METHOD FOR ACTIVE CONTROL OF WAKE-NACELLE AND CORRESPONDING AIRCRAFT INTERACTION

Abstract

METHOD FOR ACTIVE CONTROL OF WAKE-NACELLE AND CORRESPONDING AIRCRAFT INTERACTION The invention relates to a method for implementing a fixed-wing aircraft, the aircraft comprising a fuselage, two wings (6) each generating a wake (20) and arranged respectively on either side of the fuselage and comprising a flap (8), and two propulsion units (10) arranged respectively downstream and at a distance from each wing, each of the propulsion units comprising a nacelle (12) housing at least two non-coaxial fans (14), said nacelle comprising a lower wall (18) extending substantially in the continuation of the wing, the lower wall having a lower surface (18.1), remarkable in that said method comprises a flight phase of the aircraft during which the flap is pivoted from a first position in which the wake is at a distance from the lower surface, to a second position (B) in which the wake is in contact with the lower surface. (Figure to be published with the abbreviation: Figure 5).

Description

Title of the invention: METHOD FOR ACTIVE CONTROL OF WAKE-NACELLE AND CORRESPONDING AIRCRAFT INTERACTION 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 involves positioning the lower wall of the nacelle in line with the fixed wing of the aircraft. In this configuration, the wing generates a wake that interacts with the nacelle and makes contact with its lower surface under normal flight conditions. This interaction will be referred to in this application as "wing wake-nacelle interaction," or "WWNI" (an acronym for "wing wake nacelle interaction"). WWNI reduces aerodynamic drag and increases the aircraft's lift, resulting in lower fuel consumption.

[0004] However, the position of the wing wake varies depending on the angle of incidence of the airflow on the wing and also depending on the level of thrust generated by the aircraft. These variations induce a displacement of the wake position relative to the lower surface. Vertical shifts in the wake position generate a significant increase in nacelle drag.

[0005] In this regard, the aircraft architecture initiated by document WO 2021 / 074516 A1 offers room for improvement in order to mitigate the phenomenon of vertical wake displacement and to maintain WWNI for all aircraft flight conditions. Description of the invention

[0006] The present invention aims to provide an aircraft and an associated method, allowing the state-of-the-art wake-nacelle interaction (WWNI) to be maintained under all aircraft flight conditions, so as to avoid the wing wake moving away from the lower surface of the nacelle, and to keep said wake in contact with the lower surface permanently, thus maintaining low drag and increased lift of the aircraft.

[0007] The invention relates to a method for implementing a fixed-wing aircraft, the aircraft comprising a fuselage, two wings each generating a wake and disposed respectively on either side of the fuselage and comprising a flap, and two propulsion units disposed 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 extending substantially in line with the wing, the lower wall having a lower surface, the method being remarkable in that it comprises a flight phase of the aircraft during which the flap is pivoted from a first position in which the wake is at a distance from the lower surface, to a second position in which the wake is in contact with the lower surface.

[0008] 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. The main direction of circulation of the air flow in the nacelle is substantially parallel to the longitudinal axis of the aircraft.

[0010] According to an advantageous embodiment of the invention, the first position differs from the second position by a deflection angle of between 0.5° and 7°. More preferably, the deflection angle is less than 5°.

[0011] Preferably, in the first position, the deflection angle of the pivoting flap is zero with respect to a reference axis that may be parallel to the longitudinal axis of the turbomachine. The deflection angle is measured between the flap and the reference axis. This first position may correspond to a cruise flight phase.

[0012] According to an advantageous embodiment of the invention, the pivoting flap is controlled proportionally to the angle of incidence of the airflow on the wing, and / or to the aircraft's pitch attitude, and / or to the aircraft's speed, and / or to the level of thrust generated by the aircraft. When several of the above criteria are taken into consideration, the proportionality can be "weighted" for each of the criteria.

[0013] In a first embodiment, the deflection angle of the flap varies from the first position to the second position proportionally to the angle of incidence of the airflow on the wing. Thus, the greater the angle of incidence, the greater the deflection angle, and vice versa.

