Improved method for calculating a flight trajectory for an aircraft, and associated navigation system, aircraft and computer program product

Abstract

The present invention relates to a method (100) for calculating a flight trajectory (T(t)) for an aircraft comprising a short / medium-term loop (120) the steps of which are iterated at a high frequency, nested in a long-term loop (110) the steps of which are iterated at a low frequency, the long-term loop leading to a long-term trajectory (TL(t)) being calculated, the long-term trajectory being calculated so as to meet safety criteria, and the short / medium-term loop (120) first leading to a short-term trajectory (TC(t)) being calculated, and then to a medium-term trajectory (TM(t)) being calculated, the short-term trajectory being calculated so as to meet optimality criteria, the medium-term trajectory joining one end of the short-term trajectory to one end of the long-term trajectory.

Description

[0001] TITLE: Improved method for calculating a flight trajectory for an aircraft; Navigation system, aircraft and associated computer program product.

[0002] The invention relates to navigation systems for an aircraft and methods, implemented by such a navigation system, for calculating a flight trajectory of the aircraft.

[0003] Document FR 3 131 956 presents a method for calculating a flight trajectory implemented by the computer of an aircraft navigation system.

[0004] This process is performed periodically using, for example, a mission description flight plan, the current aircraft position, and current operational conditions.

[0005] First, a set of trajectories is calculated by uncertified algorithms. This set of trajectories includes a nominal trajectory and several diversion trajectories.

[0006] The nominal trajectory is calculated from, for example, an aircraft flight plan and allows the aircraft to carry out the mission assigned to it, such as reaching a destination airport.

[0007] Each diversion trajectory is calculated to respond to one or more particular hazards occurring during the flight of the aircraft, while the latter is guided along the nominal trajectory.

[0008] In a second step, all the calculated trajectories are validated for their safety by a certified algorithm.

[0009] Finally, in a third step, at each instant of the flight, a trajectory from this set of trajectories is selected as a flight trajectory, and is transmitted, as an instruction, to an aircraft guidance system. When a hazard occurs, the corresponding diversion trajectory is selected as a new flight trajectory and allows the aircraft to leave the nominal trajectory and land on the nearest runway.

[0010] The flight path followed therefore ensures the safety of the flight from start to finish.

[0011] The architecture of the navigation system presented in this state-of-the-art document is interesting because it allows the generation of trajectories, including diversion trajectories, by non-certified algorithms, then their validation by a certified algorithm.

[0012] This goes against the architecture of conventional FMS (Flight Management System), in which an algorithm for calculating the flight path from the flight plan information is regularly executed during the aircraft's flight to calculate a single nominal trajectory. And, to be certain that the flight path thus calculated is valid, it is the algorithm itself that must be previously certified. In addition, this algorithm must be executed on a computer that is also certified (or critical computer).

[0013] We therefore understand that the principle set out in document FR 3 131 956 is particularly promising.

[0014] However, while the flight path followed by the aircraft guidance system meets end-to-end safety criteria, this flight path is not always optimal. Indeed, the trajectories of all trajectories, including the nominal trajectory, may be suboptimal if they are not updated in real time based on current flight conditions.

[0015] Furthermore, the adaptability of this flight trajectory to operational constraints remains low. Indeed, the calculation of the entire set of trajectories is costly in terms of computing resources and computing time. However, the power of the computers on board an aircraft, particularly if it is a drone, is highly constrained, and does not allow for very frequent updating of these trajectories.

[0016] The invention therefore aims to improve the navigation system according to the state of the art.

[0017] For this purpose, the invention relates to a method for calculating a flight trajectory for an aircraft, characterized in that the method comprises a short / medium term loop, the steps of which are iterated at a high frequency, nested in a long-term loop, the steps of which are iterated at a low frequency, the long-term loop leading to the calculation of a long-term trajectory, the long-term trajectory being calculated to meet safety criteria, and the short / medium term loop leading first to the calculation of a short-term trajectory, then to the calculation of a medium-term trajectory, the short-term trajectory being calculated to meet optimality criteria, the medium-term trajectory joining the short-term trajectory with the long-term trajectory.

