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