On March 19, 1966, the magazine Air et Cosmos published an article entitled "Sud-Aviation studies a new light helicopter: the X-300", initially also referred to by the acronym HLO (Hélicoptère Léger d’Observation). The new four-seat aircraft, expected to make its appearance during 1967, was to be the French counterpart to the Hughes 500. On the drawing boards of Sud Aviation, the project that would become the Gazelle was taking shape. Fifty years after its debut in Swiss skies, we look back at its history.

Origins and development

Following the signing of the historic cooperation agreement on November 29, 1962 between Sud Aviation and the British Aircraft Corporation, which launched the development of the Concorde, another milestone for the Franco-British aerospace industry was reached a few years later.
On May 17, 1965, a memorandum of understanding was signed between the French and British governments to initiate several joint aeronautical programmes. Among them was a cooperative programme in the field of helicopters.
The 1965 agreement was governmental in nature and established the framework for future collaboration. The actual industrial agreement between Sud Aviation and Westland Helicopters followed on February 22, 1967 (Messmer–Reilly agreement) and was formally implemented in 1968. This partnership gave rise to the Puma, Gazelle, and Lynx helicopter programmes.
Following the commercial success of the Alouette II, François Legrand, who had headed the Design Office of Sud Aviation's Helicopter Division since 1962, began considering a possible successor.
In the ten years since its maiden flight on March 12, 1955, the Alouette II had undergone a number of developments. The original version, designated SE 3130, had been followed by several variants, some developed as experimental testbeds and others intended for series production.
Between late 1965 and early 1966, Legrand and René Mouille - a gifted aeronautical engineer whose life will be briefly presented later - began exchanging a series of notes outlining the principal characteristics of the new helicopter. By February 1966, these ideas had taken sufficiently concrete shape for Mouille to present the project to Sud Aviation's management. At this preliminary stage, the design was identified by the designation X-300.

Conceived as the successor to the Alouette II, the X-300 was intended to be lighter and faster. Maintenance requirements would be reduced through the adoption of a rigid rotor of the Bölkow type. Most of the mechanical components would be retained from the Alouette II, with the exception of the tail rotor, which would be fully shrouded.
The X-300 was therefore not intended to be merely a further development of the Alouette II, but an entirely new helicopter built upon the experience gained with the Alouette II fleet, which had by then accumulated approximately one million flight hours.
The X-300 designation was soon abandoned when the new aircraft received its official designation: Sud Aviation SA 340. Responsibility for its development was entrusted to René Mouille.
The SA 340 programme was guided by four principal objectives: a simple and robust design, low acquisition and maintenance costs, high performance, and competitiveness with rival helicopters.
The new HLO was intended to perform a wide range of missions, including observation, light transport of personnel and equipment, casualty evacuation with stretcher-borne patients, search and rescue, and light attack. For certain operational roles, the helicopter - equipped with an autopilot and appropriate navigation systems - was also expected to be capable of flying in all weather conditions and operating from ships.
Because of its intended multi-role capabilities, the projected weight and dimensions of the X-300 were increased during the design phase. Cabin capacity was also expanded from four to five seats.
The SA 340 programme was officially launched on May 2, 1966. To assess both the aircraft's appearance and its practical layout, a full-scale mock-up constructed from wood and metal was built, allowing engineers to make modifications quickly and easily.
Although the earliest illustrations still presented a somewhat artistic impression of the helicopter, they also clearly showed that the SA 340 differed significantly from the Alouette II. The most striking features were the new tail rotor and the fully streamlined fuselage, which gave the aircraft a much sleeker appearance. Another major innovation was the adoption of a rigid rotor system based on the Bölkow design.

During the early stages of the SA 340's development, several powerplants were evaluated. Among the engines considered were the Allison T63, Continental T65, Bristol Siddeley/Turbomeca Orédon III, Pratt & Whitney PT6B, AirResearch TSE331, and Turbomeca Astazou XIV. Ultimately, however, the Turbomeca Astazou II was selected.

1967 – The first SA 340 prototype

By February 1967, construction of the first SA 340 prototype was nearing completion. Work progressed at a rapid pace, and the prototype, registered F-WOFH (construction number 340-001), was ready for its maiden flight, which took place on April 7, 1967 at Marignane. At the controls was the renowned test pilot Jean Boulet, accompanied by flight-test mechanic André Ganivet.

The aircraft's overall appearance differed considerably from the Gazelle we know today. Powered by a Turbomeca Astazou 2N turboshaft engine, the first prototype incorporated several components borrowed from the Alouette III, including the blades of the tail rotor, the main transmission, and the horizontal stabiliser assembly. It also retained the Alouette II's tail rotor right-angle gearbox.
Less than a month after its maiden flight, the prototype was considered sufficiently mature to be presented to the public at the 27th Paris Air Show at Le Bourget, held in May–June 1967.
A careful examination of the photographs taken in that period reveals that, in the weeks leading up to its public debut, the helicopter had already undergone its first modifications. For example, the vertical fins fitted to the tailplane had been removed.
The initial flight-test programme soon revealed serious vibration problems, even at relatively low airspeeds. These issues were eventually resolved, although, as will be seen later, vibration would reappear during subsequent stages of the development programme.
In the aeronautical environment of the 1960s, designers and engineers routinely refined prototypes throughout the development and flight-test phases, following what is now commonly described as the "learn by doing" approach. By adopting this pragmatic method, they acquired practical knowledge that could not have been obtained through theoretical studies or wind-tunnel testing alone.

1967/1968 – Construction of the second SA 340 prototype

By the end of the summer of 1967, construction of the second prototype (SA 340-002, registered F-ZWRA) was well advanced. It incorporated a number of important innovations, most notably a new tail rotor enclosed within a large vertical fin made of laminated composite material and topped by a fixed horizontal tailplane.
The idea of enclosing a helicopter's tail rotor within a duct originated in the mid-1960s, when the aeronautical industry was conducting extensive research into ducted propellers.
This new configuration was designed primarily to improve the safety of ground personnel by enclosing one of the most exposed and potentially hazardous components of a conventional helicopter, the tail rotor, but also enhanced safety during flight operations.
To obtain the necessary aerodynamic data, a scale model was built and tested in a wind tunnel.
Other significant changes compared with the SA 340-001 concerned the mechanical assemblies, which were redesigned specifically for the new aircraft. The diameter of the main rotor was increased, as was the chord of its blades.
The introduction of a new main transmission and a newly designed rotor mast for the SA 340-002 reduced the helicopter's empty weight by approximately 90 kg (198 lb) compared with the first prototype.
The SA 340-002 was powered by a Turbomeca Astazou IIN1 turboshaft developing 600 hp, compared with the 530 hp of the previous engine. This increase was achieved through a higher operating temperature and a greater exhaust gas velocity.