[0014] Alternatively or in parallel, the deflection angle increases as a function of the increase in the attitude and / or speed of the aircraft and / or the level of thrust generated by the aircraft, and vice versa.

[0015] Alternatively, the control can be ensured by a non-linear relationship following a polynomial or exponential type function.

[0016] Advantageously, the flap pivot control makes it possible to ensure active control of the aircraft's wake-nacelle interaction (WWNI) in all the flight conditions.

[0017] According to an advantageous embodiment of the invention, the aircraft includes means for detecting air on the lower surface aimed at detecting the detachment of the wake from the lower surface and the pivoting of the flap is regulated to restore contact of the wake to the lower surface.

[0018] Advantageously, the detection means allow for a control or verification function to be performed in parallel with the servo-controlled management of the flap's deflection angle. Indeed, after the proportional servo-control, the deflection angle can increase or decrease further when moving from the first to the second position in order to ensure that the wake is in contact with the lower surface of the nacelle, thus securing the servo-control of the pivoting flap.

[0019] According to an advantageous embodiment of the invention, the pivoting flap is configured to pivot upwards, in a direction perpendicular to an axis of the blower, when the wake is externally away from the lower surface of the nacelle, so as to bring said wake back into contact with said lower surface. Here, the wake is located downwards and below the lower surface of the nacelle; the wake is said to be out of contact.

[0020] According to an advantageous embodiment of the invention, the pivoting flap is configured to pivot downwards when the wake is directed towards the blowers, so as to bring said wake back into contact with the lower surface. Here, the wake passes through the interior of the nacelle; this is called wake ingestion.

[0021] Advantageously, pivoting the flap allows the vertical offset of the wake position to be corrected by raising or lowering said position until said wake is in contact with the lower surface, as during WWNI in so-called normal flight conditions, i.e. conditions in which the angle of incidence of the airflow on the wing is substantially low and constant, and the thrust level is also substantially constant.

[0022] Alternatively, the pivoting flap can be formed of several segments actuated independently of each other and covering all or part of the span of the nacelle, in order to adjust more finely and locally the correction of the wake offset over a part of the total span of the lower surface of the nacelle.

[0023] According to an advantageous embodiment of the invention, the flight phase of the aircraft corresponds to an ascent or cruise or descent phase.

[0024] Preferably, the pivoting flap according to the method of the invention is not operated during the aircraft's takeoff phase. To this end, during said takeoff phase, the flap remains stationary. Here, "stationary" means that the flap is preferably in its initial position and remains stationary in rotation within a frame of reference attached to the aircraft.

[0025] The invention also relates to a fixed-wing aircraft comprising a fuselage, two wings each generating a wake and arranged respectively on either side of the fuselage and comprising a flap, 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 lower surface and extending substantially in the extension of the wing, the aircraft being remarkable in that it comprises means for controlling the pivoting of the flap, from a first position in which the wake is at a distance from the lower wall, to a second position in which the wake is in contact with the lower wall.

[0026] The control means preferably correspond to a set of components comprising at least the detection means, actuators capable of pivoting the flap, and a control unit capable of executing the process of the invention.

[0027] According to an advantageous embodiment of the invention, the control means ensure that the wake is attached to the lower wall in all circumstances, in particular by regulating the position of the flap according to a detected position of the wake.

[0028] Preferably, the regulation of the flap position is based on aerodynamic models simulated upstream to predefine the flap angle, and advantageously, the detection means act as a corrective means for the aerodynamic models from the simulation.

[0029] According to an advantageous embodiment of the invention, the aircraft includes detection means and means for processing signals from the detection means in order to determine the relative position of the wake with respect to the lower wall.

[0030] Preferably, the control means further include the means for processing the signals from the detection means.

[0031] Advantageously, the present invention makes it possible to restore WWNI, allowing the wake to be in permanent contact with the lower surface even during flight conditions that induce changes in the angle of attack of the airflow over the wing and in the thrust level. The invention therefore makes it possible to guarantee WWNI and thus reduce aerodynamic drag and increase the aircraft's lift under all flight conditions.

