PROPEL GROUP, AIRCRAFT AND IMPLEMENTATION AT THE TIME OF TAKEOFF

Abstract

PROPULSION GROUP, AIRCRAFT AND IMPLEMENTATION AT THE TIME OF TAKEOFF The present invention relates to a method of implementing a fixed-wing aircraft, the aircraft comprising a fuselage, two wings (106) disposed respectively on either side of the fuselage and comprising a respective trailing edge, and two propulsion groups disposed respectively downstream and at a distance from each wing, each of the propulsion groups comprising a nacelle (112) housing at least two non-coaxial fans (14), said nacelle comprising a lower wall (118) provided with a leading edge and extending substantially in the continuation of the wing, the method being remarkable in that it comprises a takeoff phase of the aircraft during which pivoting means (106.3, 118.1) are progressively rotated, from a first position in which the amount of airflow (F) directed towards the fans is maximized, to a second position in which the trailing edge of the wing is opposite the leading edge of the lower wall. (Figure to be published with the abbreviation: Figure 10).

Description

Title of the invention: PROPULSION GROUP, AIRCRAFT AND IMPLEMENTATION AT THE TIME OF TAKEOFF technical field

[0001] This application relates to the field of fixed-wing aircraft and their implementation. Previous art

[0002] Document WO 2021 / 074516 Al introduces a modern aircraft architecture in which two oblong, lifting nacelles are arranged on either side of the fuselage. Each nacelle incorporates several fans driven in rotation by a gas turbine, itself supplied with gas by a compressor.

[0003] This design makes it possible to reduce aerodynamic drag and increase the lift of the aircraft, resulting in a decrease in fuel consumption.

[0004] However, such a design involves positioning a lower wall of the nacelle in line with the fixed wing of the aircraft, which results in a significant loss of thrust during takeoff.

[0005] The natural stream tube - that is, when considering the nacelle alone - is disturbed by the presence of the wing, which can generate a separation on the lower wall of the nacelle.

[0006] This explains the loss of thrust at low aircraft speeds, for example during takeoff. In this respect, the aircraft architecture initiated by document WO 2021 / 074516 Al offers room for improvement in order to mitigate the phenomenon of air separation at the nacelle inlet. Description of the invention

[0007] The present invention aims to provide a propulsion unit, an aircraft and an associated method, benefiting from the advantages of the prior art in terms of low drag and increased lift and also allowing, in addition, to guarantee thrust at low forward speed of the aircraft, in particular for the purpose of minimizing the distance required for takeoff of said aircraft and the consumption inherent therein.

[0008] The invention relates to a method for implementing a fixed-wing aircraft, the aircraft comprising a fuselage, two wings arranged respectively on either side of the fuselage and comprising a respective trailing edge, and two propulsion units arranged respectively downstream and at a distance from each wing, each of the propulsion units comprising a nacelle housing at least two non-coaxial fans, said nacelle comprising a lower wall provided with a leading edge and extending substantially in line with the wing, the method being remarkable in that it includes an aircraft takeoff phase during which pivoting means are progressively pivoted, from a first position in which the amount of airflow directed towards the blowers is maximized, to a second position in which the trailing edge of the wing is opposite the leading edge of the lower wall.

[0009] The nacelle profile is not substantially circular but rather oblong, the nacelle housing at least two non-coaxial blowers. The upper and lower walls of the nacelle are load-bearing.

[0010] Maximizing the amount of airflow directed towards the blowers can correspond to an increase in the volume of air entering the nacelle, by means of an increase in the nacelle opening section.

[0011] According to an advantageous embodiment of the invention, the pivoting means comprise a pivoting flap forming the trailing edge of the wing or a pivoting slat forming the leading edge of the lower wall.

[0012] Preferably, the pivoting flap is capable of pivoting upwards, i.e., radially inwards, in a direction perpendicular to a longitudinal axis of the turbine or to an axis of the blower. Preferably, the pivoting nozzle is capable of pivoting downwards, i.e., radially outwards. The main direction of circulation of the air flow in the nacelle is substantially parallel to the longitudinal axis of the aircraft.