The second prototype, F-ZWRA, made its maiden flight on April 17, 1968, with Jean Boulet at the controls. It marked a major milestone in rotary-wing aviation, as it was the first helicopter to fly with a shrouded tail rotor.
Flight testing confirmed that directional control about the yaw axis with the new tail rotor differed little from that provided by the conventional anti-torque rotor fitted to the first prototype. The measurements also showed, however, that more power was required to hover with the shrouded rotor. In the hover, a conventional tail rotor absorbed approximately 10% of the engine's available power, whereas the Fenestron required around 14%. Under these conditions, the conventional tail rotor therefore proved more efficient.
In forward flight, however, the advantage shifted decisively in favour of the Fenestron. During cruise, it required only about 4% of the available power—roughly half that needed by a conventional tail rotor. This improvement resulted from the vertical fin, which was designed to generate aerodynamic side force in forward flight, thereby offsetting a significant proportion of the main rotor torque and reducing the workload of the Fenestron.
Since a helicopter spends far more time in cruise flight than in the hover during normal operations, overall fuel consumption proved to be slightly lower with the Fenestron.
Flight tests also showed that the vertical fin became aerodynamically effective at speeds above approximately 100 km/h (54 kts).
Noise, which had initially been a source of concern for the engineers, proved to be no more objectionable than that produced by a conventional anti-torque tail rotor.
The early trials did reveal, however, that operating the Fenestron required greater pedal forces than a conventional tail rotor.
Flight testing also showed that, under certain combinations of wind conditions and aircraft attitude, the ducted anti-torque rotor could experience a reduction in aerodynamic efficiency, creating the risk of an uncommanded yaw. To overcome this undesirable behaviour, the Fenestron underwent numerous refinements. Among the most significant was the adoption of cambered rotor blades, whose curved aerofoil section generated greater aerodynamic lift and improved overall efficiency.
On May 14, 1968, the SA 340-002 was demonstrated in flight at Marignane before journalists of the aviation press for the first time. Flown by Jean Boulet, the helicopter had accumulated approximately ten flight hours and had already reached a speed of 250 km/h (135 kts), a remarkable achievement for such an innovative aircraft. It was the first helicopter to combine all of the following features:

• a rigid main rotor;
• composite main rotor blades made of glass fibres embedded in a polymer resin (the Bölkow system);
• a shrouded anti-torque tail rotor;

The origin of the name “Fenestron”

The appearance of the SA 340-002 popularised the name Fenestron, which today is a registered trademark of Airbus Helicopters. As a protected trademark, the term cannot be used freely by competing manufacturers and is therefore properly written as Fenestron®.
Since the introduction of the Gazelle, and although it has also been adopted on a small number of foreign helicopter designs — such as the Russian Kamov KA-60 — the Fenestron, conceived by the engineers of Sud Aviation and subsequently refined by those of Aérospatiale, Eurocopter, and today Airbus Helicopters, has become a genuine hallmark of the company's helicopter designs.
The name derives from the Provençal dialect word fenestrou, meaning "little window." It belongs to the Provençal variety of the occitan language and is the diminutive of fenèstra ("window"). The name was chosen because the anti-torque rotor, enclosed within the circular duct built into the vertical fin, resembled a small window. According to information released by the manufacturer, it was the aerodynamicist Paul Fabre, a native of Aix-en-Provence with strong ties to his Provençal heritage, who coined the term for the new tail rotor.
According to a story long circulated within Sud Aviation, François Legrand was not particularly fond of the word fenestrou. The name was therefore modified to Fenestron, a choice that ultimately proved both enduring and highly successful.
Developing the Fenestron required Sud Aviation's engineers to start from first principles. Every aspect of the system had to be devised from scratch, including the diameter of the duct, the number of rotor blades, their aerodynamic geometry (aerofoil profile and aspect ratio), as well as the attachment and control mechanisms. The first-generation Fenestron featured simple metallic blades evenly spaced around the rotor hub.
According to information officially released by the manufacturer, the invention was conceived and subsequently patented by René Mouille (the project's technical director), Charles Tresch, and Daniel Mao.
A second-generation Fenestron was introduced in the late 1970s, benefiting from advances in composite materials and manufacturing technology. Since then, its efficiency and flight performance have been steadily improved through the optimisation of blade aerofoils, refinements to the duct geometry, the introduction of outlet stator vanes, and numerous other aerodynamic enhancements.

The redistribution of the rotor blades to prevent noise from being concentrated at a dominant frequency, together with the introduction of a stator fitted with thin, swept vanes and a reduction in rotor rotational speed, proved to be an extremely effective combination for lowering the Fenestron's acoustic signature.
The Fenestron has continued to evolve ever since. The progress achieved is readily apparent when comparing the first installed on the SA 340-002 with the latest version fitted to today's Airbus H160.
In a 1968 aviation magazine article, the author asked of the new tail rotor: "Will the Fenestron, or anti-torque rotor enclosed within the fin, become a model for others to follow?" (Le Fenestron, ou rotor anti-couple noyé dans l'épaisseur de la dérive, fera-t-il école ?)
The question raised at the time has since been answered decisively. The Fenestron's widespread success has firmly established it as one of the defining innovations in modern helicopter design.

Main rotor problems

As previously noted, the SA 340 was equipped with a Bölkow-type rigid main rotor, developed by the engineering team led by Ludwig Bölkow (1912–2003), who is widely regarded as one of Germany's greatest aerospace engineers.
In addition to reducing weight, the rigid rotor system (starres Rotorsystem in German) greatly simplified both construction and maintenance. It also eliminated the problem of ground resonance, a phenomenon to which conventional articulated rotor systems were susceptible.
The rotor hub was manufactured from a titanium alloy, while the main rotor blades were built from a composite structure of glass fibre and synthetic resin, a revolutionary concept at a time when all-metal blades were still the industry standard. Combined with the rigid rotor hub, these composite blades were able to absorb aerodynamic loads through their inherent flexibility. Until then, such loads had required complex hinges and dampers within the rotor head.
Eager to gain experience with this emerging technology, Sud Aviation entered into a partnership with Bölkow GmbH of Ottobrunn as early as June 1964. Beginning in November 1965, the SE 3180-02 prototype was experimentally fitted with a rigid rotor hub to evaluate the new system.
The helicopter made its maiden flight on January 24, 1966 and accumulated approximately 1,000 flight hours. During the test programme, vibration problems again emerged.
The SA 340-002 was also fitted with a three-bladed rigid rotor hub inspired by the Bölkow design, but developed internally by Sud Aviation. Built in two versions, it was named MIR, an acronym derived from Moyeu Intégralement Rigide ("fully rigid hub").
After being evaluated for approximately one year, this rotor system was also abandoned due to persistent vibration problems and a tendency to suddenly pitch up at high speeds, an inherent characteristic of early rigid rotor systems that had not yet been fully refined.
The main rotor blades themselves were also tested and progressively improved during the flight-test programme. Their development initially required new expertise, which Sud Aviation acquired through its close cooperation with Bölkow.
The first blade designs were supplied by the German technical office. Beginning in May 1968, they were replaced by an improved version. In October 1968, Sud Aviation introduced a further optimised blade design developed by the technical offices at La Courneuve. This final version was manufactured by Bölkow using moulds produced by Sud Aviation.
It is worth recalling that Bölkow GmbH merged on November 1, 1968 with Messerschmitt AG and Hamburger Flugzeugbau, a subsidiary of the Blohm group.
The newly formed company adopted the name Messerschmitt-Bölkow-Blohm (MBB) on May 14, 1969 and became West Germany's leading aerospace manufacturer.

