page_title: Fenestron
section_title: History
hierarchical_section_title: Fenestron / History
caption_attribution_description: English: Reco/liaison helicopter Sud-Aviation Gazelle SA 342M (registration: F-MABW #3458) of the French Army's Light Aviation (ALAT), Army's Helicopters Squadron (EHADT). Location: Pyrenees mountains, near Lourdes, France. Français&#160;: Hélicoptère Sud-Aviation Gazelle SA 342M (immatriculation&#160;: F-MABW #3458) de reconnaissance/liaison de l'Aviation Légère de l'Armée de Terre (ALAT, France), Escadrille Hélicoptères de l'Armée De Terre (EHADT). Lieu&#160;: Pyrénées, près de Lourdes, France.
context_page_description: A Fenestron is a protected tail rotor of a helicopter operating like a ducted fan. The term Fenestron is a trademark of multinational helicopter manufacturing consortium Airbus Helicopters. The word itself comes from the Occitan term for a small window, and is ultimately derived from the Latin word fenestra for window.
  The Fenestron differs from a conventional tail rotor by being integrally housed within the tail unit of the rotorcraft and, like the conventional tail rotor it replaces, functions to counteract the torque of the main rotor. While conventional tail rotors typically have two or four blades, Fenestrons have between seven and eighteen blades; these may have variable angular spacing so that the noise is distributed over different frequencies. By placing the fan within a duct, several distinct advantages over a conventional tail rotor are obtained, such as a reduction in tip vortex losses, the potential for substantial noise reduction, while also shielding both the tail rotor itself from collision damage and ground personnel from the hazard posed by a traditional spinning rotor.
context_section_description: The concept of the Fenestron was first patented in Great Britain by the Glaswegian engineering company G. & J. Weir Ltd. It was designed by British aeronautical engineer C. G. Pullin as an improvement to helicopters in British patent number 572417, and is registered as having been filed during May 1943. At that time, Weir had been participated in development work for the Cierva Autogiro Company, who was the holding company for the patent. In concept, the invention was to function as a viable replacement for the conventional tail rotor arrangement, aiming to produce improvements in both safety and performance upon such equipped rotorcraft. However, this early work in Britain would not directly lead to any released product by Cierva making use of this innovation. Instead, the Fenestron would only be further developed during the 1960s by an unrelated company.
  The Fenestron was first practically applied by the French aircraft manufacturer Sud Aviation, who had decided to introduce it upon the second experimental model of their in-development SA 340 (the first prototype had been furnished with a conventional anti-torque tail rotor). The SA 340's fenestron was designed by French aerodynamicist Paul Fabre; unusually, this unit had its advancing blade set at the top in defiance of conventional practice, but this was reasoned to pose little impact upon this particular helicopter. Fitted accordingly, on 12 April 1968, the SA 340 became the first rotorcraft to fly using a Fenestron tail unit. Having been determined to have been satisfactory, this tail unit was retained and was put into production on a refined model of the rotorcraft, which was designated Aérospatiale SA 341 Gazelle.
  Over time, the design and performance of the Fenestron has been improved by Sud Aviation and its successor companies, as well as by other companies. During the late 1970s, Aérospatiale (which Sud Aviation had merged into) launched a second generation all-composite unit; it primarily featured a reversal of the blade's direction of rotation as well as adopting a 20 per cent larger diameter duct for greater efficiency. This unit was fitted onto the Aérospatiale SA 360 Dauphin, along with its more successful AS365 Dauphin model and its derivatives. While further flight experiments were conducted using an even larger Fenestron upon an SA 330 Puma medium lift helicopter around the same time frame, it was concluded that there were practical limits to how large a helicopter such a configuration would be suited to, and production examples of the Puma retained a conventional tail rotor instead.
  During the 1990s, a third generation Fenestron was produced by Eurocopter (Aérospatiale's multinational successor), equipped with unevenly-spaced blades in order to optimize its noise levels; this unit was first fitted onto the company's EC135 helicopter, and was later incorporated into the designs of the EC130 and the EC145, the latter of which having original been produced for over a decade with a conventional tail rotor. During the 2010s, multinational helicopter manufacturer Airbus Helicopters (a rebranded version of the Eurocopter entity) developed the Fenestron further for their new H160, a medium-twin sized rotorcraft; in this revision, the fan duct was intentionally sloped by 12 degrees to achieve improved performance and greater stability when being operated with higher payloads and flown at lower speeds.
  A Fenestron is normally paired with a larger vertical stabiliser unit that also performs the role of compensating for torque; this configuration has the effect of reducing wear on the Fenestron blades and transmission system, which in turn leads to maintenance savings. Furthermore, the adoption of larger diameter units, while posing some engineering challenges, normally increases their efficiency and decreases their power requirements. Advanced implementations of the Fenestron are provisioned with stators and adjustable weights in order to optimise the blades for a reduction in power required and pitch control loads imposed. During the 2010s, Airbus Helicopters s
caption: An SA 342M Gazelle of the French Army's Light Aviation (ALAT), the first Fenestron-equipped helicopter to enter production
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