FLIGHT ASSISTANCE SYSTEM FOR FORMATION FLIGHT

Description

TECHNICAL FIELD

[0001] The present invention relates to a system for assisting aircraft formation flight. More particularly, the present invention relates to a system for assisting the positioning of a follower aircraft relative to a wake vortex (also called a marginal vortex) of a lead aircraft during formation flight. STATE OF PRIOR ART

[0002] Wake vortices, also known as wingtip vortices or wingtip vortices, are counter-rotating wake turbulence at the wingtips of an aircraft in flight due to a pressure difference between the lower and upper surfaces of the wings. Wake vortices can persist for several minutes after an aircraft has passed, and can disrupt the comfort of passengers on another aircraft passing nearby in the meantime. Safety distances between aircraft in flight are applied by ATC to take wake vortices into account and avoid possible flight difficulties related to their existence.

[0003] In formation, a leader aircraft is followed by one or more follower aircraft, which may experience discomfort related to the wake vortices of the leader aircraft. However, by controlling their position relative to the wake vortices, the follower aircraft can benefit from an upward airflow phenomenon induced by the wake vortices, thus reducing drag and fuel consumption. On the other hand, if the follower aircraft penetrate the space between the wake vortices of the leader aircraft, the follower aircraft experience a downward airflow phenomenon that is induced by the wake vortices and that impairs their performance. Similarly, turbulence is experienced by a follower aircraft if one of its wings penetrates a wake vortex. This turbulence causes significant discomfort for the passengers of the follower aircraft.

[0004] Solutions exist to enable a follower aircraft to position itself automatically in relation to a wake vortex generated by a lead aircraft. For example, reference may be made to French patent application FR 3041121 A1. Although the solution disclosed therein enables a follower aircraft to effectively benefit from the upward airflow phenomenon induced by a wake vortex of a lead aircraft, the aforementioned discomfort may be experienced by passengers of the follower aircraft.

[0005] Document FR 3049076 A1 is known, which discloses a method for controlling the trajectory of a following aircraft relative to the trajectory of a leading aircraft in order to benefit from the phenomenon of upward airflow induced by wake vortices, by calculating coefficients of disturbing lateral moments generated by the wake vortices.

[0006] Also known is document FR 3079942 A1, which discloses a method for controlling the trajectory of a following aircraft relative to the trajectory of a leading aircraft in order to benefit from the phenomenon of upward airflow induced by wake vortices, using a sectional approach.

[0007] Also known is US 2003 / 0222795 A1, which discloses a wake vortex avoidance system that uses readily available in-flight airborne and atmospheric parameters to model and predict wake vortices in real time. The system predicts the location and motion of the wake vortex based on a nominal wake vortex model, and performs an uncertainty analysis on the wake vortex model to determine a wake danger zone (no-fly zone) to be presented to the pilot (e.g., as a three-dimensional display).

[0008] It is then desirable to provide a formation flight assistance solution that can alleviate the aforementioned discomfort, while benefiting from the upward airflow phenomenon induced by the wake vortex of the lead aircraft. STATEMENT OF THE INVENTION

[0009] A method of assisting aircraft formation flight is proposed, the method being implemented by a system in the form of electronic circuitry on board an aircraft acting as a follower aircraft, the method comprising the following steps: obtaining information relating to a lead aircraft generating a wake vortex inducing an upward airflow from which the system aims to benefit the follower aircraft; determining an effect of the wake vortex experienced by the follower aircraft as a difference between measurements, carried out by sensors of the follower aircraft, and a modeling of the follower aircraft in a wake vortex-free environment; using a recursive Bayesian filter, determining an estimated position of the wake vortex from the information relating to the lead aircraft obtained and a wake vortex model, and determining an estimation uncertainty on the estimated position of the wake vortex by comparing the effect of the wake vortex experienced by the follower aircraft and a theoretical effect of the wake vortex on the follower aircraft according to the wake vortex model;determining a potential discomfort window around the estimated position of the wake vortex, based on the estimation uncertainty on the estimated position of the wake vortex; and defining and applying an approach trajectory to the wake vortex and keeping the follower aircraft outside the potential discomfort window, by controlling a placement of the follower aircraft at a predefined distance from the estimated position of the wake vortex when the potential discomfort window has dimensions that allow it and at a predefined margin of the potential discomfort window otherwise. ;

[0010] Thus, the following aircraft benefits from the upward airflow phenomenon induced by the wake vortex of the leading aircraft, without generating discomfort for the passengers of the following aircraft.

