this reason a drain 5 is placed on the lower part of the rss 3 zone on the trailing edge 6 traditionally this drain 5 placed astride the trailing edge 6 has an elliptical cross section the small axis 7 fig2 being horizontal and orthogonal to the trailing edge 6 the drain 5 has its longitudinal axis slightly raised of order 7 degrees above the axis of the aerodynamic flow in flight the major axis 8 of the elliptical cross section of the drain whose outlet has a beveled edge is shown in fig3 the plane of the outlet is parallel to the trailing edge 6 the drain 5 projects behind the trailing edge 6 a distance 9 on the order of about 120 mm for an approximately drain 5 with a 126 mm major axis 8 and approximately 58 mm minor axis 7 the dimensions of the axes are taken on the outside of the conduit forming the drain 5 the walls of which have a thickness on the order of about 3 mm fig4 illustrates a mode of making the drain 10 according to the invention substituted for drain 5 made up of the conduit flattened on its sides to better understand the shape of the drain 10 fig5 to 8 will also be referred to fig5 is a lateral elevation view of the drain 10 making apparent on a largely flat lateral side 11 a of the drain 10 an inclined opening in the shape of a louver 12 having a generally narrow rectangular section more specifically the shape of a parallelogram and a.