[0014] Advantageously, the pivoting nozzle in the first position allows the air from the underside of the aircraft wing to be captured, which allows said air to be introduced into the nacelle and directed towards the blowers.

[0015] According to an advantageous embodiment of the invention, the pivoting means comprise a pivoting flap forming the trailing edge of the wing and a pivoting slat forming the leading edge of the lower wall.

[0016] Advantageously, the combination of the pivoting of the pivoting flap with the pivoting of the slat makes it possible to minimize the phenomenon of air separation while increasing the volume of air directed towards the fans, thus maximizing the thrust of the aircraft during takeoff.

[0017] According to an advantageous embodiment of the invention, the first position differs from the second position by an angle between 10° and 50°.

[0018] Preferably, in the second position, the pivot angle of the pivoting means is zero with respect to a reference axis which may be parallel to the longitudinal axis of the turbomachine.

[0019] The angular range between the first and second positions is more preferably between 10° and 30°, and even more preferably is equal to 20°.

[0020] According to an advantageous embodiment of the invention, the pivoting means are linked to the speed of the aircraft so that the second position is reached before the aircraft reaches a decision speed of "VI".

[0021] Beyond the speed of decision-making, the pivoting flap can be used as a high-lift element of the aircraft, allowing the aircraft to be promoted to lift after the take-off phase.

[0022] According to an advantageous embodiment of the invention, the pivoting means are controlled inversely proportionally to the speed of the aircraft during the takeoff phase.

[0023] Thus, the pivot angle varies from a position maximizing the air intake into the nacelle (first position) at an initial zero speed to a reference position (second position) once a speed is reached.

[0024] Thus, the higher the advance speed, the lower the pivot angle, and vice versa.

[0025] Alternatively, the control can be ensured by a non-linear relationship following a polynomial or exponential type function, or even following a timer since prior to the takeoff of an aircraft, the time prior to reaching the decision speed "VI" can be estimated.

[0026] Preferably, the method includes a cruise flight phase during which the pivoting means remain stationary. Here, "stationary" means that they are preferably in the second position and remain stationary in rotation within a reference frame attached to the aircraft.

[0027] Preferably, the pivoting means according to the method of the invention are operated only during the takeoff phase of the aircraft. To this end, during the flight of the aircraft, i.e., after takeoff, the pivoting means are preferably in the second position.

[0028] The invention also relates to a fixed-wing aircraft comprising a fuselage, two wings arranged respectively on either side of the fuselage and comprising a respective trailing edge, and two propulsion units arranged respectively downstream and at a distance from each wing, each of the propulsion units comprising a nacelle housing at least two non-coaxial fans, said nacelle comprising a lower wall provided with a leading edge and extending substantially in the continuation of the wing, the aircraft being remarkable in that it comprises pivoting means configured to be pivoted, from a first position in which the quantity of airflow directed towards the fans is maximized, to a second position in which the trailing edge of the wing is opposite the leading edge of the lower wall.

[0029] According to an advantageous embodiment of the invention, the pivoting means comprise a pivoting flap forming the trailing edge of the wing and extending preferably- tiellement over the entire span of the gondola.

[0030] According to an advantageous embodiment of the invention, the pivoting means comprise a pivoting beak forming the leading edge of the lower wall and preferably extending over the entire span of the nacelle.

[0031] Alternatively, the pivoting means can be sectioned into segments actuated independently of each other and covering all or part of the span of the nacelle, in order to more finely adjust the air inlet section and therefore the flow rate.

[0032] The invention also relates to a propulsion unit for an aircraft according to the invention, the propulsion unit comprising a nacelle housing at least two non-coaxial fans, said nacelle comprising a lower wall, notable in that the lower wall comprises a nozzle disposed upstream of the fans, said nozzle being pivotable, from a first position in which the quantity of airflow directed towards the fans is maximized, to a second position in which said nozzle is able to be disposed opposite the trailing edge of a wing of the aircraft.

