METHOD AND SYSTEM FOR MONITORING AN ESTIMATE OF THE GROSS MASS OF AN AIRCRAFT

Abstract

A method for monitoring an estimate of the gross mass of an aircraft includes: obtaining or calculating (202) a first estimate of the gross mass, resulting from the addition of an estimate of the mass of the aircraft without fuel with an estimate of the mass of fuel carried on board the aircraft; obtaining or calculating (203) a second estimate of the gross mass of the aircraft, based on a first numerical (aerodynamic) model of the aircraft; calculating (205), for a computational cycle of rank i among a plurality of successive computational cycles executed during an acceleration phase at takeoff of the aircraft, a third estimate of the gross mass, based on a second numerical model of the aircraft different from the first; and if the difference between the first and second estimates exceeds a predetermined threshold, validating one and invalidating the other (206), based on the third estimate. Figure to be published with the abstract: Fig. 2

Description

Title of the invention: METHOD AND SYSTEM FOR MONITORING AN ESTIMATE OF THE GROSS MASS OF AN AIRCRAFT technical field

[0001] The present invention relates to a method and a system for monitoring an estimate of the gross mass of an aircraft.

[0002] In common usage, the term "weight" is often used to refer to the mass of an object, although these are in fact different concepts (the weight P of an object corresponds to its mass m multiplied by the intensity of the gravitational field g at its location: P = mg). For this reason, and somewhat incorrectly, the acronym GW (for "Gross Weight") is sometimes used later in the description to refer to the gross mass of the aircraft, whereas strictly speaking it refers to the gross weight of the aircraft.

[0003] Furthermore, in the remainder of this description, the term "gross mass estimate" refers to the result of an estimation, that is, an action aimed at determining the value of the gross mass. PRIOR TECHNOLOGY

[0004] The mass of the aircraft is an important data point for calculating characteristic speeds (displayed in the cockpit) and flight control laws.

[0005] Currently, an initial estimate of the aircraft's gross mass (denoted GWinitiaie in the remainder of the description) results from adding an estimated mass of the aircraft without fuel (or ZFW, for "Zero Fuel Weight") to an estimated mass of fuel carried on board the aircraft (or FOB, for "Fuel On Board"). Thus, we have: GWinitiaie = ZFW + FOB. The estimated mass of the aircraft without fuel (ZFW) is entered by the aircraft crew into an FMS (Flight Management System). Since this entry is manual, it is subject to errors. The estimated mass of fuel carried on board the aircraft (FOB) is provided by an FQMS (Fuel Quantity and Management System).

[0006] A second estimate of the gross mass of the aircraft (denoted GWæro in the rest of the description) is based on a numerical model which is an aerodynamic model of the aircraft typically having as input parameters: a speed, a pitch, an altitude, a configuration of leading edge high-lift devices (or "slats" in English) and trailing edge high-lift devices (or "flaps" in English), and an angle of attack (or AOA for "Angle of Attack" in English). of the aircraft. This aerodynamic model is hosted by an avionics computer of the aircraft, in particular a flight control computer, for example an FCGS type system (for "Flight Control and Guidance System" in English) or a FAC type system (for "Flight Augmentation Computer" in English).

[0007] Currently, a gross mass check of the aircraft is in place. The principle consists of comparing the first estimated GWinitial with the second estimated GWex. If a discrepancy is detected (for example, a difference exceeding several tonnes), the crew is notified (display of a "CHECK GW" or "CHECK WEIGHT" message). Since the aircraft avionics are not capable of determining which of the two estimates is incorrect, the procedure recommended to the crew, in the Flight Crew Operating Manual (FCOM), is to perform a check of the aircraft's unfueled mass (ZFW), which has been previously entered by the crew into the FMS type system.If the aircraft's unfueled mass (ZFW) appears correct, the operations manual advises the crew that the estimated GWaero is potentially incorrect and that, consequently, certain parameters calculated on board (by the FCGS or FAC type system) based on this GWaero estimate, particularly the characteristic speeds displayed in the cockpit, are potentially incorrect and should be disregarded. Considering the GWaero estimate potentially incorrect means acknowledging an error in its calculation, which could be attributed to a computer problem or a problem (failure) with one or more sensors acquiring one or more of the input parameters (primarily the angle of attack) of the aerodynamic model used for the calculation.

