Method and system for determining flight parameters of an aircraft

Disclosed are a method and system for improving real-time determination of flight parameters of an aircraft during flight. A selection module selects and delivers measured values of input parameters to an estimation unit, and the estimation unit uses the input parameters to estimate at least two selected flight parameters. The input parameters are received by the estimation unit on the basis of identified flight mechanics equations associated with the selected flight parameters. The estimation unit includes an extended Kalman filter, which is configured to receive the values of the input parameters and to output joint estimations of the selected flight parameters based on the flight mechanics equations, during the flight of the aircraft.

The present invention relates to a method and a system for the determination of flight parameters of an aircraft, during a flight of the latter.

BACKGROUND OF THE INVENTION

The introduction of electric flight controls and the greater level of automation of modern transport airplanes have made it possible to significantly improve their safety. This technological leap has allowed the formulation of more secure piloting laws—in particular implemented by the automatic pilot—which participate actively in the protection of airplanes, in particular during abnormal situations, faults with the flight systems, dangerous environmental conditions, etc.

However, the use of numerous piloting laws has increased the dependency of flight systems on the measurements of the parameters of the state of an airplane. In particular, certain flight parameters now turn out to be indispensable for ensuring the flight of an airplane, so that it becomes necessary to have reliable values of these parameters. The indispensable parameters include, in particular, the anemometric and inertial parameters, their processing being performed by the ADIRS system (the acronym standing for “Air Data and Inertial Reference System”) which delivers information pertaining to the speed, the altitude and the inertial data (in particular the trim) of the airplane.

DESCRIPTION OF THE PRIOR ART

Currently, the values of the flight parameters are established on the basis of the measurements originating from suitably adapted sensors, so that the validity of these values depends essentially on the validity of the measurements performed by these sensors. However, in the case of external sensors, outside disturbances (for example icing or else the fouling of the sensors) may impair the precision and the correctness of the measurements performed by these external sensors.

Hence, in order to satisfy the regulatory and safety obligations imposed by air safety authorities, it is necessary to ensure the reliability, the precision and the availability of the values of the flight parameters.

Accordingly, one of the known solutions, implemented currently, relies on hardware redundancy: this entails amplifying the number of sensors and computers making it possible to obtain the value of a given flight parameter.

However, the detection of inconsistent and/or erroneous values of a given flight parameter may lead, in certain extreme cases, to not considering any of the values obtained by the sensors, so that no value associated with said flight parameter considered is then available. Such an absence of value can cause a change in the piloting laws used by the onboard flight systems.

This is why, in order to avoid the extreme cases of total absence of value of one or more parameters, it is known to estimate, with the aid of a Kalman filter, at least some of the indispensable flight parameters. For example, it is known that the angle of incidence may be estimated by means of a Kalman filter configured on the basis of flight mechanics equations defining the evolution of the angle of incidence in the course of a flight. To carry out such an estimation, the Kalman filter receives as input a measurement of the air speed (the angle of incidence being intimately related to the latter)—obtained by onboard sensors—and delivers, as output, an estimation of the angle of incidence.

However, when the measured value of the air speed is erroneous (for example on account of a fault with the sensors), the estimate of the angle of incidence turns out also to be defective. The estimation carried out by Kalman filtering of a unique flight parameter does not therefore make it possible to circumvent a disturbance in the measurement or measurements of the input parameters that is necessary for the estimation of the flight parameter considered, since, in such a case, the estimation obtained is also erroneous and therefore unusable.

The object of the present invention is to remedy these drawbacks and, in particular, to circumvent a defect of measurement of one or more of the input parameters of the Kalman filter, so as to guarantee the availability of a reliable value of the flight parameter considered at the output of the latter filter.

SUMMARY OF THE INVENTION

To this end, according to the invention, the method for improving the real-time determination of flight parameters of an aircraft, in the course of a flight of the latter, is noteworthy in that the following steps are performed:at least two flight parameters of said aircraft to be estimated are selected;the flight mechanics equations which are associated respectively with the selected flight parameters and for which there exists a dependency relationship between said selected flight parameters are identified;on the basis of said identified flight mechanics equations associated with said selected parameters, an extended Kalman filter is configured, which receives values of input parameters comprising at least said selected flight parameters; andduring a flight of said aircraft, the extended Kalman filter is implemented so that it delivers, as output, joint estimations of said selected flight parameters.