[0018] According to particular embodiments, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0019] - the long-term loop comprises the steps of: consolidating a plurality of safety constraints; calculating, as a function of the plurality of safety constraints, a current position of the aircraft, a plurality of technical capabilities characteristic of the aircraft, and a mission assigned to the aircraft, a set of long-term trajectories at the current time, said set comprising a nominal trajectory and a plurality of diversion trajectories; and, Selecting, as a long-term trajectory at the current time, from the set of long-term trajectories at the current time, the nominal trajectory or one of the diversion trajectories.

[0020] - the short / medium term loop comprises the steps of: consolidating a plurality of operational constraints and a plurality of safety constraints; calculating, as a function of the plurality of operational constraints, the plurality of safety constraints, a current position of the aircraft and a mission, a short-term trajectory at the current time; calculating, as a function of the plurality of safety constraints, the short-term trajectory and the long-term trajectory, a medium-term trajectory.

[0021] - at each time step, the long, medium and short term trajectories are aggregated into a flight trajectory, the flight trajectory being transmitted to an aircraft guidance system.

[0022] - once the long, medium and short term trajectories are aggregated into a flight trajectory, the flight trajectory is validated according to safety criteria before being transmitted to the aircraft guidance system.

[0023] - a time step being equal to one second, the short / medium term loop is iterated with a period of one second, and the long term loop is executed with a period of 60 seconds.

[0024] - the mission is a flight plan.

[0025] The invention also relates to a navigation system intended to be carried on board an aircraft, characterized in that it is adapted to implement the method of calculating a previous flight trajectory.

[0026] The invention also relates to an aircraft carrying a navigation system conforming to the preceding navigation system.

[0027] The invention also relates to a computer program product comprising software instructions which, when executed by an on-board computer of an aircraft, implement a navigation method in accordance with the preceding method.

[0028] The invention and its advantages will be better understood upon reading the following detailed description of a particular embodiment, given solely as an illustrative and non-limiting example, this description being made with reference to the appended drawings in which:

[0029] - Figure 1 is a schematic representation, in the form of functional modules, of the navigation system according to the invention;

[0030] - Figure 2 is a block representation of the trajectory calculation method implemented by the navigation system of Figure 1; and, - Figure 3 is a representation of the temporal evolution of the flight trajectory calculated by the navigation system of Figure 1.

[0031] Generally speaking, the method according to the invention consists of combining long-term navigation, ensuring flight safety until landing, and short-term navigation, allowing optimal completion of the mission.

[0032] According to the state of the art, long-term navigation relies on a set of trajectories, from which the safe trajectory is selected. However, these trajectories are neither optimal nor particularly dynamically adaptable.

[0033] Short-term navigation meets the criteria of optimality and high adaptability, as the short-term trajectory is constructed as the flight progresses. However, this short-term trajectory alone does not ensure flight safety, as it does not cover the entire flight until landing.

[0034] Finally, according to the invention, a medium-term trajectory is calculated making it possible to link the short-term and long-term trajectories calculated separately.

[0035] The flight trajectory then results from the concatenation of the short, medium and long term trajectories.

[0036] The flight path is advantageously validated for safety before being transmitted to the aircraft guidance system.

[0037] In the following, the qualifiers short, medium and long term are rather to be seen according to a distance scale, rather than a time scale, although these two scales are correlated through the aircraft speed parameter.

[0038] Operational constraints are those related to the mission (mission objective, performance criteria, etc.). Safety constraints are those related to flight safety (obstacles, no-fly zones for safety reasons, aircraft performance to be respected to avoid a crash).

[0039] Figure 1 represents a preferred embodiment of a navigation system according to the invention, intended to be carried on board an aircraft.

[0040] The navigation system 10 is adapted to calculate a flight trajectory periodically and transmit it to a guidance system 20 of the aircraft, as an instruction, in order to pilot the aircraft on this trajectory. Usually, the guidance system is in fact integrated into the navigation system.

[0041] The navigation system 10 is a computer comprising calculation means, such as a processor, and storage means, such as a memory. The memory stores in particular the instructions of computer programs, in particular a program whose execution allows the implementation of the method for calculating a flight trajectory according to the invention. The execution of this program makes it possible to provide the navigation system 10 with a plurality of functionalities, represented schematically in the form of functional modules in FIG. 1.