[0011] In a particular embodiment, the recursive Bayesian type filter is a particle filter.

[0012] In a particular embodiment, the determination of the estimated position of the wake vortex and the potential discomfort window is carried out in the following manner: determining, for each potential position from a set of potential positions determined from the determined geometric position of the wake vortex, a probability value of the presence of the wake vortex at said potential position, the probability value in question being determined by comparing the effect of the wake vortex experienced by the following aircraft and a theoretical effect of the wake vortex on the following aircraft according to the wake vortex model when the wake vortex is located at said potential position; forming the potential discomfort window by grouping potential positions of the wake vortex having a probability value greater than a first predetermined threshold.

[0013] In a particular embodiment, when the system detects that the potential discomfort window has dimensions which allow the following aircraft to be placed at said predefined distance from the estimated position of the wake vortex, the system commands the following aircraft to perform movements with a load factor lower than a second predetermined threshold.

[0014] In a particular embodiment, the movements in question are preferably vertical oscillatory or pseudo-oscillatory movements.

[0015] Also provided is a computer program product comprising instructions causing an implementation of the method as set forth above in any of its embodiments, when the instructions are executed by a processor. Also provided is an information storage medium on which such a computer program product is stored, thereby causing an implementation of said method, when the instructions are read from the information storage medium and executed by a processor.

[0016] Also proposed is an aircraft formation flight assistance system, in the form of electronic circuitry on board an aircraft intended to act as a follower aircraft in formation flight, the electronic circuitry being configured to implement the following steps: obtaining information relating to a lead aircraft generating a wake vortex inducing an upward airflow from which the system aims to benefit the follower aircraft; determining an effect of the wake vortex experienced by the follower aircraft as a difference between measurements, carried out by sensors of the follower aircraft, and a modeling of the follower aircraft in a wake vortex-free environment; using a recursive Bayesian filter, determining an estimated position of the wake vortex from the information relating to the lead aircraft obtained and a wake vortex model, and determining an estimation uncertainty on the estimated position of the wake vortex by comparing the effect of the wake vortex experienced by the follower aircraft and a theoretical effect of the wake vortex on the follower aircraft according to the wake vortex model;determining a potential discomfort window around the estimated position of the wake vortex, based on the estimation uncertainty on the estimated position of the wake vortex; and defining and applying an approach trajectory to the wake vortex and keeping the follower aircraft outside the potential discomfort window, by controlling a placement of the follower aircraft at a predefined distance from the estimated position of the wake vortex when the potential discomfort window has dimensions that allow it and at a predefined margin of the potential discomfort window otherwise. ;

[0017] Also provided is an aircraft acting as a follower aircraft in formation flight, which includes a formation flight assistance system as set forth above. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above-mentioned features of the invention, as well as others, will appear more clearly on reading the following description of at least one exemplary embodiment, said description being made in relation to the attached drawings, among which: [ Fig. 1 ] schematically illustrates, in top view, an aircraft equipped with a formation flight aid system; [ Fig. 2 ] schematically illustrates an example of hardware architecture on which the formation flight assistance system can be based; [ Fig. 3 ] schematically illustrates, in front view, a positioning of a follower aircraft relative to a lead aircraft during a formation flight; [ Fig. 4 ] schematically illustrates, in top view, the positioning of the follower aircraft relative to the lead aircraft during formation flight; [ Fig. 5 ] schematically illustrates a modular architecture of the formation flight support system; [ Fig. 6 ] schematically illustrates an algorithm for controlling the positioning of the follower aircraft relative to the lead aircraft during formation flight; [ Fig. 7 ] schematically illustrates an algorithm for determining a probability of presence of a wake vortex at a given position, in a particular embodiment; and [ Fig. 8 ] schematically illustrates an example of a potential discomfort window determined for the following aircraft, in a particular embodiment. DETAILED PRESENTATION OF IMPLEMENTATION METHODS

[0019] There Fig. 1 schematically illustrates, in top view, an aircraft 100 equipped with a system 120 for assisting formation flight, more particularly when the aircraft 100 acts as a follower in a formation flight, in order to benefit from an upward airflow phenomenon induced by a wake vortex of a leading aircraft.

