Patent Publication Number: US-11661205-B2

Title: System and method for air filtration with self-cleaning filter medium for an aircraft engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to French patent application No. FR 20 06839 filed on Jun. 30, 2020, the disclosure of which is incorporated in its entirety by reference herein. 
     TECHNICAL FIELD 
     The present disclosure concerns a system and a method for air filtration with a self-cleaning filter medium for filtering an oxidizer for an aircraft engine, for example in a rotorcraft. 
     BACKGROUND 
     Indeed, an aircraft is normally equipped with a power plant comprising at least one combustion engine supplied with air by an air intake. In order to convey air into this air intake, the aircraft may comprise an air supply system bringing an environment external to the aircraft into fluidic communication with the air intake of the engine. 
     A first type of air supply is described as dynamic. A dynamic air supply system comprises an air vent facing in the direction of forward travel of the aircraft in order to be supplied with outside air as a result of the forward speed of the aircraft and the wind, and the engine sucking in air during operation. 
     A second type of air supply is described as static. A static air supply system is only supplied with air as a result of the engine sucking in air during operation. 
     These two types of air supply can be combined within the same air supply system. 
     Moreover, “pollutants” such as dust, sand, snow and frost are likely to penetrate into an air supply system. These pollutants are likely to degrade engine performance through erosion or clogging. 
     Therefore, an air supply system can be equipped with an air filtration device in order to at least limit the intake of pollutants. 
     Two known types of filtration devices are effective for small pollutants, namely vortex particulate filter devices or indeed barrier filter devices. 
     A filtration device of the barrier filter type is also known as an “inlet barrier filter”. A filtration device of the barrier filter type comprises a filter referred to as a “filter medium”. Such a filter medium comprises a porous barrier. Small passages run all the way through the thickness of the porous barrier. These passages prevent objects larger than the dimensions of the passages from passing through the barrier. For example, a filter medium may comprise one or more layers of fibers, such as cotton fibers or synthetic fibers, each layer optionally being concertina-folded in order to maximize its filtering surface area. Air therefore passes through the filter medium, and the pollutants that are not able to pass through a passage remain stuck against an outer face of the filter medium. Therefore, a filtration device with a filter medium is very effective. However, the filter medium generates installation losses that depend on its clogging. 
     Various techniques can be used to evaluate the clogging of a filter medium. For example, document WO2018/200941 discloses a pressure measuring device. 
     When the filter medium is clogged, a maintenance operation is carried out in order to replace it. In an aircraft, the clogging of the filter medium varies depending on the environmental conditions encountered and the use of the aircraft. For example, a filter medium that filters air upstream of a helicopter engine tends to clog more quickly when the helicopter flies at low speeds in sandy air. The service life of a filter medium is therefore variable depending on its use, and can be relatively short in extreme conditions. 
     The disclosure aims to optimize this service life. 
     Document FR 2 904 046 does not address this issue, describing a combined air supply system without a filter medium. This air supply system comprises a dynamic air intake vent opening on a pipe. The dynamic air intake vent is capable of being closed by a closure means and is equipped with a grating. Moreover, the air supply system comprises a filtering intake provided with a plurality of vortex particulate filters, the filtering intake opening on the pipe. 
     Similarly, document FR 2 906 569 describes an air supply system comprising at least one filtering radial air intake having vortex particulate filters and one non-filtering radial air intake, the filtering and non-filtering radial air intakes being arranged around a turboshaft engine. A moveable closure means is configured to close the filtering and non-filtering radial air intakes one after another. 
     Document FR 2 924 471 describes an air supply system having an air intake section. A filtration device comprises a foldable filter means arranged at the air intake section and a control means that applies force to the filter means so as to adjust the filtering power of the filtration system. 
     Document FR 2 952 401 also describes an air supply system without a filter medium. This air supply system comprises a dynamic air intake pipe provided with a grating protecting against the intake of external matter. The grating is capable of moving in translation relative to the dynamic air intake pipe depending on its clogging. The air supply system also comprises a side intake and a means for closing said side intake controlled by said translational movement of the grating. 
