Abstract:
A device including an inertial reference station for measuring an aircraft heading. An inertial reference unit which is mountable on a wheel of a nose landing gear by a fixing system, and is used for measuring the heading of said landing gear in a non-steering position. A data processing unit includes a comparison unit for carrying out a comparison between the measured heading of the nose landing gear and the measured aircraft heading in such a way that the orientation of the nose landing gear is calculated with respect to the aircraft body.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a method and a device for measuring the orientation of the nose landing gear of an aircraft, in particular of a transport aircraft. 
     BACKGROUND OF THE INVENTION 
     It is known that when running over the ground, for example over an accessway or a runway of an airport, the steering of an aircraft is performed by way of the deflection of the nose landing gear. In order for a pilot to be able to carry out such steering over the ground under the best possible conditions, it is of course necessary that, in the undeflected position, the nose landing gear be parallel to the fuselage of the aircraft so that a rightward (or leftward) deflection command causes a proportional deflection of the wheels to the right (or to the left) and that with no deflection, the aircraft runs straight ahead. 
     The orientation of the nose landing gear is generally adjusted at the stage of manufacture of said gear. However, despite the existence of such initial adjustment, it may happen that subsequently the wheels of the nose landing gear are no longer oriented entirely parallel to the fuselage so that the pilot must then compensate for a drift of the aircraft to one side when he wishes to run straight ahead, for example in the center of a runway. Such a maladjustment must of course be corrected, in particular for reasons of comfort of ground running, as well as for safety reasons. 
     However, to be able to correct such a maladjustment, it is necessary to know the exact orientation of said nose landing gear with respect to the longitudinal axis of the aircraft. 
     SUMMARY OF THE INVENTION 
     A laser measurement tool is currently available, comprising in particular an adapter that has to be fixed on the wheels of the landing gear, an associated laser pointer, a central unit and targets. This measurement tool, although accurate and satisfactory overall, exhibits a few drawbacks:
         it requires a clear environment around the aircraft;   its implementation is relatively lengthy;   its overall mass is very high;   its volume is significant; and   it must be used inside (in a hall), the measurements carried out possibly being disturbed by rain and/or wind.       

     The object of the present invention is to remedy these drawbacks. It relates to an effective and inexpensive method which is easy to implement, for measuring the orientation of the nose landing gear of an aircraft which is furnished with an inertial reference rig comprising at least one first inertial reference unit. 
     For this purpose, according to the invention, said method is noteworthy in that:
         a) a second inertial reference unit is mounted on one of the wheels of said nose landing gear;   b) with the aid of said second inertial reference unit, the heading of said nose landing gear is measured in the absence of deflection of the latter;   c) with the aid of at least said first inertial reference unit of said inertial reference rig, the heading of the aircraft is measured; and   d) said measured heading of the nose landing gear is compared with said measured heading of the aircraft in such a way as to deduce therefrom the orientation of said nose landing gear with respect to the fuselage of the aircraft.       

     Thus, by virtue of the consideration of the two headings, the measurements of the orientation are very accurate. 
     Moreover, the implementation of said method is simple and fast, in particular with respect to the aforesaid laser measurement tool, since only the second inertial reference unit need be manipulated and mounted on a wheel. Furthermore, the mass and the volume are reduced. 
     In a preferred embodiment, said second inertial reference unit forms part of said inertial reference rig (which already exists on the aircraft) and, in step a), said second inertial reference unit is dismantled from the aircraft, before being mounted on said wheel. Thus, no device outside the aircraft is necessary for carrying out the measurement of the orientation of the nose landing gear. 
     Preferably, in step a), said second inertial reference unit is mounted on a plate which is fixed on the rim of said wheel and, more precisely, on parts of screws of said rim which overhang cooperating nuts. Thus, the installation of said second inertial reference unit may be carried out easily, and in a fast and accurate manner. 
     Advantageously, said inertial reference rig moreover comprises a third inertial reference unit, and the heading of the aircraft is determined with the aid of the measurements carried out by said first and third inertial reference units, thereby making it possible to refine the measurements of heading. 
     When one wishes (in addition to the measurement) also to adjust the orientation of said nose landing gear, advantageously, as soon as the difference between said measured heading of the nose landing gear and said measured heading of the aircraft is greater than a first predetermined value, the orientation of said nose landing gear is modified in such a way as to obtain a difference which becomes less than a second predetermined value (which is of course less than said first predetermined value). 
     The present invention also relates to a device for measuring the orientation of the nose landing gear of an aircraft which is furnished with an inertial reference rig comprising at least a first inertial reference unit. 
     According to the invention, said device is noteworthy in that it comprises:
         said inertial reference rig which is capable of measuring the heading of the aircraft;   a second inertial reference unit which is capable of being mounted, by way of a fixing system, on a wheel of the nose landing gear and which is then capable of measuring the heading of said nose landing gear in a position corresponding to an absence of deflection; and   an information processing unit comprising means making it possible to carry out the comparison between said measured heading of the nose landing gear and said measured heading of the aircraft in such a way as to be able to deduce therefrom the orientation of said nose landing gear with respect to the fuselage of the aircraft.       