[0042] The navigation system 10 thus comprises a module 15 for updating the safety constraints at the current time CS(t). This module takes in particular as input the technical capabilities Cap of the aircraft as planned by its designer (such as autonomy, power, finesse, etc.), the meteorological information provided by the local meteorological agency, and the airspaces and altitudes authorized for the flight in order to guarantee its safety, provided by the aeronautical information services.

[0043] The navigation system 10 comprises a long-term trajectory calculation module 12. In accordance with the state of the art, the module 12 takes as input, for example, the mission M to be carried out, which may take the form, for example, of a flight plan, the current position P(t) of the aircraft, the characteristic Cap capabilities of the aircraft, and the safety constraints at the current time CS(t). The module 12 delivers as output a set of trajectories at the current time t. This set is denoted E(t).

[0044] The set E(t) comprises a nominal trajectory Tn(t) and a plurality of diversion trajectories T d(t), whose starting points are located along the nominal trajectory Tn(t). In both cases, these are long-term trajectories.

[0045] Advantageously, the navigation system 10 also includes a validation module 8, in accordance with the state of the art, making it possible to validate the safety of the set of trajectories E(t).

[0046] The navigation system 10 comprises a database 11 making it possible to record the set of trajectories at the current time E(t) validated by the module 8.

[0047] The navigation system 10 comprises a selection module 13 making it possible to select, in the database 11, a long-term trajectory at the current time TL(t) from among all the trajectories E(t).

[0048] The navigation system 10 includes a module 17 for updating the operational constraints at the current time COp(t). This module takes in particular as input the mission objectives specified by the aircraft operator and any geographical constraints (authorized airspace, relief, obstacles) and technical constraints (performance of the payload) influencing the success of the mission.

[0049] The navigation system 10 comprises a short-term trajectory calculation module 14. The module 14 takes, for example, as input the operational conditions at the current time Cop(t), the mission M, the characteristic Cap capabilities of the aircraft, the safety constraints at the current time CS(t), and the position P(t) at the current time of the aircraft. The module 14 delivers as output a short-term trajectory at the current time, TC(t).

[0050] The navigation system 10 comprises a medium-term trajectory calculation module, 16. The module 16 takes as input the short-term trajectory at the current time, TC(t) at the output of the module 14, the long-term trajectory at the current time, TL(t) at the output of the module 13 (essentially the starting point of the selected nominal long-term trajectory Tn(t), the characteristic Cap capabilities of the aircraft and, preferably, the safety constraints at the current time CS(t) at the output of the module 15. The module 16 delivers as output a medium-term trajectory at the current time, TM(t).

[0051] The medium-term trajectory connects the short-term trajectory and the long-term trajectory. This connection must ensure continuity in aircraft position and speed. Flight constraints are taken into account to make each connection.

[0052] The navigation system 10 comprises an aggregation module 18 which, from the short-term trajectories at the current time, TC(t), medium-term trajectories at the current time, TM(t), and long-term trajectories at the current time, TL(t), calculates a single object or flight trajectory at the current time T'(t).

[0053] Advantageously, the navigation system 10 also comprises a validation module 19, in accordance with the state of the art, making it possible to validate the safety of the flight trajectory T'(t) before transmitting it, as the flight trajectory T(t), to the guidance module 20. The validation module 19 may take into account the validation of the entire trajectory E(t) possibly carried out beforehand by the validation module 8.

[0054] The trajectory calculation modules 12, 14 and 16 each execute an algorithm known to those skilled in the art to calculate the long-term, short-term and medium-term trajectories respectively. For example, the following may be implemented: algorithms of the same type as those of a state-of-the-art FMS, if the aircraft must follow aeronautical procedures (particularly for long-term trajectories); conventional trajectory and / or path calculation algorithms for missions such as surveillance, tracking, rescue, etc.; algorithms based on machine learning.

[0055] Figure 2 represents a preferred embodiment of the flight trajectory calculation method according to the invention.