     Document EP 1 326 698 describes a cleaning system with a pulse jet oriented so as to direct an air pulse into a clean air chamber inside a filter structure. 
     Document FR 2 250 671 A1 describes an air supply system configured to supply air to an engine. This air supply system comprises a movable ogive and an inertial separator filtration device. 
     Document U.S. Pat. No. 2,407,194 A is also known. 
     SUMMARY 
     The object of the present disclosure is therefore to propose a method and system for supplying air with a filter medium, which is advantageously relatively lightweight, with the aim of optimizing the service life of the filter medium. 
     Therefore, the disclosure relates to a method for supplying air to an aircraft engine, in particular a combustion engine, at an air supply flow rate via an air supply system of the aircraft, said air supply system comprising a dynamic air intake vent that can be closed by a closure member, said closure member being movable between a closed position in which the closure member closes said dynamic air intake vent and an open position in which the closure member does not close said dynamic air intake vent, said air supply system comprising a static air intake vent equipped with a filtration device, said closure member being in the closed position during a filtered operating mode during which air from an external environment situated outside the aircraft is filtered by the filtration device. 
     The filtration device comprising a filter medium, this method comprises, during flight, an unfiltered operating mode that comprises the following steps: 
     positioning of the closure member in the open position, so as to no longer close dynamic air intake vent; and 
     during a phase of forward travel of the aircraft, dynamic intake of a flow of air as a result of the forward travel of the aircraft via the dynamic air intake vent at an air intake flow rate higher than a minimum flow rate necessary in order to obtain said air supply flow rate; then 
     transfer of a first portion of said flow of air to said engine and transfer of a second portion of said flow of air to the filter medium, said second portion of said flow of air passing through the filter medium to return to the external environment in order to clean the filter medium. 
     The expression “dynamic intake of a flow of air as a result of the forward travel of the aircraft via the dynamic air intake vent” means that the flow of air enters the air supply system via the dynamic air intake vent at least as a result of the forward travel of the aircraft, and possibly also due to suction from an engine. 
     The expression “between a closed position in which the closure member closes said dynamic air intake vent and an open position” means that the closure member can be moved from the open position to the closed position and from the closed position to the open position. Intermediate positions may optionally be reached, the closure member remaining arranged in such intermediate positions at least temporarily. 
     In this context, the air supply system can be either in a filtered operating mode during which the closure member is in the closed position, or in an unfiltered operating mode during which the closure member is in the open position. 
     During the filtered operating mode, the air situated in the external environment passes through the filter medium in a direction, referred to for the sake of convenience as the “filtration direction”, travelling from an outer face of the filter medium in contact with the external environment towards an inner face of the filter medium. Any pollutants in the air are blocked by the filter medium at its outer face, within the operating limits of this filter medium, obviously. The air cleaned of any pollutants is then conveyed to the engine by the air supply system. The filter medium fulfils its function by tending to prevent the intake of potentially damaging pollutants by the engine, such as dust, earth or sand, for example. 
     According to the disclosure, the method also comprises an unfiltered operating mode including a phase of supplying air to and automatically cleaning the filter medium, the filter medium being immobile, which is implemented during a flight phase referred to as a “phase of forward travel of the aircraft”. Such a phase of forward travel is, for example, a phase during which the aircraft at least moves forwards in a direction from the tail towards a nose of the aircraft. When this phase of supplying air to and cleaning the filter medium is implemented, the closure member is placed in its open position. Because the aircraft is travelling forwards, an air supply duct of the air supply system is boosted with air by the dynamic air intake vent. In particular, the dynamic air intake vent is innovatively oversized in order to capture more air than necessary in order to obtain the air supply flow rate required by the engine. The dynamic air intake vent can be sized in a conventional manner, by calculations and/or simulations and/or tests, in order to allow a flow rate higher than a predetermined air supply flow rate specified for the engine to be obtained. Due at least to the difference in flow rate between the actual air intake flow rate and the minimum flow rate needed to supply the engine, a first portion of the flow of air is conveyed towards the engine and sucked in by this engine whereas a second portion of this flow of air is discharged out of the air supply system via the only possible path. In particular, this second portion of the incoming flow of air passes through the filter medium in the opposite direction to the previously described filtration direction. Therefore, any pollutants previously captured by the outer face of the filter medium are blown back out to the external environment. The clogging level of the filter medium then drops and moves away from a clogging threshold requiring a maintenance operation. 
