Patent Publication Number: US-2022228541-A1

Title: Turbofan engine comprising a system for blocking the flow path of the bypass stream comprising veils

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the French patent application No. 2100620 filed on Jan. 22, 2021, the entire disclosures of which are incorporated herein by way of reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a turbofan engine which comprises flexible veils and a pneumatic deployment system which deploys the veils to block the flow path of the bypass stream and which folds the veils to free the flow path of the bypass stream, and an aircraft comprising at least one such turbofan engine. 
     BACKGROUND OF THE INVENTION 
     An aircraft comprises a fuselage, on each side of which there is fixed a wing. Under each wing there is suspended at least one turbofan engine. Each turbofan engine is fixed under the wing via a pylon which is fixed between the structure of the wing and the structure of the turbofan engine. 
     The turbofan engine comprises an engine and a nacelle which is fixed around the engine. The turbofan engine has, between the nacelle and the engine, a bypass flow path in which a bypass stream circulates. 
     The nacelle comprises a plurality of reversing doors, each being rotationally movable on the structure of the nacelle between a retracted position in which it is outside of the bypass flow path and a deployed position in which it is positioned across the bypass flow path in order to deflect the bypass stream to a window which is in the wall of the nacelle and which is opened between the bypass flow path and the outside of the nacelle. 
     Thus, the bypass stream is deflected outwards and, more specifically, towards the front of the turbofan engine in order to produce a counter-thrust. 
     Although the reversing doors give full satisfaction, it is desirable to find different mechanisms, in particular less heavy mechanisms. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to propose a turbofan engine which comprises flexible veils and a pneumatic system which deploys the veils to block the flow path of the secondary stream and which folds the veils to free the flow path of the secondary stream. 
     To this end, a turbofan engine is proposed that has a longitudinal direction and that comprises an engine and a nacelle surrounding the engine which comprises a fan casing, in which a flow path of a secondary stream is delimited between the nacelle and the engine and in which an air stream circulates from the front to the rear of the turbofan engine, the nacelle comprising: 
     a fixed structure fixed to the fan casing, 
     a movable cowl which is movable in translation on the fixed structure in a direction of translation between an advanced position in which the movable cowl is positioned in such a way that it is close to the fan casing and a retracted position in which the movable cowl is positioned in such a way that it is away from the fan casing to define between them an open window between the flow path and the outside of the nacelle, 
     a set of actuators ensuring the displacement of the movable cowl between the advanced position and the retracted position, and vice versa, 
     a plurality of flexible veils, having a first edge fixed to the movable cowl and a second edge opposite the first edge, in which the veil can alternately assume a folded position in which the veil is housed in the movable cowl or a deployed position in which the veil is extended between the first edge and the engine across the flow path, and 
     a pneumatic system arranged to displace the second edge of each veil in order to displace the veil from the folded position to the deployed position and to displace the second edge of each veil in order to displace the veil from the deployed position to the folded position, in which the pneumatic system comprises: 
     a rigid main roll fixed inside the movable cowl to the rear of the window, 
     for each veil, at least one extendable secondary roll secured to the main roll and in which the inside of each secondary roll is in fluidic continuity with the inside of the main roll, in which the second edge of the veil is fixed to each of the secondary rolls, and 
     a pressurization and depressurization system which, alternately, generates a pressure in the main roll and therefore in each secondary roll to inflate them in the transition from the advanced position to the retracted position, or generates a depression in the main roll and therefore in each secondary roll to deflate them in the transition from the retracted position to the advanced position. 
     Replacing the reversing doors and their driving mechanisms with flexible veils and a pneumatic system allows for a weight reduction. 
     Advantageously, the pressurization and depressurization system comprises: 
     a Venturi-effect tube with an inlet section, an outlet section and an intermediate section between the inlet section and the outlet section, in which the inlet section is fluidically connected to an air take-off point in the flow path, 
     a bypass line of which an inlet is fluidically connected to the inlet section and of which an outlet is fluidically connected to the intermediate section, 
     a terminal line of which an inlet is fluidically connected to the bypass line and of which an outlet is fluidically connected to the main roll, 
     a first valve disposed at the inlet of the bypass line and which can alternately assume an open position allowing the passage between the inlet section and the bypass line or a closed position preventing the passage between the inlet section and the bypass line, 
     a second valve disposed at the inlet of the terminal line and which can alternately assume a first position allowing the passage between the bypass line and the terminal line from the inlet of the bypass line and preventing the passage between the terminal line and the bypass line to the outlet of the bypass line, and a second position allowing the passage between the terminal line and the bypass line to the output of the bypass line and preventing the passage between the bypass line and the terminal line from the inlet of the bypass line, and 
     a third valve disposed at the outlet of the bypass line and which can alternately assume an open position allowing the passage between the bypass line and the outlet section or a closed position preventing the passage between the bypass line and the outlet section. 