[0020] In a particular embodiment, the system 120 is integrated into the avionics 150 of the aircraft 100.

[0021] The aircraft 100 is equipped with numerous sensors 130, as is usually the case in aeronautics: temperature sensors, vibration sensors (for example in the form of accelerometers), pressure sensors, inertial sensors, etc. These sensors 130 provide information, supplemented by information communicated by radio frequency (e.g., air-ground or satellite communications), allowing the avionics 150 to determine parameters relating to the aircraft 100 in flight (speed, attitude, altitude, etc.) and to its environment (atmospheric pressure, air speed, etc.). Each sensor 130 is connected to the avionics 150 by electrical wiring, or a communication system (communication bus, communication network, etc.) 140, as shown in a purely illustrative manner in the Fig. 1 .

[0022] As disclosed subsequently, the system 120 relies on information provided by the avionics 150, in particular thanks to the sensors 130, as well as on information provided by the lead aircraft and pre-established models, to help position the aircraft 100, acting as a follower aircraft, so as to benefit from the upward airflow phenomenon without causing discomfort for the passengers of the aircraft 100.

[0023] Preferably, the system 120 is disengageable and is activated during formation flight phases where the aircraft 100 is following. For example, the system 120 is activated / deactivated on command from a pilot of the aircraft 100.

[0024] There Fig. 2 schematically illustrates an example of hardware architecture on which the system 120 may be based.

[0025] The system 120 then comprises, connected by a communication bus 210: a processor or CPU (Central Processing Unit) 201; a RAM (Random Access Memory) 202; a ROM (Read Only Memory) 203, for example a Flash memory; a data storage device, such as a hard disk HDD (Hard Disk Drive), or an ISM (Information Storage Medium) 204 reader, such as an SD (Secure Digital) card reader; at least one communication interface 205 allowing the system 120 to interact more particularly with the avionics 150, as well as with the avionics of the lead aircraft or with ground equipment serving as a relay with the avionics of the lead aircraft.

[0026] The processor 201 is capable of executing instructions loaded into the RAM 202 from the ROM 203, an external memory (not shown), a storage medium, such as an SD card, or a communications network (not shown). When the system 120 is powered on, the processor 201 is capable of reading instructions from the RAM 202 and executing them. These instructions form a computer program causing the processor 201 to implement the modular architecture, behaviors, steps, and algorithms described herein.

[0027] All or part of the modular architecture, behaviors, steps and algorithms described herein may thus be implemented in software form by executing a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor) or a microprocessor, or be implemented in hardware form by a machine or a dedicated component (chip) or a set of components (chipset), such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). The system 120 therefore comprises electronic circuitry arranged and configured to implement the modular architecture, as well as the behaviors, steps and algorithms described herein.

[0028] There Fig. 3 schematically illustrates, in front view, a positioning of a follower aircraft 302 relative to a lead aircraft 301 during a formation flight. The aircraft 301 and 302 are in cruising flight. The movement of the lead aircraft 301 generates wake vortices 303. If the follower aircraft 302 maintains a distance D between a minimum threshold Dmin (for example, Dmin = 20 meters) and a maximum threshold Dmax (for example, Dmax = 30 meters) from the marginal vortices outside the trajectory of the lead aircraft 301, the follower aircraft 302 benefits from the aforementioned upward airflow phenomenon, thus reducing drag and fuel consumption for the follower aircraft 302.Between the minimum threshold Dmin and the maximum threshold Dmax, placing the follower aircraft 302 at a distance Dconf (for example, Dconf = 25 meters, plus or minus a predefined margin) makes it possible to benefit significantly from the upward airflow phenomenon, while ensuring the comfort of the passengers of the follower aircraft 302.

[0029] In addition to the Fig. 3 , there Fig. 4 schematically illustrates the positioning of the follower aircraft 302 relative to the lead aircraft 301 in top view.

