Fenestron

[8] 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.

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).

[10] 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.

[5] 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.

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.

[15] 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 stated that it expected the design of the Fenestron to continue to be refined, in order to suit rotorcraft of increasing tonnages and to enable additional innovations to be made in the field.

Ducted fan tail rotors have also been used in the Russian Kamov Ka-60 medium-lift helicopter,[17] and also on the Japanese military's Kawasaki OH-1 Ninja reconnaissance rotorcraft.