctive fenestron tail. Four SA 341 prototypes were flown, including one for the British firm Westland Helicopters. On 6 August 1971, the first production, Gazelle, conducted its first flight. On 13 May 1967, a Gazelle demonstrated its speed capabilities when two world speed records were broken on a closed course, achieving speeds of 307 km/h over 3 kilometres and 292 km/h over 100 kilometres.
Early on, the Gazelle had attracted British interest, culminating in issuing a major joint development and production work share agreement between Aerospatiale and Westland. The deal, signed in February 1967, allowed the production in Britain of 292 Gazelles and 48 Aérospatiale Pumas ordered by the British armed forces; in return, Aérospatiale was given a work share in the manufacturing programme for the 40 Westland Lynx naval helicopters for the French Navy. Additionally, Westland would have a 65% work share in the manufacturing and be a joint partner to Aérospatiale on further refinements and upgrades to the Gazelle. Westland would produce 262 Gazelles of various models, mainly for various branches of the British armed forces, Gazelles for the civil market were also produced.
In service with the French Army Light Aviation (ALAT), the Gazelle is used primarily as an anti-tank gunship (SA 342M) armed with Euromissile HOT missiles. A light support version (SA 341F) equipped with a 20 mm cannon is used, as well as anti-air variants carrying the Mistral air-to-air missile (Gazelle Celtic based on the SA 341F, Gazelle Mistral based on the SA 342M). The latest anti-tank and reconnaissance versions are called Gazelle Viviane and carry the Viviane thermal imagery system. The Gazelle is being replaced in frontline duties by the Eurocopter Tiger but will continue to be used for light transport and liaison roles.
It also served in various roles with all branches of the British armed forces: the Royal Air Force, the Royal Navy (including supporting the Royal Marines), and the British Army. The British forces used four versions of the Gazelle.
The SA 341D was designated Gazelle HT.3 in RAF service, equipped as a helicopter pilot trainer (hence HT). The RAF used the SA 341E for communications duties and VIP transport as the Gazelle HCC.4. The SA 341C was purchased as the Gazelle HT.2 pilot trainer for the Royal Navy; the Squirrel HT1 has replaced training variants. The SA 341B was equipped to a specification for the Army Air Corps as the Gazelle AH.1 (from Army Helicopter Mark 1).
The Gazelle proved to be a commercial success, which led Aerospatiale to quickly develop and introduce the SA 342 Gazelle series, which was equipped with uprated powerplants. Licensed production of the type did not just occur in the UK; Egyptian firm ABHCO also conducted domestic manufacturing. Yugoslavian production by SOKO reportedly produced a total of 132 Gazelles. As the Gazelle became progressively older, newer combat helicopters were brought into service in the anti-tank role; thus, those aircraft previously configured as attack helicopters were often repurposed for other secondary support duties, such as an Air Observation Post (AOP) for directing artillery fire, airborne forward air controller (ABFAC) to direct ground-attack aircraft, casualty evacuation, liaison, and communications relay missions.
Originally developed as a replacement for Aérospatiale's Alouette helicopter, some aspects of the Gazelle, such as its purpose and layout, were based on the previous model. The Gazelle featured several important innovations. It was the first helicopter to carry a fenestron or fantail; this is a shrouded multi-blade anti-torque device housed internally upon the vertical surface of the Gazelle's tail, which replaces a conventional tail rotor entirely. While requiring a small increase in power at slow speeds, the Fenestron has advantages such as being considerably less vulnerable and having low power requirements during cruise speeds. It has been described as "far more suitable for high-speed flight". The fenestron is likely one of the key advances that allowed the Gazelle to become the world's fastest helicopter in its class.
The main rotor system was initially based upon the rigid rotor technology developed by Messerschmitt-Bölkow-Blohm for the MBB Bo 105; however, due to control problems experienced while at high speeds upon prototype aircraft, the rigid rotor was replaced with a semi-articulated one on production aircraft. The difficulties experienced with the early design of the main rotor were one of the factors contributing to the lengthy development time of the Gazelle. The individual rotor blades were crafted out of composite materials, primarily composed of fibreglass, and designed for an extremely long operational lifespan; composite rotor blades would become a common feature of later helicopters. The main rotor maintains a constant speed in normal flight and has a "wide range of tolerance" for autorotation.
The Gazelle can transport up to five passengers and up to 1,320 pounds of cargo on the underside cargo hook or up to 1,100 pounds of freight in 80 cubic feet of internal space in the rear of the cabin.
Armed variants would carry up to four HOT (Haut subsonique Optiquement Téléguidé Tiré d'un Tube) wire-guided anti-tank missiles or a forward-firing 20mm cannon mounted to the fuselage sides with its ammunition supply placed in the cabin. Various optional equipment can be installed upon the Gazelle, such as fittings for engine noise suppression, 53-gallon ferry tanks, a rescue winch capable of lifting up to 390 pounds, emergency flotation gear, particle filter, high landing skids, cabin heater, adjustable landing lights, and engine anti-icing systems. While the Gazelle had been developed under a military-orientated design programme, following the type's entry into service, increasing attention to the commercial market was paid as well. The type was marketed to civil customers; notably, civilian operator Vought Helicopters at one point had a fleet of at least 70 Gazelles. Civil-orientated Gazelles often included an external baggage access door mounted beneath the main cabin.
The Gazelle was the first helicopter adapted for single-pilot operations under instrument flight conditions. Honeywell developed an advanced duplex autopilot system to allow the pilot not to be overworked during solo flights; the Gazelle was chosen as the platform to develop this capability as it was one of the faster and more stable helicopters in service at that point and had a reputation for being easy to fly. The docile flying abilities of the Gazelle are such that it has been reported as being capable of comfortably flying without its main hydraulic system operation at speeds of up to 100 knots. The flight controls are highly responsive; unusually, the Gazelle lacks a throttle or a trimming system. Hydraulic servo boosters are present on all flight control circuits to mitigate control difficulties in the event of equipment failure.
The Gazelle was designed to be easy to maintain, all bearings were life-rated without needing continuous lubrication, and most fluid reservoirs were rapidly inspected. The emphasis in the design stage of achieving minimal maintenance requirements contributed towards the helicopter's low running costs; many components were designed to have a service life of over 700 flying hours and, in some cases, 1,200 flight hours before requiring replacement. Due to the performance of many of the Gazelle's subsystems, features pioneered upon the Gazelle, such as the fenestron, would appear in later Aerospatiale designs.
As the Gazelle continued to serve into the 21st century, several major modernisation and upgrade programs were undertaken, commonly adding new avionics to increase the aircraft's capabilities. Aerotec group offered an overhaul package to existing operators, which comprised upgraded ballistic protection, night vision goggles, new munitions, including rockets and machine guns, and 3D navigational displays. QinetiQ developed a Direct Voice Input (DVI) system for the Gazelle, which enables voice control over many aspects of the aircraft, lowering the demands placed upon the crew. In September 2011, QinetiQ and Northrop Grumman proposed outfitting former British Gazelles with autonomous flight management systems derived from the Northrop Grumman MQ-8 Fire Scout, converting them into unmanned aerial vehicles (UAV) to meet a Royal Navy requirement for an unmanned maritime aerial platform.
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