[0033] Advantageously, the nozzle is able to pivot downwards, the latter can increase a cross-section in the direction of flow of the airflow entering the nacelle, thus allowing the increase of the volume of air directed towards the blowers, which prevents the occurrence of possible internal detachments.

[0034] Advantageously, the present invention makes it possible to restore the maximum theoretical thrust of the nacelle considered in isolation from the wing, at low forward speed of the aircraft, thus allowing the latter to quickly reach the decision speed, which results in a reduced takeoff distance of the aircraft.

[0035] In addition to the technical advantages discussed above, the invention is particularly advantageous in that it has a positive impact on fuel consumption.

[0036] The invention also has the advantage of being adaptable to existing aircraft, as it does not require modification of a standard wing or fuselage. Brief description of the drawings

[0037] [Fig.1] represents an aircraft according to the invention;

[0038] [Fig.2] represents a graph tracing the evolution of the thrust generated at a zero forward speed by a propulsion unit alone and by a propulsion unit arranged downstream of a wing of an aircraft according to the prior art;

[0039] [Fig.3] illustrates a cross-sectional view of the propulsion unit alone generating the thrust measured in the graph of [Fig.2];

[0040] [Fig.4] illustrates a cross-sectional view of the propulsion unit arranged downstream of the wing of the aircraft and generating the thrust measured in the graph of [Fig.2];

[0041] [Fig.5] illustrates a cross-sectional view of a wing and the nacelle in a first position according to a first embodiment of the invention;

[0042] [Fig.6] illustrates a cross-sectional view of the wing and nacelle of the [Fig.5] in a intermediate position;

[0043] [Fig.7] illustrates a cross-sectional view of the wing and nacelle of the [Fig.5] in a third position;

[0044] [Fig.8] illustrates a cross-sectional view of the wing and a nacelle in a first position according to a second embodiment of the invention;

[0045] [Fig.9] illustrates a cross-sectional view of the wing and nacelle of the [Fig.8] in a second position;

[0046] [Fig. 10] illustrates a cross-sectional view of the wing and nacelle in a first position according to a third embodiment of the invention;

[0047] [Fig.11] illustrates a cross-sectional view of the wing and nacelle of [Fig.10] in a second position. Detailed description

[0048] The figures represent the elements schematically. Some dimensions may be exaggerated to facilitate reading the drawings.

[0049] Upstream and downstream are understood in the direction of airflow. The longitudinal direction is the direction of the aircraft's longest dimension, i.e., parallel to the fuselage (corresponding to the X-axis of [Fig. 1]). The transverse direction (Y-axis of [Fig. 1]) is perpendicular to the fuselage and horizontal when the aircraft is on the ground.

[0050] It is understood that particular embodiments of the invention are drawn but that the figures do not in any way limit the scope of protection which is only dictated by the claims.

[0051] Also, each element of each figure can be combined with each other element of each other figure according to all technically possible combinations.

[0052] Fig. 1 shows an aircraft 2. This consists of a fuselage 4 and two wings 6, fixed relative to the fuselage 4. The wings are fitted with flaps 8.

[0053] On either side of the fuselage 4 and downstream of the wings 6 are located two propulsion units 10. By "propulsion unit" is meant a module capable of generating thrust necessary for the flight of the aircraft 2.

[0054] The propulsion group 10 includes a nacelle 12. This includes, among other things, a lower wall, an upper wall and vertical walls connecting the lower wall to the upper wall and subdividing the nacelle into several compartments, and each of these includes a blower.

[0055] The nacelle 12 can be mechanically connected to the fuselage 4 and / or the wing 6 by means of connecting links. An arm extending substantially transversely from the fuselage 4 can for example connect nacelle 12 to fuselage 4 on the downstream side of nacelle 12.

[0056] The nacelle 12 comprises a plurality of fans. These can be driven in rotation by a respective turbine. Each fan can be part of a self-contained unit (turbine-jet type with compressor, combustion chamber, and turbines). Alternatively, the turbines driving the fans can be driven by a pressurized gas produced elsewhere in the aircraft: for example, a common compressor for several fans can supply the nacelle turbines with pressurized gas. In another embodiment, the fans are driven by an electric motor.