     During the unfiltered operating mode, if the aircraft is not in said phase of forward travel as previously defined, the engine can suck in air via the filter medium and/or the dynamic air intake vent. 
     Consequently, during the phase of supplying air to and cleaning the filter medium, this method makes it possible to clean the filter medium during flight, without taking action on the filter medium, i.e., above the ground, using an oversized dynamic air intake vent while the aircraft is moving forwards. 
     This method therefore makes it possible to protect an engine from pollutants in the flight phases where this is required, at least as long as the filter medium is not totally clogged, and to clean the filter medium during flight if necessary and/or if possible. 
     The method thus makes it possible, depending on the use of the aircraft, to increase the service life of the filter medium and delay a maintenance operation. 
     The method may further comprise one or more of the following features, taken individually or in combination. 
     The filtered operating mode can be implemented as a function of one or more of the following parameters. 
     Thus, the method can comprise a step of detecting air pollution in said external environment, the implementation of the unfiltered operating mode, and indeed of the filtered operating mode, being a function at least of said air pollution in said external environment. 
     The air can be considered to be unpolluted when this air contains, in a certain volume, a number of particles lower than a particle threshold. 
     Additionally or alternatively to the preceding possibilities, the method may comprise a step of detecting a clogging level of said filter medium, the implementation of the unfiltered operating mode, and indeed of the filtered operating mode, being a function at least of said clogging level. 
     Additionally or alternatively to the preceding possibilities, said method comprises a step of detecting that said aircraft is moving in said at least one phase of forward travel, the implementation of the unfiltered operating mode, and indeed of the filtered operating mode, being a function at least of said detection that said aircraft is moving in said at least one phase of forward travel. 
     Said at least one phase of forward travel can comprise a phase of movement of said aircraft in a predetermined direction relative to a reference frame of said aircraft and at a speed higher than a speed threshold. For example, such a speed threshold is of the order of 100 knots or 115 miles per hour. 
     According to one example compatible with the preceding examples, said method may comprise a step of detecting the nature of the overflown terrain, the implementation of the unfiltered operating mode being a function at least of said nature. For example, said nature can be chosen from a list comprising at least one of the following elements: a desert area, a populated area, a town, a forest, a stretch of water, etc. The nature of the overflown terrain can be evaluated by combining the current geographical position of the aircraft, for example its latitude and its longitude, with a stored map containing said terrain and its nature. 
     Additionally or alternatively, the method may comprise a step of generating a control signal with a control, activated by a pilot, the implementation of the unfiltered operating mode being a function at least of said control signal. 
     The air supply system may comprise one or more manual, voice or visual controls, for controlling the closure member and therefore for directly or indirectly choosing the operating mode of the air supply system. 
     For example, one control may be used to control an actuator moving the closure member between its closed position and its open position. 
     According to another example, a control may allow a pilot to choose one mode of operation from a list of modes of operation, each mode of operation controlling the closure member as a function of at least one of the preceding parameters. 
     The various preceding conditions can be cumulative and possibly hierarchical. The conditions used and/or the hierarchy can vary depending optionally on a chosen mode of operation. 
     For example, the filtered operating mode can be implemented automatically by moving the closure member to its closed position if pollution is detected, and indeed also if the filter medium has a clogging level lower than a clogging threshold. 
