Abstract:
Disclosed is a ventilating air intake arrangement of an aircraft. The arrangement includes at least one air duct connected to an air intake orifice. At least one confined zone connects with the air duct and the air intake orifice, and the confined zone is configured in a manner in which outside air enters through the air intake orifice. A controllable mobile element modifies the flow of air entering the confined zone by varying a cross section of the air duct. A control unit is used to control the controllable mobile element, with the control unit being arranged so as to control the controllable mobile element to vary the cross section of the at least one air duct as a function of speed and altitude of the aircraft.

Description:
BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART 
     The present invention relates to a method and a device for detecting dissymmetry of thrust in an aircraft under braking with reverse thrust, for example during a landing or during an aborted takeoff. The invention also relates to an aircraft provided with such a device. 
     It is known that many aircraft, particularly civilian transport aircraft, are equipped with thrust reversers to improve the braking of said aircraft taxiing along the ground by applying reverse thrust. 
     It is also known that, under braking on the ground, reverse thrust is applied manually by the crew of said aircraft by, for example, bringing the throttle control levers of the various engines from an intermediate landing position into a reverse thrust position corresponding to the deployment of the thrust reversers of the engine and the application of an appropriate engine speed. 
     However, because of the high workload (particularly in the case of aircraft that have two or more engines) which is particularly stressful during landing, one of the pilots may forget to position the throttle control lever of one of the engines in reverse thrust position, which means that that engine will continue to apply forward thrust, unlike the other engines which are applying rearwardly directed thrust. An oversight such as this then leads to dissymmetry in the thrust of the aircraft engines and makes this engine more difficult to control, or may even make it uncontrollable. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to remedy these disadvantages and, in particular, to detect such an dissymmetry in the thrust. 
     To this end, according to the invention, the method for detecting dissymmetry of thrust in an aircraft provided with at least two engines that are symmetric with respect to the fuselage, each equipped with a thrust reverser, under braking with reverse thrust, the speeds of said engines being controlled individually by control levers respectively associated with said engines and able to occupy several positions including a position corresponding to reverse thrust applied by said thrust reversers, is notable in that:
     a) it is detected that said aircraft is in contact with the ground;   b) when said aircraft is in contact with the ground, a check is performed to ensure that each of said control levers is in said reverse thrust position;   c) if at least one of said control levers is not in said reverse thrust position, at least the engine associated with said control lever that is not in the reverse thrust position is set to low idle speed; and   d) said step c) is aborted when at least said control lever that is not in said reverse thrust position is brought into the latter position by deliberate action by one of the pilots of said aircraft.   

     Thus, by virtue of the invention, by setting those engines to low idle speed the control lever of which is not in the reverse thrust position, no forward thrust is applied to the aircraft, which means that the lateral dissymmetry in thrust on this aircraft is smaller. In consequence, the aircraft is easier to control, further improving braking and making it safer. 
     It is also possible perhaps to abort said step c) when the taxi speed of said aircraft is at most equal to a predetermined speed threshold. 
     As a preference, said predetermined speed threshold is at least approximately equal to the taxi speed allowed on a taxiway. 
     According to one advantageous feature of the invention, with said aircraft provided with a thrust controller that can be deactivated when at least one of said control levers is in said reverse thrust position, said thrust controller is especially reactivated to set to low idle speed that engine the control lever of which is not in said reverse thrust position. Furthermore, with said thrust controller provided with manual deactivation means, said step c) may be aborted by deliberate operation of said deactivation means by one of the pilots of said aircraft; and if said thrust controller is deactivated, said engine is advantageously kept at low idle speed at least until such time as said associated control lever is no longer in said reverse thrust position. 
     Thus, additional action by the pilots on the control lever that is not in the reverse thrust position is needed in order to alter the low idle speed of the associated engine, set beforehand by the thrust controller, even when this thrust controller has been manually deactivated by the pilots. The result of this is to make the transition of the thrust controller from the activated state to the deactivated state safer. 
     As an alternative, in the event of deactivation of said thrust controller, it is possible perhaps to revert directly to manual control of the speed of the engine or engines the associated control lever of which is not in the reverse thrust position. 
     Advantageously, following detection of contact between the aircraft and the ground and detection that one or more levers is or are not in the reverse thrust position, a warning is intended for the pilots of said aircraft is emitted to alert them to the fact that these levers are not in the reverse thrust position, for example prior to implementation of the speed-setting step c). 
     According to another feature of the invention, with a timeout initiated upon contact of said aircraft with the ground, said step c) is aborted when said timeout has elapsed. As an alternative or in addition, it may be possible to prevent step c) from being implemented after said timeout has elapsed, when said step c) has not been initiated prior to said timeout having elapsed. 
     In addition, following braking with reverse thrust and the setting to the low idle position of those engines the control lever of which is not in the reverse thrust position, as mentioned hereinabove, said step c) is aborted as soon as each of said control levers is brought into a position corresponding to takeoff. 
     Moreover, with said aircraft equipped with sensors that detect contact with the ground, contact of said aircraft with the ground is considered to be established if, for example, the following conditions are satisfied:
         the altitude of said aircraft is at most equal to a predetermined altitude threshold;   said aircraft is in a landing configuration; and   said sensors detect contact between said aircraft and the ground.       