1968 – Pre-production units

Following the construction of the two prototypes (SA 340-001 and SA 340-002), which were intended to validate the adopted technical solutions and provide an initial assessment of performance, the programme called for the construction of four pre-production helicopters.
The first of these pre-production aircraft, designated SA 341-01 and registered F-ZWRH, was broadly similar to the second prototype. Construction began on November 1, 1967, and the helicopter made its maiden flight on August 2, 1968, once again with Jean Boulet at the controls, while both SA 340 prototypes were still undergoing flight testing and evaluation.
Compared with the prototypes, this first pre-production aircraft incorporated several important changes. It was powered by a Turbomeca Astazou IIN2, featured a fuselage lengthened by 10 cm (4 in) to accommodate the stretcher adopted by the British armed forces, and was fitted with a modified MIR main rotor equipped with folding blades. The blade chord had also been increased to 300 mm. The horizontal stabiliser, however, had not yet reached its definitive position or configuration. Testing of various tailplane arrangements continued for some time on both the prototypes and the pre-production aircraft, as the T-tail was affected by aerodynamic interference generated by the wake of the main rotor.
Because it differed significantly from the two SA 340 prototypes, the SA 341-01 was initially employed in a dedicated flight-test programme aimed at refining the design, particularly the rotor suspension system. These test flights were interspersed with periods of downtime during which modifications, adjustments, and improvements were introduced based on the analysis of the test results.

The second (SA 341-02, registered F-ZWRA) and fourth (SA 341-04, registered F-ZWRK) pre-production aircraft, completed later, remained in France. The SA 341-02, which made its maiden flight shortly afterwards, was assigned primarily to endurance and reliability trials, which were essential for assessing the helicopter's behaviour during prolonged operational use.
The SA 341-02, intended for an initial evaluation by the ALAT (Aviation Légère de l'Armée de Terre, the French Army Light Aviation), made its first flight in October 1969.
As production of the new helicopter was to be shared between Sud Aviation and Westland Helicopters, the British manufacturer began assuming an increasingly important role in the construction of the aircraft during the pre-production phase, foreshadowing the industrial work-sharing arrangements established under the Franco-British cooperation agreement.
The SA 341-03, registered F-FWRI, was subsequently dismantled and shipped to the United Kingdom, where it was reassembled by Westland Helicopters as the prototype of the Gazelle AH Mk.1, the version intended for the British Army. During this process, it was fitted with several items of British equipment, including a new radio installation.
The SA 341-03 was the first aircraft to be equipped with the second-generation Fenestron, featuring a diameter of 695 mm (27.4 in) and integrated into an all-metal vertical fin. Another significant modification was the addition of horizontal stabilisers, which had been absent from earlier aircraft. Re-registered as XW276, it made its first flight in this configuration on April 28, 1970.
It is reasonable to assume that the Franco-British engineering teams encountered numerous practical challenges throughout the programme. In addition to language barriers, they had to reconcile design and manufacturing procedures based on two different systems of measurement, the metric system and the Anglo-American imperial system, with inevitable consequences for both engineering and production.
Sud Aviation's Helicopter Division, officially established on April 30, 1968 as the successor to the company's specialist helicopter department, employed approximately 7,000 people by June 1968, including around 750 engineers and technicians in the design office, and operated roughly 1,500 machine tools.

1969 – It would be called “Gazelle”

In the summer of 1969, the joint Franco-British steering committee made another important decision. Following established company tradition, the new helicopter would be named after an animal. The SA 341 became the “Gazelle”, a name that, conveniently, was spelled and pronounced almost identically in both French and English.
After four years of development, testing, and continuous refinement, the programme was finally ready to enter full-scale production.
In November 1969, by which time the six aircraft built had accumulated approximately 500 flight hours, the decision was officially taken to begin the first phase of preparations for the Gazelle's serial production.
Initial production forecasts indicated a requirement for at least 450 helicopters, including 250 aircraft intended for the British armed forces.
On August 6, 1971, the first production aircraft (serial number 1001), registered F-WIEP, made its maiden flight with Jean Boulet at the controls. Its definitive production configuration embodied the experience gained during the extensive flight-test programme carried out with the prototypes and pre-production aircraft.

The differences were immediately apparent. The glazed areas were enlarged, both in the doors and in the lower section of the cabin, while access doors to the rear seats were now fitted on both sides of the fuselage. Less obvious at first glance was the redesigned tail boom. The original laminated composite structure, considered excessively flexible, was replaced by a sheet-metal construction that provided greater rigidity while also reducing both weight and manufacturing costs.
For the first time, all the innovations developed throughout the lengthy experimental programme were brought together in a single aircraft. Flight testing of F-WIEP nevertheless showed that development was not yet complete. Problems of ground resonance and in-flight vibration persisted, requiring a further year of engineering work and forcing the manufacturer to temporarily slow the pace of production.
The first Gazelles to leave the assembly line therefore continued to serve as flying testbeds for further refinements. As is often the case with highly innovative aeronautical programmes, the technical issues encountered during the early stages of development were resolved only gradually through an extensive programme of flight testing and successive design modifications.
The first production SA 341G (serial number 1003) – the G has been the first of the two civil variants to enter series production - was initially registered F-OCRX and made its maiden flight on November 10, 1971. Used by the manufacturer as a demonstrator aircraft, it was presented in the United States in January 1972 at the annual meeting of the American Helicopter Association.
The SA 341G Gazelle received its French civil type certification on June 7, 1972.
In the United States, the Federal Aviation Administration (FAA) granted certification on September 18, 1972. Aérospatiale subsequently obtained FAA approval for single-pilot Category I IFR (Instrument Flight Rules) operations with the SA 341G Gazelle. It was the first helicopter in the world to receive this certification. When equipped with a Sperry Flight Director (FD) coupled to SFENA servo-actuators — already used in the automatic flight-control and stability augmentation systems of both fixed-wing aircraft and helicopters — the Gazelle could fly in reduced-visibility conditions.
The FAA also approved a medical evacuation configuration capable of carrying two stretchers mounted along the left side of the cabin, while still retaining one passenger seat on the right-hand side behind the pilot.
In North America, the Gazelle was initially marketed by Vought Helicopter Inc. and later by Aérospatiale Helicopter Corporation, the French manufacturer's U.S. subsidiary, which employed approximately 800 people by the early 1980s. Through this organisation, Aérospatiale significantly strengthened its commercial presence in both the United States and Canada.
In 1976, the cost of a SA 341G Gazelle was about 297,000 USD. By comparison, an SA 315B Lama was sold for approximately 276,000 USD, while the cost of a SA 319B Alouette III was around 310,000 USD.
In the civil market, however, the commercial success of the SA 341/342 Gazelle was ultimately overshadowed by the arrival of the AS 350 Écureuil. Although somewhat slower, the Écureuil proved to be an exceptionally versatile and, above all, more economical helicopter. It offered a larger cabin with seating for one additional passenger and could carry a greater external sling load (700 kg compared with the Gazelle's 550 kg). It also featured the simpler Starflex rotor system and the more modern Arriel 1B engine. According to the available operational data, the Gazelle's operating costs were generally higher than those of the AS 350B Écureuil.
Among the Gazelle's principal military operators were the armed forces of France and the United Kingdom, together with those of Egypt, Libya, Iraq, Syria, Yugoslavia, and Ecuador.