     According to one example, the choice of the filtered or unfiltered operating mode can only be made by a pilot by means of a control provided for this purpose. The pilot can therefore choose the position of the closure member depending on the flight conditions and/or the mission to be carried out, and/or the environment and/or his choice whether or not to optimize the service life of the filter medium. 
     According to one example, the unfiltered operating mode is implemented automatically by positioning the closure member in its open position only if said aircraft is moving in said at least one phase of forward travel and/or if the clogging level of the filter medium is greater than or equal to a clogging threshold. 
     It is also possible to provide various modes of operation that can be chosen by a pilot with a suitable control. 
     For example, according to an economic mode of operation, the closure member is positioned by default in its closed position and positioned in its open position only as long as no pollution is detected and the forward speed is higher than the speed threshold. 
     According to a mode of operation for optimum protection, the closure member is positioned by default in its open position, then positioned in its closed position until the end of the flight if pollution is detected and if, at the same time, the overflown terrain is a desert area. 
     According to a mode of operation that prioritizes performance, the closure member is positioned by default in its closed position, then positioned in its open position as long as no pollution is detected and the overflown terrain is a town. 
     In all instances, the unfiltered operating mode may be implemented automatically by positioning the closure member in its open position if the clogging level of the filter medium is greater than or equal to a clogging threshold. 
     These various modes of operation are provided as examples in order to indicate that the different variants cited above are compatible with each other. 
     In addition to a method, the disclosure also relates to a system suitable for applying this method, or indeed configured to apply this method. 
     This air supply system is configured to supply air to an aircraft engine at an air supply flow rate, said air supply system comprising a dynamic air intake vent that can be closed by a movable closure member, said closure member being movable between a closed position in which the closure member closes said dynamic air intake vent and an open position in which the closure member does not close said dynamic air intake vent, said air supply system comprising a static air intake vent equipped with a filtration device. 
     Moreover, the filtration device comprises a filter medium that opens on an air supply duct of said air supply system. This air supply duct opens directly, or via one or more pipes, on the engine to be supplied with air. Said dynamic air intake vent is fluidically connected to the air supply duct upstream of the filter medium in a direction from the dynamic air intake vent towards the engine to be supplied. Said dynamic air intake vent is oversized in order to dynamically take in a flow of air during a phase of forward travel of said aircraft in an unfiltered operating mode, at an air intake flow rate higher than a minimum flow rate necessary in order to obtain said air supply flow rate, in order for a first portion of said flow of air to be conveyed to said engine and a second portion of said flow of air to exit said air supply duct via said filter medium for cleaning purposes. 
     Therefore, the filter medium and the dynamic air intake vent both lead to the air supply duct, this air supply duct having an outlet configured to supply air to the engine. 
     The expression “Said dynamic air intake vent is fluidically connected to the air supply duct upstream of the filter medium in a direction from the dynamic air intake vent towards the engine to be supplied” means that the filter medium leads to the air supply duct between said outlet of the air supply duct and the dynamic air intake vent. For example, the filter medium comprises an inner face that locally delimits the air supply duct between said outlet of the air supply duct and the dynamic air intake vent. 
     For example, the filter medium is stationary in a reference frame of the air supply system, in particular relative to the other components of the system and, for example, to the air supply duct, unlike a rotary device. 
     The system may comprise one or more of the following features, taken individually or in combination. 
     Thus, the air supply system may comprise an actuation device equipped with an actuator cooperating with said closure member, said actuator being configured to move said closure member between the open position and the closed position. 
     The actuation device may comprise a controller that may or may not be independent of the actuator, and may or may not be dedicated to this application, for controlling the actuator by applying the method of the disclosure as a function of one or more analog or digital received signals. 
     For example, the air supply system may comprise at least one control that can be activated by a pilot, said at least one control being connected via a wired or wireless link to the actuation device. 
     For example, the air supply system may comprise at least one pollution sensor connected via a wired or wireless link to the actuation device, said pollution sensor being configured to emit a pollution signal carrying information indicating whether the air present in the external environment is polluted. 