     In order to implement the method according to the invention, there is advantageously provided a device on board an aircraft provided with at least two engines that are symmetric with respect to the fuselage, each equipped with a thrust reverser, and the engine speeds of which are controlled individually by control levers respectively associated with said engines and able to occupy several positions including a position corresponding to reverse thrust applied by said thrust reversers. 
     Advantageously, said device comprises:
         means of detecting contact between said aircraft and the ground;   means of determining that at least one of said control levers has not been positioned in said reverse thrust position;   engine speed setting means capable of setting to low idle speed said engine the control lever of which is not in said reverse thrust position until such time as at least said control lever, which is not in said reverse thrust position, is brought into the latter position by deliberate action by one of the pilots of said aircraft.       

     If appropriate, three additional conditions for aborting the imposition of low idle speed on said engine may be:
         the taxi speed of said aircraft is at most equal to a predetermined speed threshold;   a timeout of predetermined duration, initiated upon contact between said aircraft and the ground, has elapsed;   each of said control levers is in a position corresponding to the takeoff position for said aircraft.       

     Advantageously, the device comprises warning means for emitting a warning to the crew when said aircraft is in contact with the ground and at least one of said control levers is not in said reverse thrust position. 
     The invention also relates to an aircraft provided with a device as specified hereinabove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the attached drawing will make it easy to understand how the invention may be embodied. In these figures, identical references denote elements that are similar. 
         FIG. 1  depicts schematically from beneath a four-engined aircraft, of which the engines are each equipped with a thrust reverser. In this  FIG. 1 , the position of the engine throttle control levers associated with each of said engines respectively, is also shown. 
         FIG. 2  is a figure similar to  FIG. 1 , which also schematically illustrates the device of the invention mounted on board said aircraft of  FIG. 1 . 
         FIG. 3  is a schematic depiction in the form of a block diagram of the device according to the invention depicted in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The aircraft AC depicted schematically from beneath in  FIG. 1 , comprises a fuselage  1  and two wings  2  which are symmetric with respect to said fuselage  1 . Mounted on each of the wings are an inboard engine Mb and Mc and an outboard engine Ma and Md, each fitted with a thrust reverser  3   b ,  3   c ,  3   a  and  3   d  respectively. Of course, as an alternative, the aircraft AC could be a two-engined aircraft or even a three-engined aircraft with two of the three engines symmetric with respect to the fuselage  1 . 
     In the usual way, the aircraft AC is provided with a thrust controller  14  (see  FIG. 3 ) able automatically, when activated by the crew (not depicted) to control the thrust of each of the four engines Ma to Md of said aircraft AC during climb, cruising and descent phases in order to reduce the workload on the crew. The thrust controller  14  is moreover deactivated during the critical phase of takeoff and of coming to a standstill on the runway for safety reasons. 
     If the thrust controller  14  is deactivated, the speed of each of the engines Ma to Md is controlled by the crew via an engine throttle control lever  4   a  to  4   d.    
     As shown by  FIG. 1 , each lever  4   a  to  4   d  may occupy any arbitrary position, for example, from among the following four positions:
         a first position I in which the thrust reverser  3   a  to  3   d  associated with the engine controlled by the lever  4   a  to  4   d  in question is in the deployed position. In this first position I, reverse thrust, applied by the thrust reverser  3   a  to  3   d , is implemented by setting the engine to an appropriate speed;   a second position II in which low idle speed is applied to said engine, the thrust reverser  3   a  to  3   d  being in the furled position;   a third position III for which an intermediate engine speed, somewhere between low idle and full throttle is applied to said engine, the thrust reverser  3   a  to  3   d  being furled; and   a fourth position IV in which the aircraft AC is in the takeoff configuration. In the fourth position IV, the thrust reverser  3   a  to  3   d  of the engine Ma to Md in question is furled and full throttle for example is applied to said engine.       