[0030] The wake vortices 303 are schematically represented in a simplified manner. Indeed, from the wings, the wake vortices 303 tend first to move closer to each other, then to maintain a substantially constant distance between them, while losing altitude compared to that at which they were generated. In addition, the wind influences the trajectory and geometry of the wake vortices 303 over time.

[0031] There Fig. 5 schematically illustrates a modular architecture of the system 120.

[0032] The system 120 comprises a sensor manager module ASensMgr 512, configured to collect in real time information relating to the measurements carried out by the sensors 130 (labeled ASens on the Fig. 5 ), including current atmospheric condition information (e.g., wind speed and direction), as well as information on effects experienced by the follower aircraft 302 (e.g., roll acceleration).

[0033] The system 120 also includes a module managing information relating to the lead aircraft 301 (wingspan, mass, geographical position, speed, altitude, attitude, etc.) LInfMgr 511. The module LInfMgr 511 receives this information, and any updates thereof in real time, from a communications management system ComMgr 501 of the avionics 150 in communication with an on-board system of the lead aircraft 301, possibly via an intermediate relay (e.g., ground communications system).

[0034] The system 120 further comprises an aircraft model manager module AModMgr 513, configured to determine effects on the follower aircraft 302 of the wake vortex 303. The aircraft model manager module AModMgr 513 uses measurements provided by the sensors ASens130 (for example, roll acceleration) to determine effects experienced by the follower aircraft 302. The module AModMgr 513 also uses a model of the follower aircraft 302, modeling effects experienced by the follower aircraft 302 in flight outside the wake of another aircraft (for example, aerodynamic properties as a function of the mass of the aircraft). For example, for a certain aileron deflection, a certain roll acceleration is expected in an environment free of wake vortex generated by another aircraft.Thus, the AModMgr module 513 is configured to determine the effects on the follower aircraft 302 of the wake vortex 303 by subtracting from the effects measured by the ASens sensors 130 those contained in said model of the follower aircraft 302.

[0035] The system 120 further comprises a wake vortex position calculation module VPosCmp 516. The VPosCmp module 516 is configured to estimate a position of the wake vortex 303 with an estimation uncertainty, which can itself be determined, and is configured to determine a spatial window, called a potential discomfort window, defined by the estimation uncertainty around the estimated position of the wake vortex 303. In a particular embodiment, the potential discomfort window defines a space in which the wake vortex 303 is assumed to be present with a probability greater than or equal to a predetermined threshold TH_vx.

[0036] The VPosCmp 516 module calculates a georeferenced geometry of the wake vortex 303.

[0037] The VPosCmp module 516 is also configured to calculate the georeferenced geometry of the wake vortex 303 from which the follower aircraft 302 can benefit from the upward airflow phenomenon, from information relating to the lead aircraft 301 (such as wingspan, mass, geographical position, speed, altitude, attitude, etc.) and information relating to the atmospheric conditions encountered (for example, wind speed and direction) by the lead aircraft 301 and the follower aircraft 302. The calculation of the georeferenced geometry of the wake vortex 303 is well known to those skilled in the art and involves several steps: construction of successive georeferenced positions through which the lead aircraft 301 has passed, calculation of a drift linked to the wind, and taking into account the physics of the wake vortex, in particular a descent speed.The VPosCmp module 516 thus performs a three-dimensional, real-time georeferenced modeling of the geometry of the wake vortex 303. Then, by projecting the position of the follower aircraft 302 onto calculated positions of the center of the wake vortex, a distance of the follower aircraft 302 from the wake vortex can be calculated. Implementation and calculation details are for example disclosed in the French patent application FR 3041121 A1 already mentioned.

[0038] To determine the georeferenced geometry of the wake vortex 303, the VPosCmp module 516 uses data (descent speed, etc.) provided by a wake vortex model. The system 120 then comprises a wake vortex model manager module VModMgr 515 providing the VPosCmp module 516 with said wake vortex model data.

[0039] The VPosCmp module 516 is thus configured to determine, using a recursive Bayesian filter, an estimated position of the wake vortex from the information relating to the lead aircraft obtained and a wake vortex model, and to determine an estimation uncertainty on the estimated position of the wake vortex by comparing the effect of the wake vortex 303 experienced by the follower aircraft 302 and a theoretical effect of the wake vortex 303 on the follower aircraft 302 according to the wake vortex model. Indeed, due in particular to measurement inaccuracies and / or model inaccuracies used, there is an uncertainty concerning the effective geometry and georeferencing of the wake vortex 303 calculated by the VPosCmp module 516 using the recursive Bayesian type filter.