[0008] There is therefore a need to provide a solution which makes it possible to determine and indicate to the crew which of the two estimates GWinitiaie and GWæro is erroneous, in the event that a divergence between these two estimates is detected during the control of the gross mass of the aircraft. Description of the invention

[0009] A method is proposed for monitoring an estimate of the gross mass of an aircraft, the method being implemented by a system in the form of electronic circuitry, the method comprising: - obtain or calculate a first estimate of the gross mass of the aircraft, resulting from an addition of an estimate of the mass of the aircraft without fuel with an estimate of the mass of fuel carried in the aircraft; - obtain or calculate a second estimate of the aircraft's gross mass, based on a first numerical model of the aircraft which is a model aircraft aerodynamics having as input parameters at least the following parameters: a speed, a pitch, an altitude, a configuration of leading edge high-lift devices and trailing edge high-lift devices, and an angle of attack of the aircraft; - calculate, for a computational cycle of rank i among a plurality of successive computational cycles executed during an acceleration phase at takeoff of the aircraft and as long as the aircraft has a speed greater than a first predetermined speed threshold and less than a second predetermined speed threshold itself greater than the first speed threshold, a third estimate of the gross mass of the aircraft, based on a second numerical model of the aircraft different from the first numerical model of the aircraft and having as input parameters at least the following parameters: an Atr duration of each of the computational cycles; a current ground speed GS(i), a thrust force TH(i), a drag force DF(i) and a lift force LF(i) of the aircraft at computational cycle of rank i; a runway slope SL at takeoff; and a ground friction coefficient CR; and - if there is a difference between the first and second estimates that exceeds a predetermined difference threshold, validate one and invalidate the other of the first and second estimates, depending on the third estimate.

[0010] Thus, the third estimate of the aircraft's gross mass (denoted GWT / 0 in the remainder of the description) makes it possible to determine (and therefore to indicate to the crew) which of the two estimates GWinMe and GWæro is erroneous, in the event that a discrepancy between them is detected (during the aircraft's gross mass check). If the first estimate GWinitiaie is validated and the second estimate GWÆRoest is invalidated (erroneous), this allows an alert to be sent to the crew (presence of a sensor or computer malfunction causing false readings from the aircraft's displayed measurements). Conversely, if the second estimate GWÆRoest is validated and the first estimate GWinitiaie is invalidated (erroneous), this allows the measurements displayed by the aircraft to be validated and rules out a sensor or computer malfunction.

[0011] According to a particular embodiment, after the aircraft speed has exceeded the second predetermined speed threshold during the takeoff acceleration phase, the third estimated speed is frozen and takes the value calculated in the last calculation cycle before the aircraft speed exceeded the second predetermined speed threshold.

[0012] According to a particular embodiment, the first predetermined speed threshold is between 25 and 35 knots and the second predetermined speed threshold is between 80 and 120 knots.

[0013] According to a particular embodiment, the third estimate is calculated, at the computation cycle of rank i, as follows:

[0014]

[0015] with:

[0016] ADr(i) = &t*GS(i)

[0017] AGS(i) = GS(i) - GS(il)

[0018] and g which represents the acceleration due to Earth's gravity, i.e. approximately 9.81 m / s2.

[0019] According to a particular embodiment, the calculation of the third estimate uses, for each of the input parameters GS(i), TH(i), DF(i) and LF(i), an average value over the duration of the calculation cycle of rank i.

[0020] According to a particular embodiment, the thrust force TH(i) of the aircraft at the computation cycle of rank i is calculated with a third numerical model of the aircraft having as input parameters at least the following parameters: - at least one piece of information relating to the aircraft's thrust, belonging to the group comprising: a NI rotational speed of a low-pressure assembly of each aircraft propulsion engine, an EPR engine pressure ratio and a TRA throttle opening angle; - at least one piece of aircraft speed information in the form of a Mach number; and - at least two pieces of information about ambient conditions, including temperature information and pressure information.