[0056] The method 100 is implemented by the navigation system 10 of FIG. 1, during the flight of the aircraft 1. The method 100 comprises a short / medium term loop 120 nested in a long term loop 110. These two loops are in fact executed in parallel, the calculations of the long term loop making it possible to obtain a set of trajectories taking more time.

[0057] For example, the short / medium term loop 120 is iterated every 1 second, while the long term loop is iterated every 60 seconds.

[0058] An iteration of the long-term loop 110 will now be presented.

[0059] In a step 111 of the loop 110, safety constraints are consolidated at the current time. Step 111 consists of executing the module 15. These are, for example, constraints linked to: the terrain (the safety altitude); the weather (winds and dangerous weather phenomena); the regulations (authorized or prohibited geographical zones, procedures to be respected); the landing strips (closure of an airport for example); the aircraft (autonomy and performance).

[0060] At the output of step 111, a safety constraint vector is provided at the current time, CS(t). This vector includes, in the mission area, the prohibited zones and the authorized zones, the procedures to be followed and the available landing runways as well as the performance parameters of the aircraft.

[0061] Then, in step 112 a set of long-term trajectories is calculated and then validated. This step consists of executing modules 12 then 8.

[0062] The purpose of this step is to update all the long-term trajectories at the current time E(t) stored in the database 11.

[0063] For step 112, for example, not only the current position P(t) of aircraft 1, the mission M to be carried out, the Cap capabilities of the aircraft, but also the safety constraint vector CS(t) are considered.

[0064] A nominal trajectory at the current time Tn(t) is calculated between the current position P(t) of the aircraft and the end of mission position indicated by the mission M (landing runway of the destination point for example).

[0065] Different diversion (or contingency) trajectories at the current time Td(t) are calculated. Each trajectory Td(t) is associated with one or more hazards to which it responds. Each trajectory Td(t) departs from the nominal trajectory at the current time Tn(t) towards alternative landing runways present near the nominal trajectory. A diversion trajectory is calculated so that, if a hazard occurs along the nominal trajectory, the aircraft leaves the nominal trajectory and follows the diversion trajectory in order to bring the aircraft back to the ground safely, taking into account the hazard.

[0066] The different trajectories in the set E(t) are potential long-term trajectories that may be suboptimal. They take into account conservative aircraft performance parameters (low climb rate and large turn radius for example) allowing the aircraft to fly the calculated trajectory even in unfavorable conditions: engine failure, failure of some control surfaces, strong wind, etc.

[0067] At the output of step 112, the set of trajectories at the current time E(t) calculated is validated from the security point of view by the validation module 8, then stored in the database 11 to be used during the iterations of the short / medium term loop 120. The content of the database 11 will be updated during the following iteration of the long term loop 110.

[0068] The short / medium term loop 120 includes the following steps:

[0069] Step 121 is used to test a condition on the aircraft state. Step 121 corresponds to the execution of module 13.

[0070] Depending on the current state S(t) of the aircraft, either the nominal trajectory or one of the diversion trajectories is selected from the database 11. The selected trajectory becomes the long-term trajectory at the current time, TL(t).

[0071] The other steps of the short / medium term loop 120 are implemented only during nominal operation of the aircraft, i.e. when the nominal trajectory has been selected as the long term trajectory at the current time TL(t).

[0072] The short / medium term loop continues with step 122.

[0073] Step 122 consists of consolidating the current operational constraints. Module 17 is executed for the current time step.

[0074] For example, the objective of the aircraft's mission M is updated at the current time step. This is the case, for example, when the objective of the mission is to pursue a target, then the position and speed of this target (delivered, for example, by a radar system on board the aircraft) are updated during step 122.

[0075] At the output of step 122, the vector of operational constraints at the current time COp(t) is obtained.

[0076] Step 124 consists of calculating a short-term trajectory at the current time, TC(t).

[0077] To do this, module 14 is executed.

[0078] This step takes for example as input the current position of the aircraft P(t), the mission M to be carried out, the characteristic Cap capabilities of the aircraft, the operational constraint vector COp(t), and the safety constraints at the current time CS(t). Advantageously, the calculation of the short-term trajectory is such that it leads to an optimal trajectory, taking into account the nominal capabilities of the aircraft. For example, if the objective is to climb to a certain level, the short-term trajectory makes it possible to go towards this objective with a climb according to the optimal slope of the aircraft 1.

