Abstract:
The disclosure herein relates to a part of an aircraft structure including a portion of a floor structure and a portion of a hull structure, connected to one another by a connecting element. In accordance with, the disclosure herein the connecting element includes a flexible cable fixed at one of the ends thereof to the portion of a floor structure and fixed at the other, second of the ends thereof to the portion of a hull structure. When the connection between the portion of a floor structure and the portion of a hull structure is subjected to tensile load, the flexible cable makes it possible to meet the standards of resistance to forward accelerations of the aircraft. When the connection is subjected to compressive load, the flexible cable relaxes and bends, which limits the requirements of withstanding compressive stresses and therefore the weight of the connecting element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to FR 14 54914 filed May 30, 2014, the entire disclosure of which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to the field of the connection between the floor structure and the hull structure in an aircraft. 
       BACKGROUND 
       [0003]    The structure  10  of an aircraft in particular comprises the hull structure and the floor structure.  FIG. 1  illustrates an example of a connection according to the prior art between a hull structure  11  and a floor structure  12 . 
         [0004]    An orthonormal coordinate system (Oxyz) is defined. 
         [0005]    The axis Ox corresponds to the longitudinal axis Ox of the aircraft. The front and the rear of the aircraft are defined along this axis Ox. The front of the aircraft corresponds to the nose side of the aircraft, where the cockpit is located. The rear of the aircraft corresponds to the tail side of the aircraft, where the vertical stabilizer is generally found. Hereinafter it will be considered that under normal flight conditions the aircraft moves along the axis Ox, along a vector oriented from the rear to the front of the aircraft. 
         [0006]    The axis Oz corresponds to the vertical axis when the aircraft is located on the ground, in a parking position. 
         [0007]    The axis Oy, with the axis Ox, defines a horizontal plane when the aircraft is located on the ground, in a parking position. The axis Oy corresponds to the transverse axis of the aircraft. 
         [0008]    The hull structure  11  in particular comprises a set of frames  11 A, forming stiffeners which are transverse relative to the axis Ox, and a set of stringers  11 B, forming longitudinal stiffeners parallel to the axis Ox. The hull structure also comprises one or more metal or composite sheets shaped in accordance with the desired profile and referred to as the skin  11 C. The skin  11 C covers the lattice structure formed by the frames  11 A and the stringers  11 B. 
         [0009]    The floor structure  12  comprises an assembly of crosspieces  12 A and rails  12 B. The rails  12 B extend along the axis Ox and serve to fix furniture elements, such as the seats. The rail  12 C is an external rail, i.e. a rail close to the hull structure or in other words close to the lateral walls of the aircraft. The crosspieces  12 A extend along the axis Oy. 
         [0010]    In the example shown in  FIG. 1  the floor structure  12  is pressed against the hull structure  11  via the intermediary of stanchions  13  extending along the axis Oz. 
         [0011]    In order to stabilize the floor structure  12 , anti-crash connecting rods  14  extend in the plane (xOy). Each anti-crash connecting rod is an elongated rigid component, mounted fixedly at each one of its ends, on the floor structure on the one hand and on the hull structure on the other hand. In the example shown in  FIG. 1  each anti-crash connecting rod  14  is fixed at a first point  14 A to the external rail  12 C and at a second point  14 B to a stringer  11 B. The first point  14 A is located close to the intersection between the external rail  12 C and a crosspiece  12 A. The second point  14 B is located close to the intersection between a stringer  11 B and a frame  11 A. Each anti-crash connecting rod  14  is inclined relative to the axis Ox. 
         [0012]    The anti-crash connecting rods  14  make it possible to hold the floor structure  12  substantially fixed relative to the hull structure  11 , even in the event of sharp deceleration of the aircraft, and in particular in the event of the aircraft crashing. A crash can be either a crash proper or an abrupt landing of the aircraft, or an impact approximating an abrupt landing in terms of the forces. In such a situation, the inertial force of the floor structure tends to move it away from the hull structure. In particular, the anti-crash connecting rods must be able to withstand an acceleration equal to 9 g along the axis Ox, towards the front of the aircraft (where g is the gravity of earth, equal to approximately 9.8 m·s −2 ). An acceleration towards the front of the aircraft (forward acceleration) may also be called “deceleration”. The force which acts on the anti-crash connecting rods is proportional to this deceleration and to the mass of the floor structure and the loads supported by the latter (aircraft furniture, passengers, etc.). In order to withstand such a deceleration, the anti-crash connecting rods have very wide sections and therefore a very considerable mass. 
       SUMMARY 
       [0013]    One objective of the present disclosure is to provide a solution for connecting the floor structure and the hull structure which makes it possible to reduce the total mass of the aircraft, while still fulfilling the requirements of withstanding an acceleration of 9 g towards the front of the aircraft. 
         [0014]    This objective is achieved with a part of an aircraft structure comprising a portion of a floor structure and a portion of a hull structure connected to one another by a connecting element. 
         [0015]    In accordance with the disclosure herein the connecting element comprises a flexible cable fixed at a first of the ends thereof to the portion of a floor structure and fixed at the other end thereof, the second end, to the portion of a hull structure. 
         [0016]    When the connection between the portion of a hull structure and the portion of a floor structure is subject to tensile load (deceleration of the aircraft), the cable gets tensioned and makes it possible to meet the current standards of withstanding an acceleration of 9 g towards the front of the aircraft. 
         [0017]    When the connection between the portion of a hull structure and the portion of a floor structure is subject to compressive load (for example lateral bending load), the flexible cable relaxes, and potentially may bend slightly. 
         [0018]    Thanks to its properties in terms of flexibility, the connecting element according to the disclosure herein does not need to be strong enough to withstand a compressive load. 
         [0019]    On the contrary, in the prior art, the use of a rigid anti-crash connecting rod mounted fixedly on the floor structure and on the hull structure requires this connecting rod to be able to withstand the compressive stresses in order to avoid buckling phenomena (instability of a structure, which, exposed to a compressive force, has a tendency to deflect in a direction perpendicular to the axis of compression). 
         [0020]    Thus, the connecting element according to the disclosure herein can have a reduced mass compared with an anti-crash connecting rod according to the prior art. 
         [0021]    A connection is thus provided between the floor structure and the hull structure making it possible to reduce the total mass of the aircraft whilst meeting the requirements of withstanding a forward acceleration of the aircraft of 9 g. For example, the mass of the connector for connecting the floor structure and the hull structure is reduced by 20% by using a connecting element according to the disclosure herein in replacement of an anti-crash connecting rod according to the prior art. The total mass saving is approximately 15 kg by use of a connecting element according to the disclosure herein. 
         [0022]    It may be considered that the disclosure herein lies in replacing connecting structure, or a connector, having an elevated compressive modulus, for example of approximately 70,000 MPa, by connecting structure having a very low compressive modulus (less than or equal to 100 MPa). 
         [0023]    The cable can be fixed to an external rail of the portion of a floor structure. 
         [0024]    The cable can be fixed to a frame and a skin of the portion of a hull structure by a coupling part. 
         [0025]    The cable preferably has a rigidity less than 1000 N·m −1 . 
         [0026]    The part of a structure according to the disclosure herein advantageously comprises a pre-tensioning device designed to continuously tension the cable. 
         [0027]    The pre-tensioning device may comprise:
       a first stop element protruding on the cable at one of the ends thereof,   a second stop element, which is mounted fixedly relative to the portion of a floor structure or the portion of a hull structure, and which is provided with an opening, through which the cable extends, and   a compression coil spring mounted concentrically with the cable and disposed between the first stop element and the second stop element, bearing thereagainst.       
 