[0021] According to a particular embodiment, the drag force DF(i) and the lift force LF(i) of the aircraft at the computation cycle of rank i are calculated with a fourth numerical model of the aircraft having as input parameters at least the following parameters: - at least one piece of information about the aircraft's speed in the form of a Mach number; - at least two pieces of ambient condition information, including temperature information and pressure information; - information on the aircraft's angle of attack; and - information relating to the current configuration of the aircraft's leading edge high-lift devices and trailing edge high-lift devices.

[0022] A computer program product is also proposed, comprising instructions leading to the execution, by a processor, of the process mentioned above according to any of its embodiments, when said instructions are executed by the processor.

[0023] A storage medium is also proposed, storing such instructions.

[0024] A monitoring system for an estimate of the gross mass is also proposed. of an aircraft, the system comprising electronic circuitry configured to implement: - obtain or calculate a first estimate of the gross mass of the aircraft, resulting from an addition of an estimate of the mass of the aircraft without fuel with an estimate of the mass of fuel carried in the aircraft; - obtain or calculate a second estimate of the gross mass of the aircraft, based on a first numerical model of the aircraft which is an aerodynamic model of the aircraft having as input parameters at least the following parameters: a speed, a pitch, an altitude, a configuration of leading edge high-lift devices and trailing edge high-lift devices, and an angle of attack of the aircraft; - calculate, for a computational cycle of rank i among a plurality of successive computational cycles executed during an acceleration phase at takeoff of the aircraft and as long as the aircraft has a speed greater than a first predetermined speed threshold and less than a second predetermined speed threshold itself greater than the first speed threshold, a third estimate of the gross mass of the aircraft, based on a second numerical model of the aircraft different from the first numerical model of the aircraft and having as input parameters at least the following parameters: an Atr duration of each of the computational cycles; a current ground speed GS(i), a thrust force TH(i), a drag force DF(i) and a lift force LF(i) of the aircraft at computational cycle of rank i; a runway slope SL at takeoff; and a ground friction coefficient CR; and - if there is a difference between the first and second estimates that exceeds a predetermined difference threshold, validate one and invalidate the other of the first and second estimates, depending on the third estimate.

[0025] An aircraft comprising a surveillance system as mentioned above is also proposed. Brief description of the drawings

[0026] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of at least one exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

[0027] [Fig.1] schematically illustrates, in side view, an aircraft equipped with a monitoring system for estimating the gross mass of an aircraft;

[0028] [Fig.2] schematically illustrates an example of a monitoring algorithm for a estimation of the gross mass of an aircraft;

[0029] [Fig.3] illustrates a particular implementation of the calculation step of the third estimated GWT / 0, included in the algorithm of [Fig.2];

[0030] [Fig.4] illustrates, in block diagram form, the monitoring system appearing on [Fig.1], in one embodiment;

[0031] [Fig.5] illustrates a particular implementation of the third calculation block estimated GWT / o, included in the block diagram of [Fig. 4]; and

[0032] [Fig.6] schematically illustrates an example of a hardware platform allowing to implement, in the form of electronic circuitry, the monitoring system for an estimate of the gross mass of an aircraft.

[0033] DETAILED DESCRIPTION OF IMPROVEMENTS

[0034] Figure 1 schematically illustrates, in side view, an aircraft 10. The aircraft 10 includes a monitoring system 101 for estimating the aircraft's gross mass. The monitoring system 101 is implemented as electronic circuitry and is typically integrated into an avionics unit 100.

[0035] The 101 monitoring system is for example hosted in a flight control computer, for example an FCGS type system (for "Flight Control and Guidance System" in English) or a FAC type system (for "Flight Augmentation Computer" in English).

[0036] Avionics 100 also typically includes an FMS (Flight Management System) (reference 102) and various other systems (not shown in [Fig. 1]) such as: an ADIRS (Air Data Inertial Reference System), a FADEC (Full Authority Digital Engine Control) system, an FWS (Flight Warning System), an EIS (Electronic Information System) including, in particular, an ECAM (Electronic Centralized Aircraft Monitoring) system, a CFDIU (Centralized Fault Display Interface Unit) system, and an SFCC (Slat Flap Control Computer) system. Avionics 100 also typically includes other electronic systems.

[0037] The monitoring system 101 implements a method (algorithm) for monitoring an estimate of the aircraft's gross mass. This method is schematically illustrated in [Fig. 2], in a particular embodiment.

