FIELD OF THE INVENTION AND PRIOR ART

This invention relates to an aircraft, such as an aeroplane, in particular a civilian aeroplane, propelled by one or more fans placed downstream of the fuselage, and more particularly the case wherein the fans are ducted by a nacelle. The invention relates to means for distributing the airflow entering into said nacelle.

The type of turbine engine having a fan at the rear of the fuselage can be found, for example, in an aircraft architecture proposed in the patent applications FR-A1-2 997 681 and FR-A-1 339 141. In this case, the turbine engine is incorporated in the continuation of the fuselage downstream thereof, in order to reduce the noise pollution and fuel consumption of the aircraft by limiting aerodynamic drag by absorption of the boundary layer.

In such an architecture, an aircraft is propelled by a turbine engine having ducted contra-rotating fans, the turbine engine being incorporated at the rear of the fuselage of the aircraft. In general, the turbine engine comprises at least two gas generators which feed a power turbine having two contra-rotating rotors for driving two fans positioned downstream of the gas generators. The gas generators have distinct lateral air intakes to feed each gas generator.

Downstream of the gas generators, the fans are positioned in the continuation of the fuselage of the aircraft and are generally fed by an annular ring connected thereto, so as to absorb at least part of the boundary layer formed around the fuselage. The diameter of the fans is approximately equal to that of the fuselage over the largest cross section thereof. The rotational speed of the fans is generally lower than that for conventional turbine engines, in particular so that the blade tip speed is subsonic.

The two fans constitute a propulsion assembly having a low compression rate and a high flow rate. In such a case, the operation and operability of said propulsion assembly are particularly sensitive to the airflow input conditions in the nacelle, in particular the orientation and homogeneity thereof.

The object of this invention is to provide a solution for adapting at least some of the parameters of the flow entering the nacelle to suit the operating conditions of the propulsion assembly.

DESCRIPTION OF THE INVENTION

For this purpose, the invention relates to an aircraft comprising a fuselage and a propulsion assembly, said propulsion assembly comprising at least one fan rotor placed at the rear of the fuselage, in the continuation thereof along a longitudinal axis, and a nacelle forming a fairing of said at least one fan rotor, through which an airflow passes, said aircraft being characterised in that it comprises a plurality of radial stator arms mounted upstream of said at least one fan rotor and extending between the fuselage and the nacelle, said radial arms comprising at least one variable-pitch movable portion designed to axially deflect said airflow, the variable-pitch movable portions being positioned at the intake of the nacelle.

The invention achieves this object by deflecting the airflow entering the fan rotor which allow to correct non-homogeneities or distortions of said airflow, created in particular during the travel thereof along the fuselage of the aircraft.

The pitch of the radial arms can also have the effect of rectifying the flow upstream of the fan rotor in order to improve the efficiency of the propulsion assembly.

Advantageously, the aircraft further comprises individual means for adjusting the pitch of the movable portion of the radial arms, so as to enable a pitch that can be adapted according to a circumferential non-homogeneity of said airflow upstream of the propulsion assembly.

The adaptive pitch can be used to improve the operability of the propulsion assembly according to the flight conditions of the aircraft.

Preferably, the movable portions of the radial arms pivot about axes which extend radially from the fuselage substantially from the same plane transverse to the longitudinal axis, in order to allow for a homogeneous deflection of the incident airflow before the passage thereof into the fan rotor.

Advantageously, at least one control ring, preferably located inside the fuselage, and one assembly of at least two connecting rods connecting said at least one control ring to each of said movable portions.

According to one feature of the invention, the aircraft comprises a plurality of supporting arms designed to support the nacelle and comprising the variable-pitch movable portions.

Preferably, the plurality of radial arms comprises at least a plurality of supporting arms, designed to support the nacelle.

The use of a plurality of upstream supporting arms increases the homogeneity and symmetry of the absorption of the forces supported by the nacelle. The stiffness thereof can thus be reduced, which contributes to reducing the mass of the assembly.

The plurality of radial arms can comprise at least a plurality of radial vanes forming said movable portion as a whole.

Said movable radial vanes have a chord that is smaller than that of the supporting arms. The vanes therefore have a smaller wake and can be present in greater numbers in order to more precisely homogenise the flow entering the nacelle.

Advantageously, the plurality of radial arms comprises at least a plurality of radial arms comprising blowing means designed to blow, into the environment around a trailing edge of said radial arms, an additional airflow supplementing said airflow in the continuation of the trailing edge.

Blowing air into the continuation of the trailing edge makes it possible to limit the localised slowing down of the flow linked to the arm, called the “wake”, by re-energising the flow. In particular, said wake is a significant source of noise when the blades of the fan rotor meet it downstream. By reducing the wake, the noise generated by the propulsion assembly of the aircraft is also reduced.

Said blowing means can be arranged so as to blow said additional airflow outside said radial arms, upstream of a variable-pitch movable portion.

Advantageously, said fan rotor has an outer diameter that is substantially equal to a maximum diameter of the fuselage, which allows the rotational speed to be kept slow while circulating a high flow of air, and allows a large portion of the boundary layer that develops on the fuselage of the aircraft to be ingested. Preferably, the rotational speed of said at least one fan rotor is less than 340 m/s at the outer periphery of said fan rotor.

The appearance of high speeds when the blades of the fan rotor deflect air can be avoided while obtaining high thrust by means of the circulated airflow. The noise pollution and propulsive losses are thus limited.

Preferably, said aircraft comprises a turbine engine comprising at least one gas generator designed to generate a primary flow, which is carried by a central flow path to at least one power turbine, said power turbine being positioned at the rear of the fuselage in the continuation thereof and driving, at its periphery, said at least one fan rotor.