     Preferably, said fixing system comprises a plate:
         which is furnished with a fixed support capable of receiving said second inertial reference unit; and   which is capable of being mounted on the rim of said wheel.       

     In a particular embodiment, said fixing system is moreover provided:
         with a protection hood, which makes it possible to protect said second inertial reference unit in particular from rain; and/or   with a fan. Thus, the device in accordance with the invention may be used without any problem in very hot weather.       

     In a preferred embodiment, said second inertial reference unit forms part of said inertial reference rig of the aircraft and is capable of being dismantled from said aircraft, thereby making it possible to reduce the cost of the device in accordance with the invention which comprises only measurement elements which already exist on the aircraft. 
     Moreover, advantageously, said second inertial reference unit is capable of being supplied electrically (in standard fashion) by a means of electrical supply of the aircraft. Thus, the device in accordance with the invention exhibits considerable autonomy. 
     Furthermore, advantageously, the inertial reference rig, for example of ADIRS type (“Air Data Inertial Reference System”), moreover comprises a third inertial reference unit, and said inertial reference rig determines the heading of the aircraft, with the aid of the measurements carried out by said first and third inertial reference units. Advantageously, at least one of said first, second and third inertial reference units is of the ADIRU type (“Air Data Inertial Reference Unit”) and comprises a gyrolaser which uses the acceleration of the earth to determine the heading. 
     Additionally, in a particular embodiment:
         said second inertial reference unit is capable of being linked to said information processing unit in such a way as to be able to transmit information to the latter which comprises at least a screen for displaying measurements; and/or   the device according to the invention moreover comprises a removable reader which is capable of being linked to said second inertial reference unit in such a way as to be able to read the heading measured by the latter and to display it on an integrated display screen.       

     The figures of the appended drawing will elucidate the manner in which the invention may be embodied. In these figures, identical references designate similar elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the schematic diagram of a measurement device in accordance with the invention. 
         FIG. 2  diagrammatically and partially shows the nose of an aircraft, with a nose landing gear extended. 
         FIG. 3  diagrammatically shows an aircraft in a plan view, on which have been represented the various headings measured by the measurement device in accordance with the invention. 
         FIG. 4  shows a support plate which is mounted on a wheel of a nose landing gear. 
         FIG. 5  shows an inertial reference unit which is carried by the support plate represented in  FIG. 4 . 
         FIG. 6  is a figure similar to that of  FIG. 5 , showing diagrammatically additional characteristics of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The device  1  according to the invention and represented diagrammatically in  FIG. 1  is intended to measure (and possibly to correct or adjust) the orientation of the wheels  2  of the nose landing gear  3  of an aircraft A, in particular of a transport aircraft, which orientation is defined with respect to the fuselage  5  of said aircraft A, and more precisely with respect to the longitudinal axis  6  of said aircraft A which is represented in  FIGS. 2 and 3 . 
     It is known that when running over the ground, for example over an access way or a runway of an airport (with a view to take off or landing), the steering of an aircraft A is controlled by a pilot who for this purpose manipulates a standard appropriate means of actuation (not represented), for example a steering wheel, intended to control the deflection of the nose landing gear  3 . The angle of deflection is the angle made by the steerable wheels  2  with the longitudinal plane of the aircraft A, during the deflection controlled by the pilot. For safety reasons, as well as for reasons of comfort of ground running, it is necessary that in the undeflected position (the aforesaid means of actuation then being in a neutral central position), the nose landing gear  3  be parallel to the fuselage  5  of the aircraft A so that:
         when the pilot carries out a rightward (respectably leftward) deflection command, it causes a proportional deflection of the wheels  2  to the right (respectively to the left); and   when there is no deflection (aforesaid neutral position), the aircraft A runs straight ahead, along its longitudinal axis  6 .       