[0038] In a step 202 (which follows a start step 201 of the algorithm), the monitoring system 101 obtains or calculates a first estimate of the gross mass of the aircraft, denoted GWinitiaie. As already described above, in relation to the prior art, this first estimate results from adding an estimate of the aircraft's mass without fuel (ZFW) to an estimate of the mass of fuel carried on board the aircraft (FOB): GWinitiaie = ZFW + FOB. In the case where the monitoring system 101 obtains (and therefore does not calculate itself) the first estimate GWinitiaie, it is, for example, calculated by the FMS 102 type system.

[0039] In a step 203, the monitoring system 101 obtains or calculates a second estimate of the gross mass of the aircraft, denoted GWæro- As also already described above, in relation to the prior art, this second estimate is a function of a first digital model of the aircraft which is an aerodynamic model of the aircraft having as input parameters at least the following parameters: a speed, a pitch, an altitude and an angle of attack of the aircraft, from for example the ADIRS type system; and a configuration of leading edge high-lift devices and trailing edge high-lift devices, from for example the SFCC type system.

[0040] In step 204, the monitoring system 101 checks whether the difference between the first and second estimates (difference denoted: | GWinitiaie - GWæro I ) is greater than a predetermined deviation threshold S (204). In a particular implementation, the threshold S is on the order of several tonnes. If the test in step 204 is positive (difference greater than S), the monitoring system 101 executes step 205 and then step 206, before proceeding to the final step 207 of the algorithm. Otherwise (difference less than or equal to S), the monitoring system 101 proceeds directly to the final step 207.

[0041] In step 205, the monitoring system 101 calculates a third estimate of the aircraft's gross mass, denoted GWT / 0, based on a second numerical model of the aircraft that differs from the first numerical model. The third estimate GWT / 0 is independent of the second estimate GWæro because they are calculated using numerical models of the aircraft that are based on different physical phenomena: the lift equation for the aerodynamic model (first numerical model) used to calculate the second estimate, and inertia (and more specifically Newton's second law) for the second numerical model used to calculate the third estimate. It should be noted that Newton's second law (or fundamental principle of dynamics) states that a resultant force exerted on an object is always equal to the product of the object's mass and its acceleration, and that the resulting acceleration and the resultant force have the same direction.The resultant force is the force equivalent to the vector sum of all the forces acting on the object. In this context (and as detailed later), the forces acting on the object are the thrust, the lift, and the... drag, ground friction and the weight of the aircraft. A particular embodiment of step 205 is described below, in relation to [Fig.3].

[0042] In step 206, the monitoring system 101 validates one and invalidates the other of the first and second estimates (GWinitiaie and GWæroX as a function of the third estimate (GWT / o)- For example, the monitoring system 101 validates the one of the first and second estimates which is closest to the third estimate, and invalidates the other.

[0043] Fig. 3 illustrates a particular implementation of step 205 of calculation of the third estimated GWT / 0, included in the algorithm of Fig. 2.

[0044] In a step 302 (which follows a start step 301), the monitoring system 101 checks whether, during an acceleration phase during takeoff, the aircraft has a speed V greater than a predetermined first speed threshold SI. In a particular implementation, the first speed threshold SI is between 25 and 35 knots (approximately between 46 and 65 km / h) in calibrated airspeed (CAS). This avoids the need to perform resource-intensive calculations during the initial takeoff phase. If the first speed threshold SI is reached (i.e., if V > S1), a step 303 is performed; otherwise, step 302 is repeated.

[0045] In step 303, the monitoring system 101 activates calculations, more specifically the third estimated GWT / ode of the aircraft's gross mass, as detailed below. The calculations are performed in successive calculation cycles.

[0046] In step 304, the monitoring system 101 triggers a new computing cycle.

[0047] In a step 305, for a calculation cycle of rank i, the monitoring system 101 performs a calculation of the third estimate GWT / 0 based on a second digital model of the aircraft different from the first digital model of the aircraft (aerodynamic model used to calculate the second estimate GWæro)- The second digital model has as input parameters at least the following parameters: an Atr duration of each of the calculation cycles; a current ground speed GS(i), a thrust force TH(i), a drag force DF(i) and a lift force LF(i) of the aircraft at the calculation cycle of rank i; a runway slope SL at takeoff; and a ground friction coefficient CR.

