Patent Publication Number: US-2023159154-A1

Title: Flexible pillar for a flexible frame of a variable geometry flight control surface

Description:
TECHNICAL FIELD 
     The disclosure herein concerns a flexible pillar for a flexible frame intended in particular to be disposed in a variable geometry flight control surface, for example a deformable aileron of an aircraft. 
     BACKGROUND 
     In aeronautics mobile surfaces are used, generally on the wings and on the tail of an aircraft, to vary lift and drag. In particular, ailerons are aerodynamic flight control surfaces situated at the trailing edge of the wings of an aircraft. They are pivoted relative to the wings in such a manner at to be able to be moved in rotation and thus to vary the exposure of their exterior surfaces to the airflow. For example, the ailerons of the two wings are generally moved in opposite directions (one is pivoted up and the other down) to produce a roll movement. 
     To this end, it is known to use rigid flight control surfaces that are caused to pivot about their rotation axis by an actuator in order to cause them to assume required positions. Their rigidity in particular enables the flight control surfaces to withstand aerodynamic forces to which they are destined to be subjected. 
     However, flight control surfaces of this kind can be difficult and costly to provide. Another solution consists in using deformable flight control surfaces, that is to say flight control surfaces the movement of which is achieved by the deformation of at least a part of their structure by an actuator. Nevertheless, existing structures do not make it possible to obtain flight control surfaces that are both easily deformable and sufficiently rigid to support high aerodynamic forces. 
     These solutions are therefore not entirely satisfactory. 
     SUMMARY 
     An object of the disclosure herein is a solution enabling the aforementioned disadvantage to be remedied. 
     To this end it concerns a flexible pillar for a flexible frame intended to be disposed on a variable geometry flight control surface having an upper skin and a lower skin. 
     In accordance with the disclosure herein, the flexible pillar includes at least one elastic element having an elongate shape in the direction of a longitudinal axis. The flexible pillar is configured to be disposed between the upper skin and the lower skin so that the elastic element can be fixed to the upper skin at a first end of the flexible pillar and can be fixed to the lower skin at a second end of the flexible pillar. The flexible pillar has a compressive and a tensile rigidity along the longitudinal axis (X-X) that is greater than a shear rigidity of the flexible pillar along a transverse axis (Y-Y) of the flexible pillar ( 1 ). 
     Thus, thanks to the disclosure herein, a support is obtained that has a longitudinal direction and is able to transmit forces between its ends in that longitudinal direction and of doing this by deforming relatively little in that longitudinal direction and being able to deform easily in a direction transverse to the longitudinal direction. 
     The elastic element of the flexible pillar advantageously comprises at least a first elastic segment at its first end, a second elastic segment at its second end and a rigid core disposed between the first elastic segment and the second elastic segment. 
     Moreover, at least the first elastic segment and/or the second elastic segment is or are constituted of an incompressible elastic material. 
     Moreover, at least the first elastic segment and/or the second elastic segment comprises at least two elastic sections and at least one metal plate that are stacked along the longitudinal axis, the metal plate or plates being interleaved between two elastic sections. 
     In a preferred embodiment the flexible pillar has a cross-section of square shape. 
     In one particular embodiment the flexible pillar has a cross-section of rectangular shape with a length intended to extend in the direction of a span of the variable geometry flight control surface in which it is intended to be fixed. 
     The disclosure herein also concerns a frame for a variable geometry flight control surface. 
     In accordance with the disclosure herein, the flexible frame includes a plurality of flexible pillars, the plurality of flexible pillars being intended to be regularly distributed in an internal space of the variable geometry flight control surface, the internal space being delimited by the upper skin and the lower skin. 
     Moreover, the rigid core of each of the flexible pillars advantageously occupies a distance along the longitudinal axis between the first elastic segment and the second elastic segment if the first elastic segment and the second elastic segment are separated by a non-zero distance. 
     The disclosure herein further concerns a variable geometry flight control surface with an upper skin and a lower skin intended to be disposed on a wing of an aircraft. In accordance with the disclosure herein, the variable geometry flight control surface includes a flexible frame disposed between the upper skin and the lower skin. 
     The disclosure herein further concerns an aircraft equipped with at least one variable geometry flight control surface on at least one of its wings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended figures will clearly show how the disclosure herein may be reduced to practice. In those figures identical references designate similar elements. 
         FIG.  1    is a view in longitudinal section of a flexible pillar in a preferred embodiment. 