         [0031]    In a variant the pre-tensioning device may comprise:
       a first stop element protruding on the cable at one of the ends thereof,   a second stop element, which is mounted fixedly relative to the portion of a floor structure or the portion of a hull structure, and which is provided with an opening, through which the cable extends, and   a spring washer mounted concentrically with the cable and disposed between the first stop element and the second stop element, bearing thereagainst.       
 
         [0035]    In accordance with another variant the pre-tensioning device may comprise:
       a first stop element, screwed around the cable, on a thread of the cable,   a second stop element, which is mounted fixedly relative to the portion of a floor structure or the portion of a hull structure, and which is provided with an opening, through which the cable extends, and   a spacer disposed between the first stop element and the second stop element,
 
a pre-tensioning force applied to the cable being adjustable by an adjustment of the position of the first stop element on the thread of the cable.
       
 
         [0039]    The pre-tensioning device preferably applies to the cable a pre-tensioning force between 1050 N and 1150 N. 
         [0040]    Different approaches for fixing an end of the cable to one from the portion of a hull structure and the portion of a floor structure will now be described. 
         [0041]    In accordance with an advantageous embodiment, an end of the cable is inserted into an opening formed in an intermediate part fixed to one from the portion of a hull structure and the portion of a floor structure, the cable being secured to the intermediate part by two nuts positioned around the cable on either side of the opening. 
         [0042]    For example:
       a first end of the cable is inserted into an opening formed in a first intermediate part fixed to the portion of a hull structure, the cable being secured to the first intermediate part by two nuts positioned around the cable on either side of the opening; and   the other end of the cable is inserted into an opening formed in a second intermediate part fixed to the portion of a hull structure, the cable being secured to the second intermediate part by two nuts positioned around the cable on either side of the opening.       
 