[0048] In a particular implementation, for a computational cycle of rank i, the third estimate is calculated according to the following equation (1):

[0049] rw _

[0050] with:

[0051] &Dr(i)= Atr*GS(i)

[0052] toGS(i) = GS(i)-GS(M)

[0053] and g which represents the acceleration due to Earth's gravity, i.e. approximately 9.81 m / s2.

[0054] The reasoning to arrive at this equation (1) is detailed at the end of this description.

[0055] To improve accuracy, the calculation of the third estimate uses, for each of the input parameters GS(i), TH(i), DF(i), and LF(i), an average value over the duration of the calculation cycle i considered (for example, an average between a value at the beginning of the calculation cycle and a value at the end of the calculation cycle) rather than considering only the value at the beginning of the calculation cycle. This is because these parameters vary significantly between the beginning and the end of the calculation cycle (also called the "time step").

[0056] In a particular implementation, the thrust force TH(i) of the aircraft at the computation cycle of rank i is calculated with a third numerical model of the aircraft having at least the following input parameters: - at least one piece of information relating to the aircraft's thrust (from, for example, the FADEC type system), belonging to the group comprising: a rotational speed NI of a low-pressure assembly of each aircraft propulsion engine, an engine pressure ratio (or EPR, for "Engine Pressure ration" in English) and a throttle Resolver Angle (or TRA, for "Throttle Resolver Angle" in English); - at least one piece of aircraft speed information (from, for example, an ADIRS-type system), in the form of a Mach number; and - at least two pieces of ambient condition information (from, for example, the ADIRS type system), including temperature information and pressure information.

[0057] In a particular implementation, the drag force DF(i) and the lift force LF(i) of the aircraft at the computation cycle of rank i are calculated with a fourth numerical model of the aircraft having as input parameters at least the following parameters: - at least one piece of aircraft speed information (from, for example, an ADIRS-type system), in the form of a Mach number; - at least two pieces of ambient condition information (from, for example, the ADIRS type system), including temperature information and pressure information; - information on the aircraft's angle of attack (from, for example, an ADIRS-type system); and - information (from, for example, the SFCC type system) relating to the current configuration of the aircraft's leading edge and trailing edge high-lift devices.

[0058] In step 306, the monitoring system 101 checks whether, during the aircraft's takeoff acceleration phase, the aircraft's speed V exceeds a predetermined second speed threshold S2, which is higher than the first speed threshold SI. In a particular implementation, the second speed threshold S2 is between 80 and 120 knots (approximately between 148 and 223 km / h) in calibrated airspeed (CAS). If the second speed threshold S2 is exceeded (i.e., if V > S2), step 307 is performed; otherwise, step 304 is repeated (triggering a new calculation cycle).

[0059] In step 307, the monitoring system 101 freezes the third estimated GWT / 0 at the value calculated in the last calculation cycle before the aircraft speed exceeds the second speed threshold S2 (i.e., at the value calculated in the last iteration of step 305).

[0060] Thus, the calculations of the third GWT / o estimate are limited to the initial takeoff phase and when the speed is between the speed thresholds SI and S2, in order to guarantee that the third GWT / o estimate is independent of the second GWæro estimate. Indeed, the second GWæro estimate is obtained with the first numerical model of the aircraft, which is an aerodynamic model. However, aerodynamic effects are not very significant at low speeds. Therefore, the third GWT / o estimate (using the second numerical model of the aircraft, which differs from the first numerical model of the aircraft) is calculated when the aircraft has a low speed (between SI and S2), that is, while the aerodynamic effects are negligible.

[0061] [Fig.4] illustrates, in block diagram form (functional diagram), the monitoring system 101 appearing on [Fig.1], in an embodiment comprising three functional blocks 101a, 101b and 101c hosted for example by the FCGS type system or the FAC type system.

[0062] The first functional block 101a is configured to calculate the second estimated GWæro of the gross mass of the aircraft, using the first digital model of the aircraft (aerodynamic model) whose input parameters have been described above (speed, pitch, altitude, angle of attack, configuration of leading edge high-lift devices and trailing edge high-lift devices).