     For example, such a pollution sensor may comprise a conventional particle sensor, a frost sensing device, etc. The particle sensor may be arranged on the outside of the air supply duct, optionally close to the dynamic air intake vent or the filter medium. 
     For example, the air supply system may comprise a forward travel sensor configured to emit a forward travel signal transmitted via a wired or wireless link to the actuation device, the forward travel signal carrying information indicating that said aircraft is moving in said at least one phase of forward travel. 
     Such a forward travel sensor may comprise a conventional speed sensing device, for example a sensing device of a satellite positioning system, a Pitot probe, etc. 
     For example, the air supply system comprises a clogging sensor configured to emit a clogging signal transmitted via a wired or wireless link to the actuation device, the clogging signal carrying information indicating that said filter medium has a clogging level greater than or equal to a clogging threshold. 
     Such a sensor can be of a known type. For example, such a sensor comprises a pressure sensing device measuring the pressure upstream of the filter medium and a pressure sensing device measuring the air pressure downstream of the filter medium, a computer of the sensor or the controller compiling the measurements in order to determine the clogging level of the filter medium. 
     According to one example compatible with the preceding examples, said air supply system may comprise a positioning sensor configured to emit a positioning signal transmitted via a wired or wireless link to the actuation device, the positioning signal carrying information indicating the geographical position of the aircraft. 
     Moreover, the disclosure also relates to an aircraft equipped with at least one engine, this aircraft comprising an air supply system according to the disclosure for conveying air present in an external environment situated outside said aircraft towards said engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure and its advantages appear in greater detail from the following description of examples given by way of illustration with reference to the accompanying figures, in which: 
         FIG.  1    is a diagram showing an air supply system having an ogive closure member; 
         FIG.  2    is a diagram showing an air supply system having a flap closure member; 
         FIG.  3    is a diagram showing the method of the disclosure; 
         FIG.  4    is a diagram showing an air supply system in the filtered operating mode; 
         FIG.  5    is a diagram showing an air supply system in the unfiltered operating mode and during a phase of forward travel; and 
         FIG.  6    is a diagram showing an air supply system in the unfiltered operating mode and not in a phase of forward travel. 
     
    
    
     DETAILED DESCRIPTION 
     Elements present in more than one of the figures are given the same references in each of them. 
       FIG.  1    is a diagram showing an aircraft  1  according to the disclosure. This aircraft  1  comprises a power plant comprising at least one engine  2 . Therefore, the aircraft  1  is equipped with an air supply system  10  for conveying air present in an external environment EXT situated outside the aircraft  1  towards at least one engine  2 . 
     The air supply system  10  is configured to supply air to an air intake  3  of the engine  2  at an air supply flow rate. Such an air intake  3  may be an axial air intake according to the example shown in  FIG.  1    but may alternatively be in the form of a radial air intake, as shown, for example, in  FIG.  2   . 
     To this end, the air supply system  10  comprises, in an internal environment INT, an air supply duct  30 . The air supply duct  30  has an outlet, i.e., on outlet section, that opens on the air intake  3  of the engine  2 . The air supply duct  30  is delimited by an outer shell that is, for example, substantially airtight. This outer shell may comprise at least one wall, at least one cover, etc. 
     In order to capture air from an external environment EXT and convey it into the engine  2  via the air supply duct  30 , the air supply system  10  comprises a static air intake vent  25 . This static air intake vent  25  comprises a passage provided in the outer shell and bringing the external environment EXT into fluidic communication with the air supply duct  30 . Moreover, the static air intake vent  25  is equipped with a filtration device  20 . This filtration device  20  comprises a filter medium  21  that covers, for example, the whole of said passage. The filter medium  21  opens on the air supply duct  30 , upstream of the engine  2 . It is noted that a filter medium  21  comprises a porous barrier, for example comprising one or more layers of fabric, foam, matting or other materials. The filter medium  21  comprises an outer face  22  facing the external environment EXT and an inner face  23  locally delimiting the air supply duct  30 , openings bringing the outer face  22  into fluidic communication with the inner face  23 . 