         [0045]    In accordance with a variant of this advantageous embodiment, an end of the cable is placed against the base of an indentation in an intermediate part, by a clip extending transversely to the cable end, the clip being fixed on either side of the cable to one from the portion of a hull structure and the portion of a floor structure. 
         [0046]    In accordance with another variant of this advantageous embodiment, an end of the cable is placed against an inner face of an orifice formed in an intermediate part, by a clip extending transversely to the cable, the clip being fixed on one single side of the cable to one from the portion of a hull structure and the portion of a floor structure. 
         [0047]    The two ends of the cable can be fixed, one to the portion of a hull structure and the other to the portion of a floor structure, by the same fixing structure from the three variants described above. In a variant, the two ends of the cable can be fixed, one to the portion of a hull structure and the other to the portion of a floor structure, by different fixing structure from the three variants described above 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    The present disclosure will be better understood upon reading the description of exemplary embodiments provided purely by way of non-limiting indication and with reference to the accompanying drawings, in which: 
           [0049]      FIG. 1  schematically illustrates part of an aircraft structure in accordance with the prior art; 
           [0050]      FIG. 2  illustrates a first embodiment of part of an aircraft structure according to the disclosure herein; 
           [0051]      FIGS. 3A and 3B  schematically illustrate the principle of the connecting element according to the disclosure herein; 
           [0052]      FIG. 4A  illustrates a detail of a second embodiment of part of an aircraft structure according to the disclosure herein; 
           [0053]      FIG. 4B  illustrates a variant of the embodiment of  FIG. 4A ; 
           [0054]      FIG. 4C  illustrates a coupling part according to the disclosure herein for fixing a cable end to the floor structure or the hull structure; 
           [0055]      FIG. 4D  illustrates a cable according to the disclosure herein in sectional view; 
           [0056]      FIGS. 4E to 4G  illustrate different variants for fixing a cable according to the disclosure herein; 
           [0057]      FIG. 5  illustrates a first embodiment of a pre-tensioning device according to the disclosure herein; 
           [0058]      FIG. 6  illustrates a second embodiment of a pre-tensioning device according to the disclosure herein; and 
           [0059]      FIG. 7  illustrates a third embodiment of a pre-tensioning device according to the disclosure herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0060]      FIG. 2  illustrates a first embodiment of part of an aircraft structure  100  according to the disclosure herein. 
         [0061]      FIG. 2  shows a portion of a floor structure  12 , i.e. a part of a floor structure.  FIG. 2  in particular illustrates a detailed view of an external rail  12 C of the floor structure  12 .  FIG. 2  also shows a portion of a hull structure  11 , i.e. a part of a hull structure.  FIG. 2  in particular illustrates a detailed view of a frame  11 A and of a skin  11 C. A connecting element  20  according to the disclosure herein connects the portion of a floor structure and the portion of a hull structure 
         [0062]    The connecting element  20  is formed of a flexible cable  21 , also referred to as a guy rope, and of, as the case may be, intermediate fixing elements, such as the coupling parts described hereinafter. 
         [0063]    The cable  21  is fixed, on the side of the first end  21 A thereof, to the portion of a hull structure  11 . In other words, the first end  21 A of the cable is fixed relative to the hull structure. In particular, the end  21 A of the cable  21  is fixed with the aid of a coupling part  22 , both to the frame  11 A and to the skin  11 C. In a variant the end  21 A of the cable is fixed, with the aid of the coupling part  22 , both to the frame  11 A and to a stringer. 
         [0064]    The coupling part  22  for example comprises a recess, in which the end  21 A of the cable is mounted fixedly, and through-holes for the passage of rivets in order to fix the coupling part to the hull structure. The coupling part  22  is sometimes referred to as an “interface fitting”. Different examples of a coupling part will be described further below, with reference to  FIGS. 4A to 4C . 
         [0065]    The cable  21  is fixed, on the side of the second end thereof  21 B, to the portion of a floor structure  12 . In the example shown in  FIG. 2  the second end  21 B of the cable is fixed to the external rail  12 C, in the vicinity of a crosspiece (not shown). In a variant, the second end  21 B of the cable is fixed both to the external rail  12 C and to the crosspiece. Here again, a coupling part (not shown) is advantageously used to provide the interface between the second end  21 B of the cable and, here, the floor structure  12 . 
         [0066]    The term “flexible cable” means that the cable has a low flexural rigidity. The flexural rigidity of the cable corresponds to the ratio between a force applied to the cable and the resultant deflection of the cable. The force applied to the cable is directed along an axis orthogonal to the longitudinal axis of the cable. The force is applied to the middle of the cable, as considered in the direction of length thereof. The resultant deflection is the displacement of a point located in the middle of the cable. A low flexural rigidity signifies that a reduced compressive force allows a high deflection of the cable. The flexural rigidity, denoted k, can be expressed thus: 
         [0000]    
       