[0079] In step 126, a medium-term trajectory at the current time, TM(t), is calculated.

[0080] This must make it possible to join the short-term trajectory TC(t) calculated at the output of step 124 and the long-term trajectory TL(t) at the output of step 121.

[0081] Step 126 is to execute module 16.

[0082] A condition for calculating the medium-term trajectory is, for example, to minimize the distance between the end point of the short-term trajectory TC(t) and the starting point of the long-term trajectory TL(t), while respecting criteria for joining these two trajectories. These criteria are based on the nominal Cap capabilities of the aircraft 1 , for example, on a minimum radius of curvature of the aircraft, a continuous speed at the junction point, etc.

[0083] Preferably the security constraints at the current time CS(t) are also taken into account in step 126.

[0084] Step 128 then consists of associating the short, medium and long term trajectories at the current time in a single flight trajectory usable by the guidance system 20 of the aircraft. For this, the aggregation module 18 is executed. A trajectory T'(t) is thus obtained from TL(t), TM(t) and TC(t).

[0085] Optionally, in step 129, the safety of the flight trajectory T'(t) at the output of module 18 is verified. This step corresponds to the execution of module 19.

[0086] This allows us to check a posteriori, that is to say once the flight trajectory has been calculated, that it is safe from start to finish.

[0087] Once validated, the flight trajectory at the current time T(t) is transmitted to the guidance module 20. If the new calculated trajectory is invalidated, the trajectory update is not continued, and the last validated trajectory is retained.

[0088] Thus, updating the short-term trajectory while retaining the nominal trajectory as a long-term trajectory makes it possible to construct a flight trajectory for the aircraft that is very responsive to changes in operational constraints Cop(t), in particular the occurrence of unexpected events. Compared to the state of the art where changes in operational constraints are only taken into account through the calculation of a new set of long-term trajectories, the invention allows for a much shorter reaction time.

[0089] Furthermore, since the short-term trajectory is optimal, the trajectory actually followed at each instant by the aircraft becomes optimal. Figure 3 illustrates the implementation of the invention. An aircraft A carries the device 10 and implements the method 100. Figure 3 illustrates the flight trajectory followed by the aircraft A over a period of 60 s.

[0090] At time t=0, the long loop 110 completes a first iteration allowing the calculation of the set of long-term trajectories E(0). It includes a nominal trajectory Tn(0) and several diversion trajectories Td(0).

[0091] During the next 60 iterations of the short / medium term loop 120, between t=0 and t=59, the long term trajectory will be selected from this set E(0). Barring any random event, the long term trajectory is therefore equal to Tn(0).

[0092] The iteration of the short / medium term loop 120 at t=0 allows the calculation of a short term trajectory TC(0), then a medium term trajectory TM(0) connecting TC(0) and Tn(0).

[0093] The iteration of the short / medium term loop 120 at t=1 allows the calculation of a short term trajectory TC(1), then a medium term trajectory TM(1) connecting TC(1) and Tn(0).

[0094] The iteration of the short / medium term loop 120 at t=2 allows the calculation of a short term trajectory TC(2), then a medium term trajectory TM(2) connecting TC(2) and Tn(0)...

[0095] The iteration of the short / medium term loop 120 at t=59 allows the calculation of a short term trajectory TC(59), then a medium term trajectory TM(59) connecting TC(59) and Tn(0).

[0096] At t=60, the long-term loop 110 completes a second iteration allowing the calculation of a new set of long-term trajectories E(60), which includes the long-term trajectories (Tn(60) or Td(60)) which will be used during the following 60 iterations of the short / medium-term loop 120.

[0097] The iteration of the short / medium term loop 120 at t=60 allows the calculation of a short term trajectory TC(60), then a medium term trajectory TM(60) connecting TC(60) and Tn(60).

[0098] The trajectory Tf actually followed by aircraft 1 is ultimately the association of the portions of the short-term trajectories TC(t) actually traveled by the aircraft between two iterations of loop 110. This trajectory is therefore optimal, at least in portions.

[0099] The present invention has many advantages.