     Moreover, the air supply system  10  comprises a dynamic air intake vent  15  that also opens on the air supply duct. This air intake vent is described as dynamic insofar as air can be captured as a result of the forward travel of the aircraft  1 . The dynamic air intake vent  15  may comprise a casing  16  of the outer shell delimiting a dynamic air intake channel  17 . For example, the casing  16  is in the form of an annular divergent section. The dynamic air intake vent  15  and, in particular, its dynamic air intake channel  17  can be directed along a dynamic axis AX 1  substantially parallel to an axis AX 0  of the aircraft  1  running from its tail AR to its nose AV. A grating can also protect the dynamic air intake channel  17 . 
     Moreover, the dynamic air intake vent  15  opens fluidically into the air supply duct  30 , upstream of the filter medium  21  in a direction  85  from the dynamic air intake vent  15  towards the engine  2 . Thus, the air entering the dynamic air intake vent  15  passes through the dynamic air intake channel  17  and into the air supply duct  30  to reach the engine  2  and the filter medium  21 . 
     The dynamic air intake vent  15 , and in particular its dynamic air intake channel  17 , can be closed by a movable closure member  45 . This closure member  45  is able to move in translation and/or to rotate between a closed position POSF shown in dotted lines in  FIG.  1    and an open position POSO shown in a solid line in  FIG.  1   . In the closed position, the closure member  45  closes the dynamic air intake vent  15 , i.e., the closure member  45  prevents air from flowing through the dynamic air intake channel  17 . Conversely, in the open position POSO, the closure member  45  does not close said dynamic air intake vent  15 , i.e., the closure member  45  does not prevent air from flowing through the dynamic air intake channel  17 . 
     According to the example of  FIG.  1   , this closure member  45  comprises an ogive that is able to move in translation along the dynamic axis AX 1 . 
     However, any other equivalent means may be used. By way of illustration,  FIG.  2    shows a flap that is able to move in rotation. 
     Therefore, the air supply system  10  comprises an actuation device  40  for moving the closure member  45  on request. The actuation device  40  is therefore equipped with an actuator  46  cooperating with the closure member  45  to move it between the open position POSO and the closed position POSF. Such an actuator  46  may be in the form of an electrical, pneumatic, hydraulic actuator, etc. According to the example in  FIG.  1   , the actuator  46  may comprise a worm screw  461  that is able to rotate along its longitudinal extension axis, the closure member  45  having a nut  451  cooperating in threaded connection with the worm screw  461 . According to the example of  FIG.  2   , the actuator  46  can be a rotary actuator comprising an output rod that is able to rotate together with the closure member  45 . 
     Moreover, the actuation device  40  may comprise a controller  47  connected via a wired or wireless link to the actuator  46  in order to order the movement of the closure member  45  as a function of one or more analog or digital signals. 
     The closure member  45  and optionally its actuator  46  can be arranged in the internal environment INT of the air supply system, as shown in solid lines in the figures. For example, an actuator  46  carries the associated closure member  45 . Fins or the like fasten this assembly to the outer shell. 
     Alternatively, as shown in dotted lines, a controller  47  may be located remotely, outside the internal environment INT. 
     Regardless of the embodiment, a controller  47  may comprise, for example, at least one processor and at least one memory, at least one integrated circuit, at least one programmable system, or at least one logic circuit, these examples not limiting the scope given to the expression “controller”. The controller  47  may thus comprise one or more computers. The term “controller” refers to a unit that is able to operate each actuator  46  depending on input data and internal logic. The term “processor” may refer equally to a central processing unit or CPU, a graphics processing unit or GPU, a digital signal processor or DSP, a microcontroller, etc. 