[0063] The second functional block 101b is configured to calculate the third estimated GWt / o of the aircraft's gross mass, based on input parameters 400. This The second functional block 101b is described in more detail below, in relation to [Fig.5].

[0064] The third functional block 101c is configured to validate one and invalidate the other of the first and second estimates (GWinitiaie and GWæroX) based on the third estimate GWT / o, in case of a difference between the first and second estimates exceeding the predetermined deviation threshold S. The first estimate GWinitiaie is provided by the FMS 102 type system, which calculates it by adding the estimated mass of the aircraft without fuel (ZFW) to the estimated mass of the fuel carried on board the aircraft (FOB). Output 401 of functional block 101c provides information, particularly for the crew, specifying which estimate is validated and which is invalidated.

[0065] Figure 5 illustrates a particular implementation of the second functional block 101b, which performs the calculation of the third estimated GWTO and itself comprises three sub-functional blocks 501, 502 and 503.

[0066] The first functional sub-block 501 is configured to calculate, at each computation cycle of rank i, the thrust force TH(i) of the aircraft, using the third digital model of the aircraft whose input parameters have been described above (NI, EPR or TRA information relating to the thrust of the aircraft, Mach number, temperature and pressure information).

[0067] The second functional sub-block 502 is configured to calculate, at each computation cycle of rank i, the drag force DF(i) and the lift force LF(i) of the aircraft, using the fourth digital model of the aircraft whose input parameters have been described above (Mach number, temperature and pressure information, angle of attack information of the aircraft, information relating to the current configuration of the leading edge high-lift devices and the trailing edge high-lift devices of the aircraft).

[0068] The third functional sub-block 503 is configured to calculate (see step 205 of [Fig.2] and step 305 of [Fig.3]), at each calculation cycle of rank i, the third estimated GWT / 0 using the second digital model of the aircraft whose input parameters are: the thrust force TH(i) (provided by the functional sub-block 501), the drag force DF(i) and the lift force LF(i) (provided by the functional sub-block 502), the predetermined coefficient CR of ground friction, the slope SL of the runway at takeoff (provided for example by a TAWS type system for Terrain Avoidance and Waming System), the predetermined duration Ah of each of the calculation cycles, the current ground speed GS(i) at the calculation cycle of rank i (provided for example by the ADIRS type system).

[0069] Fig. 6 schematically illustrates an example of a hardware platform enabling the implementation, in the form of electronic circuitry, of the system 101 for monitoring an estimate of the gross mass of aircraft 10.

[0070] The hardware platform then comprises, connected by a communication bus 610: a processor or CPU (Central Processing Unit) 601; a RAM (Random Access Memory) 602; a ROM (Read Only Memory) 603, for example of type ROM (Read Only Memory) or EEPROM (Electrically-Erasable Programmable ROM); a storage unit, such as a HDD (Hard Disk Drive) 604 or a storage media reader, such as an SD (Secure Digital) card reader; and an interface manager 605. The interface manager 605 allows the monitoring system 101 to interact with one or more pieces of equipment of the aircraft 10, and more particularly with avionics equipment 100 of the aircraft 10.

[0071] The processor 601 is capable of executing instructions loaded into RAM 602 from ROM 303, external memory (not shown), a storage medium (such as an SD card), or a communication network (not shown). When the hardware platform is powered on, the processor 601 is capable of reading instructions from RAM 602 and executing them. These instructions form a computer program causing the processor 601 to carry out all or part of the steps and operations described herein.

[0072] All or part of the steps and operations described herein can thus be implemented in software form by the execution of a set of instructions by a programmable machine, for example a DSP (Digital Signal Processor) or a microcontroller, or be implemented in hardware form by a dedicated machine or electronic component (chip) or a dedicated set of electronic components (chipset), for example an FPGA (Field-Programmable Gate Array) or ASIC (Application-Specific Integrated Circuit). Generally speaking, the 101 monitoring system comprises electronic circuitry adapted and configured to implement the steps and operations described herein.

[0073] Reasoning to arrive at the aforementioned equation (1)

[0074] During the takeoff phase, the aircraft dynamics are modeled on the same basis as that expressed in patent document FR3145217A1, assuming zero performance degradation. To this end, two assumptions are made: - the runway is not contaminated; and - no major anomalies occurred during takeoff (in other words, the execution of the process described in the patent document FR3145217A1 did not trigger an alarm and no aborted takeoff was recommended to the crew).