         
           
             k 
             ∝ 
             
               
                 E 
                 · 
                 I 
               
               
                 L 
                 3 
               
             
           
         
       
     
         [0067]    with L the length of the cable, E the modulus of elasticity under tension of the cable, and I the inertia under flexion of the cable. The rigidity of the cable  21  is particularly less than 1000 N·m −1 , or even less than 500 N·m −1 , or even less than 100 N·m −1 . 
         [0068]    The cable  21  can be made of metal, for example of aluminium, of titanium or of steel. Steel has an advantageous ratio between its ultimate tensile strength and its density, of approximately 0.15. Stainless steel is advantageously used, in particular for its resistance to corrosion. In a variant the cable  21  is made of a composite material, for example comprising carbon fibres or poly(p-phenylene terephthalamide) fibres (KEVLAR®). 
         [0069]    The cable advantageously has a cylindrical form. The diameter of the cable may be between 6 mm and 15 mm, for example 8 mm, 10 mm or 12 mm. The length of the cable may be between 400 mm and 600 mm, for example 470 mm. 
         [0070]    The cable  21  and extends in the plane (y0x) as defined in the introduction. Nevertheless, a component along the axis Oz could be envisaged. 
         [0071]    The cable  21  is placed at an angle relative to the axis Ox and Oy, for example at an angle between 20° and 80° relative to the axis Ox. This angle is less than 90°. 
         [0072]    In other words, the flexible cable and the floor structure are connected together solely at one of the ends of the flexible cable, and the flexible cable and the hull structure are connected together solely at the other of the ends of the flexible cable. 
         [0073]    In particular, the flexible cable extends along an axis connecting the floor structure and the hull structure, this axis having at least one component along the longitudinal axis of the aircraft, and one component along the transverse axis of the aircraft. It can be the that this axis is oriented at an angle relative to the longitudinal axis of the aircraft. 
         [0074]    In other words, the flexible cable extends in a straight line between the floor structure and the hull structure, this straight line having at least one component along the longitudinal axis of the aircraft, and one component along the transverse axis of the aircraft. In particular, this straight line is located in the plane formed by the longitudinal and transverse axis Ox and Oy. 
         [0075]    Such an arrangement makes it possible to absorb loads parallel to the longitudinal axis of the aircraft. 
         [0076]    For example, the end of the cable connected to the hull structure is located towards the front of the aircraft, whereas the end of the cable connected to the floor structure is located towards the rear of the aircraft. In other words, the end of the cable connected to the hull structure is located in front of the end of the cable connected to the floor structure, along the longitudinal axis 
         [0077]      FIGS. 3A and 3B  illustrate, schematically, the principle of the connecting element according to the disclosure herein. 
         [0078]    In  FIG. 3A  the connection between the hull structure and the floor structure is tensioned, in particular along the longitudinal axis of the aircraft (see arrows  31 ). In other words, the floor structure  12  tends to pull away from the hull structure  11  (crash situation, for example). The cable tenses. Under these conditions the cable satisfies the criterion of resistance to a forward acceleration of the aircraft of 9 g. In particular, the cable  21  is dimensioned so as to avoid rupture when subjected to such conditions. This condition is met in particular by a suitable choice of the diameter of the cable. The cable is dimensioned so that, under normal conditions of use (tensioning less than 9 g towards the front of the aircraft), the stresses experienced do not lead to permanent deformation. In other words, under normal conditions of use, any potential deformation of the cable is an elastic deformation. 
         [0079]      FIG. 3B  Illustrates the case in which the connection between the hull structure and the floor structure is subjected to compressive load, in particular along the longitudinal axis of the aircraft (see arrows  32 ). In other words, the floor structure  12  tends to move towards the hull structure  11 . In this case the cable is simply relaxed. Thanks to the flexural properties of the cable  21 , there is no risk of bowing, as could be the case with a rigid part, such as an anti-crash connecting rod according to the prior art. The connecting element according to the disclosure herein thus offers a simple and effective solution so that the connection between the hull structure and the floor structure can withstand compressive loads, whilst offering a reduced mass. 
         [0080]    The disclosure herein presents a high simplicity of installation and maintenance, the parts being easily accessible and there being no need for cumbersome adjustments or specific tooling. 
         [0081]    It is also noted that the connections used, between the cable and the floor structure and between the cable and the hull structure, have no degree of freedom. There are thus no potential difficulties associated with the existence of at least one degree of freedom, for example an increase in the wear of the mechanical parts. 
         [0082]      FIG. 4A  illustrates a detail of a second embodiment of a part of an aircraft structure according to the disclosure herein.  FIG. 4A  shows:
       a first coupling part  22 A, making it possible to fix a first end of the cable (not shown) to the portion of a floor structure, in particular to the rail  12 C; and   a second coupling part  22 B, making it possible to fix a second end of the cable (not shown) to the portion of a hull structure (not shown).       
 
