Abstract:
A device and method for estimating a side-slip angle (β e ) of an aircraft moving in the air includes a receiving unit which receives a measured side-slip angle (β l ) presented locally by the air relative to the aircraft, and a determining unit which determines the side-slip angle (β e ) of the aircraft as a function of the measured angle (β l ) and of an information item about the incidence (α) of the aircraft.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device, to a system and to a method for estimating a side-slip angle of an aircraft. 
     A traditional method for estimating the side-slip angle of an aircraft moving in the air is to use dedicated transducers that locally measure the orientation, in a horizontal plane, of air streams relative to the aircraft, immediately providing access to the side-slip from the relative movement of the aircraft in the air at the measurement location. 
     When it is determined locally in this way, the side-slip information item delivered by the transducer is usually transmitted to the different systems of the aircraft (whether they are display or navigation systems using this information item) as an information item representative of the side-slip angle of the entire aircraft in the air flow. 
     Nevertheless, a difference exists between the locally measured side-slip angle and the general side-slip angle of the aircraft, especially because of the particular situation of the transducer in question. For example, the side-slip angle β A  of the airplane may be effectively defined as the angle between the axis X of the fuselage and the flight direction {right arrow over (V)} A  in the air mass projected onto a horizontal plane associated with the airplane. 
     SUMMARY OF THE INVENTION 
     In order in particular to remedy this disadvantage and consequently to improve the estimate of the side-slip angle of the aircraft, the invention proposes a device for estimating a side-slip angle of an aircraft moving in the air, characterized by means for receiving a measured side-slip angle presented locally by the air relative to the aircraft and by means for determining the side-slip angle of the aircraft as a function of the measured angle and of an information item about the incidence of the aircraft. 
     In this way it is possible to correct the measurement error associated with the positioning of the transducer, which error has been noticed by the inventors to depend in particular on the angle of incidence of the aircraft. 
     According to a first possible embodiment, the means for determining the side-slip angle of the aircraft may comprise means for multiplying the measured side-slip angle by a first factor that depends on the incidence information item and/or means for adding a second factor that depends on the incidence information item. 
     According to another possible embodiment, the means for determining the side-slip angle of the aircraft comprise means for reading the side-slip angle of the aircraft in a correspondence table having at least the measured angle and the incidence information item as entries. 
     In this case it is also possible to provide means for selecting the said correspondence table as a function of an information item indicative of the configuration of the lift devices of the aircraft, thus making it possible to adapt the correction to the aerodynamic configuration of the aircraft. 
     The invention therefore also proposes a system for estimating a side-slip angle of an aircraft moving in the air, with means for measuring a side-slip angle presented locally by the air relative to the aircraft, characterized by means for determining the side-slip angle of the aircraft as a function of the measured angle and of an information item about the incidence of the aircraft. 
     In terms of method, the invention proposes a method for estimating a side-slip angle of an aircraft moving in the air, characterized by the following steps:
         measuring a side-slip angle presented locally by the air relative to the aircraft;   determining the side-slip angle of the aircraft as a function of the measured angle and of an information item about the incidence of the aircraft.       