[0032] In addition to the technical advantages discussed above, the invention is particularly advantageous in that it has a positive impact on fuel consumption.

[0033] The invention also has the advantage of being adaptable to existing aircraft, because it does not require modification of a standard wing or fuselage. Brief description of the drawings

[0034] [Fig. 1] represents an aircraft according to the invention;

[0035] [Fig.2] illustrates a cross-sectional view of a nacelle arranged downstream of a wing of the aircraft;

[0036] [Fig.3] is an enlarged view of a wake-nacelle interaction shown between the wing and the gondola of the [Fig.2];

[0037] [Fig.4] illustrates a cross-sectional view of the wing and nacelle in a first position in which the wake is at a distance from a lower surface of the nacelle;

[0038] [Fig. 5] illustrates a cross-sectional view of the wing and nacelle of the [Fig. 4] in a second position;

[0039] [Fig.6] illustrates a cross-sectional view of the wing and nacelle in the first position in which the wake is ingested by the gondola;

[0040] [Fig.7] illustrates a cross-sectional view of the wing and nacelle of the [Fig.6] in a second position. Detailed description

[0041] The figures represent the elements schematically. Some dimensions may be exaggerated to facilitate reading the drawings.

[0042] 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.

[0043] 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.

[0044] Also, each element of each figure can be combined with each other element of each other figure according to all technically possible combinations.

[0045] 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 equipped with flaps 8.

[0046] 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.

[0047] 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.

[0048] The nacelle 12 can be mechanically connected to the fuselage 4 and / or the wing 6 by means of connecting devices. An arm extending substantially transversely from the fuselage 4 can, for example, connect the nacelle 12 to the fuselage 4 on the downstream side of the nacelle 12.

[0049] The fans can be driven in rotation by their respective turbines. Each fan can be part of a self-contained unit (such as a turbojet engine with a 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 turbines in the nacelles with pressurized gas. In another embodiment, the fans are driven by an electric motor.

[0050] Fig. 2 illustrates a cross-sectional view of the nacelle 12 arranged downstream of the wing 6 of the aircraft.

[0051] The nacelle 12 of the propulsion group 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.

[0052] The blower 14 generates an annular airflow Fl whose principal direction is coaxial with the axis 14.1 of the blower. The blower 14 is attached to a shaft supported by bearings. Support arms (not shown) can be arranged downstream of the blower 14 to connect the bearings to the upper wall 16 and lower wall 18.

[0053] 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.

[0054] 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.

[0055] Wing 6 has an extrados 6.1 and an intrados 6.2.

[0056] The aircraft comprising the wing 6 and the nacelle 12 shown in [Fig.2] is in a cruise flight condition, i.e. the angle of incidence of the airflow on the wing 6 is substantially low and constant, and the thrust level is also substantially constant.

[0057] In this configuration, the wing 6 has, at the right of its extrados 6.1 and its intrados 6.2, a boundary layer which forms a wake 20 extending downstream from the trailing edge of the wing 6 to the lower wall 18 of the nacelle 12.

[0058] The wake 20 is in contact with the nacelle 12 exclusively on a lower surface 18.1 of the lower wall 18. Advantageously, when the wake 20 is in contact with the lower surface 18.1, the propulsion group 10 is capable of generating a reference thrust for the aircraft.

[0059] Figure 3 is an enlarged view A of a wake-nacelle interaction shown between wing 6 and nacelle 12 of [Fig.2]. This ideal interaction between wake 20 and lower surface 18.1 will be designated as WWNI in this description.

[0060] The wake 20 exhibits an axial velocity deficit. Thus, there is (almost) no axial vorticity (i.e., no vortices).