         [0085]    The second coupling part  22 B consists here of two basic parts:
       a first basic part  22 C, similar to the first coupling part  22 A and receiving the second end of the cable; and   a second basic part  22 D, fixed directly to the hull structure and to the first basic part  22 C by rivets. The second basic part  22 D is fixed in particular both the to the frame  11 A and to the skin  11 C and makes it possible to avoid an obstacle, such as a conduit  27 .       
 
         [0088]    In accordance with a variant illustrated in  FIG. 4B , the second coupling part  22 B consists here of three basic parts:
       a first basic part  22 C, similar to the first coupling part  22 A and receiving the second end of the cable;   a second basic part  221 D, fixed directly to one from the frame  11 A and the skin  11 C, and to the first basic part  22 C; and   a third basic part  222 D, fixed directly to the other from the frame  11 A and the skin  11 C, and to the first basic part  22 C.       
 
         [0092]      FIG. 4C  illustrates a detailed view of the first coupling part  22 A illustrated in  FIGS. 4A and 4B . 
         [0093]    The first coupling part  22 A is shown in a perspective view. It comprises an opening  221 A, through which the first end of the cable is inserted. The diameter of the opening  221 A is slightly greater than the diameter of the cable. The opening is formed in a wall  222 A of the first coupling part  22 A. The wall  222 A is preferably orthogonal to the longitudinal axis of the cable, when this is tensed. 
         [0094]    The first coupling part  22 A also comprises a recess  223 A, within which the first end of the cable is housed, as well as a fixing element for fixing the cable to the first coupling part (see  FIG. 4E ). 
         [0095]    The recess  223 A for example has inner walls having three faces, these walls together having a U-shaped section. In particular, the wall  222 A receiving the opening is surrounded by two lateral walls parallel to one another. This U shape makes it possible to easily insert the fixing element in the recess  223 A when assembling a connecting element according to disclosure herein. After having inserted the fixing element in the recess  223 A, the first end of the cable is introduced into the recess by sliding the end of the cable into the opening  221 A. The fixing element is then fixed to the cable, as explained with reference to  FIG. 4E . 
         [0096]    The first coupling part  22 A also comprises a planar support part  224 A, able to be pressed against a planar surface and fixed to this planar surface by rivets mounted in the through-holes  225 A. 
         [0097]      FIG. 4D  illustrates a sectional view of a cable  21  according to the disclosure herein. The cable  21  is formed of a primary stranded wire formed by an assembly of a number of secondary stranded wires  21 C twisted together. The example shown in  FIG. 4D  has six secondary stranded wires  21 C. Each secondary stranded wire  21 C is a stranded wire formed by an assembly of wires twisted together, for example steel wires. 
         [0098]      FIGS. 4E to 4G  illustrate different variants for fixing a cable according to the disclosure herein. 
         [0099]      FIG. 4E  illustrates a detailed view of the embodiment illustrated in  FIG. 2  and also makes it possible to illustrate the fixing of an end of the cable in a coupling part as shown in  FIGS. 4A to 4C . 
         [0100]    The cable  21  is inserted into an opening formed in the coupling part  22 . Two nuts  42 A and  42 B are positioned on either side of the opening and are screwed on respective threads of the end of the cable. The threads are formed for example in a local excess thickness of the cable. The nuts  42 A and  42 B have diameters greater than the diameter of the opening, such that the end of the cable and the coupling part are clamped together between the two nuts and thus fixed to one another. The nut  42 B can be located in a recess in the coupling part. It forms a fixing element as mentioned with reference to  FIG. 4C . 
         [0101]      FIGS. 4F and 4G  illustrate two variants for fixing a cable end. These two variants involve a coupling part. The cable end fixed to the hull structure  11  has been shown by way of example. 
         [0102]      FIGS. 4F and 4G  are sectional views in a plane orthogonal to the longitudinal axis of the cable, when the cable is tensed. 
         [0103]    In the variant shown in  FIG. 4F , the coupling part  22  comprises an indentation  251 , against the base of which the end of the cable presses. The base of the indentation  251  extends along an axis parallel to the plane of the hull structure  11 , against which the coupling part  22  bears. The axis of the depth of the indentation  251  extends along an axis orthogonal to the plane of the hull structure  11 , against which the coupling part  22  bears. The end of the cable is placed against the base of the indentation by a clip  252 , which extends over part of the lateral face of the cable, such that the cable is secured between this clip and the base of the indentation. The clip  252  is fixed to the hull structure  11 , on either side of the cable, by two nuts  253  and two screws  254 . 