     Advantageously, the turbofan engine comprises: 
     for each veil, a roller mounted to rotate freely on the movable cowl behind the window when the movable cowl is in retracted position, in which the first edge of the veil is fixed to the roller, in which, in folded position, the veil is wound around the roller or, in deployed position, the veil is unwound from the roller, 
     a deployment mechanism arranged to displace the second edge of each veil in order to displace the veil from the folded position to the deployed position, and 
     a folding mechanism arranged to drive each roller in rotation in order to displace the veil associated with the roller from the deployed position to the folded position. 
     Advantageously, the deployment mechanism comprises: 
     for each second edge, a plate secured to the second edge, 
     for each plate, at least one pulling pulley mounted to rotate freely on the plate, 
     a cable which passes through each pulling pulley, and 
     for each end of the cable, a declutchable displacement system which ensures the pulling of the end. 
     Advantageously, there is a pulling pulley at each end of the plate. 
     Advantageously, each displacement system comprises a set of guiding pulleys and an electric winder on which the cable is wound. 
     According to a particular embodiment, the folding mechanism comprises, for each roller, a deflection pulley fixed coaxially to the roller, a winding pulley fixed to the fixed structure, a winding cable, of which one end is fixed to the fixed structure and of which the other end is fixed to the winding pulley and in which the winding cable passes through the deflection pulley, a nitrogen damper of which a cylinder is fixed to the fixed structure and of which a piston slides in the cylinder, and a transformation system which ensures the transformation of the rotational movement of the winding pulley into a translational movement of the piston and vice versa. 
     According to a particular embodiment, the folding mechanism comprises, for each roller, a deflection pulley fixed coaxially to the roller, a winding pulley, a winding cable, of which one end is fixed to the fixed structure and of which the other end is fixed to the winding pulley and in which the winding cable passes through the deflection pulley, and a declutchable electric winder to which the winding pulley is fixed. 
     The invention also proposes an aircraft comprising at least one turbofan engine according to one of the preceding variants. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention mentioned above, and others, will become more clearly apparent on reading the following description of an exemplary embodiment, the description being given in relation to the attached drawings, in which: 
         FIG. 1  is a side view of an aircraft comprising a turbofan engine according to the invention, 
         FIG. 2  is a perspective view of the turbofan engine according to the invention in the deployed position of the veils, 
         FIG. 3  is a schematic representation of a turbofan engine according to the invention seen in cross section through a radial plane and in advanced and folded position, 
         FIG. 4  is a schematic representation of a turbofan engine according to the invention seen in cross section through a radial plane and in retracted and deployed position, 
         FIG. 5  is a representation of a pressurization and depressurization system in a pressurization position implemented in the context of the invention, 
         FIG. 6  shows the pressurization and depressurization system of  FIG. 5  in pressure-maintaining position, 
         FIG. 7  shows the pressurization and depressurization system of  FIG. 5  in depressurization position, 
         FIG. 8  is a schematic and front-view representation of a deployment mechanism in folded position, 
         FIG. 9  is a schematic and front-view representation of the deployment mechanism in deployed position, and 
         FIG. 10  is a perspective view of a folding mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, the terms relating to a position are taken with reference to the direction of advance of an aircraft as represented in  FIG. 1  by the arrow F. 
       FIG. 1  shows an aircraft  10  which comprises a fuselage  12 , on each side of which is fixed a wing  14  which bears at least one turbofan engine  100  according to the invention. The turbofan engine  100  is fixed under the wing  14  via a pylon  16 . 
       FIG. 3  and  FIG. 4  show the turbofan engine  100  which has a nacelle  102  and an engine  20  which is housed inside the nacelle  102 . The turbofan engine  100  also comprises a fan casing  202 . 
     In the following description, and by convention, X denotes the longitudinal direction of the turbofan engine  100  which is parallel to the longitudinal axis of the aircraft  10  oriented positively to the front of the aircraft  10 , Y denotes the transverse direction which is horizontal when the aircraft is on the ground, and Z denotes the vertical direction, these three directions X, Y and Z being orthogonal to one another. 
