partition 13 deforms the lengthwise vertical wall 108 is drawn downward by the lower wall 15 of said fuselage 10 leading to the pairs of cross beams 103 104 that are drawn together in fig5 the lengthwise cross section view shows four cross beams 103 104 belonging to four pairs of adjacent cross beams 103 104 the pairs of cross beams 103 104 are placed parallel to each other of course it is possible to supply the floor 100 with more or fewer pairs of cross beams 103 104 in function of the length of the floor 100 the external ends 106 of the pairs of cross beams 103 104 are connected to the external lengthwise beams 101 102 in such a way as to allow a degree of freedom sufficient to pivot and allow bending of said pairs of cross beams 103 104 following the deformations of the fuselage 10 similarly the external ends 107 of the cross beams 103 104 are connected to the external lengthwise beams 108 102 in such a way as to allow a degree of freedom sufficient to pivot and allow bending of said pairs of cross beams 103 104 following the deformations of the fuselage 10 the shortening of the floor during the connection of the side walls 11 12 of the fuselage 10 is therefore possible by connecting the pairs of cross beams 103 104 to each other and by lowering the internal ends 107 of said cross beams 103 104 103 104 in the direction of the lower wall 15 of.