     In the usual way, when the aircraft AC is under braking with reverse thrust (for example during a landing), the pilots bring the control levers  4   a  to  4   d , for example, from the third position III into the first position I in order manually to control braking with reverse thrust. 
     Now, it may happen that one of the pilots of the aircraft AC forgets to bring one of the control levers  4   a  to  4   d  into the first position I. Thus, as shown by the example of  FIG. 1 , the control lever  4   c  of the engine Mc is not positioned in reverse thrust position I, whereas the others (levers  4   a ,  4   b  and  4   d ) are. 
     Thus, the thrust reversers  3   a ,  3   b  and  3   d  associated with the engines Ma, Mb and Md are deployed, whereas the reverser  3   c  of engine Mc remains in the furled position. The thrust from the engines Ma, Mb and Md (embodied by the arrow PI) is then directed toward the rear of the aircraft AC, unlike that from the engine Mc (embodied by the arrow PN) which is directed forward, thus giving rise to a thrust dissymmetry in the aircraft AC. 
     As  FIG. 2  shows, the aircraft AC implementing the invention, is similar to the one described hereinabove in conjunction with  FIG. 1 , except that it advantageously comprises a device  5  capable of setting the engine Mc, for which the control lever  4   c  has not been brought into the reverse thrust first position I, to low idle speed. 
     More specifically, as illustrated in  FIG. 3 , the device  5  of the invention notably comprises:
         determining means  6  for determining the failure to position at least one of the control levers  4   a  to  4   d  in said first position I. These determining means  6  may receive the signals S 1 , S 2 , S 3  and S 4  representative of the position of control levers  4   a  to  4   d  respectively. The determining means  6  are also able to deliver, at their output  7 , a signal S 5  representative of a failure to position at least one of the control levers  4   a  to  4   d  in the first position I. Thus, according to the example of  FIG. 2 , the determining means  6  deliver a signal S 5  representative of the fact that the control lever  4   c  associated with engine Mc is not in the first position I;   detection means  8  detecting contact between said aircraft AC and the ground. These detection means  8  may receive the following figures:
           a signal S 6  representative of contact between the aircraft AC and the ground and emitted, for example, by pressure sensors (not depicted);   a signal S 7  representative of the fact that the aircraft AC is in a predetermined landing configuration; and   a signal S 8  representative of the altitude of the aircraft AC when this altitude is at most equal to a predetermined altitude threshold;   
           such that, when they simultaneously receive all of these signals S 6  to S 8 , the detection means  8  are able to transmit, on their output  9 , a signal S 9  representative of contact between the aircraft AC and the ground. Moreover, as soon as contact between the aircraft AC and the ground is signaled, it is possible to trigger a timeout of predefined magnitude T;   a logic gate  10 , of the two-input AND gate type receiving the signals S 5  and S 9 . When S 5  and S 9  reach the inputs of the AND gate  10 , this gate is able to deliver, on its output  11 , an activation signal S 10  specifying which engines (engine Mc in the example of  FIG. 2 ) do not have their control lever ( 4   c  in the example) in the first position I;   warning means  12  which are controlled by the signal S 10 . These warning means  12  are able to deliver, on their output  13 , a signal S 11  that can trigger an audible warning in the cockpit of the aircraft AC and/or a visible warning on the flight interfaces; and   the thrust controller  14  which can receive the signal S 10 . According to the invention illustrated for example in  FIG. 2 , as soon as the signal S 10  is received, the thrust controller  14  is especially reactivated in such a way that, via the signal S 12  delivered on its output  15 , it sets the speed of engine Mc (the control lever  4   c  of which is not in the first position I) to low idle speed, preferably after (for example a few seconds after) the warnings are triggered. The engine Mc is kept at this low idle speed by the thrust controller  14  until it receives a deactivation signal S 13 , for example representative of the fact that at least one of the following conditions is satisfied:
           the control lever  4   c  for engine Mc is brought into the first position I by deliberate action by one of the pilots of the aircraft AC;   the taxi speed of the aircraft AC is at most equal to a predetermined speed threshold, preferably at least approximately equal to the taxi speed allowed along a taxiway;   after the engine Mc controlled by the lever  4   c  that is not in the reverse thrust position has been set to low idle speed, during braking with reverse thrust, each of the control levers  4   a  to  4   d  of engines Ma to Md is brought into the takeoff position IV;   the timeout triggered upon contact between the aircraft AC and the ground has elapsed.   
               

     Furthermore, through a deliberate operation on a deactivation button (not depicted), one of the pilots can manually deactivate the thrust controller  14 . The engine Mc can then be kept automatically at low idle speed as long as no change in the position of its control lever  4   c  is observed or, alternatively, it is possible to revert to manual control of the speed of the engine Mc by the pilots by means of the associated control  4   c.