Rotorcraft top fairing fitted with a movable member for guiding a stream of air flowing towards the rear of the rotorcraft

A rotorcraft provided on top with a waterdrop-shaped fairing arranged below the rotary wing of a main rotor of the rotorcraft and overlying a cover covering a power plant of the rotorcraft. The trailing edge(s) of the fairing is/are provided with a respective movable member guiding a first stream of air flowing along the fairing and escaping from the trailing edge towards the rear of the rotorcraft in flight. By way of example, the movable member is arranged as a flap or as a bladed roller that may potentially be motor-driven as a function of the effects of the first stream of air on the behavior of the rotorcraft in flight.