Thus, by virtue of the invention, at least two flight parameters which are inter-related by way of specially identified flight mechanics equations are estimated simultaneously with the aid of the appropriately configured extended Kalman filter. An error in one or more values of the input parameters is thus circumvented. Indeed, an erroneous value of an input parameter of the extended Kalman filter, used during the estimation of a selected flight parameter, no longer necessarily causes erroneous estimation of the latter, since it is, by virtue of the invention, possible to reconstruct the estimation of said selected flight parameter on the basis, in particular, of the estimation of the other selected flight parameter, to which it is coupled through the intermediary of the flight mechanics equations identified.

Stated otherwise, the present invention provides a co-estimation of at least two previously selected flight parameters, inter-related by flight mechanics equations, even when one or more input values of the filter are erroneous. This guarantees the availability of the values of the selected flight parameters implemented in the aircraft piloting laws. The invention therefore makes it possible to provide a backup estimation of the selected flight parameters when the sensors of the airplane no longer make this possible in a conventional way.

Preferably, said Kalman filter being defined by the following matrices:the covariance matrix R related to the measurement noise and associated with the diagonal matrix of the measurement noise V; andthe covariance matrix Q related to the evolution noise and associated with the diagonal matrix of the evolution noise W,
the following additional steps are performed:it is verified that the values of said input parameters are admissible; andin the case of detection of a defect of a value of an input parameter, the current value of at least one of the elements of at least one of the covariance matrices R and Q is adapted, in real time.

Thus, it is possible to modify the settings of the extended Kalman filter through an adaptation of the gains, so as to make allowance for faults (should outside phenomena affect the operation of the sensors embedded aboard the aircraft) in certain measurements—obtained by the onboard sensors—which affect the values of the input parameters. By adapting the values of the covariance matrices R and Q, more confidence is placed either in the measurements performed by the onboard sensors, or in the estimations of the extended Kalman filter.

Preferably:in a preliminary step, a plurality of presettings of the covariance matrices R and Q related respectively to the measurement and evolution noise is defined, said presettings thus defined each being associated with a defective value of one of said input parameters; andto adapt the current value of said covariance matrices Q and R related to the measurement noise and evolution noise in the case of detection of a defect of the value of an input parameter, the predefined presetting, corresponding to the detected defective value, is assigned to the covariance matrices R and Q related to the measurement noise and evolution noise.

Furthermore, as a variant or as a supplement, in the case of detection of a defect of a value of one of said input parameters measured by one or more sensors embedded aboard said aircraft, said defective measured value is substituted by the estimated corresponding value delivered as output of said extended Kalman filter.

In this way, the defective measurements are no longer taken into account, by the extended Kalman filter, in estimating the selected flight parameters.

Moreover, it is advantageously possible to perform the following steps:at least one of said selected flight parameters for which said Kalman filter delivers an estimation is considered;from among the values of the input parameters of said Kalman filter are selected those corresponding to said flight parameter considered which originate from sensors embedded aboard said aircraft;an inconsistency tied to at least one of said selected values is detected; andthe current value of said flight parameter selected is determined on the basis of the remaining selected value or values and of the estimation of said selected flight parameter, while excluding the detected inconsistent value or values.

Thus, the determination of the current value of the selected flight parameters is obtained without reference to the inconsistent measured value or values. An item of information, namely the estimation of the selected flight parameter considered, is added so as to increase the availability of the current value of said parameter, even in the case of unavailability or of inconsistency of one or more corresponding measured values. Thus, the type of values allowing the determination of a selected flight parameter is diversified, so as to guarantee the delivery of a current value associated with said parameter. By ensuring the delivery of a current value of the selected flight parameters even in the case of a fault with all the associated sensors din this case it is possible to use the estimation provided by the extended Kalman filter), the risk of a change of the piloting laws involving the flight parameter considered is reduced. The availability of the so-called normal laws is therefore increased, thus ensuring continuity of the control performance of the aircraft.

Moreover, in an implementation of the method in accordance with the invention, the state vector associated with said extended Kalman filter is defined by the following twelve states:the angle of incidence α;the speed in the terrestrial frame ν;the speed relative to the ground V;the pitch rate q;the attitude θ;the altitude h;the net motive thrust TB;the bias bnxprojected in the direction corresponding to the longitudinal acceleration nx;the bias bnyprojected in the direction corresponding to the lateral acceleration ny;the wind speed Wxalong the x axis of the terrestrial frame (x,y,z);the wind speed Wyalong the y axis of the terrestrial frame (x,y,z); andthe wind speed Wzalong the z axis of the terrestrial frame (x,y,z).