[0040] The VPosCmp module 516 is thus configured to determine the potential discomfort window associated with the estimated position of the wake vortex, as a function of the estimation uncertainty on the estimated position of the wake vortex. In an exemplary embodiment, the VPosCmp module 516 determines the potential discomfort window by applying a distance dependent on the estimation uncertainty (for example, proportional to the estimation uncertainty or linearly dependent on the estimation uncertainty), around the estimated position of the wake vortex 303. Thus, the greater the estimation uncertainty, the greater the dimensions of the potential discomfort window. The accuracy of the estimation can then be improved by gaining observability, in order to make it possible to reduce the dimensions of the potential discomfort window.

[0041] In another exemplary embodiment, using a particle filter, the VPosCmp module 516 determines the theoretical effect of the wake vortex 303 on the follower aircraft 302 at different potential positions of said wake vortex 303 in view of the previously calculated georeferenced geometry, and compares, for each position among said different potential positions, this theoretical effect with the effect on the aircraft 302 of said wake vortex 303 determined by the AModMgr module 513 (for example, using pitching moment data). The VPosCmp module 516 then determines a probability value of the presence of the wake vortex 303 at said position.Thus, if the theoretical effect is too low compared to the effect actually experienced by the following aircraft 302 according to the measurements of the ASens sensors 130, that is to say that the probability value is lower than the predetermined threshold TH_vx, it is unlikely that the wake vortex 303 is at this position. The spatial window in which the wake vortex 303 is assumed to be present with a probability greater than or equal to the predetermined threshold TH_vx is a space of potential discomfort for the passengers of the following aircraft 302, because of turbulence which is potentially experienced by the following aircraft 302 and which is due to said wake vortex 303. This spatial window then constitutes the aforementioned window of potential discomfort.

[0042] In a particular embodiment, the VPosCmp module 516 determines a probability value of presence of the wake vortex 303 at each said position for different wake vortex characteristics (vortex diameter, velocity profiles, circulation profiles, etc.).

[0043] As an alternative to the particle filter presented above, the VPosCmp module 516 may include another type of recursive Bayesian filter, such as a Kalman filter. Other approaches for estimating the position of the wake vortex 303 and the associated estimation uncertainty, such as a calculation of local gradients, may be derived from the general knowledge of those skilled in the art.

[0044] The VPosCmp module 516 performs distance calculations relative to the wake vortex 303 in a two-dimensional space, in a [Y,Z] plane in a [X,Y,Z] geodetic reference frame, as shown in the Fig. 8 The three-dimensional space [X,Y,Z] in which the georeferenced geometry of the wake vortex 303 is calculated makes it possible to ensure trajectory tracking, and the cross-section in the plane [Y,Z] is used to determine the potential discomfort window, i.e. the estimated position of the wake vortex 303 taking into account the calculation uncertainties.

[0045] In a particular embodiment, the VPosCmp module 516 is composed of two sub-modules, for reasons of computational capacity: a first sub-module with a coarse estimator of the position of the wake vortex 303 (with a first precision) and a second sub-module with a refinement estimator (with a second precision better than the first precision). The first sub-module can then perform a geometric calculation which is relatively coarse and does not take into account all the dynamics of wind and the wake vortex. The second sub-module then uses a finer model, which is initialized on the results of the first sub-module, and which corrects calculation uncertainties of the first sub-module by means of a more precise estimator (recursive Bayesian filter, etc.).

[0046] The system 120 further comprises a trajectory management module VAppCmp 517, for placing the following aircraft 302 at an adequate distance D from said potential discomfort window or from the estimated position of the wake vortex 303 as the case may be. The module VAppCmp 517 manages the trajectory of the following aircraft 302 so that the following aircraft 302 remains outside the potential discomfort window. More precisely, the module VAppCmp 517 controls the placement of the following aircraft 302 at a predefined distance from the estimated position of the wake vortex 303 (namely at the distance Dconf) when the potential discomfort window has dimensions that allow it and at a predefined margin of the potential discomfort window otherwise.