     This system and this method may incorporate optional characteristics corresponding to those envisioned hereinabove for the estimation device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will become clearer upon reading the description hereinafter, given with reference to the attached drawings, wherein: 
         FIG. 1  represents a system for estimating a side-slip angle, implemented according to the teachings of the invention; 
         FIG. 2  represents the front part of an airplane incorporating side-slip sensors. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The system of  FIG. 1  comprises a side-slip transducer or sensor  2 , which delivers a measurement of a local side-slip angle β l  representing the orientation of the air flow at the location of the sensor (relative to a fixed reference associated with the aircraft). 
     Such a side-slip sensor is, for example, of the “weather vane” type, or in other words formed from a vane mounted on a pivot in such a way as to become positioned in the local air flow at the level of the sensor, parallel to the air flow at this location. 
       FIG. 2  illustrates an example of the positioning of a side-slip sensor  2  on the fuselage surface, in the forward part of an aircraft (in this case an airplane)  20 , precisely in the region situated forward of cockpit  22  (the term “forward” being understood in traditional manner, or in other words toward nose  26  of the airplane, in the direction X also illustrated in  FIG. 2 ). 
     The measured side-slip angle β l  is therefore the angle formed locally between the orientation of the velocity vector {right arrow over (V)} l  of the air flow at the level of the sensor and the direction X projected onto a horizontal plane. 
     For the purpose of redundancy, other side-slip sensors may be provided on the surface of the airplane fuselage, such as, for example, sensors  2 ′,  2 ″ visible in  FIG. 2 . 
     The signals measured by each of the side-slip sensors may undergo the treatment described hereinafter for side-slip sensor  2 . Alternatively, the signals issued by two or more side-slip sensors may be combined in order to deduce therefrom an average signal, which will undergo the treatment described hereinbelow. 
     The system illustrated in  FIG. 1  also comprises a device  4  for determining the angle of incidence α of the aircraft. 
     Such a device includes, for example, an incidence sensor (possibly of the weather vane type). It is recalled that the angle of incidence α is the angle formed, by projection onto a vertical plane, between the axis X of the fuselage and the flight direction V A  in the air mass. 
     The local side-slip information item β l  emitted by side-slip sensor  2  (or, alternatively, by a set of side-slip sensors as already mentioned) and the angle of incidence α determined by device  4  are transmitted to a side-slip correction module  10 , which generates, on the basis of these information items, an information item β e  representative of the side-slip angle estimated for the entire airplane  20  (hereinafter “airplane side slip”) according to methods that will now be described. 
     It is recalled here that this side-slip angle is the angle formed, in a horizontal plane, between the velocity vector of the airplane in the air and a reference associated with the airplane. 
     In a first embodiment, correction module  10  stores a plurality of correspondence tables in memory. 
     Each correspondence table contains a set of values of the estimated side-slip angle β e , each associated with particular values of the local side-slip angle β l  and with the angle of incidence α (which therefore constitute the entries of the correspondence table). 
     Furthermore, each correspondence table is associated with particular conditions of configuration of lift devices (of the slats and flaps type), thus making it possible to adapt the correction of the side-slip angle as a function of the aerodynamic configuration of airplane  20  (this configuration having an effect on the difference that exists between the measured local side-slip angle β l  and the side-slip angle of the entire airplane, or in other words the value to be estimated). 
     Thus correction module  10  selects a correspondence table as a function of the configuration information item CONFIG representative of the position of high-lift devices  6  and, in the selected correspondence table, it reads the estimated value of the airplane side-slip angle β e  associated with the values of the local side-slip angle β l  and of the angle of incidence α that module  10  receives respectively from side-slip sensor  2  and from device  4  for determining the angle of incidence. 
     The estimated airplane side-slip angle β e  is then transmitted to the different airplane systems  12  and  14  using this information item, namely, for example, an indicator of the side-slip angle for the crew, the flight control calculators, the automatic pilot, etc. 
     Correction module  10 , in common with device  4  for determining the angle of incidence, can be implemented in the form of a processor executing a program that makes it possible to apply the functionalities just described, especially reading of data in correspondence tables stored in a memory associated with this processor. 
     Such a system can be integrated into the heart of the “air” data calculator, with which airplane  20  is equipped, commonly known by the abbreviation ADC (for “Air Data Computer”). 
     The correspondence tables mentioned hereinabove are, for example, filled in during flight tests with a dedicated apparatus provided with other sensors for measuring the side-slip angle (in order to obtain a precise representation of the side-slip of the airplane). This step corresponds to calibration of correspondence tables, which can then be used as standard for all machines of the same type. 
     According to a second conceivable embodiment, correction module  10  is able to determine the estimated side-slip angle β e  of the airplane as a function of the angle of incidence α of the airplane and of the measured local side-slip angle β l , by means of a formula that models the correction to be applied and, for example, is of the following type:
 
β e =(β l   +Z ) K+I,  
 
with  K=Aα   2   +B.α+C  
 
 I=Dα   2   +Eα+F,  
 
     where Z permits a correction of the angular adjustment of side-slip sensor  2  if necessary, for example in order to prevent it from reaching its stop (if the sensor possesses such a stop) in the range of local side-slip angles under consideration, and A, B, C, D, E, F are parameters that can if necessary depend on the local side-slip angle β l  (thus making it possible also to influence the amplitude of the correction by means of the side-slip angle). The changes of deflection of the high-lift devices can be managed by using, for example, a correspondence table containing such parameters for each deflection. 
     The values of the coefficients A, B, C, D, E, F depend on the location of the side-slip transducer. For example, the following orders of magnitude can be encountered: A˜10 −3 , B˜10 −2 , C˜10 −1 , D˜10 −3 , E˜10 −1 , F˜1. 
     The foregoing examples are merely possible modes of implementation of the invention, which is not limited thereto.