         FIG.  2    is a view in cross-section of a variable geometry flight control surface including a flexible frame in accordance with one particular embodiment. 
         FIG.  3    is a view in cross-section of a flight control surface showing one example of deformation of a variable geometry control surface including a flexible frame in accordance with one particular embodiment. 
         FIG.  4    is a perspective view of a variable geometry flight control surface including a flexible frame in accordance with an embodiment. 
         FIG.  5    is a diagrammatic view from above of a distribution of the flexible pillars of a flexible frame in accordance with one embodiment in which the flexible pillars have a cross-section of square shape. 
         FIG.  6    is a diagrammatic view from above of a distribution of the flexible pillars of a flexible frame in accordance with one embodiment in which the flexible pillars have a cross-section of rectangular shape. 
         FIG.  7    is a perspective view of an aircraft equipped with variable geometry flight control surfaces on its wings in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The flexible pillar  1  in accordance with the disclosure herein and one embodiment of which is represented diagrammatically in  FIG.  1    is a pillar intended to form part of a flexible frame  2  for a variable geometry flight control surface  3  ( FIG.  2   ,  FIG.  3    and  FIG.  4   ). 
     By “pillar” is meant a support having a longitudinal axis intended to be disposed between two objects in such a manner as to transmit forces between the objects. 
     Moreover, “a variable geometry flight control surface” is a mobile aerodynamic element such as a flight control surface of an aircraft (generally situated on the wings), the structure of which is designed to be deformable. It is therefore possible, for example by an actuator, to deform a flight control surface of this kind in such a manner as to vary its form or its orientation. That deformation can in particular replace movement of a normal rigid flight control surface. 
     In a preferred embodiment the variable geometry flight control surface  3  on which the flexible pillar  1  is intended to be disposed includes an upper skin  4  and a lower skin  5 . In this embodiment the flexible pillar  1  represented in  FIG.  1    includes at least one elastic element  6  of elongate shape in the direction of a longitudinal axis X-X. The elastic element  6  has at least a first end  8  along the longitudinal axis X-X adapted to be fixed to the upper skin  4  and a second end  9  along the longitudinal axis X-X adapted to be fixed to the lower skin  5 . 
     The ends  8  and  9  of the elastic element  6  may be fixed to the upper skin  4  and to the lower skin  5 , respectively, by glue or any other mechanical assembly. 
     Moreover, the flexible pillar  1  has a compressive and a tensile rigidity along the longitudinal axis X-X that is greater than a shear rigidity of the flexible pillar  1  along a transverse axis Y-Y of the flexible pillar  1 . The transverse axis Y-Y may be orthogonal to the longitudinal axis X-X, as in the  FIG.  1    example. By “rigidity” is meant the ability of a body to oppose deformation. In other words, the flexible pillar  1  is configured to deform relatively little when it is loaded in compression or in tension in the direction of the longitudinal axis X-X. Moreover, the flexible pillar  1  is also configured to oppose a slight resistance when it is loaded in shear, that is to say when it is subjected to slicing forces, namely forces at least one component of which is substantially orthogonal to the longitudinal axis X-X. 
     In the  FIG.  1    embodiment the flexible pillar  1  is fixed at the ends  8  and  9 . Consequently, it is the end surfaces of the flexible pillar  1  at these ends  8  and  9  that are intended to be subjected to exterior mechanical loads, for example during the deformation of the variable geometry flight control surface  3  as described in detail hereinafter. 
     Accordingly, in this embodiment the flexible pillar  1  may be subjected to exterior mechanical loads inducing forces that are applied at the level of the ends  8  and  9 . These exterior mechanical loads to which the flexible pillar  1  is subjected may in particular be broken down into compression, tension and shear forces. The compression forces are oriented along the longitudinal axis X-X in the sense toward the transverse axis Y-Y and diagrammatically represented by arrows C 1  and C 2  ( FIG.  1    and  FIG.  3   ). The tension forces are oriented along the longitudinal axis X-X away from the transverse axis Y-Y and represented by arrows T 1  and T 2  ( FIG.  1    and  FIG.  3   ). The shear forces, or slicing forces, are oriented orthogonally to the longitudinal axis X-X and represented by arrows S 1  and S 2  ( FIG.  1    and  FIG.  3   ). 
     The elastic element  6  is preferably made of an elastomer-type material. However, it may equally be made of other materials the properties of hyper-elasticity and of quasi-incompressibility of which make it possible to obtain the ratio between the rigidity of the flexible pillar  1  in compression/tension and the shear rigidity as described hereinabove. 