Furthermore, according to this implementation, said input parameters of the extended Kalman filter comprise inertial parameters, anemometric parameters, parameters specific to said aircraft and intermediate parameters arising from onboard modelings.

Moreover, the present invention also relates to a system for determining, in real time, flight parameters of an aircraft, in the course of a flight of the latter, which comprises an extended Kalman filter able to receive values of input parameters and which is noteworthy:in that said extended Kalman filter is configured on the basis of flight mechanics equations establishing a dependency relationship between at least two preselected flight parameters of said aircraft to be estimated belonging to said input parameters; andin that said extended Kalman filter is formed so as to deliver, during a flight of said aircraft, joint estimations of said selected flight parameters.

Preferably, said Kalman filter is defined by the following matrices:the covariance matrix R related to the measurement noise and associated with the diagonal matrix of the measurement noise V; andthe covariance matrix Q related to the evolution noise and associated with the diagonal matrix of the evolution noise W,
and said system comprises:means for verifying whether the values of said input parameters of the extended Kalman filter are admissible; andmeans for adapting in real time, in the case of detection, by said verification means, of a defect of a value of an input parameter, the current value of at least one of the covariance matrices R and Q.

Furthermore, said system comprises means for replacing the defective value or values by their value estimated by the extended Kalman filter, when they are available.

The present invention relates moreover to an aircraft which comprises at least one system such as described hereinabove.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1has been represented, in a schematic manner, a control chain1of an aerodynamic control surface2(for example an aileron) of an aircraft (not represented), in which chain is implemented a system3for determining, in real time, flight parameters of the aircraft involved in the actuation of the control surface2.

As shown by this figure, the control chain1comprises:an information unit4, formed of a plurality of measurement sensors and of computers embedded aboard the aircraft, which is capable of delivering, in a standard manner, measured values of parameters of the aircraft (such as the angle of incidence, the angle of pitch, the angle of roll, the air speed, the altitude, etc.);the system3, detailed hereinafter, for the determination, in real time, of flight parameters, which receives, as input, the values measured by the information unit4, by way of the link L0;an automatic pilot5of the aircraft which implements numerous piloting laws for the management of the flight controls: depth, ailerons, direction, power delivered by the engines, etc. With each piloting law is associated a particular automatic piloting mode of the automatic pilot5, so that the engagement of the automatic piloting modes causes the activation of the corresponding piloting laws. The automatic pilot5is able to receive values of flight parameters which have been determined by the determination system3and transmitted by way of switching means C, to which it is connected by the link L2. Furthermore, it is capable of delivering, as output, control commands destined for a control system7(comprising an actuator) for the control surface2;manual piloting means6comprising in particular piloting facilities (for example the stick) for controlling the aircraft in the course of a flight. They are able to receive flight parameter values which have been determined by the determination system3and transmitted by way of the switching means C, to which they are connected by the link L3. Furthermore, the manual piloting means6are able to deliver, as output, control commands destined for the control surface2control system7;the switching means C connected to the determination system3, to the automatic pilot5and to the manual piloting means6, respectively by the links L1, L2and L3. The switching means C make it possible to toggle either to automatic piloting mode, or to manual piloting mode. They are able to transmit either to the automatic pilot5, or to the manual piloting means6, the flight parameter values which have been determined by the determination system3; andthe control system7for adjusting the positioning of the control surface2. This control system7is able to receive, through the link L4, control commands originating from the automatic pilot5or manual piloting means6and to adjust, consequently, the inclination of the control surface2.

According to the invention, the determination system3of the invention comprises:a unit8for estimating previously selected flight parameters, the set of these selected flight parameters defining a measurement vector Z(t); anda unit9for determining the current value of flight parameters of the aircraft, which is able to receive the estimation {circumflex over (Z)}(t) (the notation “^” designating an estimation) of the measurement vector Z(t).

As shown byFIG. 2, the estimation unit8comprises an extended Kalman filter10, with which are associated a state vector X(t), the measurement vector Z(t) and a control vector U(t). The Kalman filter10is defined by the following equations:

{X⁡(t)=F⁡(X⁡(t),U⁡(t))+W⁡(t)(State⁢⁢equation)Z⁡(t)=H⁡(X⁡(t),U⁡(t))+V⁡(t)(Measurement⁢⁢equation)
in which:F is the state matrix;H is the matrix associated with the measurement noise;W(t) is the evolution noise vector;V(t) is the measurement noise vector; andthe notation “●” designates the derivative with respect to time.