[0061] Three different velocity profiles are illustrated in [Fig. 3] to schematically represent the phenomena at play between the wing and the nacelle. A first velocity profile 20.1 at the trailing edge of the wing 6 exhibits strong friction at the upper surface 6.1 and the lower surface 6.2 with the wake 20. The continuity of the medium means that the central part of the second velocity profile 20.2, located between the trailing edge of the wing 6 and the leading edge of the lower wall 18, is slowed down. The wake 20 takes the form of a third velocity profile 20.3 once it reaches the lower surface 18.1.

[0062] Advantageously, the low speed within the wake generates low friction between the wake 20 and the lower surface 18.1, which makes it possible to reduce the friction drag of the nacelle and, at the same time, to completely eliminate the shock wave drag of the lower surface 18.1 of the nacelle for the case of flight of the aircraft in transonic, i.e. local flow velocity is greater than or equal to a number of Mach 1 (supercritical flow).

[0063] Fig. 4 illustrates a cross-sectional view of the wing 6 and the nacelle 12 in a first position A in which the wake 20 is at a distance from the lower surface 18.1 of the nacelle 12.

[0064] This figure corresponds to the aircraft during a flight phase in climb, cruise, or descent, in which said aircraft is subject to changes in the angle of attack [3] of the airflow F over the wing 6, and / or to changes in the thrust level generated by the propulsion unit 10. These changes induce a vertical displacement (along Z) of the wake 20, the latter having moved away from the lower surface 18.1 downwards in [Fig. 4]. Preferably, we speak of the displacement of the wake 20 from the lower surface 18.1 starting from a few millimeters or even from 0.5 cm. This displacement can be caused, for example, by an angle of attack [3] greater than 20° or by an engine speed above the nominal thrust (under normal flight conditions). The angle of incidence [3 being defined between a profile chord 6.3 of the wing 6 and the airflow F.

[0065] This configuration has a negative impact on the aircraft's proper functioning. Indeed, here the WWNI illustrated in Figures 2 and 3 is lost, and therefore the advantages associated with low drag and increased lift are lost. This configuration corresponds to a first position of the flap 8 relative to the nacelle, substantially parallel to axis 14.1.

[0066] Preferably, the aircraft includes air detection means 18.2 on the lower surface 18.1 for detecting the detachment and / or separation of the wake 20 of the lower surface 18.1.

[0067] Preferably, the detection means 18.2 are arranged opposite the lower surface 18.1 or opposite the leading edge of the lower wall 18. However, these detection means 18.2 may be arranged on the wing 6 or on the fuselage of the aircraft.

[0068] The detection means 18.2 may correspond to a pressure sensor, and / or a Lidar sensor for measuring the position and power of the wake, and / or a flow / speed sensor or any other similar sensor. Preferably, the detection means 18.2 correspond to a total pressure sensor of the "Rake" type.

[0069] Preferably, the aircraft further comprises means for processing signals from the detection means 18.2 in order to determine the relative position of the wake 20 with respect to the lower surface 18.1. Advantageously, this also makes it possible to ensure that the WWNI is reached well before the flow becomes locally supersonic (critical point) when there is no WWNI, so that the formation of the shock wave can be avoided.

[0070] The aircraft includes a pivoting flap 8 forming the trailing edge of the wing 6. The flap can pivot substantially about an axis 6.4 parallel to the transverse axis Y of [Fig. 1]. The pivoting of the flap aims to re-establish contact between the wake 20 and the lower surface 18.1.

[0071] Fig. 5 illustrates a cross-sectional view of the wing 6 and nacelle 12 of Fig. 4 in a second position B, once the position of the flap 8 has been regulated to restore the wake 20 to contact with the lower surface.

[0072] The flap 8 can correspond to at least one of the flaps 8 of the wing 6 illustrated in [Fig.1].

[0073] The flap 8 can extend over the entire span of the nacelle. Alternatively, the flap 8 can be composed of several segments that can be acted upon independently of each other. In another alternative, not shown, the trailing edge of the wing 6 can be formed from a deformable material allowing it to have controlled deflection (such as flexible fabric or elastomer, for example).