[0057] Fig. 2 represents a graph showing the evolution of thrust as a function of engine speed on a test bench (at zero advance speed of the nacelle in the airflow).

[0058] Graph 100 shows the thrust for a propulsion unit alone (visible in [Fig.3]) and for a propulsion unit arranged downstream of a wing of an aircraft according to the prior art (visible in [Fig.4]).

[0059] Graph 100 of [Fig.2] illustrates at least partially the technical problem that the present invention aims to solve.

[0060] Curve 102 shows the evolution of the thrust generated by the propulsion group alone and curve 104 shows the thrust of the propulsion group preceded by a wing.

[0061] It can be observed that the evolution 102 is almost exponential, which corresponds to normal operating conditions of an aircraft.

[0062] As for curve 104, it departs from the reference curve 102 at 10,000 rpm and plateaus around 15,000 rpm at a thrust level corresponding to almost half the thrust measured at the same engine speed without the wing. The reasons for this regression are discussed later.

[0063] Fig. 3 illustrates a cross-sectional view of the propulsion unit alone generating the measured thrust and represented according to the evolution 102 of the graph of Fig. 2.

[0064] The propulsion group nacelle 10 comprises at least two non-coaxial fans 14, only one of which is visible in this section along an axis 14.1 of the fan 14.

[0065] The blower 14 is attached to a shaft supported by bearings. Support arms can be arranged downstream of the blower 14 to connect the bearings to the upper wall 16 and lower wall 18.

[0066] The fan 14 generates an annular airflow Fl whose principal direction is coaxial with the fan axis 14.1. The air streamline 20 F entering the nacelle is in contact exclusively with the nacelle and exhibits no anomalies. In this configuration, the propulsion unit 10 is capable of generating a reference thrust for the aircraft.

[0067] The streamline 20 represents an aerodynamic envelope of the airflow F entering an aircraft nacelle at a very low forward speed or even at zero speed, such as a takeoff phase for example.

[0068] In order to ensure a certain lift and a reduction in drag, it is advantageous to position the nacelle in line with the wing. The aerodynamic influence of the wing on the nacelle is illustrated in [Fig. 4].

[0069] Figure 4 illustrates a cross-sectional view of the propulsion unit arranged downstream of the aircraft wing. The thrust of such an assembly is represented by curve 104 of the graph in Figure 2.

[0070] The nacelle 12 is positioned so that the lower wall 18 is substantially at the same height (along Z) as a trailing edge of the wing 6.

[0071] Wing 6 has an extrados 6.1 and an intrados 6.2.

[0072] The distance H represents the gap between the trailing edge of the wing 6 and a leading edge of the lower wall 18. The distance H can measure between a few tens of centimeters and several meters.

[0073] Under the same speed conditions as those of [Fig.3], the arrangement of the lower wall 18 in the extension of the wing 6 of the aircraft creates separations 22 of the airflow both at the trailing edge of the wing 6 at the extrados 6.1 and at the leading edge of the lower wall 18 inside the nacelle 12. Indeed, the lower wall 18 creates an adverse static pressure gradient inside the nacelle 12, which slows the flow over the extrados 6.1 and promotes separation towards the trailing edge of the wing 6.

[0074] The separation 22 of the flow from the lower wall 18 causes a depression over at least 20% of an air inlet section in the nacelle 12. This reduces the thrust deliverable by the propulsion unit 10, thus explaining the loss of thrust at low speed of the aircraft.

[0075] In this regard, the three embodiments of the invention which will be detailed in this description, aim to eliminate the low-speed separations 22 of the aircraft.

[0076] Figures 5 to 7 illustrate a cross-sectional view of a wing 106 and the nacelle 12 according to a first embodiment of the invention. These figures represent the wing 106 and the nacelle 12 in three different positions during a takeoff phase of the aircraft 2 of [Fig. 1].

[0077] With reference to [Fig.5], the arrangement of the wing 106 and the nacelle 12 is in a first position in which the aircraft is at rest and ready for imminent takeoff.