     The turbofan engine  100  has, between the nacelle  102  and the engine  20 , a flow path  204  in which circulates a bypass stream  208  coming from the air intake through a fan  300  and which therefore flows in the direction of flow which goes from front to rear of the turbofan engine  100 . 
     The nacelle  102  has a fixed structure  206  which is fixedly mounted on the fan casing  202 . The fixed structure  206  is composed, in particular here, of a front frame  210  mounted around the fan casing  202  and of outer panels  212  fixed to the front frame  210  and forming an outer aerodynamic surface. 
     The nacelle  102  has a movable assembly  214  which has a movable cowl  216  which, here, forms the outer walls of the jet nozzle. 
     The nacelle  102  also has cascades  221  which are secured to the movable assembly  214 . 
     The movable cowl  216  is mounted to be movable in translation in a direction of translation that is overall parallel to the longitudinal direction X on the fixed structure  206  of the nacelle  102 . 
     The movable cowl  216  is movable between an advanced position ( FIG. 3 ) and a retracted position ( FIG. 4 ) and vice versa. In advanced position, the movable cowl  216  is positioned as far forward as possible with respect to the direction of advance so that the movable cowl  216  is close to the outer panels  212  and the fan casing  202  and thus forms a continuous aerodynamic surface. In retracted position, the movable cowl  216  is positioned as far back as possible with respect to the direction of advance so that the movable cowl  216  is away from the outer panels  212  and the fan casing  202  so as to define between them a window  220  which opens between the flow path  204  and the outside and where the cascades  221  are positioned. 
     In advanced position, the movable cowl  216  and the outer panels  212  extend one another so as to define the outer surface of the nacelle  102 , and the movable cowl  216  and the fan casing  202  extend one another so as to define the outer surface of the flow path  204 . In advanced position, the cascades  221  are accommodated between the outer panels  212  and the fan casing  202 . 
     In retracted position, the movable cowl  216  and the fan casing  202  and the outer panels  212  are at a distance and define between them the open window  220  between the flow path  204  and the outside of the nacelle  102 . That is to say, the air of the bypass stream  208  passes through the window  220  to go back outside the turbofan engine  100  by passing through the cascades  221 . 
     The translation of the movable cowl  216  is performed by any appropriate means such as, for example, systems of runners between the beams of the fixed structure  206  and the movable cowl  216 . 
     The nacelle  102  also comprises a set of actuators (not represented) ensuring the translational displacement of the movable cowl  216  between the advanced position and the retracted position and vice versa. Each actuator is controlled by a control unit, for example of processor type, which controls the displacements in one direction or the other depending on the needs of the aircraft  10 . 
     Each actuator can, for example, take the form of a dual-acting cylinder (two working directions) of which the cylinder is fixed to the fixed structure  206  and a rod is fixed to the movable cowl  216 . 
     The fan casing  202  and the outer panels  212  delimit the window  220  upstream with respect to the direction of flow and the movable cowl  216  delimits the window  220  downstream with respect to the direction of flow. 
       FIG. 2  shows the movable cowl  216  and the engine  20  which is represented here by a chain-dotted line cylinder. 
     The nacelle  102  comprises a plurality of veils  252  in which each is flexible and here overall takes the form of a trapezoid. Each veil  252  can alternately take a folded position ( FIG. 3 ) or a deployed position ( FIGS. 2 and 4 ). Each veil  252  has a fixed first edge and a movable second edge opposite the first edge. Each first edge is fixed to the movable cowl  216 , inside the movable cowl  216 , outside of the flow path  204  and behind the window  220  when the movable cowl  216  is in retracted position. 
     In folded position, each veil  252  is housed in the movable cowl  216  and in deployed position, the veil  252  is extended between the first edge and the second edge which extends close to the engine  20  across the flow path  204  in order to block it. Thus, the second edge is away from the first edge in the deployed position and close to the first edge in folded position. 
     Here, each first edge is inscribed in a plane at right angles to the longitudinal direction X and is at right angles to the radial direction with respect to the longitudinal direction X and passing through the middle of the first edge. 
     The nacelle  102  also comprises a pneumatic system  350  which is arranged to displace the second edge of each veil  252  in order to displace the veil  252  from the folded position to the deployed position and to displace the second edge of each veil  252  in order to displace the veil  252  from the deployed position to the folded position. 
     The pneumatic system  350  is synchronized with the displacement of the movable cowl  216  for the transition from the folded position to the deployed position to correspond to the transition from the advanced position to the retracted position, and for the transition from the deployed position to the folded position to correspond to the transition from the retracted position to the advanced position. 