In the exemplary embodiment of the Kalman filter10, the state vector X(t) is defined by the following twelve flight parameters:the angle of incidence α;the speed ν of the aircraft in the terrestrial frame (x,y,z);the speed V of the aircraft relative to the ground;the pitch rate q;the longitudinal attitude θ;the altitude h;the net motive thrust TB;the bias bnxprojected in the direction corresponding to the longitudinal acceleration nx;the bias bnyprojected in the direction corresponding to the lateral acceleration ny;the wind speed Wxalong the x axis of the terrestrial frame (x,y,z);the wind speed Wyalong the y axis of the terrestrial frame (x,y,z); andthe wind speed Wzalong the z axis of the terrestrial frame (x,y,z).

The measurement vector Z(t) is, for its part, defined by the following nine flight parameters:the aerodynamic angle of incidence αa;the aerodynamic angle of sideslip βa;the speed of the air Va;the pitch rate q;the longitudinal attitude θ;the altitude h;the vertical speed Vz;the normal load factor Nz;the speed V of the aircraft relative to the ground.

According to the invention, the flight parameters, which define the measurement vector Z(t), are chosen because they are inter-related by way of specially identified flight mechanics equations. The identified flight mechanics equations thus make it possible to establish a dependency relationship between the various chosen flight parameters forming the measurement vector Z(t).

The extended Kalman filter10is configured on the basis of the identified flight mechanics equations associated with the selected flight parameters forming the measurement vector Z(t). An initial parametrization of the filter10is also performed.

Furthermore, the control vector U(t) is formed by the following sixteen flight parameters:the roll rate p;the pitch rate q;the yaw rate r;the angle of roll φ;the attitude θ;the longitudinal acceleration nx;the lateral acceleration ny;the angle of incidence α;the angle of sideslip β;the speed of the air Va;the mass M of the aircraft;the inertia Iyy;the lifting force FZa;the pitch moment Ma;the real net static motive thrust TBS;the moment due to the net motive thrust MTB.

The set of values of the parameters of the measurement vector Z(t) and of the control vector U(t) define the inputs of the extended Kalman filter10.

The determination system3comprises a first module11for selecting, from among the measured values originating from the information unit4that it has received through the link L5, those which will form the inputs of the estimation unit8, and in particular of the extended Kalman filter10. Stated otherwise, the first selection module11delivers, as output, the selected measured values of the input parameters. The first selection module11delivers the measured values of the control vector U(t) directly to the extended Kalman filter10, by way of the link L8.

Such as illustrated inFIG. 2, the operation of the Kalman filter10exhibits two distinct phases, namely:a prediction phase (represented, in a symbolic manner, by the block12), in the course of which the estimations {circumflex over (X)}(t) and {circumflex over (Z)}(t) are obtained; andan update phase (represented, in a symbolic manner, by the block13), in which the measured values of the parameters forming the measurement vector Z(t)—received through the link L9—are used to correct the estimations {circumflex over (X)}(t) and {circumflex over (Z)}(t) delivered during the estimation phase (block12).

According to the invention, the extended Kalman filter10is formed so as to deliver in real time, during a flight of said aircraft, joint estimations of the selected flight parameters forming the measurement vector Z(t) (such as for example the aerodynamic angle of incidence αaand the air speed Va).

In the exemplary embodiment considered, the extended Kalman filter10is defined by the following equations:

⁢{u=V⁢⁢cos⁢⁢α⁢⁢cos⁢⁢βv=V⁢⁢sin⁢⁢βw=V⁢⁢sin⁢⁢αcos⁢⁢β(ua,va,wa) are respectively the air speeds in the terrestrial frame (x,y,z), such that:

The determination system3also comprises a first verification module14which receives, as input, the measured values of the parameters of the measurement vector Z(t), so as to verify whether the measured values received are admissible, as a function of given admissibility criteria, or, conversely, are considered defective (for example because they are erroneous or inconsistent). The first verification module14is, for example, formed of comparators and of voters (not represented inFIG. 2). It is able to deliver, as output, a signal in which the defective measured values are logged.

Although, in the present example, the first selection11and verification14modules are located outside the estimation unit8, they could, as a variant, be integrated with the unit8.

Moreover, the estimation unit8comprises a module15for adapting the parametrization of the extended Kalman filter10which receives, as input, the measured values selected by the first selection module11, the output signal of the first verification module14and the estimation {circumflex over (Z)}(t) of the measurement vector Z(t) delivered as output by the filter10, by way respectively of the links L10, L11and L12.