     Of course, to be able to correct a possible maladjustment (lack of parallelism in the neutral position of the steerable wheels  2  with respect to the longitudinal axis  6 ), it is necessary to know the value of this maladjustment, that is to say the exact value of the orientation of said nose landing gear  3  with respect to the longitudinal axis  6  of the aircraft A. 
     The device  1  in accordance with the invention is intended to measure such an orientation. This device  1  is applied to an aircraft A which is furnished with an inertial reference rig  7 , for example of ADIRS type (“Air Data Inertial Reference System”), that is to say an inertial reference rig integrating the functions of an anemobarometric rig, and comprising at least one first inertial reference unit  8 , preferably of ADIRU type (“Air Data Inertial Reference Unit”). 
     According to the invention, said device  1  comprises, as represented in  FIG. 1 :
         said inertial reference rig  7  which is capable of measuring the heading C 1  of the aircraft A, that is to say the heading C 1  along the longitudinal axis  6  of said aircraft A as represented by an arrow E 1  in  FIGS. 2 and 3 ;   a second inertial reference unit  9  which is capable of being mounted, by way of a fixing system  10 , on a wheel  2  of the nose landing gear  3 , as specified hereinbelow, and which is then capable of measuring the heading C 2  of said nose landing gear  3  in a (neutral) position corresponding to an absence of deflection of the wheels  2 , as is represented by an arrow E 2  in  FIGS. 2 and 3 ; and   an information processing unit  11  comprising means  12 ,  13  making it possible to carry out the comparison between said measured heading C 2  of the nose landing gear  3  and said measured heading C 1  of the aircraft A in such a way as to be able to deduce therefrom the exact angular orientation of said nose landing gear  3  with respect to the fuselage  5  of the aircraft A.       

     Said information processing unit  11  which is carried on board the aircraft A is connected by a fixed link  14  to said inertial reference rig  7  and can be connected by a removable link  15  (represented by dashes) to said inertial reference unit  9 . 
     Moreover, said information processing unit  11  comprises a display means  12  which is capable of displaying on a visualization screen  16 :
         in a first variant, the values of heading C 1  and C 2  measured respectively by said inertial reference rig  7  and said inertial reference unit  9 . An operator who has thus knowledge of said heading values C 1  and C 2  can then personally carry out the aforesaid comparison between these two values;   in a second variant, the difference (or the deviation) between these heading values C 1  and C 2 , that is to say the result of the aforesaid comparison; and   in a third variant, at one and the same time said heading values C 1  and C 2  and said difference.       

     To implement these latter two variants, said information processing unit  11  can comprise a means of comparison  13  which automatically calculates said difference between the values C 1  and C 2 . 
     In a particular embodiment, the device  1  in accordance with the invention moreover comprises a removable reader  17  which is capable of being linked by a link  18  (represented by dashes) to said inertial reference unit  9  in such a way as to be able to read the heading measured by the latter and to display it on an integrated display screen  19 . This allows an operator to read the value in immediate proximity to the wheel  2  of the aircraft A on which said inertial reference unit  9  is mounted without having to access the flight deck where the visualization screen  16  is generally situated. 
     In a particular embodiment, the inertial reference rig  7  moreover comprises another inertial reference unit  20 , and said inertial reference rig  7  determines the heading C 1  of the aircraft A, with the aid of the measurements carried out by said two inertial reference units  8  and  20 . 
     Preferably, at least one of said inertial reference units  8 ,  9  and  20  comprises a standard gyrolaser, which is an apparatus for measuring the angular speed, the principle of which is based on the propagation of coherent light. It is known that such a gyrolaser uses the acceleration of the earth to determine the heading. 
     Furthermore, in a preferred embodiment, said inertial reference unit  9  forms part of said inertial reference rig  7  of the aircraft A, and is capable of being dismantled from said aircraft A (where it is initially installed) so as to be mounted on the wheel  2  with a view to the measurement of the heading C 2  (before being remounted on the aircraft A at the conclusion of the measurements), this making it possible to reduce the cost of said device  1  in accordance with the invention which thus comprises only measurement elements which already exist on the aircraft A. The same holds for the information processing unit  11 . Consequently, the reader  17  alone (which moreover is not indispensable to the implementation of the present invention) does not form part of the aircraft A. 
     Moreover, when it is mounted on the wheel  2 , said inertial reference unit  9  is capable of being supplied electrically (in standard fashion) by a means (not represented) of standard electrical supply of the aircraft A. Thus, the device  1  in accordance with the invention exhibits considerable autonomy, since it does not require supply outside the aircraft A, or any battery for charging. 
     Additionally, in a particular embodiment represented in  FIGS. 4 ,  5  and  6 , said fixing system  10  comprises a plate  21 , made of wood or metal for example:
         which is furnished with a fixed support  22  capable of receiving said inertial reference unit  9 , as represented in  FIGS. 5 and 6 ; and   which is capable of being mounted on the rim  23  of said wheel  2 , preferably the right wheel of the nose landing gear  3 , parallel to said rim  23 .       