[0047] The VAppCmp module 517 is configured to determine an approach trajectory to said wake vortex 303 and is further configured to track the wake vortex 303 and align the trajectory of the follower aircraft 302 accordingly so as to keep the follower aircraft 302 outside the window of potential discomfort while seeking to benefit from the upward airflow induced by the wake vortex 303. Typically, the VAppCmp module 517 calculates successive target positions forming the trajectory to be followed by the follower aircraft 302 with the following constraints: not entering the window of potential discomfort (the dimensions of which may change depending on the new measurements collected in real time), while seeking to benefit from the upward airflow induced by the wake vortex; collecting new measurements to enable the probability distribution to be corrected and thus improving the estimation performance and reducing the size of the window of potential discomfort; and defining comfortable, or even imperceptible, trajectories for the passengers of the following aircraft 302.

[0048] In a particular embodiment, the VAppCmp module 517 is configured to, when it detects that the potential discomfort window has dimensions that allow the following aircraft to be placed at the distance Dconf relative to the estimated position of the wake vortex (while therefore remaining outside the potential discomfort window), command the following aircraft 302 to perform movements with a load factor lower than a predetermined threshold TH_lf. Thus, the system 120 gains observability on the wake vortex 303 in a comfortable, or even imperceptible, manner for the passengers of the following aircraft 302.

[0049] The system 120 further comprises an aircraft command control manager module ACtrlMgr 518, configured to convert each trajectory determined by the VAppCmp module 517 into maneuvering commands for the follower aircraft 302. The maneuvering commands are then transmitted to a flight control management system ACtrl 502 (servocontrols) of the avionics 150, for example integrated into an automatic pilot system.

[0050] There Fig. 6 schematically illustrates an algorithm for controlling the positioning of the follower aircraft 302 relative to the lead aircraft 301 during formation flight.

[0051] In a step 601, the system 120 performs an estimation of the geometry of the wake vortex 303 for which the following aircraft 302 seeks to benefit from the upward flow phenomenon, as already described in relation to the VPosCmp module 516.

[0052] In a step 602, the system 120 determines a window of potential discomfort for the passengers of the following aircraft 302, as already described also in relation to the VPosCmp module 516.

[0053] In a step 603, the system 120 defines an approach trajectory towards the wake vortex 303, which is converted into aircraft maneuvering commands in a following step 604. This approach trajectory ensures that the potential discomfort window is not entered, while gaining observability in order to reduce the dimensions of the potential discomfort window (optimizing the performance of the VPosCmp module 516).

[0054] Once the approach trajectory has been carried out, the system enters a tracking phase in which the system 120, and more particularly the VAppCmp module 517, defines the successive positions of the trajectory of the follower aircraft 302 while respecting the following conditions: when the dimensions of the potential discomfort window are large to the point that the follower aircraft 302 cannot position itself at the distance Dconf, the system 120 defines the trajectory of the follower aircraft 302 to remain at a distance equal to a predefined margin of the potential discomfort window; and when the dimensions of the potential discomfort window are small enough for the follower aircraft 302 to position itself at the distance Dconf, the system 120 maintains the follower aircraft 302 at the distance Dconf.

[0055] As the flight progresses, the system 120 continues to acquire measurements made by the sensors 130. Using these measurements, the system 120 updates the potential discomfort window and thus adjusts the trajectory while respecting the above conditions.

[0056] The real-time collection of new measurements made by the sensors 130 in the execution of the approach trajectory towards the wake vortex 303, and in the tracking phase, makes it possible to update in real time the position and dimensions of the potential discomfort window. The VAppCmp module 516 exploits the potential discomfort window to allow the collection of data as close as possible to the wake vortex 303, where they are most relevant to reduce the estimation uncertainty, without the passengers of the following aircraft 302 having to suffer any discomfort.