Like many other French-designed helicopters, the Gazelle remained in production for a long period. According to the sources consulted, production in France continued until 1992, when serial number 2237 rolled off the assembly line.
In addition to Aérospatiale, the Gazelle was also manufactured by Westland Helicopters in the United Kingdom, the Arab British Helicopter Company (ABHCo) in Egypt, and Vazduhoplovna Industrija SOKO in Bosnia and Herzegovina (then part of Yugoslavia).
In total, 1,416 Gazelles were built across all production lines, a figure comparable to the production runs of the Alouette II and Alouette III.
Westland produced 294 aircraft before ending production in 1984. At SOKO, the Gazelle remained in production between 1971 and 1992, with 176 helicopters completed. The Arab British Helicopter Company (ABHCo) assembled 30 Gazelles under licence, completing its programme in 1985. The Astazou XIV engines for these helicopters were assembled by the Arab British Engine Company (ABECo).
In a statement issued by Eurocopter in 2002, the French manufacturer reported that the worldwide Gazelle fleet had accumulated a total of 5.65 million flight hours.
With the gradual retirement of military-operated aircraft, sightings of the Gazelle have become increasingly uncommon, particularly in the civil sector. Most of the helicopters that remain airworthy today are privately owned and flown for personal use.
Although the Gazelle did not undergo the extensive evolutionary developments that characterised later French helicopters such as the Écureuil and the Dauphin, it nevertheless made a significant contribution to the advancement of helicopter technology.
Its distinctive Fenestron became the foundation for subsequent generations of Airbus helicopters, including the EC120 Colibri, EC130, EC135, and, more recently, the H160.
The shortcomings of the original rigid rotor system developed for the Gazelle also helped accelerate the development and eventual adoption of technically simpler and more effective rotor-head concepts, notably the Starflex and Spheriflex systems, which became defining features of later generations of French helicopters.

Variants

Over the years, numerous Gazelle variants were developed, the majority for military use. Several were designed for highly specialised operational roles. The principal versions are listed below:

• SA 341A – initial production version
• SA 341B – British Army version, designated AH.1
• SA 341C – Royal Navy training version, designated HT.2
• SA 341D – Royal Air Force training version, designated HT.3
• SA 341E – Royal Air Force communications version, designated CC.4
• SA 341F – version for the ALAT (French Army Light Aviation)
• SA 341G – civil production version
• SA 341H – export military version
• SA 342J – civil version powered by the Astazou XIVH engine
• SA 342K – export military version
• SA 342L – civil version fitted with the improved Fenestron
• SA 342M – military anti-tank version capable of carrying four HOT anti-tank guided missiles

Civil employ

Today, as previously noted, most airworthy SA 341G Gazelles are privately owned and flown for recreational or personal purposes.
During its civil career, however, the Gazelle was employed in a wide variety of civil roles. These included passenger and cargo transport, aerial observation and traffic surveillance, aerial photography and cinematography, pilot training, and offshore support operations.

In France, the Secours Aérien Français (SAF) operated the SA 342 variant on search-and-rescue missions in the French Alps.

Technical description

The fuselage of the SA 341G Gazelle comprises the cabin, the lower structure, the centre section, and the tail boom. The cabin features a metal framework covered by Plexiglas panels, providing excellent visibility for the five occupants.
The pilot’s seat is positioned on the right-hand side. The two front seats are identical and adjustable longitudinally. The rudder pedals have two adjustment positions to accommodate pilots of different builds.
Access to the cabin is provided through two large jettisonable doors of mixed metal-and-Plexiglas construction. Between the two front seats is the central instrument pedestal, which carries the flight, navigation, and mechanical parameter instruments, as well as the radio control units. Behind this pedestal, in the forward section of the aircraft, is the battery compartment, accessible through a hatch in the helicopter’s nose.

The rear cabin can accommodate three passengers seated on a single bench seat. Access to the rear seats is facilitated by two rear-hinged half-doors. By removing the passenger seat backrest, access is gained to the space beneath the mechanical floor (plancher mécanique), which can be used as a baggage compartment.
On request, the cabin section could be extended by approximately 20 cm (8 in), providing greater comfort for passengers seated in the rear.
Externally, the most noticeable differences are the greater width of the rear half-doors and of the fuselage section between the doors and the tail boom. The two vertical fins mounted on the horizontal stabiliser are also smaller.
This version, informally known as the “Stretched Gazelle,” was derived from the civil SA 341G variant and was produced in limited numbers.
As with other French helicopters of the period, some components, such as door handles and locks, were sourced from the automotive industry and were manufactured for Renault and Peugeot vehicles.
The centre section supports the cabin and the landing gear, which consists of two fixed skids attached to the airframe by two curved cross tubes fitted with streamlined aerodynamic fairings.
These cross tubes are resilient structural elements that deform within predetermined limits during landing, helping to absorb impact energy and reduce loads transmitted to the airframe.
The cross tubes support four curved struts (two forward and two aft) that extend upward to the lower fuselage structure. Each strut terminates in a metal fitting bolted to the structural attachment points of the fuselage. These attachment points are reinforced and form part of the helicopter’s primary structure.
The Gazelle could be equipped with two types of landing gear: rigid or flexible.
The rigid landing gear was fitted with two shock absorbers on each side of the rear cross tube and a cockpit lever operated by the pilot. This lever acted on a mechanical device known as the mobile plate (plateau mobile), allowing the stiffness of the system to be adjusted in order to prevent the onset of ground resonance.
The lever controlled the locking and unlocking of an element of the main transmission system connected to the helicopter structure. In practice:

• during flight, the system had to remain unlocked, allowing limited movement of the structure and enabling it to absorb deformation loads.
• during landing, the system had to be locked, increasing overall rigidity and preventing landing gear oscillations from triggering ground resonance. 