     In order to determine the position in which the closure member  45  should be located, the air supply system  10  may comprise one or more of the following sensors. The term “sensor” is to be interpreted in the broad sense, a sensor being able to comprise at least one sensing device emitting an analog or digital measurement signal, or indeed a computing unit itself capable of emitting a signal depending on the received measurement signal and internal logic. 
     Thus, the air supply system  10  may comprise at least one control  51  connected via a wired or wireless link to the actuation device  40 . The control or controls may be activated by a pilot, manually or by a voice instruction or indeed by a movement, in order to transmit a control signal  510  to the controller  47 . A control  51  may be in the form of a switch with at least two positions, a touch-sensitive surface allowing one possibility to be chosen from several possibilities and, for example, from several modes of operation, etc. 
     The air supply system  10  may comprise at least one pollution sensor  52  connected via a wired or wireless link to the actuation device  40 . The pollution sensor or sensors  52  are configured to emit a pollution signal  520 , transmitted to the controller  47 , carrying information indicating whether the air present in the external environment EXT is polluted. For example, a pollution sensor  52  may comprise a conventional frost sensing device and/or a pollution sensor  52  can sense particles of sand or dust in order to evaluate the number of particles in the air, etc. The controller  47  can receive this number of particles and compare it to a particle threshold in order to determine that the air is not polluted when the measured number of particles is lower than the particle threshold. According to another method, the pollution sensor  52  comprises a unit making this comparison and transmitting a pollution signal indicating whether or not the air is polluted. 
     The air supply system  10  may comprise a forward travel sensor  53  configured to emit a digital or analog forward travel signal  530  transmitted via a wired or wireless link to the controller  47 . The forward travel signal  530  carries information indicating whether or not said aircraft  1  is moving according to a flight phase referred to as “a phase of forward travel”. For example, a forward travel sensor  53  may comprise a speed sensing device for evaluating the speed air of the aircraft or another type of speed. The controller  47  may receive this speed and compare it with a speed threshold in order to determine that the aircraft  1  is carrying out a so-called phase of forward travel when the measured speed is higher than a speed threshold. According to another method, the forward travel sensor  53  comprises a unit making this comparison and transmitting a forward travel signal  530  indicating whether or not the aircraft  1  is carrying out a so-called phase of forward travel. 
     The air supply system  10  may comprise a clogging sensor  54  emitting an analog or digital clogging signal  540 , transmitted via a wired or wireless link to the controller  47 , the clogging signal  540  carrying information indicating whether or not said filter medium  21  has a clogging level greater than or equal to a clogging threshold. For example, a clogging sensor  54  may comprise one or more pressure sensing devices. The controller  47  can receive one or more measurement signals, and can decode them in order to deduce therefrom a clogging level compared with a clogging threshold in order to determine whether the filter medium  21  needs to be cleaned. According to another method, the clogging sensor  54  comprises a unit making this comparison and transmitting a clogging signal  540  indicating whether or not the filter medium  21  needs to be cleaned. 
     The air supply system  10  may comprise a positioning sensor  55  configured to emit a positioning signal  550  transmitted via a wired or wireless link to the actuation device  40 , the positioning signal  550  carrying information indicating the geographical position of the aircraft  1 . In the same way as set out above, the controller  47  can process the positioning signal  550  in order to determine said geographical position or can receive this geographical position. The controller  47  or the positioning sensor  55  can apply instructions in order to deduce therefrom the nature of the overflown terrain by using a model of the terrain. 
     Moreover, said dynamic air intake vent  15  is oversized in order to be able to take in more air than necessary for the operation of the engine during a phase of forward travel of the aircraft  1  when the closure member  45  is in its open position POSO in order to apply the method shown in  FIG.  3   . 
     In reference to  FIG.  3   , during a selection step STPB, the actuation device  40  is configured to determine whether the closure member  45  needs to be positioned in its closed position in order to apply a filtered operating mode MODF shown in  FIG.  4    or in its open position in order to apply an unfiltered operating mode MODO shown in  FIGS.  5  and  6   . 