[0078] The aircraft includes pivoting means 106.3 corresponding to a pivoting flap 106.3 forming the trailing edge of the wing 106. The pivoting can be done substantially around an axis 106.5 parallel to the transverse axis Y of [Fig.l].

[0079] The pivoting flap 106.3 can correspond to at least one of the flaps 8 of the wing 6 illustrated in [Fig.1].

[0080] The pivoting flap 106.3 can extend over the entire wingspan of the aircraft or at least over the entire span of the corresponding nacelle. Alternatively, the flap 106.3 can be composed of several segments that can be actuated independently of each other.

[0081] Preferably, the pivoting flap 106.3 is opposite the nacelle 12, and extends transversely over at least 80% of a total extent of the lower wall 18.

[0082] In this first position, the pivoting flap 106.3 is inclined at an angle α with respect to the axis of the blower 14.1 (which is substantially parallel to the longitudinal axis X of [Fig. 1]). The angle α is preferably less than 60° and greater than 10°. The angle α is here equal to 50°, but can alternatively be 30° or 20°.

[0083] Preferably, the pivoting flap 106.3 extends over at least 10% and at most 40% of the axial dimension (horizontal direction on the [Fig.5]) of the wing 6.

[0084] Advantageously, the inclination of the pivoting flap 106.3 at angle α allows the airflow F to be introduced into the nacelle 12 and retained at the intrados 106.2 of the wing. Furthermore, the incoming airflow F is guided towards a radially central position of the fan 14, which promotes air intake and prevents the formation of the separations 22 illustrated in [Fig. 4].

[0085] With reference to [Fig.6], the arrangement of the wing 106 and the nacelle 12 is in an intermediate position in which the aircraft is accelerating (which can be done on the ground) before the aircraft climbs, in particular before reaching the decision speed “VI”.

[0086] In this configuration, the angle aa has a smaller value than that of the first position illustrated in [Fig. 5]. Indeed, the angle a decreases as the speed increases during the acceleration phase of the aircraft.

[0087] In this respect, the higher the speed before reaching the decision speed, the lower the angle α. This allows the air to be guided progressively towards the nacelle and maintains the lowest streamline as homogeneous as possible without presenting a risk of separation.

[0088] The reduction of angle a can be managed by an aircraft servo system.

[0089] With reference to [Fig. 7], the arrangement of the wing 106 and the nacelle 12 is in a position where the aircraft is in flight after the acceleration phase. Here, the aircraft has reached or exceeded the decision speed.

[0090] In this configuration, the pivoting flap 106.3 is opposite the leading edge of the lower wall 18 of the nacelle 12, and the angle α of inclination is zero, i.e. the flap pivoting 106.3 presents a direction parallel to the axis 14.1 of the blower 14.

[0091] In this configuration, the speed of the aircraft is sufficient so that the flow does not present a risk of separation (those illustrated in [Fig.4]).

[0092] Advantageously, the airflow F entering the nacelle is guided parallel to the axis 14.1 all along the longitudinal extension of the wing 106, allowing increased lift of the aircraft and no air separation.

[0093] The first position differs from the second position by an angle between 10° and 50°. This difference may correspond to an angular deflection of the pivoting flap 106.3. The pivoting flap 106.3 may alternatively be able to pivot downwards, beyond a neutral position.

[0094] Figures 8 and 9 illustrate a cross-sectional view of the wing 6 and a nacelle 112 according to a second embodiment of the invention.

[0095] Identical elements between different embodiments shall have the same reference signs, while similar elements but including differences according to the relative embodiment shall be incremented by 100.

[0096] Figures 8 and 9 show the same positions and flight phases of the aircraft indicated in Figures 5 and 7.

[0097] The arrangement of the wing 6 and the nacelle 112 is in the first position. In this configuration, the aircraft includes pivoting means 118.1 corresponding to a pivoting slat 118.1 forming the leading edge of the lower wall 118 of the nacelle 112. The pivoting can be done substantially around the transverse axis Y of the [Fig. 1].