         [0104]    In the variant shown in  FIG. 4G , the intermediate part comprises an aperture or orifice  261 . In the sectional view of  FIG. 4G , the aperture  261  is of elongate form in a direction orthogonal to the longitudinal axis of the tensed cable, and parallel to the plane of the hull structure  11 , against which the coupling part  22  bears. The end of the cable is inserted into the aperture  261  at a wide part of this aperture. This cable end is then moved in translation in the aperture, in the direction of elongation thereof, in order to reach a narrowed portion of the aperture. The end of the cable is pressed against the base of this narrowed portion of the aperture  261 . A clip  262  holds the end of the cable pressed against the base of this narrowed portion of the aperture  261 . The end of the cable is in contact, over more than half of the perimeter thereof, with the base of this narrowed portion of the aperture  261 . The clip  262  has a first planar portion, bearing against the hull structure  11 . A second planar portion, inclined at 90° relative to the first planar portion, extends towards the cable and passes adjacently to the cable. A third portion of the clip surrounds the cable, on the side opposite the hull structure  11 . The clip  262  is fixed to the hull structure  11  by a screw  264  and a nut  263   
         [0105]    A person skilled in the art will be able to conceive numerous other variants for fixing a cable end, without departing from the scope of the present disclosure. 
         [0106]    The cable  21  is advantageously subjected to a pre-tensioning force. 
         [0107]    The total tensile force applied to the cable is then equal to the pre-tensioning force, to which a tensile force (positive) or compressive force (negative) is added, corresponding to the load of the connection between the floor structure and the hull structure, caused by the accelerations or decelerations of the aircraft. 
         [0108]    The pre-tensioning force is selected such that the cable is continuously tensed, even when the connection between the hull structure and the floor structure is subjected to compressive load, due to an acceleration of the aircraft. 
         [0109]    Thus, when the connection between the hull structure and the floor structure is subjected to compressive load (acceleration of the aircraft), the cable is weakly tensed, and when the connection between the hull structure and the floor structure is tensioned (deceleration of the aircraft), the cable is heavily tensed. 
         [0110]    The pre-tensioning force applied to the cable is therefore the tensile force that is applied to the cable, in the absence of loading of the connection between the hull structure and the floor structure due to an acceleration or a deceleration of the aircraft. 
         [0111]    The fact that the cable  21  is permanently tensed prevents it from vibrating, in response to vibrations of the aircraft. If the cable were to vibrate, it would produce an acoustic signal, in the manner of a guitar string. Such a signal would constitute a noise nuisance for the crew members and for the passengers. 
         [0112]    Since the natural frequencies of the cable are directly linked to the pre-tension applied thereto, the control of the pre-tension of the cable makes it possible to guarantee a decoupling between the natural modes of the cable and the low frequencies of excitation originating from the surrounding structure (with high energy level and between 0 and 100 Hz). 
         [0113]    The floor structure and the hull structure must not be subjected to forces corresponding to an excessively high tension of the cable, otherwise they risk being damaged. In particular, the total tensile force applied to the cable must be less than 3300 N. In order to provide a wide safety margin, it is considered that the pre-tensioning force must be less than 1500 N. 
         [0114]    It is also known that the natural frequency of the cable is proportional to the square root of the total tensile force applied thereto. 
         [0115]    For example, the natural frequencies have been calculated depending on the total tensile force applied to the cable for three steel cables measuring, respectively, 8 mm, 10 mm and 12 mm in diameter. Knowing the particular aircraft model in question, it is deduced from this that the total tensile force must be between 950 N and 1250 N in order to satisfy the set of conditions above. Taking into account the fact that the cable will also be subject to tensile load or compressive load on account of the accelerations or decelerations of the aircraft, a pre-tensioning force between 1050 and 1150 N, for example approximately 1100 N, is advantageously selected. A pre-tensioning force equal to 1100 N typically corresponds to an elongation of 1.75 mm of the length of the cable, relative to the length thereof at rest, i.e. when it is not subjected to any tensile or compressive stress. 
         [0116]    A pre-tensioning force to be applied to the cable can be adjusted, depending on the placement of the cable in the aircraft. 