The pilot therefore had to remember to change the lever position during each phase of flight in order to prevent this dangerous phenomenon, which could potentially destroy the aircraft.
The flexible landing gear, by contrast, was not fitted with shock absorbers. The rear cross tube was attached at its centre through a hinged joint whose attachment point was located inside the baggage compartment. In addition, the front cross tube was mounted on pivots allowing movement in two directions.
Most of the early Gazelles were subsequently modified to incorporate the flexible landing gear system.
During the years of operation, several airworthiness directives were issued concerning corrosion inspections of the landing gear cross tubes and arches, as deterioration of these components could compromise the structural strength of the system. Periodic inspections and any necessary replacement work subsequently became an integral part of the scheduled maintenance programme for the SA 341G.
To facilitate ground handling of the helicopter, two detachable wheels fitted to the skids could be installed.
The central fuselage section incorporates, at approximately two-thirds of its height, the mechanical floor (plancher mécanique), on which the main transmission and its associated accessories are installed. Beneath it there are the fuel tank and the baggage compartment, where items such as the skid-mounted ground handling wheels can be stored. Footrests are provided on both sides of the fuselage to allow inspection of the rotor head and transmission system.
The engine is installed behind the main transmission. Both are protected by composite-material cowlings. The helicopter can be flown without these covers, however if the engine cowling is missing, the maximum permissible speed is restricted.
On the rear right side of the fuselage, a maintenance hatch fitted with a grille provides access to the auxiliary fuel tank, the engine and main transmission oil coolers, the main transmission area, and various electrical components.
The rear fuselage structure includes the lightweight-alloy tail boom, fitted with two fixed horizontal stabilisers carrying two vertical endplate fins.
The vertical fin has an asymmetric profile designed to provide aerodynamic compensation for the reaction torque produced by the main rotor during cruise flight. The Fenestron is located at the centre of the fin’s aerodynamic duct and is supported by three structural supports.

On the left-hand side, a metal casing protects the rotor hub. On the right-hand side are the rear transmission gearbox and its associated oil reservoir.
The Fenestron’s 13 metal blades are feature an asymmetric aerofoil profile. The rotor speed is 5,774 rpm.
Throughout its history, the Fenestron’s performance and flight characteristics have been continuously improved through the development of blade aerofoil sections, refinements to the duct geometry, the introduction of a stator, and numerous other technical improvements.
The vertical fin is of metal construction, but its upper section features a composite-material fairing topped by an anti-collision light. Another composite fairing is installed at the base of the fin and protects the structure in the event of contact with the ground caused by excessive nose-up attitude during landing or take-off.

Engine

The SA 341G Gazelle is powered by a Turbomeca Astazou IIIA turboshaft engine, which develops a maximum take-off and continuous power output of 440 kW (598 shp) at 43,500 rpm. Its dry weight is approximately 147 kg (324 lb).

The engine consists essentially of a two-stage compressor (the first stage being axial and the second centrifugal), an annular combustion chamber with radial flow fitted with a central rotating atomiser, and a three-stage axial turbine. Fuel is injected into the engine shaft and, through centrifugal force, expelled through small orifices machined into the shaft itself. This system produces a disc-shaped fuel spray pattern and represents a particularly efficient solution developed by Turbomeca.
The engine also incorporates a coaxial reduction gearbox consisting of three gear trains and two reduction stages, together with a transmission support casing that also serves as the inner wall of the oil tank.
The accessories are grouped around the rear section of the reduction gearbox. The engine is equipped with a conventional hydromechanical fuel-control system and a traditional lubrication circuit.
Because the compressor and the power turbine driving the output shaft are rigidly connected to the same shaft, the Astazou IIIA is technically classified as a single-shaft (fixed-coupled) turboshaft engine.
Unlike a direct-drive (single-shaft) engine, a free-turbine engine has a mechanically independent power turbine. The gas generator consists of the compressor and the gas-generator turbine, while the power turbine drives the output shaft through no direct mechanical connection to the gas generator.
The annular air intake is protected against accidental foreign-object ingestion by a protective grille. For operations in particularly dusty environments, special anti-sand filters known as particle separators can be installed; these extract a portion of compressed air to separate dust and debris before they enter the engine. The engine can also be fitted with an anti-icing shield.
The turbine exhaust duct is slightly offset to the left-hand side.
At sea level under standard atmospheric conditions, average fuel consumption is approximately 160–170 litres per hour.

Transmission

The engine drives the rotor system through the transmission, via a freewheel unit and a centrifugal clutch. Equipped with two reduction stages, the transmission is attached to the mechanical floor by means of an elastic mounting plate that absorbs vibrations and is held in position by two inverted “V”-shaped supports.
At the transmission input, the rotational speed is 6,179 rpm, while at the output it is reduced to 378 rpm, which is the speed transmitted to the main rotor.

An inclined drive shaft connects the transmission to the intermediate gearbox, located beneath the turboshaft engine. Its purpose is to redirect the angle between the inclined shaft and the rear connecting shaft.
At the output of the intermediate gearbox, the rear drive shaft runs along the length of the tail boom and is supported by two bearing-mounted supports. On civil versions of the Gazelle, this drive shaft is protected by a fairing.
The rear drive shaft connects to the tail gearbox, installed within the Fenestron assembly. This gearbox performs two functions: it reduces the rotational speed transmitted by the drive shaft and changes the direction of the drive axis by 90 degrees, transferring power to the anti-torque rotor.
The main transmission is rated for a maximum takeoff power (MTOP) of 440/598 kW/hp (MCP 440/598 kW/hp).

Main Rotor

The main rotor hub is of the semi-articulated type and is therefore equipped with only two types of articulation for each of the three blades: a pitch-change articulation (controlled by the collective pitch lever) and a flapping articulation.
Blade drag movement is controlled by a rubber-metal elastic element (silent block), which performs two functions: it provides an elastic restoring force, returning the blade to its equilibrium position, and, thanks to the viscoelastic properties of the material, damps oscillations by dissipating their energy.
Each blade is fitted with its own oil reservoir, with a capacity of 1.13 litres (0.30 US gal), ensuring permanent lubrication of the blade articulations. Each blade is also equipped with a stretch indicator (a fuse screw) designed to detect deterioration of the torsional bundle that maintains the blade in position.

Cyclic pitch changes are controlled by pitch links connected to the swashplate, while collective pitch changes are transmitted through a spherical joint sliding along the rotor shaft.
The blades are manufactured from glass fibre and resin, with stainless-steel leading edges and an internal structure incorporating a plastic honeycomb core. They can be manually folded for storage or transport. The aerofoil section is a symmetrical NACA 0012, with a 6°20′ twist and a chord of 300 mm.
Each blade measures 4.819 m in length and weighs 36.2 kg (79.8 lb). It is fitted with a polyurethane adhesive strip on the leading edge for protection and a balancing tab (trim tab) on part of the trailing edge. Each blade tip is fitted with a metal end cap.
No reliable data regarding the Gazelle’s main rotor inertia could be found. Manufacturers generally do not publish such information in operational manuals. These figures are normally contained within design or certification documentation, which is not readily accessible.
Based on available information, however, the Gazelle is widely recognised among pilots as having a low-inertia main rotor, a characteristic that influences both its handling qualities and autorotation performance.