     In deployed position, the veils  252  are positioned behind the window  220  to form a barrier in the flow path  204  to deflect the bypass stream  208  coming from the front towards the window  220 . In deployed position, the second edge of each veil  252  comes around the engine  20 . 
     The operation therefore comprises, from the advanced/folded position, ordering the activation of the actuators to displace the movable cowl  216  from the advanced position to the retracted position, which drives the displacement of the cascades  221  facing the window  220 . 
     During this displacement, the pneumatic system  350  deploys each veil  252  across the flow path  204 . 
     In reverse, the operation thus comprises, from the retracted/deployed position, in ordering the activation of the actuators to displace the movable cowl  216  from the retracted position to the advanced position, which drives the displacement of the cascades  221  to their initial position. 
     During this displacement, the pneumatic system  350  folds each veil  252  onto the outside of the flow path  204 . 
     The use of several flexible veils  252  allows the assembly to be lightened compared to the use of reversing doors from the state of the art. Furthermore, the veils  252  make it possible to adjust the efficiency and the aeramatch which characterize a thrust reverser. The term “aeramatch” here denotes the ratio between the outlet section of the nozzle in direct jet mode and the outlet section of the jet nozzle in thrust-reversing mode. 
     The pneumatic system  350  comprises a main roll  352  fixed inside the movable cowl  216  to the rear of the window  220  and that overall takes the form of a torus around the longitudinal direction X and, for each veil  252 , at least one secondary roll  354  which is secured to the main roll  352  and in which the inside of each secondary roll  354  is in fluidic continuity with the inside of the main roll  352 . The material constituting the main roll  352  is rigid, for example metal, and the material constituting the secondary rolls  354  is highly extendible, for example made of rubber. 
     Each secondary roll  354 , for example, takes the form of a pipe of which a first end is fixed to the main roll  352  and of which a second end is free and plugged. Each secondary roll  354 , for example, takes the form of a pipe of which the two ends are fixed to the main roll  352  thus forming a loop. 
     For each secondary roll  354  associated with a veil  252 , the second edge of the veil  252  is fixed to each secondary roll  354 , either at the free second end, or in the middle of the pipe depending on the type of secondary roll  354 . In any case, the second edge is fixed to the secondary roll  354  so that when the secondary roll  354  is inflated, the second edge is positioned around the engine  20 . The greater the number of secondary rolls  354  for a veil  252 , the better will be the tension of the second edge in deployed position. 
     The pneumatic system  350  comprises a pressurization and depressurization system which, alternately, generates a pressure in the main roll  352  and, therefore, in each secondary roll  354  to inflate them, or generates a depression in the main roll  352  and, therefore, in each secondary roll  354  to deflate them. The pressurization and depressurization system is controlled by the control unit according to requirements. 
     Thus, upon the transition from the advanced/folded position to the retracted/deployed position, the control unit controls the pressurization and depressurization system to make it generate a pressure and inflate the secondary rolls  354  and thus deploy the veils  252 , and, upon the transition from the retracted/deployed position to the advanced/folded position, the control unit controls the pressurization and depressurization system to make it generate a depression and deflate the secondary rolls  354  and thus fold back the veils  252 . 
     The pressurization and depressurization system can, for example, be a fan controlled by the control unit and that can alternately generate a pressure or a depression in the main roll  352 . 
       FIGS. 5 to 7  show a particular pressurization and depressurization system  550 . The particular pressurization and depressurization system  550  comprises a Venturi-effect tube  552  which has an inlet section  554 , an outlet section  556  and an intermediate section  558  between the inlet section  554  and the outlet section  556 , in which the diameter of the intermediate section  558  is less than the diameters of the inlet  554  and outlet  556  sections. 
     The inlet section  554  is fluidically connected to a point for taking of hot air from the flow path  204  and the outlet section  556  is fluidically connected, for example, to a heating system of the cabin of the aircraft  10 . 
     The particular pressurization and depressurization system  550  also comprises a bypass line  560  of which an inlet is fluidically connected to the inlet section  554  and of which an outlet is fluidically connected to the intermediate section  558 . 
     The particular pressurization and depressurization system  550  comprises a terminal line  562  of which an inlet is fluidically connected to the bypass line  560  and of which an outlet is fluidically connected to the main roll  352 . 