         [0117]      FIGS. 5 to 7  show different examples of pre-tensioning devices, designed to apply the pre-tension as defined above, thanks to which the cable is continuously tensioned. 
         [0118]      FIG. 5  illustrates a first embodiment of a pre-tensioning device  50 . 
         [0119]    In accordance with this embodiment, the end of  21 B of the cable is housed and fixed in a casing  51 , forming a first stop element. The section of the casing  51 , in a plane orthogonal to the longitudinal axis of the cable  21 , has a surface area greater than that of the section of the cable  21  in such a plane. The longitudinal axis of the cable is defined when this is tensed, between the two fixing points thereof. The fixing of the end  21 B of the cable to the casing can be provided as described with reference to  FIGS. 4E to 4G . 
         [0120]    The cable  21  extends through a guide  52 , without being fixed to this guide. 
         [0121]    The guide  52  is fixed relative to the floor structure. It can be formed in a portion of the external rail. 
         [0122]    In a variant the guide  52  is fixed relative to the hull structure and the end  21 A of the cable is of interest. 
         [0123]    The guide  52  has an opening  52 A, through which the cable  21  extends. The opening  52 A has, for example, a circular section in a plane orthogonal to the longitudinal axis of the cable, of diameter slightly greater than the diameter of the cable. 
         [0124]    The guide  52  comprises a cavity  52 B. The cavity  52 B has a cylindrical form, the axis of the cylinder being the same as the longitudinal axis of the cable  21 . A face  52 C of the cavity receives the opening  52 A. The cavity  52 B is open on the side of the cylinder opposite the face  52 C. The face  52 C of the guide forms a second stop element. 
         [0125]    A coil spring  53  extends in the cavity  52 B, between the casing  51  and the face  52 C of the guide. The coils of the spring surround the cable  21 . In other words, the coil spring  53  is concentric with the cable  21 . The cavity  52 B forms a guide for the coil spring  53 . The coil spring  53  is a compression spring, bearing on one side against the face  52 C of the recess, and on the other side against the casing  51 . The coil spring  53  thus exerts a force parallel to the longitudinal axis of the cable (see arrow  54 ). This force tends to distance the casing  51  receiving the end  21 B of the cable from the other end of the cable. This force constitutes a pre-tensioning force as defined hereinbefore. 
         [0126]      FIG. 6  illustrates a second embodiment of a pre-tensioning device  60 . 
         [0127]    In accordance with this embodiment, the end  21 B of the cable is provided with a thread, making it possible to fix a screw  61  around the cable  21 . A washer  62  is placed around the cable  21  and forms a first stop element. 
         [0128]    The pre-tensioning device  60  also comprises a support  63  provided with an opening  63 A, through which the cable  21  extends. The cable  21  extends through the support  63 , without being fixed to this support. 
         [0129]    The support  63  is fixed relative to the floor structure. It can be formed in a portion of the external rail. 
         [0130]    In a variant the support  63  is fixed relative to the hull structure, and the end  21 A of the cable is of interest. 
         [0131]    The opening  63 A for example has a circular section in a plane orthogonal to the longitudinal axis of the cable, of diameter slightly greater than the diameter of the cable. 
         [0132]    The support  63  forms a second stop element. 
         [0133]    A spring washer  64  (also referred to as an elastic washer or Belleville washer) extends between the support  63  and the washer  62 . The spring washer  64  is concentric with the cable  21 . The spring washer  64  bears on one side against the washer  62 , and on the other side against the support  63 , in particular a surface of the support facing the washer  62 . The spring washer  64  thus exerts a force parallel to the longitudinal axis of the cable (see arrow  65 ). This force tends to move the washer  62 , and with it the screw  61  and the end  21 B of the cable, away from the other end of the cable. This force constitutes a pre-tensioning force as defined hereinbefore 
         [0134]      FIG. 7  illustrates a third embodiment of a pre-tensioning device  70 . 
         [0135]    In accordance with this embodiment, the end  21 B of the cable is provided with a thread  71  extending around the cable and over a length of approximately 10 mm. The thread is formed for example in a local excess thickness of the cable  21 . 
         [0136]    A nut  72  is screwed onto this thread  71 . The nut  72  forms a first stop element. 
         [0137]    The pre-tensioning device  70  also comprises a support  73  provided with an opening  73 A, through which the cable  20  extends. The cable  21  extends through the support  73 , without being fixed to this support. 