Torsion bars

The torsion bar is the component that connects each blade to the rotor hub. It must provide sufficient axial strength and stiffness to withstand centrifugal forces, while also allowing enough torsional flexibility to permit smooth changes in blade pitch angle.
To perform these functions, each torsion bar is made up of approximately 12,000 ultra-high-strength steel wires (resistant both mechanically and to corrosion), each with a diameter of 0.15 mm. The wires are arranged longitudinally in a bundle and wrapped around two end rings, which provide the attachment points for the connecting pins linking the assembly to the rotor hub and the blade.
The wires are held together by two steel clips around which a secondary winding is applied. Its main purpose is to maintain the compactness and integrity of the assembly. Furthermore, to protect the steel wires as much as possible from external environmental attack, each individual wire and the complete bundle are covered with a yellow polyurethane sheath.
Although this configuration provides effective protection against atmospheric corrosion, it makes non-destructive inspection of the internal wires extremely difficult. In practice, the visual inspection requirements for the torsion bar allow the presence of cracks in the polyurethane covering, but the bar must be rejected if even a single broken wire is discovered. A broken wire is an indication of a potentially much more serious internal deterioration of the bundle, which is extremely difficult to assess directly.

The importance of inspections

In 1975, following the deterioration of several torsion bars caused by water and oil infiltration beneath the protective sheath, destructive examinations revealed that approximately 20–30% of the wires had failed. The tests also showed abnormal elongation of the bars under high loads, corresponding to the conditions experienced during autorotation.
In response, Eurocopter, through Mandatory Service Bulletin No. 65.10, introduced a device for monitoring torsion-bar elongation on the main rotor.
The system consists of a scribed fuse screw attached to the helicopter blade and a fixed stop attached to the rotor hub. If the torsion bar stretches abnormally under load, the screw moves from its original position, comes into contact with the stop, and may eventually break.
The initial and/or adjustment clearance between the screw and the stop was set at 3 ± 0.2 mm.
The maintenance manual provides a detailed description of this monitoring device and the associated inspection procedures. In particular, after every flight, each device must be checked. If the screw has broken or if there is evidence that contact between the screw and the stop has occurred during flight, the screw must be replaced and an autorotation test must be carried out.
In the event of a broken screw, the maintenance instructions require replacement of the torsion bar.

The accident of the SA 341G Gazelle I-OLLY

The helicopter registered I-OLLY (serial number 1065, built in 1973), operated by the Piedmont-based company Heliwest Srl, was one of the SA 341G Gazelles used for commercial operations in the Alpine area.
The aircraft was involved in an accident on May 28, 2001 at Prà del Rio, in the Susa Valley (Piedmont, Italy).
That morning, the helicopter was being used to transport building materials and personnel involved in the construction of an electrical substation for the 2006 Winter Olympic Games. At 12:20, after taking off to perform another transport flight, the aircraft initially climbed vertically. As it began transitioning into forward flight towards the valley, one of the main rotor blades separated from the hub. The helicopter fell from a height of approximately 15–20 metres (50–65 ft) and immediately caught fire upon impact.

As a result of the crash, the helicoopter technician, who had not yet fastened his seat belt and was seated in the rear cabin alongside one of the passengers, was thrown approximately 3–4 metres away from the burning wreckage. This allowed him to assist the rear passenger in escaping from the helicopter before the flames completely engulfed the fuselage.
At the conclusion of the investigation, the Italian National Flight Safety Agency (ANSV – Agenzia Nazionale per la Sicurezza del Volo) determined in its final report that the accident was caused by the structural failure of a main rotor torsion bar.
Eurocopter conducted fractographic examinations of the failed torsion bar in its own laboratories. The component had been installed in 1985 and had accumulated 2,928 flight hours, which was 2,072 hours less than the established safe-life limit of 5,000 hours.
The investigation determined that the torsion bar failure resulted from a fatigue process that progressively reduced the strength of the steel wires forming the torsion bar assembly.
The component exhibited localised corrosion of the steel wires, with the most significant damage occurring in the area of the retaining clips, where cracks had developed in the polyurethane protective coating.
Fractographic analysis confirmed that a slow but progressive corrosion process had taken place precisely in the area subjected to high stresses, caused by interaction between the wires and the steel clip components. This gradually compromised the structural integrity of the torsion bar until it could no longer withstand operational loads.
Ageing of the polyurethane protective sheath allowed corrosive agents from the external environment to penetrate the assembly. This was followed by damage caused by pitting corrosion and stress-corrosion cracking.
The torsion bar failure involving I-OLLY was the first such occurrence affecting the Gazelle fleet, which at that time had been in service for more than 30 years and had accumulated over 5 million flight hours across both military and civil variants.
On November 16, 2001, another similar accident occurred at Batcombe, Somerset (United Kingdom), involving Westland Gazelle AH.1 ZA777. The accident claimed the life of 28-year-old Captain Simon Hill, an Army Air Corps recruitment officer who was returning to his base at Middle Wallop.
To prevent further accidents, Eurocopter initiated a series of measures, including the introduction of new flight limitations concerning torsion bars across the SA 341/342 Gazelle fleet. Among the restrictions introduced was a reduction in the calendar life limit of torsion bars. Subsequently, optional redesigned torsion bars were introduced as replacements for the original components.

Fuel system

The main fuel tank is located within the central fuselage structure, beneath the mechanical floor. It has a capacity of 457 litres (120.7 US gal), of which 455 litres (120.2 US gal) are usable.
The fuel filler neck is located on the right-hand side of the fuselage. Beneath the main fuel tank, an optional 90-litre (23.7 US gal) metal auxiliary tank can be installed.
For long-range ferry flights, an additional fuel tank with a capacity of 200 litres (52.8 US gal) can also be fitted.

Flight controls and hydraulic system

The flight control system follows a conventional architecture consisting of control rods (fixed, semi-fixed, or adjustable), bell cranks, and, only for the anti-torque rotor control, control cables.
The control rods, actuated by the collective and cyclic pitch controls, operate three hydraulic servos (each equipped with a hydraulic accumulator) positioned around the main transmission. These servos transmit the pilot’s inputs to the main rotor through the swashplate. The hydraulic pump is installed on the forward section of the main transmission (BTP – boîte de transmission principale).
The pedals are connected to the Fenestron actuator through a system consisting of control rods, a pulley assembly, and control cables running along the upper part of the tail boom, parallel to the tail rotor drive shaft.
A rear hydraulic servo, installed on the tail rotor gearbox, operates the control spider of the tail rotor head.
Damping of yaw-control movements is provided by a simple oil-filled piston equipped with a calibrated bypass and connected to the control crossbar. This device reduces excessively rapid pedal movements, improving stability and control precision.
In the event of a hydraulic system failure, the actuators automatically revert to direct mechanical control.
Control of the helicopter remains possible even in the event of hydraulic failure, although increased pilot physical effort is required.
The flight controls are equipped with magnetic brakes, which allow the pilot to hold the cyclic control in the desired position, and with an optional stability augmentation system.