     For this purpose, said plate  21  is fixed on the rim  23  of said wheel  2  with the aid of nuts  24  which cooperate with parts of screws  25  of said rim  23  which overhang cooperating nuts  26 , as represented for bolts not used in  FIGS. 4 to 6 . Thus, the installation of said plate  21  and hence of said inertial reference unit  9  may be carried out easily, and in a fast and accurate manner. 
     Said fixing system  10  moreover comprises a standard connector  27  which is intended to cooperate with a cooperating connector (not represented) at the inertial reference unit  9 , when the latter is mounted on the support  22  ( FIGS. 5 and 6 ). The connector  27  is fixed to the support  22  and is connected to a cable or bundle  28  comprising at least one of the aforesaid data transmission links  15  and  18 . 
     In a particular embodiment represented very diagrammatically in  FIG. 6 , said fixing system  10  is furnished moreover:
         with a protective hood  29 , thereby making it possible to protect said inertial reference unit  9  in particular from rain; and/or   with a standard fan  30 . Thus, the device  1  in accordance with the invention can be used with no problem in very hot weather.       

     Said device  1  therefore exhibits very numerous advantages. In particular:
         its measurements are very accurate;   fitment thereof is simplified, reliable and accurate, in particular with respect to that of a standard laser measurement tool of aforesaid type. Also it becomes easily possible to carry out systematic monitoring of the orientation of the nose landing gear  3  (even in the assembly plant) so that each aircraft A leaving assembly plants is within the tolerances of the airlines as regards the orientation of the nose landing gear  3 ;   its cost is reduced;   it exhibits considerable autonomy;   its measurements are not disturbed by poor weather conditions (rain, heat, wind, etc.); and   it can be used on any type of aircraft A comprising an inertial reference rig  7  capable of measuring the heading C 1  of the aircraft A.       

     Within the framework of the present invention, when one wishes (in addition to making measurements) also to correct the orientation of said nose landing gear  3 , as soon as the difference (in angular value) between said measured heading C 2  of the nose landing gear  3  and said measured heading C 1  of the aircraft A is greater than a first predetermined angular value, for example 3°, the orientation of said nose landing gear  3  is corrected so as to obtain a difference (or deviation) of heading which becomes less than a second predetermined angular value, for example 0.1°. 
     In a preferred embodiment, for which the inertial reference unit  9  forms part of the inertial reference rig  7  of the aircraft A, the following successive steps are implemented during the measurement and the adjustment (or correction) of the orientation of said nose landing gear  3 :
         during preparation:
           the inertial reference unit  9  is dismantled from the aircraft A;   the fixing system  10  is installed on the wheel  2 , and the cable  28  is connected to the information processing unit  11 ;   the inertial reference unit  9  is installed on said fixing system  10 ;   
           during a subsequent measurement and a subsequent adjustment:
           the aircraft A is supplied electrically and hydraulically,   the inertial reference rig  7  and the inertial reference unit  9  are powered up;   the heading C 1  of the aircraft A is measured with the aid of the inertial reference rig  7 ;   the heading C 2  of the nose landing gear  3  is measured with the aid of the inertial reference unit  9 ;   said headings C 1  and C 2  are compared;   as a function of this comparison, the orientation of the wheels  2  is adjusted in standard fashion if necessary;   optionally, measurements of heading and a comparison are redone to verify that the adjustment has been properly carried out;   
           during a final reinstatement:
           the inertial reference unit  9  is dismantled and it is reinstalled on the aircraft A in its customary place;   the fixing system  10  is dismantled.