         [0138]    The support  73  is formed for example by a part of the external rail as shown in  FIG. 1 . Thus, the support  73  is fixed relative to the floor structure. 
         [0139]    In a variant the support  73  is fixed relative to the hull structure. 
         [0140]    The opening  73 A for example has a circular section in a plane orthogonal to the longitudinal axis of the cable, of diameter slightly greater than the diameter of the cable. 
         [0141]    The support  73  also comprises a cavity  73 B of cylindrical form, the axis of the cylinder being the same as the longitudinal axis of the cable  21  when tensed. A face  73 C of the cavity receives the opening  73 A. The face  73 C is preferably orthogonal to the longitudinal axis of the cable. The cavity  73 B is open on the side of the cylindrical cavity opposite the face  73 C, on the side of the nut  72 . A bushing  74  is inserted with force into the cavity  73 B. The cable  21  thus extends also through a central opening  74 A of the bushing  74 , without being fixed to the bushing. The bushing  74  is a bushing made of bronze, nitrogen shrunk-fit, which makes it possible to protect the support  73 , in particular when the support is formed by part of the external rail, made of aluminium. The bushing  74  has a cylindrical portion that fits in the cavity  73 B, and has an annular portion which has a greater thickness and which bears against a face  73 D of the support  73 . The face  73 D of the support is preferably parallel to the face  73 C. It extends orthogonal to the longitudinal axis of the cable. It is located on the side of the cavity  73 B opposite the face  73 C, and surrounds the open face of this cavity. 
         [0142]    The annular portion of the bushing  74  forms a second stop element. In a variant, the bushing  74  is omitted and it is directly the surface  73 D that forms a second stop element. 
         [0143]    A spacer  75  is disposed between the bushing  74  and the nut  72 . The spacer  75  is concentric with the cable  21  and has an inner diameter slightly greater than the diameter of the cable. Thus, the cable is not fixed relative to the spacer  75 . The spacer  75  bears on one side against the nut  72 , and on the other side against the bushing  74 . The spacer  75  thus exerts a force parallel to the longitudinal axis of the cable (see arrow  76 ). This force tends to move the nut  72 , and with it the end  21 B of the cable, away from the other end of the cable. This force constitutes a pre-tensioning force as defined hereinbefore. 
         [0144]    By adjusting the position of the nut  72  on the thread  71 , the pre-tensioning force exerted thanks to the spacer  75  is adjusted. This embodiment thus has the advantage of allowing a precise, simple and rapid adjustment of the pre-tensioning force. In particular, a dynamometric key can be used to tighten the nut  72 , which makes it possible to control the tightening torque of the nut  72  against the spacer  75 , and thus the pre-tensioning force exerted due to the spacer. 
         [0145]    In the example shown in  FIG. 7  the pre-tensioning device also comprises:
       a key  77  for holding the cable  21  in position through the bushing  74 ;   a tube  75 A for holding the spacer  75  in position between the nut  72  and the bushing  74 , the tube  75 A extending around the spacer  75  and having a length less than that of the spacer;   a bushing  75 B for holding the spacer  75  in position between the nut  72  and the bushing  74 , the bushing  75 B extending inside the spacer  75  and around the cable  21  and having a length less than that of the spacer and an inner diameter slightly greater than that of the cable  21 ; and   two lock-nuts  78  screwed on the thread  71  of the cable, for securing the positioning of the nut  72 . The lock-nuts  78  are connected to the cable  21  by a lock wire, which makes it possible to retain the nuts even if these were to unscrew.       
 
         [0150]    The person skilled in the art will be able to conceive numerous other variants of pre-tensioning devices, without departing from the scope of the present disclosure. 
         [0151]    It may be advantageous to preserve anti-crash connecting rods according to the prior art at some points of the fuselage of an aircraft. Nevertheless, three quarters of these anti-crash connecting rods can be replaced each by a respective connecting element according to the disclosure herein. The mass saving for an entire aircraft is thus considerable. 
         [0152]    It may also be advantageous to replace a cable  21  with a plurality of parallel cables. Series production of identical cables can thus be implemented. The same cables are then used for all aircraft models, whatever the mass of the floor structure and the mass of that which is to be supported by the floor structure (seats, passengers, luggage, etc.). It is the placement in parallel of a plurality of cables that makes it possible to withstand a forward acceleration of the aircraft of 9 g, whatever the mass subjected to this acceleration. 
         [0153]    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.