[0098] Preferably, the swiveling nozzle 118.1 includes an axis of rotation axially adjacent to the blower 14. In this respect, the pivoting axis 118.3 of the swiveling nozzle 118.1 may include an axial position substantially identical to that of the blowers 14.

[0099] Indeed, the swiveling beak 118.1 extends over at least 10% and at most 30% of the axial dimension of the gondola (horizontal direction on the [Fig.8]).

[0100] Preferably, the swiveling nozzle 118.1 extends over the entire span of the lower wall 118 (along Y). Alternatively, the swiveling nozzle 118.1 is sectioned into independent segments, each of which can be specific to a blower.

[0101] In this first position, the pivoting beak 118.1 is inclined at an angle [3 with respect to a longitudinal direction 118.2 (parallel to Z on the [Fig.1]) and passing through its pivot axis 118.3.

[0102] Preferably, the direction 118.2 of the leading edge of the lower wall 118 is substantially perpendicular to the axis 14.1 of the blower 14 (which is substantially parallel to the longitudinal axis X of the [Fig.1]), but said direction 118.1 may have an angle of at most 20° or 10° with the axis 14.1.

[0103] In this first position at zero aircraft speed, the angle [3 defined by the inclination of the pivoting beak 118.1 with respect to the direction 118.2, is preferably less than 60° and greater than 10°. Here, the angle [3 is equal to 50°, or equal to 30° or equal to 20°.

[0104] Advantageously, the angle [3 in the first position allows to maximize the volume of air entering the nacelle in order to maximize the thrust and to avoid the creation of air separation at low forward speeds of the aircraft.

[0105] Similar to the pivoting flap 106.3 of [Fig.5], the angle [3 of the pivoting beak 118.1 is controlled to decrease as the speed increases during the acceleration phase of the aircraft.

[0106] Fig. 9 illustrates a cross-sectional view of wing 6 and nacelle 112 of Fig. 8 in a second position.

[0107] In this configuration, the pivoting beak 118.1 is opposite the trailing edge of the wing 6, and the angle [3 of inclination is preferably zero.

[0108] Advantageously, the airflow F entering the nacelle is guided parallel to the axis 14.1 all along the longitudinal extension of the wing 6, allowing increased lift of the aircraft and preventing air separation.

[0109] The first position differs from the second position by an angle between 10° and 50°. This difference may correspond to an angular deflection of the pivoting nozzle 118.1. Alternatively, the nozzle may, if necessary, pivot upwards beyond the position illustrated in [Fig.9].

[0110] The reduction of angle [3 is preferably managed by the same control system as that ensuring the management of angle a.

[0111] Figures 10 and 11 illustrate a cross-sectional view of the wing 106 and the nacelle 112 according to a third embodiment of the invention.

[0112] This third mode corresponds to a combination of the two previous modes. In this respect, the pivoting means include both the pivoting flap 106.3 illustrated in Figures 5 to 7, and the pivoting slat 118.1 of Figures 8 and 9. This technical solution therefore acts both at the trailing edge of the aircraft wing and at the leading edge of the lower wall of the nacelle.

[0113] Figures 10 and 11 show the same aircraft positions and flight phases indicated in Figures 5 and 7.

[0114] The arrangement of the wing 106 and the nacelle 112 is in the first position. In this configuration, the quantity of airflow F directed towards the fans is maximized by the combined pivoting of the pivoting flap 106.3 and the pivoting nozzle 118.1. In this respect, the angles a and [3 are preferably equal.

[0115] Advantageously, the deflection of the flap 106.3 allows the airflow to be guided along the upper surface 106.1 towards the fans 14, and in parallel, the deflection of the pivoting nozzle 118.1 allows a portion of the air located directly above the lower surface to be captured. by increasing the air intake section in nacelle 112.

[0116] Fig. 11 illustrates a cross-sectional view of the wing and nacelle of Fig. 10 in the second position.

[0117] In this configuration, the swiveling spout 118.1 is opposite the flap 106.3, and the angles a and [3 are preferentially nuis.