[0057] In a particular embodiment, the system 120 commands the following aircraft 302 to perform movements with a low load factor, i.e. a load factor lower than the predetermined threshold TH_lf, which is a threshold beyond which the movements of the aircraft are considered uncomfortable, or perceptible, for the passengers. The movements in question are in the plane [Y,Z] (vertical and / or lateral movements). The movements in question are preferably vertical oscillatory or pseudo-oscillatory movements. These movements make it possible to move the following aircraft 302 relatively to the wake vortex 303 and to acquire new measurements from the sensors 130 (gain in “observability”), in order to refine the definition of the potential discomfort window.

[0058] In step 604, the system 120 converts the trajectory defined in step 603 into aircraft maneuvering commands so as to cause the follower aircraft 302 to follow the defined trajectory.

[0059] In a step 605, the system 120 applies to the follower aircraft 302 the maneuvering commands obtained in step 604. The algorithm then loops back to step 601, so as to take into account the changes in the position and geometry of the wake vortex 303, any changes in atmospheric conditions, and to change the potential discomfort window accordingly.

[0060] There Fig. 7 schematically illustrates an algorithm for determining a probability of the presence of a wake vortex at a given position, thus enabling the determination of the window of potential discomfort for the following aircraft 302, in a particular embodiment adapted to the use of a particle filter. To do this, the algorithm calculates a probability distribution of spatial location of the wake vortex 303. To calculate this probability distribution, the algorithm calculates, for example, likelihoods.

[0061] In a step 701, the system 120 selects a potential position of the wake vortex 303 from a set of potential positions. The set of potential positions is defined by uncertainty analysis, in view of the estimation accuracy (e.g., accuracy of the particle filter), or empirically during flight test phases by comparison of modeled data and measurement data.

[0062] In a particular embodiment, the system 120 integrates a particle filter and each particle represents a potential position of the wake vortex 303 (or its center) in the [Y,Z] frame of reference.

[0063] In a step 702, the system 120 determines a theoretical effect of the wake vortex 303 on the following aircraft 302, considering that the wake vortex 303 is located at the position selected in step 701. The system 120 uses to do this the aforementioned wake vortex model (provided by the VModMgr module 515).

[0064] In a step 703, the system 120 collects measurements made by the sensors 130, and in a step 704, determines a real effect on the aircraft 302 of the wake vortex 303 using the measurements of the sensors 130 (determined by the AModMgr module 513). In the measurements of the sensors 130, the effect of the wake vortex 303 is predominant compared to other disturbances which would be captured by the sensors 130. The effect on these measurements of these other disturbances is therefore negligible.

[0065] In a step 705, the system 120 compares the theoretical effect of the wake vortex 303 on the follower aircraft 302 as determined in step 702 with the effect of the wake vortex 303 on the follower aircraft 302 as determined in step 704. The difference between the theoretical effect of the wake vortex 303 on the follower aircraft 302 as determined in step 702 and the effect of the wake vortex 303 experienced by the follower aircraft 302 as determined in step 704 provides a probability value of the presence of the wake vortex 303 at the position selected in step 701.

[0066] The system 120 proceeds in this way for each potential position of said set of potential positions. A probability value (of presence of the wake vortex) is thus associated with each potential position of said set of potential positions. As already indicated, the probability value can be calculated for different wake vortex parameter values ​​(diameter, etc.). The system 120 then divides the potential positions into two categories: those whose associated probability is greater than or equal to the predetermined threshold TH_vx, and those whose associated probability is less than the predetermined threshold TH_vx. A grouping of the potential positions whose associated probability is greater than or equal to the predetermined threshold TH_vx forms the aforementioned potential discomfort window. The situation is schematically illustrated in Fig. 8, where potential wake vortex positions 800a have an associated probability greater than or equal to the predetermined threshold TH_vx, and are therefore included in the potential discomfort window 801, and where potential wake vortex positions 800b have an associated probability less than the predetermined threshold TH_vx, and are therefore excluded from the potential discomfort window 801.