[0100] In particular, the short-term trajectory allows for efficiency gains, while the long-term trajectory is conservative. Decoupling calculations between short-term, medium-term, and long-term trajectories allows for parallel calculations, thereby reducing the workload on the onboard computer.

[0101] Furthermore, the performance constraints on the computer are also reduced thanks to the long-time loop which makes it possible to reduce the frequency at which all the long-term trajectories are updated, which is, in the calculation of the flight trajectory, the part requiring the most computing resources.

[0102] Thus, the navigation function according to the invention provides the aircraft with a safe, optimized flight path adapted to the operational conditions, on which the aircraft can guide itself.

[0103] The invention is applicable to any navigation function, in particular for autonomous aircraft, primarily drones.

[0104] It applies to air transport (passengers or freight), in particular for autonomous aircraft (drones and unmanned aircraft).

[0105] When the method is carried out in the form of one or more software programs, that is to say in the form of a computer program, also called a computer program product, it is also capable of being recorded on a medium, not shown, that is readable by a computer. The computer-readable medium is, for example, a medium capable of storing electronic instructions and of being coupled to a bus of a computer system. For example, the readable medium is an optical disk, a magneto-optical disk, a ROM memory, a RAM memory, any type of non-volatile memory (for example FLASH or NVRAM) or a magnetic card. A computer program comprising software instructions is then stored on the readable medium.

Claims

CLAIMS 1. Method (100) for calculating a flight trajectory (T(t)) for an aircraft (A), characterized in that the method comprises a short / medium term loop (120), the steps of which are iterated at a high frequency, nested in a long term loop (110), the steps of which are iterated at a low frequency, the long term loop (110) leading to the calculation of a long term trajectory (TL(t)), the long term trajectory being calculated to meet safety criteria, and the short / medium term loop (120) leading first to the calculation of a short term trajectory (TC(t)), then to the calculation of a medium term trajectory (TM(t)), the short term trajectory being calculated to meet optimality criteria, the medium term trajectory joining the short term trajectory with the long term trajectory.

2. Method according to claim 1, in which the long-term loop (110) comprises the steps of: consolidating (111) a plurality of safety constraints; calculating (112), as a function of the plurality of safety constraints, a current position of the aircraft, a plurality of technical capabilities characteristic of the aircraft, and a mission assigned to the aircraft, a set of long-term trajectories at the current time (E(t)), said set E(t) comprising a nominal trajectory (Tn(t)) and a plurality of diversion trajectories (Td(t)); and, Selecting (121), as a long-term trajectory at the current time (TL(t)), from the set of long-term trajectories at the current time (E(t)), the nominal trajectory or one of the diversion trajectories.

3. Method according to claim 1 or claim 2, in which the short / medium term loop (120) comprises the steps of: consolidation (122) of a plurality of operational constraints and a plurality of safety constraints; calculation (124), as a function of the plurality of operational constraints, the plurality of safety constraints, a current position of the aircraft and a mission, of a short-term trajectory at the current time (TC(t)); calculation (126), as a function of the plurality of safety constraints, the short-term trajectory and the long-term trajectory, of a medium-term trajectory.

4. Method according to any one of the preceding claims, in which, at each time step, the long, medium and short term trajectories are aggregated (128) into a flight trajectory, the flight trajectory being transmitted to a guidance system (20) of the aircraft.

5. Method according to claim 4, in which, once the long, medium and short term trajectories have been aggregated into a flight trajectory, the flight trajectory is validated (129) according to safety criteria before being transmitted to the aircraft guidance system.

6. Method according to any one of the preceding claims, in which, a time step being equal to one second, the short / medium term loop (120) is iterated with a period of one second, and the long term loop (110) is executed with a period of 60 seconds.

7. A method according to any preceding claim, wherein the mission is a flight plan.

8. Navigation system (10) intended to be carried on board an aircraft (A), characterized in that it is adapted to implement a method for calculating a flight trajectory according to any one of claims 1 to 7.

9. Aircraft (A) carrying a navigation system (10), characterized in that the navigation system conforms to the navigation system of claim 8.

10. Computer program product comprising software instructions which, when executed by an on-board computer of an aircraft, implement a navigation method in accordance with the method according to any one of the claims

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