     In a preferred embodiment represented in  FIG.  1    the elastic element  6  of the flexible pillar  1  includes at least an elastic segment  10  and an elastic segment  11 . The elastic segment  10  and the elastic segment  11  are arranged so as to be stacked along the longitudinal axis X-X. Moreover, the flexible pillar  1  may include a rigid core  12  disposed between the elastic segment  10  and the elastic segment  11 . The elastic segments  10  and  11  and the rigid core  12  are arranged so as to be stacked in the direction of the longitudinal axis X-X. They may be fixed together by fixing means, for example by glue. 
     Moreover, at least the elastic segment  10  and/or the elastic segment  11  may be constituted of an incompressible elastic material. 
     The elastic segments  10  and  11  are preferably made of an elastomer-type material. In particular, this may be a material of vulcanized elastomer type. The rigid core  12  is made of a rigid material. For example, it may be made of a carbon composite material or an isotropic material such as a metal or plastic material. 
     In this embodiment the elastic segments  10  and  11  and the rigid core  12  have elongate rectangular parallelepiped shapes in the direction of the longitudinal axis X-X. In particular, they are configured to be fixed together so that the interfaces between the segments  10  and  11  and the rigid core  12  are orthogonal to the longitudinal axis X-X of the flexible pillar  1 . The elastic segments  10  and  11  preferably have the same dimensions. In particular, the elastic segment  10  may have a length L 1  along the longitudinal axis X-X that is equal to a length L 2  of the elastic segment  11  along the longitudinal axis X-X. Moreover, the elastic segments  10  and  11  may be made of the same material. 
     In one particular implementation of this embodiment the rigid core  12  and/or the elastic segments  10  and  11  may have six-sided solid shapes the edge surfaces of which are not parallel. The interfaces between the elastic segments  10  and  11  and the rigid core  12  are at an angle to the longitudinal axis X-X that is not a right angle. This makes it possible, for example, to adapt the shape of the flexible pillar  1  to particular configurations of the variable geometry flight control surface  3  on which it is intended to be disposed. For example, in  FIG.  2    the two cores  12  on the right of the figure have non-parallel edge surfaces. 
     In one particular embodiment represented in  FIG.  1    the elastic segments  10  and  11  each comprise at least two elastic sections stacked along the longitudinal axis X-X. In particular, the elastic segment  10  includes an elastic section  13  and an elastic section  14 . Similarly, the elastic segment  11  includes an elastic section  15  and an elastic section  16 . The elastic sections  13 ,  14 ,  15  and  16  preferably have the same dimensions. Moreover, the elastic segments  10  and  11  each include at least one metal plate interleaved between their elastic sections. In particular, the elastic segment  10  includes a metal plate  17  interleaved between the elastic sections  13  and  14 . Similarly, the elastic segment  11  includes a metal plate  18  interleaved between the elastic sections  15  and  16 . The metal plates  17  and  18  preferably have the same dimensions. Moreover, they may be made of the same material, for example of steel. 
     In one implementation of this embodiment the elastic sections and the metal plates are arranged so as to be stacked along the longitudinal axis X-X so that the interfaces between the elastic sections and the metal plates are orthogonal to the longitudinal axis X-X. This in particular makes it possible to increase the rigidity of the flexible pillar  1  in compression and in tension along its longitudinal axis X-X. 
     The composition of the elastic segments  10  and  11  as described hereinabove is non-limiting. In fact, they may include a plurality of elastic sections and of metal plates disposed between them in varied manners (interleaved or not, with interfaces orthogonal to the longitudinal axis X-X or not), for example to adjust the rigidity of the flexible pillar  1  in compression and/or in tension to suit particular circumstances. 
     In one embodiment represented in  FIG.  1    and  FIG.  5    the flexible pillar  1  has a cross-section of square shape. In this embodiment the elastic segments  10  and  11  and the rigid core  12  also have a square cross-section. Thus, the flexible pillar  1  has the shape of a cube or of a rectangular parallelepiped. 
     Moreover, in this embodiment the lengths L 1  and L 2  of the elastic segments  10  and  11  are equal. In a non-limiting manner, the elastic sections  13 ,  14 ,  15  and  16  may have a thickness, namely a length along the longitudinal axis X-X, between 2 mm and 20 mm inclusive, preferably a thickness of 5 mm. Moreover, the metal plates  17  and  18  may have a thickness between 0.5 mm and 1.5 mm inclusive, preferably a thickness of 1 mm. 