[0074] Preferably, the flap 8 is opposite the nacelle 12, and extends transversely over at least 80% of a total extent of the lower wall 18 (according to Y on [Fig. 1] )•

[0075] In this second position B, the flap 8 is inclined at a deflection angle α with respect to the axis of the fan 14.1 (which is substantially parallel to the longitudinal axis X of [Fig. 1]). The deflection angle α is preferably less than 7° and greater than 0.5°. The angle α is here preferably equal to 5°. Indeed, small variations in angle make it possible to compensate for the deviation of the wake 20 from its ideal position.

[0076] Preferably, the flap 8 extends over at least 5% and at most 50% of the axial dimension (horizontal direction on the [Fig.5]) of the wing 6, and more preferably, the flap 8 extends over 20% to 30% of the axial dimension of the wing 6.

[0077] Advantageously, the inclination of the flap 8 of the deflection angle a allows the wake 20 to be brought back into contact with the lower surface 18.1 so as to correct the displacement of the wake 20 and to restore the advantageous wake-nacelle interaction (WWNI).

[0078] The transition from the first position A of [Fig.4] to the second position B is achieved with a pivoting of the flap 8 upwards (deflection illustrated by a dashed arrow), corresponding to an increase (in an anti-clockwise direction around the axis 6.4) of the deflection angle a which can be managed by a servo system of the aircraft.

[0079] In this regard, the aircraft includes means for controlling the pivoting of the flap 8, preferably corresponding to a set of components such as detection means, actuators capable of pivoting the flap 8, and a control unit capable of executing the method of implementing the aircraft of the invention.

[0080] Advantageously, the control of the deflection of the flap 8 allows the air to be guided progressively towards the lower surface 18.1 of the nacelle and to maintain a wake trajectory 20 that is as homogeneous and constant as possible.

[0081] The flap 8 can alternatively or additionally be capable of pivoting downwards, beyond a neutral position. This is illustrated by the situation shown in Figures 6 and 7.

[0082] Fig. 6 illustrates a cross-sectional view of the wing 6 and the nacelle 12 in a first position A in which the wake 20 is ingested by the nacelle 12. This situation can occur for example when the angle of attack is greater than the design angle of attack (design complying with WWMI).

[0083] Here, the wake 20 is displaced from its ideal position upwards (along Z). To this end, the wake 20 is directed towards the fans 14; this is referred to as wake ingestion by the nacelle 12. This wake 20 ingestion can be caused, for example, by an angle of attack greater than the design angle of attack or by an engine speed greater than the nominal speed.

[0084] The first position A illustrated in [Fig.6] has a negative impact on the proper functioning of the aircraft, i.e. increased drag, reduced lift, and overall instability of the aircraft, because the WWNI illustrated in Figures 2 and 3 is lost.

[0085] The flow entering the turbomachine is disturbed and angularly inhomogeneous.

[0086] In the same way as in the previous case (figures 4 and 5), it is necessary to pivot the flap to correct the position of the wake.

[0087] Figure 7 illustrates a cross-sectional view of wing 6 and nacelle 12 of Figure 6 in the second position B.

[0088] It should be noted that in the present application, the expression "the second position" refers to the position of the flap which is such that the wake 20 is in contact with the lower surface 18.1. Indeed, Figures 5 and 7 both illustrate "the second position" (although this is not materialized by the same angle of deflection of the flap): the flap 8 is pivoted upwards in [Fig.5] and downwards in [Fig.7].

[0089] The transition from the first position A of [Fig.6] to the second position B is achieved with a downward pivoting of the flap 8 (deflection illustrated by a dashed arrow), corresponding to a decrease (clockwise around the axis 6.4) of the deflection angle a which can be managed by an aircraft servo system.

[0090] Advantageously, the flap 8 is regulated so as to move the wake 20 out of the nacelle 12 and to bring the latter back into contact with the lower surface 18.1, thus correcting the vertical offset of the wake 20 and restoring the WWNI.

[0091] The same control and servo elements as described above in relation to Figures 4 and 5 can be used.