     To this end, during optional steps STPA 1 , STPA 2 , STPA 3 , STPA 4 , STPA 5 , the sensor or various sensors listed above transmit the signals  510 ,  520 ,  530 ,  540 ,  550  to the controller  47 . 
     Therefore, the implementation of the unfiltered operating mode MODO can be a function: 
     at least of the air pollution in the external environment EXT evaluated during a step STPA 2  of detecting air pollution implemented with the pollution sensor  52 ; and/or 
     at least of a control signal  510  emitted by a control during a step STPA 1  of generating a control signal  510  with a control  51 , activated by a pilot; and/or 
     at least of a clogging level of said filter medium  21  evaluated during a step STPA 4  of detecting a clogging level implemented by a clogging sensor  54 ; and/or 
     at least of the detection that said aircraft  1  is moving in a phase of forward travel evaluated during a detection step STPA 3  implemented with the forward travel sensor  53 ; and/or 
     at least of the nature of the overflown terrain evaluated during a step STPA 5  of detecting the nature of the overflown terrain implemented with the positioning sensor  55  in order to determine the position of the aircraft  1  and plot this position on a map showing the nature of the terrain. 
     Thus, depending on the current case, the controller  47  can transmit a control signal to the actuator  46  during flight. During a step STPC, the actuator  46  positions the closure member in its closed position POSF during the filtered operating mode MODF. In reference to  FIG.  4   , the air then passes through the filter medium  21 , in the direction shown by the arrow  90 , in a filtration direction SF running from the outer face  22  to the inner face  23 . Pollutants are stuck against the outer face  22 . The filtered air flows through the air supply duct  30  in the direction shown by the arrow  91  to the air intake  3  of the engine  2 . 
     According to various examples, the filtered operating mode MODF is applied as long as pollutants are detected in step STPA 2  and optionally as long as the filter medium  21  is considered to have a clogging level lower than the clogging threshold following step STPA 4 , or indeed as long as the aircraft  1  is flying over a desert area according to an evaluation carried out in step STPA 5 . 
     Conversely, the controller  47  can transmit a control signal to the actuator  46  such that, during a step STPD 0 , the actuator  46  positions the closure member  45  in its open position POSO in order to apply the unfiltered operating mode MODO. 
     During a phase of forward travel of the aircraft  1  and in reference to  FIG.  5   , the dynamic air intake vent  15  then implements a step STPD 11  of dynamic intake of a flow of air  95  as a result of the forward travel of the aircraft  1 . The dynamic air intake vent  15  makes this flow of air  95  flow in the internal environment INT at an air intake flow rate higher than a minimum flow rate necessary in order to obtain said air supply flow rate required at the air intake  3  of the engine  2 . 
     As a result of this air boost, the air supply duct  30  implements a step STPD 12  of transferring a first portion  96  of the flow of air  95  to said engine  2  by suction, the air being sucked in by the engine  2 , and transferring a second portion  97  of said flow of air  95  to the filter medium  21 . Therefore, this second portion  97  of said flow of air  95  passes through the filter medium  21  in the opposite direction SN to the usual filtration direction in order to return to the external environment EXT. The second portion  97  of the flow of air  95  may tend to dislodge pollutants from the outer face  22  of the filter medium  21  and expel them to the external environment EXT in order to clean this outer face  22 . 
     When not in this phase of forward travel and in reference to  FIG.  6   , air can enter the air supply duct  30 , for example via the dynamic air intake vent  15  and the dynamic air intake channel  17  in the direction shown by the arrow  99  and via the filter medium  21  in the direction shown by the arrow  98 . 
     Naturally, the present disclosure is subject to numerous variations as regards its implementation. Although several implementations are described above, it should readily be understood that an exhaustive identification of all possible embodiments is not conceivable. It is naturally possible to replace any of the means described with equivalent means without going beyond the ambit of the present disclosure and the claims. 
     For example, an air intake of the engine of  FIG.  1    could be an axial air intake and the air intake of the engine of  FIG.  2    could conversely be an axial air intake.