[0075] The distance ADr(i) actually traveled by the aircraft, during the calculation cycle of rank i during the takeoff phase, is expressed as follows:

[0076] ADr(i) = AG^z)

[0077] where: - A tr represents the (predetermined) duration of each of the computational cycles; and - GS(i) represents the current ground speed of the aircraft at the computation cycle of rank i.

[0078] The theoretical distance travelled by the aircraft during the cycle The rank i calculation during the takeoff phase is expressed as follows:

[0079] ADt(i) =

[0080] where: - A tt represents the theoretically spent time by the aircraft, since the previous computation cycle of rank i-1, to increase its ground speed to the current ground speed GS(i).

[0081] Newton's second law states that a resultant force FR exerted on an object is always equal to the product of the object's mass m and its acceleration a: FR = m * a. In the present case, Newton's second law can be written as follows: 100821 ÏF^ = GW^}

[0083] where: - EFn(ï) represents an estimate of the resultant force exerted on the aircraft during the takeoff phase (force equivalent to the vector sum of all forces acting on the aircraft); - GW represents the gross mass of the aircraft (which we are trying to estimate); and - A GS(ï) represents the variation in the aircraft's current ground speed since the previous computation cycle of rank i-1.

[0084] Starting from the previous equation, we can write:

[0085] A ( A GS^GW) / EF / i)

[0086] By replacing A tt with this expression in the equation of A Dt(i), we obtain:

[0087] a Dt (i) = (A GS(i)*GW / EFn(i)) *GS(i)

[0088] In the present context, we have:

[0089] YFn(n = THa)-DF(i) - (SL*GW*g) - [CR*(g.GW-LF(j))]

[0090] where: TH(i) represents a thrust force of the aircraft at the computational cycle of rank i; DF( i ) represents an aircraft drag force at computation cycle of rank i; LF{i) represents a lift force of the aircraft at the computational cycle of rank i; SL represents a slope SL of the runway at takeoff (expressed as a percentage); represents the acceleration due to Earth's gravity, approximately 9.81 m / s²; and - CR represents a coefficient of ground friction.

[0091] By replacing pn(i) with this expression in the equation of A Dt(i), we obtain:

[0092] A Dt(t) = TH(îFDF(iHSL^W*g^^

[0093] Assuming that the performance degradation is zero (see above for the two corresponding assumptions), we can write:

[0094] ^Dr(i) = AA(ï)

[0095] Starting from this equality, and replacing A Dt( i) with its expanded expression above, and isolating GW, we obtain the aforementioned equation (1) giving the third estimated GWT / 0 of the gross mass of the aircraft, that is:

[0096] ADtfn(TH(iyDF^^ “ [AGsay*G,sW^^

Claims

1. Demands Method for monitoring an estimate of the gross mass of an aircraft (10), the method being implemented by a system (101) in the form of electronic circuitry, the method comprising: - obtain or calculate (202) a first estimate of the gross mass of the aircraft (GWinitiaie), resulting from an addition of an estimate of the mass of the aircraft without fuel (ZFW) with an estimate of the mass of fuel carried on board the aircraft (FOB); - obtain or calculate (203) a second estimate of the gross mass of the aircraft (GWæro), a function of a first numerical model (101a) of the aircraft which is an aerodynamic model of the aircraft having as input parameters at least the following parameters: a speed, a pitch, an altitude, a configuration of leading edge high-lift devices and trailing edge high-lift devices, and an angle of attack of the aircraft; - calculate (205), for a computational cycle of rank i among a plurality of successive computational cycles executed during an acceleration phase at takeoff of the aircraft and as long as the aircraft has a speed greater than a first predetermined speed threshold and less than a second predetermined speed threshold itself greater than the first speed threshold, a third estimate of the gross mass of the aircraft (GW™), as a function of a second numerical model (101b) of the aircraft different from the first numerical model (101a) of the aircraft and having as input parameters at least the following parameters: an Atr duration of each of the computational cycles; a current ground speed GS(i), a thrust force TH(i), a drag force DF(i) and a lift force LF(i) of the aircraft at computational cycle of rank i; a runway slope SL at takeoff; and a ground friction coefficient CR; and - if the difference between the first and second estimates exceeds a predetermined difference threshold (204), validate one and invalidate the other (206) of the first and second estimates, depending on the third estimate.