Electrical system and lighting

The Gazelle was originally equipped with a 40 Ah nickel-cadmium battery and a starter-generator that supplies direct current at a voltage of 28.5V.
In addition to cockpit and cabin lighting, the helicopter is fitted with three navigation lights installed in accordance with regulatory requirements, an anti-collision beacon mounted on the top of the vertical fin, and a retractable landing light installed in the forward lower section beneath the cabin.

Dimensions, weight and payload

The SA 341G Gazelle has an empty weight of approximately 958 kg (2,112 lb), while the maximum authorised take-off weight is 1,800 kg (3,970 lb).
The maximum external load that can be carried on the barycentric hook is 700 kg (1,540 lb).
The main rotor has a disc area of 86,59 m² (932,11 sq ft), while the Fenestron has an area of 0,38 m² (4,08 sq ft).
The drawing below shows the three principal views of the aircraft.

Accessories

The versatility of the SA 341G Gazelle could be further enhanced through a wide range of optional equipment. Some of the available accessories included dual flight controls, cabin heating system, raised landing gear (increasing ground clearance by approximately 15 cm), snow skis, fixed floats Aerazur ARZ 74-845-A, emergency flotation gear, sand filter, loudspeakers (for police operations), auxiliary 200-litre (53 US gal) fuel tank, stretcher installation, electric hoist (Breeze BL-16-600-11 or Air Equipment AE-76-370), both with a lifting capacity of 136 kg (300 lb), cargo hook (Cargo Aids installations 341° 82.1100 and 821101, or E.R.C. 341A 82.2960), VIP interior configuration, SAS (Stability Augmentation System), additional instrumentation, supplementary front-seat safety harnesses, blue-tinted upper cabin windows, windshield wipers, wire-strike protection system, IFR instrumentation. 
Emergency flotation devices could be installed above the landing skids, regardless of whether the Gazelle was equipped with the high or low landing gear configuration.

A Gazelle in the Swiss Alps

Only three SA 341G Gazelles (in addition to two SA 342J) have been registered in Switzerland to date. The first was HB-XFW, serial number WA 1124, built in 1974.
In spring 1976, the helicopter was purchased by the newly established Graubünden-based helicopter operator Air Grischa. The aircraft was entrusted to Erwin Schafrath, a highly experienced pilot who at the time had accumulated 4,500 flight hours and had previously served in the Austrian Army before joining Eliticino.

Unlike today, the Swiss civil helicopter sector in the 1970s was characterised by a highly diverse range of aircraft types. From 1971 onwards, commercial operators had increasingly relied on the SA 315B Lama for supplying mountain construction sites, while light transport operations were mainly carried out with aircraft such as the Bell 206 Jet Ranger and the Hughes 500C or 500D. These helicopters could carry three to four passengers or an underslung load of approximately 400–500 kg (882-1,102 lb).
Transport operations involving heavier loads exceeding 800–900 kg (1,763-1,984 lb) were generally assigned to the Agusta-Bell 204B or the S-58T operated by Heliswiss, and from 1978 onwards to the Bell 214B-1 BigLifter.
The decision by Air Grischa to purchase the French helicopter was probably driven by the need for an aircraft capable of carrying five occupants, offering higher speed and a greater external-load capability than its American competitors—namely 550 kg (1,212 lb) instead of 400–500 kg.
Before receiving its Swiss registration, HB-XFW had been registered in the United Kingdom as G-BBSH. At Gatwick Airport, Erwin Schafrath carried out his first familiarisation flights between April 29 and 29, 1976. The helicopter was subsequently flown to Dijon (France), then to Sion, and finally to Stans, where it remained for approximately one and a half months.
On April 30, the new aircraft was added to Erwin Schafrath’s pilot licence. From June 14, the helicopter began operating under its Swiss registration HB-XFW. The first commercial flights were carried out from June 28, after the Gazelle had been equipped with an external cargo hook and the external mirrors.
Depending on the region in which it was operating, HB-XFW was based at Bad Ragaz/GR, Lugano-Agno/TI, and occasionally San Vittore/GR.

Erwin Schafrath was probably the first pilot throughout the Alpine region to use the Gazelle for supply flights to construction sites, mountain huts, and alpine farms. Although half a century has now passed since those first flights, many people still remember his “aerobatics” with the helicopter, whose manoeuvrability was truly remarkable. The flight logs shows that operations were extremely intensive, particularly during the summer months.
The HB-XFW was also made available to the Graubünden police for aerial traffic surveillance along the A13 motorway, a route inaugurated in 1970 that crosses eastern Switzerland from north to south, linking St. Margrethen, near the Austrian border, with Bellinzona (Ticino).
The first police officer in Switzerland to be trained as a commercial helicopter pilot specifically for this role was Florian Lütscher.

The accident

On August 18, 1979, the latter had planned to use HB-XFW to transport a suspended load weighing approximately 300 kg (661 lb), consisting of a net containing furniture and wooden boards to be transported to a mountain hut at Alp I Cebi (1,720 m – 5,643 ft).
After taking off from the operational area of the cantonal police centre, located at the southern entrance of the San Bernardino Tunnel (1,631 m – 5,350 ft), with one passenger on board, the pilot lifted the load and verified that the torque indication was within the prescribed limits. He then began forward flight with a slight climb rate.
After approximately 100–150 metres (330-500 ft) , the helicopter suddenly began to lose altitude and yawed to the left towards the A13 motorway. Despite increasing collective pitch, the pilot was unable to arrest the descent.
In order not to endanger motorists travelling on the road, instead of releasing the load, he pulled the collective to obtain the maximum available power in an attempt to return to the departure area. At this point, the engine produced a burst of loud impacts.
This noise, known as compressor surge, occurs when the compressor operates beyond its stable operating limit. Under these conditions, airflow through the compressor is disrupted and may temporarily reverse, causing strong explosions or “bangs”, vibrations, sudden changes in temperature and pressure, loss of power, and sometimes flames at the intake or exhaust.
Immediately after crossing the motorway, the pilot lowered the collective. However, because of the low altitude and the sudden loss of power, he was unable to prevent the helicopter from striking the embankment of the motorway access ramp, with the load still attached.
Both occupants suffered severe injuries in the accident, and the helicopter was completely destroyed. Thus ended, in a dramatic manner, the operational career of HB-XFW.