     The particular pressurization and depressurization system  550  also comprises: 
     a first valve  564  disposed at the inlet of the bypass line  560  and which can alternately take an open position allowing the passage between the inlet section  554  and the bypass line  560  or a closed position preventing the passage between the inlet section  554  and the bypass line  560 , 
     a second valve  566  disposed at the inlet of the terminal line  562  and which can alternately take a first position allowing the passage between the bypass line  560  and the terminal line  562  from the inlet of the bypass line  560  and preventing the passage between the terminal line  562  and the bypass line  560  to the outlet of the bypass line  560 , and a second position allowing the passage between the terminal line  562  and the bypass line  560  to the outlet of the bypass line  560  and preventing the passage between the bypass line  560  and the terminal line  562  from the inlet of the bypass line  560 , and 
     a third valve  568  disposed at the outlet of the bypass line  560  and which can alternately take an open position allowing the passage between the bypass line  560  and the outlet section  556  or a closed position preventing the passage between the bypass line  560  and the outlet section  556 . 
     Each valve  564 ,  566 ,  568  is position-controlled by the control unit. 
       FIG. 5  corresponds to the inflation of the secondary rolls  354 . The first valve  564  is in open position, the second valve  566  is in the first position, and the third valve  568  is in closed position. The air coming from the flow path  204  is then directed into the main roll  352  and into each secondary roll  354  to inflate them, and each veil  252  is brought into deployed position. 
       FIG. 6  corresponds to a position keeping the secondary rolls  354  in the inflated state. The first valve  564  is in closed position, the second valve  566  is in the first position or in the second position, and the third valve  568  is in closed position. The air which is in the main roll  352  and in each secondary roll  354  is then blocked. 
       FIG. 7  corresponds to the deflation of the secondary rolls  354 . The first valve  564  is in closed position, the second valve  566  is in the second position, and the third valve  568  is in open position. The air of the main roll  352  and of each secondary roll  354  is sucked by the Venturi effect into the intermediate section  558  and each secondary roll  354  is deflated and each veil  252  is returned to folded position. 
     In the embodiment of  FIGS. 8 and 9 , the direct fixing of the first edge of each veil  252  to the movable cowl  216  is replaced by an indirect fixing through rollers  254 . This embodiment makes it possible to improve the deployment and the folding of the veils  252  by assisting the pneumatic system  350 . 
     The nacelle  102  thus comprises, for each veil  252 , a roller  254  mounted to rotate freely on the movable cowl  216 . Each roller  254  is mounted inside the movable cowl  216 , outside the flow path  204  and behind the window  220  when the movable cowl  216  is in retracted position. The rollers  254  are distributed angularly around the longitudinal direction X along the perimeter of the movable cowl  216 . 
     In folded position, each veil  252  is wound around the associated roller  254 . 
     Thus, in folded position, the veil  252  is wound around the roller  254  and in deployed position, the veil  252  is unwound from the roller  254  and extended between the roller  254  and the engine  20  across the flow path  204  in order to block it. The first edge of each veil  252  is thus fixed to the associated roller  254  and the second edge is away from the roller  254  in the deployed position and close to the roller  254  in folded position. 
     Here, the axis of rotation of each roller  254  is inscribed in a plane at right angles to the longitudinal direction X and is at right angles to the radial direction with respect to the longitudinal direction X and passing through the middle of the roller  254 . 
     The nacelle  102  also comprises a deployment mechanism which is arranged to displace the second edge of each veil  252  in order to displace the veil  252  from the folded position to the deployed position and a folding mechanism which is arranged to drive each roller  254  in rotation in order to displace the veil  252  associated with the roller  254  from the deployed position to the folded position. 
     As previously, the deployment and folding mechanisms are synchronized with the displacement of the movable cowl  216  for the transition from the folded position to the deployed position to correspond to the transition from the advanced position to the retracted position, and for the transition from the deployed position to the folded position correspond to the transition from the retracted position to the advanced position. 
     During the displacement from the advanced/folded position to the retracted/deployed position, the deployment mechanism assists in the deployment of each veil  252  across the flow path  204 . 
     In reverse, during the displacement from the retracted/deployed position to the advanced/folded position, the folding mechanism folds each veil  252  on the outside of the flow path  204 . 
       FIGS. 8 and 9  show a deployment mechanism  500  according to a particular embodiment. In these  FIGS. 8 and 9 , only three veils  252  are represented for ease of understanding, but the other veils  252  are disposed angularly around the longitudinal direction X. 