Claims

1. Method for assisting the formation flight of aircraft, the method being implemented by a system (120) in the form of electronic circuitry on board an aircraft (100) acting as a follower aircraft (302), the method comprising the following steps: - acquiring information relating to a leader aircraft (301) generating a wake vortex inducing an upward airflow, which the system (120) intends the follower aircraft (302) to benefit from; - determining (704) an effect of the wake vortex experienced by the follower aircraft (302) as a difference between measurements, taken by sensors (130) of the follower aircraft (302), and modelling of the follower aircraft in a wake vortex-free environment; - determining, using a recursive Bayesian filter, an estimated position of the wake vortex on the basis of the information obtained relative to the leader aircraft (301) and of a wake vortex model, and determining an estimation uncertainty of the estimated position of the wake vortex by comparing the effect of the wake vortex experienced by the follower aircraft (302) and a theoretical effect of the wake vortex on the follower aircraft (302) according to the wake vortex model; - determining (602) a potential discomfort window around the estimated position of the wake vortex; and - defining (603) and applying (605) an approach trajectory to the wake vortex; characterized in that the potential discomfort window around the estimated position of the wake vortex is determined as a function of the estimation uncertainty of the estimated position of the wake vortex and the method further comprises the following step: - keeping the follower aircraft (302) outside the potential discomfort window, by controlling a placement of the follower aircraft (302) at a predefined distance from the estimated position of the wake vortex when the dimensions of the potential discomfort window are such that this is allowed, and at a predefined margin from the potential discomfort window otherwise.

2. Method according to Claim 1, wherein the recursive Bayesian filter is a particle filter.

3. Method according to Claim 2, wherein the estimated position of the wake vortex and the potential discomfort window are determined as follows: - determining (705), for each potential position from among a set of potential positions determined on the basis of the determined geometric position of the wake vortex, a probability value for the presence of the wake vortex at said potential position, with the probability value in question being determined by comparing the effect of the wake vortex experienced by the follower aircraft (302) and a theoretical effect of the wake vortex on the follower aircraft (302) according to the wake vortex model when the wake vortex is located at said potential position; - forming the potential discomfort window by grouping together (801) potential positions of the wake vortex with a probability value above a first predetermined threshold.

4. Method according to any one of Claims 1 to 3, wherein, when the system (120) detects that the dimensions of the potential discomfort window allow the follower aircraft (302) to be placed at said predefined distance from the estimated position of the wake vortex, the system (120) commands the follower aircraft (302) to perform load factor movements below a second predetermined threshold.

5. Method according to Claim 4, wherein the movements in question are preferably vertical oscillatory or pseudo-oscillatory movements.

6. Computer program product comprising instructions causing the method according to any one of Claims 1 to 5 to be implemented, when the instructions are executed by a processor.

7. Information storage medium storing instructions causing the method according to any one of Claims 1 to 5 to be implemented, when the instructions are read from the information storage medium and executed by a processor.

8. System (120) for assisting the formation flight of aircraft, in the form of on-board electronic circuitry in an aircraft (100) intended to act as a follower aircraft (302) in the formation flight, the electronic circuitry being configured to implement: - a module for acquiring information relating to a leader aircraft (301) generating a wake vortex inducing an upward airflow, which the system intends the follower aircraft (302) to benefit from; - a module for determining an effect of the wake vortex experienced by the follower aircraft (302) as a difference between measurements, taken by sensors (130) of the follower aircraft (302), and modelling of the follower aircraft in a wake vortex-free environment; - a module for determining, using a recursive Bayesian filter, an estimated position of the wake vortex on the basis of the information obtained relative to the leader aircraft (301) and of a wake vortex model, and for determining an estimation uncertainty of the estimated position of the wake vortex by comparing the effect of the wake vortex experienced by the follower aircraft (302) and a theoretical effect of the wake vortex on the follower aircraft (302) according to the wake vortex model; - a module for determining a potential discomfort window around the estimated position of the wake vortex; and - modules for defining and applying an approach trajectory to the wake vortex; characterized in that the module for determining the potential discomfort window around the estimated position of the wake vortex is such that the potential discomfort window around the estimated position of the wake vortex is determined as a function of the estimation uncertainty of the estimated position of the wake vortex, and the electronic circuitry is further configured to implement: - a module for keeping the follower aircraft (302) outside the potential discomfort window, by controlling a placement of the follower aircraft (302) at a predefined distance from the estimated position of the wake vortex when the dimensions of the potential discomfort window are such that this is allowed and at a predefined margin from the potential discomfort window otherwise.

9. Aircraft (100) acting as a follower aircraft (302) in formation flight, which comprises a system for assisting formation flight according to Claim 8.