[0118] Takeoffs are thus avoided and the aircraft's propulsion group is able to provide the maximum thrust necessary for the aircraft to take off.

[0119] Indeed, the propulsion group according to one of the three embodiments of the present invention is capable of generating a low-speed thrust comparable to the thrust that would be delivered without a wing arranged directly upstream of the nacelle.

[0120] In this regard, by regulating the pivoting of the pivoting means 106.3, 118.1 appropriately according to the speed of the aircraft, the propulsion group of the invention can generate a thrust similar to that illustrated by curve 102 of [Fig.2].

Claims

Demands

1. A method for operating a fixed-wing aircraft (2), the aircraft (2) comprising a fuselage (4), two wings (6; 106) arranged respectively on either side of the fuselage (4) and comprising a respective trailing edge, and two propulsion units (10) arranged respectively downstream and at a distance (H) from each wing (6; 106), each of the propulsion units (10) comprising a nacelle (12; 112) housing at least two non-coaxial fans (14), said nacelle (12; 112) comprising a lower wall (18; 118) having a leading edge and extending substantially in line with the wing (6; 106), the method being characterized in that it comprises a takeoff phase of the aircraft during which pivoting means (106.3, 118.1) comprising a pivoting flap (106.3) forming the trailing edge of the wing (106), are progressively pivoted, from a first position in which the pivoting flap (106.3) is inclined with respect to an axis (14.1) blowers (14), to a second position in which said pivoting flap (106.3) is opposite the leading edge of the lower wall (18; 118).

2. Method according to claim 1, characterized in that the pivoting means (106.3, 118.1) comprise a pivoting flap (106.3) forming the trailing edge of the wing (106) and a pivoting slat (118.1) forming the leading edge of the lower wall (118).

3. A method according to any one of claims 1 or 2, characterized in that the first position differs from the second position by an angle between 10° and 50°.

4. A method according to any one of claims 1 to 3, characterized in that the pivoting means (106.3, 118.1) are servo-controlled to the speed of the aircraft (2) so that the second position is reached before the aircraft (2) reaches a decision speed “VI”.

5. A method according to any one of claims 1 to 4, characterized in that the pivoting means (106.3, 118.1) are inversely servo-proportional to the speed of the aircraft (2) during the takeoff phase.

6. Fixed-wing aircraft (2) comprising a fuselage (4), two wings (6; 106) arranged respectively on either side of the fuselage (4) and comprising a respective trailing edge, and two propulsion units (10) arranged respectively downstream and at a distance (H) from each wing (6; 106), each of the propulsion units (10) comprising a nacelle (12;

7.

8.

9. 112) accommodating at least two non-coaxial fans (14), said nacelle (12; 112) comprising a lower wall (18; 118) having a leading edge and extending substantially in line with the wing (6; 106), the aircraft (2) being characterized in that it comprises pivoting means (106.3, 118.1) comprising a pivoting flap (106.3) forming the trailing edge of the wing (106), configured to be pivoted, from a first position in which the pivoting flap (106.3) is inclined with respect to an axis (14.1) of the fans (14), to a second position in which said pivoting flap (106.3) is opposite the leading edge of the lower wall (18; 118). Aircraft (2) according to claim 6, characterized in that the pivoting flap (106.3) preferentially extends over the entire span of the nacelle (12). Aircraft (2) according to claim 6 or 7, characterized in that the pivoting means (118.1) comprise a pivoting beak (118.1) forming the leading edge of the lower wall (118) and extending preferably over the entire span of the nacelle (12). Propulsion unit (10) for an aircraft (2) according to claim 6, the propulsion unit (10) comprising a nacelle (112) housing at least two non-coaxial fans (14), said nacelle comprising a lower wall (118), characterized in that the lower wall (118) comprises a nozzle (118.1) disposed upstream of the fans (14), said nozzle (118.1) being pivotable, from a first position in which the quantity of airflow (F) directed towards the fans (14) is maximized, to a second position in which said nozzle (118.1) is able to be disposed opposite the trailing edge of a wing (6; 106) of the aircraft.