     In a particular embodiment represented diagrammatically in  FIG.  6    the flexible pillar  1  has a cross-section of rectangular shape. Moreover, the rectangular shape has a length intended to extend over a span of the variable geometry flight control surface  3  in which the flexible pillar  1  is intended to be disposed. In this case the transverse axis Y-Y is oriented substantially perpendicularly to the length of the rectangular cross-section of the flexible pillar  1 . The flexible pillar  1  is therefore configured to have a low rigidity in shear (compared to the rigidities in compression and in tension) and thus to be easily deformable in that direction. 
     However, the shapes described hereinabove for the flexible pillar  1  are non-limiting. In fact, the flexible pillar  1  may have varied and complex shapes, for example with a cross-section the shape of which varies along the flexible pillar  1  along the longitudinal axis X-X. 
     The flexible pillar  1  as described hereinabove is intended to form part of a flexible frame  2  represented from  FIG.  2    to  FIG.  6   . The flexible frame  2  is for example intended to be disposed on a flight control surface of an aircraft. 
     In accordance with the disclosure herein the flexible frame  2  includes a plurality of flexible pillars  1 . The flexible pillars  1  of the flexible frame  2  are preferably spaced from one another in order to form a regular grid. The flexible frame  2  intended to be disposed in an internal space E of the variable geometry flight control surface  3  delimited by the upper skin  4  and the lower skin  5  is therefore adapted to occupy the internal space E in a homogeneous manner. 
     However, in particular embodiments the flexible frame  2  may include a plurality of flexible pillars  1  spaced from one another in order to form an irregular grid. In this case the flexible frame  2  is configured to occupy the internal space E in which it is intended to be disposed in a heterogeneous manner, namely with irregular spaces between the flexible pillars  1 . This can make it possible to obtain mechanical properties, and in particular elastic properties, that differ from one place to another in the flexible frame  2 . For example, this makes it possible to obtain a greater rigidity in zones having a higher density of flexible pillars  1  and conversely to obtain a lesser rigidity in zones having a lower density of flexible pillars  1 . 
     In the embodiment represented in  FIG.  2    and in  FIG.  4    the flexible frame  2  includes flexible pillars  1  that are identical except for the shape of their rigid core  12 . In fact, in this embodiment the frame  2  is intended to be disposed in an internal space E of the variable geometry flight control surface  3  that is wider at a so-called “open” end  19  than at another, so-called “closed” end  20  close to the trailing edge. The length of the flexible pillars  1  along the longitudinal axis X-X must therefore be adapted to suit the shape of the profile of the variable geometry flight control surface  3 . 
     To this end, as represented in  FIG.  1    and  FIG.  2    the rigid core  12  of each of the flexible pillars  1  occupies a distance D along the longitudinal axis X-X between the elastic segment  10  and the elastic segment  11 . In the situation where the distance D separating the elastic segment  10  and the elastic segment  11  is zero, the flexible pillar  1  in question need not include a rigid core  12 . Thus, as in the example represented in  FIG.  2   , all the flexible pillars  1  of the flexible frame  2  have a length L along the longitudinal axis X-X ( FIG.  1   ) corresponding to the length L 1  of the elastic segment  10  plus the length L 2  of the elastic segment  11 , which is the same. In this embodiment only the distance D occupied by the rigid core  12  may vary from one flexible pillar  1  to another. 
     Moreover, in particular embodiments some flexible pillars  1  of the flexible frame  2  may have a non-completely longitudinal shape, such as the flexible pillar  1  situated toward the edge  20  in the  FIG.  2    example. In this case the distance D between the elastic segment  10  and the elastic segment  11  varies in the direction of the transverse axis Y-Y. In order to occupy a distance D of this kind the rigid core  12  may have a shape the length of which along the longitudinal axis X-X also varies in the direction of the transverse axis Y-Y, for example a trapezium shape. 
     The flexible frame  2  as described hereinabove is intended to be disposed on a flight control surface of an aircraft and especially on a variable geometry flight control surface  3  represented from  FIG.  2    to  FIG.  6   . 