     For each veil  252 , the deployment mechanism  500  comprises a plate  502  secured to the second edge of the veil  252  and which ensures the rigidity of the second edge. Each secondary roll  354  associated with the veil  252  can be fixed to this plate  502 . 
     Each plate  502  bears at least one pulling pulley  504  mounted to rotate freely on the plate  502 . Here, for reasons of balance, the plate  502  bears a pulling pulley  504  at each end of the plate  502 , that is to say, at each end of the second edge. 
     For several veils  252 , the deployment mechanism  500  also comprises a cable  506  which passes through each pulling pulley  504  of the several veils  252 . In the embodiment of the invention presented in  FIGS. 8 and 9 , there are two cables  506 , one for the port veils  252  (not represented) and one for the starboard veils  252 . Obviously, a different distribution is possible. 
     For each end of the cable  506 , the deployment mechanism  500  comprises a displacement system  508  which ensures the pulling of the end. Thus, a pull on each end of the cable  506  will tauten the cable  506  and deploy each veil  252  by displacement of the associated plate  502  under the effect of the cable  506 . 
     Each displacement system  508  here comprises a set of guiding pulleys  510  and an electric winder  512  onto which the cable  506  is wound. 
     The folding mechanism comprises a mechanism which ensures the rotation of each roller  254  in the direction of winding of the veil  252  on the roller  254 . 
     When the folding mechanism is activated, the deployment mechanism must be declutched so as not to generate any force retaining the veil  252 . In the case of  FIGS. 8 and 9 , each displacement system  508 , and more particularly each electric winder  512 , must be declutched to turn freely. 
       FIG. 10  shows a folding mechanism  700  according to a particular embodiment. 
     For each roller  254 , the folding mechanism  700  comprises a deflection pulley  520  fixed coaxially to the roller  254 , a winding pulley  702  fixed to the fixed structure  206  and a winding cable  522 , of which one end is fixed to the fixed structure  206  and of which the other end is fixed to the winding pulley  702  and in which the winding cable  522  passes through the deflection pulley  520 . 
     For each roller  254 , the folding mechanism  700  comprises a nitrogen damper  704  which comprises a cylinder  706  fixed to the fixed structure  206  and a piston  708  sliding in the cylinder  706 . 
     For each roller  254 , the folding mechanism  700  also comprises a transformation system  710  which ensures the transformation of the rotational movement of the winding pulley  702  into a translational movement of the piston  708  and vice versa. 
     The transformation system  710  here takes the form of a rack and pinion system. 
     From the advanced position, the movable assembly  214  retracts, which tends to displace the deflection pulley  520  towards the rear and therefore to unwind the winding cable  522  from the winding pulley  702 . 
     Through action of the transformation system  710 , the rotation of the winding pulley  702  causes the piston  708  to be driven into the cylinder  706  and therefore results in a compression of the nitrogen present in the nitrogen damper  704 . 
     In reverse, from the retracted position, when the movable assembly  214  advances, the winding cable  522  slackens and the pressure of the nitrogen against the piston  708  pushes the latter back, and, through action of the transformation system  710 , the translational displacement of the piston  708  drives the rotation of the winding pulley  702  which winds the winding cable  522  and thereby drives the rotation of the deflection pulley  520  which, in turn, drives the roller  254  and therefore the winding of the veil  252 . 
     According to another embodiment, the folding mechanism can comprise a declutchable electric winder to which the winding pulley  702  is fixed and which thus replaces the nitrogen damper  704  and the transformation system  710 . The folding mechanism then comprises, for each roller  254 , a deflection pulley  520  fixed coaxially to the roller  254 , a winding pulley  702 , a winding cable  522 , of which one end is fixed to the fixed structure  206  and of which the other end is fixed to the winding pulley  702  and in which the winding cable  522  passes through the deflection pulley  520 , and a declutchable electric winder to which the winding pulley  702  is fixed. The declutching of the electric winder allows the deployment of the veil  252  when the deployment mechanism  500  is actuated. 
     The control unit or controller is connected to the various elements to activate them according to requirements. For example, the control unit controls the rotation in one direction or in another of each electric winder and of each actuator displacing the movable cowl  216 . 
     Each veil  252  must have adequate structural characteristics to withstand the forces generated by the bypass stream  208  and be flexible enough to be able to fold. According to a particular embodiment, each veil  252  is composed of a flexible mesh structure onto which is fixed a flexible skin such as a fabric, for example. 
     The invention has been more particularly described in the case of a nacelle under a wing but it can be applied to a nacelle situated at the rear of the fuselage. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.