[0092] Also, certain flight conditions may cause the flap to move not from a neutral position to a high or low position, but from a low position to a high position or vice versa. Such a pivoting may correspond to extreme aircraft flight conditions resulting in a significant shift in the position of the wake 20, particularly in the event of sudden vertical gusts experienced by the aircraft. In this regard, the method of the invention may include a dynamic flap deflection law to counteract the unsteady movements of the wake 20 during gusts.

Claims

Demands

1. A method for operating a fixed-wing aircraft (2), the aircraft (2) comprising a fuselage (4), two wings (6) each generating a wake (20) and disposed respectively on either side of the fuselage (4) and comprising a flap (8), and two propulsion units (10) disposed respectively downstream and at a distance (H) from each wing (6), each of the propulsion units (10) comprising a nacelle (12) housing at least two non-coaxial fans (14), said nacelle (12) comprising a lower wall (18) extending substantially in line with the wing (6), the lower wall (18) having a lower surface (18.1), the method being characterized in that it comprises a flight phase of the aircraft (2) during which the flap (8) is pivoted from a first position (A) in which the wake (20) is at a distance from the lower surface (18.1), towards a second position (B) in which the wake (20) is in contact with the lower surface (18.1), and in that the aircraft (2) includes means for detecting air (18.2) on the lower surface (18.1) for detecting the detachment of the wake (20) from the lower surface (18.1) and the pivoting of the flap (8) is regulated to restore contact of the wake (20) to the lower surface (18.1).

2. Method according to claim 1, characterized in that the first position (A) differs from the second position (B) by a deflection angle (a) between 0.5° and 7°.

3. A method according to any one of claims 1 or 2, characterized in that the pivoting flap (8) is servo-controlled proportionally to the incidence (|3) of the airflow (F) on the wing (6), and / or to the attitude of the aircraft (2), and / or to the speed of the aircraft (2), and / or to the level of thrust generated by the aircraft (2).

4. A method according to any one of claims 1 to 3, characterized in that the pivoting flap (8) is configured to pivot upwards, along a direction (Z) perpendicular to an axis (14.1) of the blower (14), when the wake (20) is externally moved away from the lower surface (18.1) of the nacelle (12), so as to bring said wake (20) back into contact with said lower surface (18.1).

5. A method according to any one of claims 1 to 4, characterized in that the pivoting flap (8) is configured to pivot downwards, along the direction (Z) perpendicular to the axis (14.1) of the blower (14), when the wake (20) is directed towards the blowers (14), so as to bring said wake (20) back into contact with the lower surface (18.1).

6. A method according to any one of claims 1 to 5, characterized in that the flight phase of the aircraft (2) corresponds to an ascent or cruise or descent phase.

7. Fixed-wing aircraft (2) comprising a fuselage (4), two wings (6) each generating a wake (20) and disposed respectively on either side of the fuselage (4) and comprising a flap (8), and two propulsion units (10) disposed respectively downstream and at a distance (H) from each wing (6), each of the propulsion units (10) comprising a nacelle (12) housing at least two non-coaxial fans (14), said nacelle (12) comprising a lower wall (18) provided with a lower surface (18.1) and extending substantially in line with the wing (6), the aircraft (2) being characterized in that it comprises means for controlling the pivoting of the flap (8), from a first position (A) in which the wake (20) is at a distance from the lower wall (18), to a second position (B) in which the wake (20) is in contact with the lower wall (18), the aircraft (2) includes means for detecting air (18.2) on the lower surface (18.1) aimed at detecting the detachment of the wake (20) from the lower surface (18.1) and the pivoting of the flap (8) is regulated to restore contact of the wake (20) to the lower surface (18.1).

8. Aircraft (2) according to claim 7, characterized in that the control means ensure that the wake (20) is attached to the lower wall (18) in all circumstances, in particular by regulating the position of the flap (8) according to a detected position of the wake (20).

9. Aircraft (2) according to claim 7 or 8, characterized in that said aircraft (2) includes means for processing signals from the detection means (18.2) in order to determine the relative position of the wake (20) with respect to the lower wall (18).

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