On January 22, 1981, the Aircraft Accident Investigation Commission concluded that the accident had been caused by an incorrect assessment by the pilot of the effects of the wind. At the time, the pilot had accumulated a total of 607 flight hours, including 123 hours on the SA 341G Gazelle.
That same summer, Air Grischa began operating the AS 350B Ecureuil HB-XFY. The new helicopter quickly demonstrated its versatility and proved highly successful. This marked the beginning of a remarkable career for the Ecureuil family, which continues to enjoy considerable success today with its latest variants.
A few months later, the SA 341G Gazelle HB-XIL was registered in the name of Air Grischa. The helicopter belonged to Beat Perren, founder of Air Zermatt. Only a few months later, although ownership remained with Perren, the helicopter was registered under the name of Air Zermatt.

This aircraft remained on the Swiss aircraft register until August 31, 1982. It was then sold to the United Kingdom, where it continued flying under the registration G-SFTA. On March 7, 1984, it was seriously damaged in an accident.
The last SA 341G Gazelle to be registered in Switzerland was HB-ZEU, registered in June 2002. For many years now, however, this helicopter, with its unmistakable sound, has no longer been seen flying in Swiss skies.

About rigid rotors…

The American experimental Doman LZ-5/YH-31 helicopter, designed by Glidden Doman (1921–2016), featured a highly innovative rotor system for its time, without the traditional flapping and drag hinges.
The blades were designed to elastically absorb movements and loads, reducing both vibrations and maintenance requirements. The tail rotor was also designed without hinges.
Despite the initial interest shown in the aircraft by both the United States Army and the United States Air Force, no further orders followed for the military LZ-5 version.
After receiving certification in the United States in 1955 and in Canada in 1956, the LZ-5 was subjected to a series of demonstrations aimed at both military authorities and civil operators. However, the initiative failed to generate the expected orders. The arrival of more modern turbine-powered helicopters ultimately marked the end of its development.

René Mouille in brief

René Mouille was one of the leading figures behind the remarkable growth of the French helicopter industry.
He was born on October 30, 1924 in Sainghin-en-Weppes, France. After studying aeronautical engineering in Lille and Paris, he joined the Société nationale des constructions aéronautiques du sud-est in 1945 (SNCASE), where he had the opportunity to work on helicopter development at a time when the technology was still in its early stages.
Involved in the development of the Alouette I and Alouette II, he contributed to the creation of a design philosophy that helped bring France to the forefront of the global helicopter industry.
René Mouille worked on major and highly successful programmes including the Alouette III, Super Frelon, Puma, Gazelle, Dauphin, and Ecureuil.
His reputation is particularly associated with several technical innovations that transformed helicopter design, including the Fenestron, the Starflex rotor, and the NAT semi-rigid rotor, in which conventional drag hinges were eliminated and replaced by viscoelastic adaptors.
Many of the solutions he developed continue to equip numerous aircraft today. 

In 1963 he was appointed technical director of the Sud Aviation helicopter division.
René Mouille witnessed an accident caused by a tail rotor spinning while the helicopter was on the ground, an experience that profoundly affected him. It convinced him that a solution was urgently needed to prevent this type of accident. This was one of the reasons that led him to propose the Fenestron.
In recognition of his achievements in aeronautics, he received numerous prestigious honors and decorations in both France and abroad.
René Mouille passed away on January 10, 2019, at the age of 94, in La Roque-d’Anthéron, leaving a significant void in the rotorcraft community.

Did you know that…

On May 14, 1971, at the flight test centre base in Istres, the SA 341-01 Gazelle, registered F-ZWRH, was suitably modified to improve its aerodynamic performance. Piloted by Denis Prost, together with flight test engineer Jean-Marie Besse, the helicopter established three world speed records for aircraft in category E-1C (helicopters weighing between 1,000 and 1,750 kg ore 2'205 - 3,858 lbs).
Until that time, these records had been held by the American Hughes 500.
The new records were:

• Speed over a 3 km course: 310 km/h - 167 kts (previous record: 277 km/h - 150 kts)
• Speed over a 15–25 km course: 310 km/h - 167 kts (previous record: 272 km/h - 147 kts)
• Closed-circuit speed over 100 km: over 296 km/h - 160 kts (previous record: 252 km/h - 136 kts)

According to the website of the Fédération Aéronautique Internationale (FAI), the Gazelle still holds several world speed records.

Aérospatiale also experimentally developed the SA 330Z Puma (F-ZWWR) and an the 350Z Ecureuil (F-WYMZ) equipped with a Fenestron. Both programs were then abandoned.

In the early 1970s, Turbomeca financed an internal turboshaft engine development programme aimed at replacing the previous Artouste and Astazou models. The new engine focused on the use of advanced materials, simplified construction, and reduced maintenance requirements in order to encourage its adoption on light helicopters.
After being tested on a test bench, the Turbomeca Arriel 1 engine was installed on the SA 341-002. The first flight of the aircraft equipped with the new engine took place on December 7, 1974, with test pilot Claude-Yves Barteau at the controls.
The Arriel 1B was later installed on the AS 350B Ecureuil and undoubtedly contributed to its commercial success.

In the famous 1983 film Blue Thunder, the futuristic helicopter used for metropolitan surveillance and equipped with cutting-edge technology is a suitably modified SA 341G Gazelle.
The idea of using the Gazelle came from designer and set decorator Mickey Michaels (1931–1999), who developed the helicopter’s appearance after considering several other models. The production company purchased two aircraft, which were then extensively modified. The changes included additional components attached to the airframe and transparent panels inspired by the design of the AH-64 Apache attack helicopter.
These modifications significantly increased the weight of the helicopters, adversely affecting their performance. For this reason, the production relied on various visual effects and filming techniques to make the aircraft appear faster and more manoeuvrable. The loop performed by pilot Frank Murphy (played by actor Roy Scheider, who became world-famous thanks to Steven Spielberg’s film Jaws, in which he portrayed the main character Martin Brody) during the final sequence was not performed with a real helicopter, but with a radio-controlled model.
The film Blue Thunder is remembered for its spectacular helicopter flight sequences and for addressing themes that were highly innovative at the time, such as mass surveillance and the use of military technology by law-enforcement agencies.

A word about tail rotors…

Heinrich Achenbach (1856–1923), a native of the Siegerland region (Germany), was a true visionary in the field of helicopters, yet remains one of the lesser-known pioneers in the history of rotary-wing aviation. This is probably due to the fact that credit for his invention has often been mistakenly attributed to two men who shared the same surname. Contrary to what is stated in many publications, it was not the brothers Fritz and Wilhelm Achenbach who presented a conceptual design in which, for the first time, a helicopter was equipped with a tail rotor, one that, incidentally, bore a striking resemblance to a Fenestron.
In 1874, Heinrich Achenbach, then a brilliant student at the Technikum in Mittweida, realised that a tail rotor could counteract the reaction torque generated by the main rotor, thereby providing the helicopter with a remarkable degree of stability.
Aware that the propulsion technologies available at the time, such as the steam boiler he had envisaged, and, naturally, the materials then available were far too heavy to allow a helicopter to take off, Achenbach abandoned his plans to build the aircraft.