2. A method according to claim 1, wherein, after the aircraft speed has exceeded the second predetermined speed threshold during the takeoff acceleration phase, the third estimated is frozen (307) and takes the value calculated at the last computation cycle before the aircraft speed exceeds the second predetermined speed threshold.

3. A method according to claim 1 or 2, wherein the first predetermined speed threshold is between 25 and 35 knots and wherein the second predetermined speed threshold is between 80 and 120 knots.

4. A method according to any one of claims 1 to 3, wherein the third estimated is calculated, at the computation cycle of rank i, in the following way: „,,, ( rW = ................... ■■■■■................. with : ADr«) = At*GS(î) AGS(i) =GS(i)-GS(i-ï) and g which represents the acceleration due to Earth's gravity, i.e. approximately 9.81 m / s2.

5. A method according to any one of claims 1 to 4, wherein the calculation of the third estimate uses, for each of the input parameters GS(i), TH(i), DF(i) and LF(i), an average value over the duration of the calculation cycle of rank i.

6. A method according to any one of claims 1 to 5, wherein the thrust force TH(i) of the aircraft at the computational cycle of rank i is calculated with a third numerical model of the aircraft (501) having as input parameters at least the following parameters: - at least one piece of information relating to the aircraft's thrust, belonging to the group comprising: a rotational speed NI of a low-pressure assembly of each propulsion engine of the aircraft, an engine pressure EPR ratio, and a throttle opening angle TRA; - at least one piece of aircraft speed information in the form of a Mach number; and

7.

8.

9.

10. - at least two pieces of information about ambient conditions, including temperature information and pressure information. A method according to any one of claims 1 to 6, wherein the drag force DF(i) and the lift force LF(i) of the aircraft at the computation cycle of rank i are calculated with a fourth numerical model of the aircraft (502) having as input parameters at least the following parameters: - at least one piece of information about the aircraft's speed in the form of a Mach number; - at least two pieces of ambient condition information, including temperature information and pressure information; - aircraft angle of attack information; and - information relating to the current configuration of the aircraft's leading edge high-lift devices and trailing edge high-lift devices. Product computer program, comprising instructions causing the execution, by a processor (601), of the method according to any one of claims 1 to 7, when said instructions are executed by the processor. Storage medium (604) storing a computer program containing instructions that cause a processor (601) to execute the method according to any one of claims 1 to 7, when said instructions are read and executed by the processor. System (101) for monitoring an estimate of the gross mass of an aircraft (10), the system comprising electronic circuitry configured to implement: - obtain or calculate a first estimate of the gross mass of the aircraft (GWinitiaie), resulting from an addition of an estimate of the mass of the aircraft without fuel (ZFW) with an estimate of the mass of fuel carried on board the aircraft (FOB); - obtain or calculate a second estimate of the aircraft's gross mass (GWæro), a function of a first numerical model of the aircraft which is an aerodynamic model of the aircraft having at least the following input parameters The following parameters: a speed, a pitch, an altitude, a configuration of leading-edge high-lift devices and trailing-edge high-lift devices, and an angle of attack of the aircraft; calculate, for a computation cycle of rank i among a plurality of successive computation cycles executed during an acceleration phase at takeoff of the aircraft and as long as the aircraft has a speed greater than a first predetermined speed threshold and less than a second predetermined speed threshold itself greater than the first speed threshold, a third estimate of the gross mass of the aircraft (GWT / O), as a function of a second numerical model of the aircraft different from the first numerical model of the aircraft and having as input parameters at least the following parameters: an Atr duration of each of the computation cycles; a current ground speed GS(i), a thrust force TH(i), a drag force DF(i) and a lift force LF(i) of the aircraft at computation cycle of rank i; a runway slope SL at takeoff; and a ground friction coefficient CR;and if the difference between the first and second estimates exceeds a predetermined difference threshold, validate one and invalidate the other of the first and second estimates, depending on the third estimate.

11. Aircraft (10) comprising a surveillance system (101) according to claim 10.