     The variable geometry flight control surface  3  may have a profiled shape, namely a shape wider at an open end  19 , intended to be mounted on a wing  23  of an aircraft AC ( FIG.  7   ), and narrower at a closed end  20  corresponding to the trailing edge of the variable geometry flight control surface  3 . Moreover, as explained above, the variable geometry flight control surface  3  may include an upper skin  4  and a lower skin  5  delimiting an internal space E. The upper skin  4  comprises an inner surface  21  oriented toward the lower skin  5  and the lower skin  5  comprises an internal surface  22  oriented toward the upper skin  4 . In particular, the upper skin  4  and the lower skin  5  join at the level of the end  20  at the trailing edge of the variable geometry flight control surface  3 . The internal space E therefore corresponds to the space between the internal surfaces  21  and  22 . This is a closed space at the end  20  and an open space at the end  19 . 
     The variable geometry of the flight control surface  3  includes a flexible frame  2  disposed in the internal space E. In particular, each flexible pillar  1  of the flexible frame  2  is fixed at its ends along the longitudinal axis X-X to the upper skin  4  and to the lower skin  5 . To be more precise, each flexible pillar  1  is fixed to the internal surface  21  at its end  8  and to the internal surface  22  at its end  9 . The flexible pillars  1  may for example be fixed by glue. 
     In one embodiment the flexible frame  2  is disposed in the variable geometry flight control surface  3  so that the transverse axis Y-Y of the flexible pillars  1  of the flexible frame  2  corresponds to a direction substantially perpendicular to the trailing edge of the variable geometry flight control surface  3 . 
     Moreover, the flexible frame  2  may be configured so that the distribution of the flexible pillars  1  in the transverse direction Y-Y is regular. Moreover, it may be configured so that the distribution is also regular along a horizontal axis Z-Z corresponding to an axis the direction of which is parallel to the direction of the span of the variable geometry flight control surface  3 , namely the direction defined by its greatest length parallel to its trailing edge. For example, the horizontal axis Z-Z corresponds to an axis orthogonal both to the transverse axis Y-Y and to the longitudinal axis X-X, as represented in  FIG.  4   ,  FIG.  5    and  FIG.  6   . 
     The variable geometry flight control surface  3  may be an aileron intended to equip a wing  23  of an aircraft AC ( FIG.  7   ). In particular, the variable geometry flight control surface  3  is configured so as to be able to be deformed, for example via an actuator, in order to assume different shapes. The deformation of the variable geometry flight control surface  3  corresponds to the deformation of the upper skin  4  and of the lower skin  5  and also of the flexible frame  2 , as represented in  FIG.  3   . In fact, in this example the variable geometry flight control surface  3  has a non-deformed shape diagrammatically represented by the dashed line  24  that is intended to be aligned with and in line with the wing  23  of the aircraft AC. When it is wished to move the variable geometry flight control surface  3  into a required position, it can be deformed, for example by an actuator, in order to cause it to assume a shape that will bring it into the required position. Such deformation is represented by way of non-limiting example in  FIG.  3   . 
     To this end, the upper skin  4  and the lower skin  5  are configured to be deformable. They may be made of metal or a composite material. Moreover, the flexible frame  2  is also deformable as described hereinabove. In particular, the rigidity in compression and in tension of the flexible frame  2  (along the longitudinal axis X-X) is such that it allows the upper skin  4  and the lower skin  5  not to be crushed one against the other during deformation stemming from aerodynamic forces. Moreover, the low shear rigidity of the flexible frame  2  (along the transverse axis Y-Y) facilitates the deformation of the upper skin  4  and the lower skin  5 . 
     Moreover, the variable geometry flight control surface  3  is intended to be disposed on an aircraft AC. In particular, the aircraft AC includes two wings  23  having at least one variable geometry flight control surface  3  on each wing  23 . The variable geometry flight control surfaces  3  are disposed at the level of the trailing edge of the wings  23 , as represented in  FIG.  3    and  FIG.  7   . 
     The flexible pillar  1  forming part of the flexible frame  2  equipping the variable geometry flight control surfaces  3  as described hereinabove has numerous advantages. In particular:
         it makes it possible to obtain a support able to transmit forces between its ends with only very slight deformation along its longitudinal axis while allowing large deformations along the transverse axis;   it makes it possible to obtain a flexible frame  2  that is easily adaptable to suit any type of deformable hollow body having varied shapes, in particular flight control surfaces for aircraft;   it makes it possible to obtain a flexible frame  2  the mechanical, in particular elastic, properties of which are adaptable as a function of the required deformations;   it makes it possible to obtain a flexible frame  2  the elastic properties of which may vary from one place to another of the flexible frame  2 , for example by changing the distribution of the flexible pillars  1  or by changing the shape or the composition of the flexible pillars  1 .       

     While at least one example embodiment of the 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 example embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” 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.