In the case of detection, by the first verification module14, of one or more defective measured values of the measurement vector Z(t) the adaptation module15delivers, as output through the link L13, the estimated values corresponding to the defective measured values—delivered by the Kalman filter10—as well as the measured values of the measurement vector Z(t) that are admissible. The defective measured values are therefore substituted by the corresponding estimated values as input to the extended Kalman filter10. Of course, as soon as the defective measured value becomes admissible again, the adaptation module15can deliver the new measured value, substituting it for the corresponding estimated value.

Moreover, the extended Kalman filter10is defined by the following matrices:the covariance matrix R related to the measurement noise and associated with the diagonal matrix of the measurement noise V; andthe covariance matrix Q related to the evolution noise and associated with the diagonal matrix of the evolution noise W.

The covariance matrix R related to the measurement noise is defined by the relation R=E[V(t)V(t)T], where E designates the mathematical expectation. In a similar manner, the covariance matrix Q related to the evolution noise is defined by the relation Q=E [W(t)W(t)T]. The matrices R and Q convey the confidence placed respectively in the measurements originating from the information unit4and in the estimation delivered by the extended Kalman filter10.

Thus, in the case of detection, by the first verification module14, of a defect of one or more measured values of the measurement vector Z(r), the adaptation module15is able to adapt, in real time, the current value of the covariance matrices R and Q, associated with the filter10.

It should be noted that, upon the appearance of a fault in the measurements, a high value is fixed on the row or rows of the matrix R that are impacted by the defect and a low value is fixed on the row or rows of the matrix Q that are impacted by the defect. Indeed, a high value of the matrix R signifies that more confidence is placed in the measurements reaching the Kalman filter10, so that extra confidence is accorded to the estimation.

Furthermore, the adaptation module15comprises a memory16in which are saved presetting pairs for the covariance matrices R and Q. In the exemplary embodiment, each presetting pair is associated with a predefined defective measured value of the measurement vector Z(t). Each presetting pair can allow selective adaptation of the covariance matrices R and Q by adjusting, for example, solely those coefficients of these matrices on which the defective measured value impinges, by way of the link L14.

In the exemplary embodiment, the two covariance matrices R and Q are adapted simultaneously. Of course, as a variant, it would be possible to envisage adapting solely the matrix R, or solely the matrix Q.

It should be noted that the matrices Q and R are initialized by predefined values, during the initial parametrization of the extended Kalman filter10.

Moreover, the determination system3comprises:a second module17for selecting, from among the measured values of the flight parameters, received from the information unit4(link L6), those for which the corresponding flight parameters are estimated by the extended Kalman filter10(this therefore entails the parameters forming the measurement vector Z(t)); anda second verification module18which receives, as input through the link L15, the measured values selected by the second selection module17. The second verification module18, for example formed of comparators and of voters, is able to verify whether the measured values received are admissible, as a function of given admissibility criteria, or, conversely, are considered defective (for example because they are erroneous or inconsistent). In the case of detection of a defect of at least one of the selected measured values, the second detection module18is able to deliver, as output, a signal in which the defective measured value or values are logged.

Although, in the present example, the second selection module17and verification module18are located outside the determination unit9, they could, as a variant, be integrated with the unit9.

Moreover, in a variant, the first and second selection modules11and17could form just a single selection module. Likewise, the first and second verification modules14and18could, as a variant, be integrated with one another to form just a single verification module.

The determination unit9furthermore comprises a module19for determining the current values of the flight parameters forming the measurement vector Z(t), which receives the measured values selected by the second selection module17, the defect signal delivered by the second verification module18and the estimation {circumflex over (Z)}(t) of the measurement vector Z(t), delivered by the estimation unit8, by way of the links L16, L17and L7. Thus, for a considered flight parameter of the measurement vector Z(t), in the case of defect of at least one measured value associated with said flight parameter considered, the module19is able to determine the current value of said flight parameter considered, on the basis of the non-defective remaining selected values associated with this flight parameter and of the estimation of said flight parameter considered, and to deliver it, as output, to the automatic pilot5and to the manual piloting means6, through the links L2and L3. Accordingly, the determination module19can also implement comparators and/or voters.

Thus, by virtue of the invention, even in the case of total unavailability of measured values associated with one of the flight parameters forming the measurement vector Z(t), a current value, corresponding to the value estimated of said parameter by the estimation unit8, can nevertheless be delivered to the automatic pilot5or to the manual piloting means6, so that they are not deprived of input value.

Moreover, although the system for determining flight parameters in accordance with the invention has been described with reference to a control chain for an aerodynamic control surface, such a system could equally well be integrated in other control chains, for example a control chain for the speed of the engines.