Abstract:
A drain, for example for an aircraft engine support strut, arranged on the trailing edge of the rear secondary structure of the strut. The drain includes a conduit with a substantially horizontal axis and a substantially rectangular cross-section, taken in a plane parallel to the trailing edge, the conduit closed at an outer extremity by a terminal portion with a substantially ogival cross-section taken in the axis of the conduit and including at least one opening for drainage with an elongated shape on at least one of the opposing lateral walls.

Description:
RELATED APPLICATION 
     The present application claims priority to French Application No. 03 14891 filed Dec. 18, 2003. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns drains installed in the fairings of the rear strut and intended to evacuate potential leaks of fluids that could be inflammable, which might originate from tanks, piping or hydraulic systems located above said rear fairing in a structure integrated with the engine strut and more commonly called a rear secondary structure (RSS). 
     These drains are pipes with a generally elliptical cross section of non-negligible size which can reach, for example, a dimension of 150 mm ×58 mm for the largest aircraft, and which projects to the rear of the rear fairing of the engine strut and generates a drag which has an impact on fuel consumption. 
     Another disadvantage of these drains is their insufficient capacity for adjusting the aspiration level. The geometry of these drains effectively provides access only to a single aspiration level. 
     Another problem posed by these drains because of their size is the risk of introduction or installation of a wild fowl that could obstruct the conduit. 
     The present invention aims to alleviate these various inconveniences by proposing a new geometry for this type of drain. 
     SUMMARY OF THE INVENTION 
     To that end, the purpose of the invention is a drain particularly for the aircraft engine support strut, arranged on the trailing edge of the rear secondary structure of said strut, comprising a conduit with a substantially horizontal axis, a substantially rectangular cross-section taken in a plane parallel to said trailing edge, the conduit closed at its outer extremity by a terminal part with a substantially ogival cross-section taken in the axis of the conduit, wherein the conduit includes at least one opening for drainage with an elongated shape on at least one of the opposite lateral walls. 
     Depending on the implementation, said conduit can be symmetric with respect to the vertical plane passing through said trailing edge, and can include a drainage opening on its two opposite lateral walls, the major axis of which is parallel to the trailing edge and these two openings can be symmetric. 
     Such a drain forms a flattened conduit fitted on its lateral flanks, which are largely flat, with elongated openings in the form of louvers assuring a more effective drainage through the formation, at the outlet of the louvers, of zones of more significant low pressure than that generated at the outlet of traditional drains; the drain according to the invention additionally generates a drag that is sensibly reduced compared to that with the same traditional drains having an equivalent drainage capacity. 
     The louvers of such a drain can have—in comparison with a conventional drain having an elliptical drainage section of 4900 mm 2 , 120 mm major axis and 52 mm minor axis, and equivalent drainage capacity—a generally rectangular shape about 230 mm long and about 11 mm wide, which is additionally intrinsically able to prevent any intrusion by wild fowl in particular. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other properties and advantages will be seen in the description below of a method of implementing the device from the invention; the description is given solely as an example and in light of the attached drawings where: 
         FIG. 1  is a perspective view of the rear of an engine of strut. 
         FIG. 2  is a partially enlarged view showing in more detail the drain from the part called rear secondary structure (RSS) of the strut. 
         FIG. 3  is a side view of the drain from  FIG. 2 . 
         FIG. 4  is a view analogous to  FIG. 2  showing a drain according to the invention in place of the conventional drain. 
         FIG. 5  is a schematic side view of the drain from  FIG. 4 . 
         FIG. 6  is a cross-section of the drain from  FIG. 5  along the line VII—VII. 
         FIG. 7  is a schematic cross-section of the drain from  FIG. 5  along the line VII—VII. 
         FIG. 8  is a comparative view of the cross-sections of the drain according to the invention and a conventional drain with an elliptical cross section. 
         FIG. 9  is a diagram illustrating the aerodynamic flow near a louver from the drain according to the invention. 
         FIG. 10  is a schematic view showing the placement of the drain in the RSS structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows schematically: an aircraft engine  1 ; an engine support strut  2 , called engine strut; a rear secondary (RSS)  3 ; and a rear fairing  4  of the strut located proximate the rear of the engine  1 . 
     Various equipment systems such as extinguishers, tanks and piping for hydraulic fluids, likely to leak liquid following, for example, loosening of the pipe joints, are traditionally installed in the RSS  3 . For 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  ( FIG. 2 ) 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  FIG. 3 ; 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. 
       FIG. 4  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 ,  FIGS. 5 to 8  will also be referred to. 
       FIG. 5  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 major axis  13  parallel to the trailing edge  6  of the structure  3 , the drain  10 &#39;s own trailing edge  14  also being preferably generally parallel to the edge  6 . 
       FIG. 8  shows a comparison of the cross sections  15 ,  16 , taken perpendicularly to their axis, of the drain  10  according to the invention and drain  5 , respectively. It will be noted that the cross section  15  of the drain  10  is rectangular with rounded corners for aerodynamic reasons and has a length L slightly greater than the major axis  8  of the elliptical cross section  16  of the drain  5 , whereas the width  1  of the cross section  15  is slightly smaller than the minor axis  7 . 
     In  FIG. 8  the dashed lines  17  and  18  symbolize the two louvers  12  put in the opposing parallel sides  11   a  and  11   b  (refer to  FIG. 7 ) of drain  10 . 
       FIG. 7  shows a cross-section parallel to the axis of the drain  10 . Note that the latter is symmetric with respect to the vertical plane containing the trailing edges  6  and  14  and that the conduit forming the drain ends in a part  19  with an ogival cross-section, also for aerodynamic reasons. 
     In  FIG. 5 , it should be noted that the louvers  12  do not extend all the way at the upper and lower edges of the drain  10  and stop ( FIG. 8 ) at the beginning of the rounded zones  20  of the corners of the drain  10 . Therefore, there remains a small zone below the drain  10  that will not be drained. To resolve this, a hole  21  can be placed in the bottom wall of the drain  10 , in the area of the trailing edge  14 , as depicted in  FIG. 5 . 
     In  FIG. 6 , the width  22  of the louvers  12 , taken between a flange of side  11   b  and the flange of the terminal part  19 , is shown. As an example, the width  22  of the louvers  12  is on the order of about 11 mm for a length  13  ( FIG. 5 ) on the order of about 238 mm. 
     In  FIG. 7 , the contour  23  of the drain  5 , slightly larger than that of drain  10 , is shown. 
       FIG. 9  shows the aerodynamic flow around the louver  12  of drain  10 . The wall  24  of the terminal part  19 , delimiting the louver  12  by its edge  25 , is slightly recessed towards the interior of the drain  10 , with respect to the adjacent part  26  intermediate the part  24  and the nose  14  (see  FIG. 7 ) of the ogive, part  26  of which is in the curve (dashes  27 ) of this side  11   b  of the drain  10 . 
     A zone  28  of maximal low-pressure is created deflecting the flux of the grazing flow E by a few degrees towards the interior of the drain  10  near the louver  12 . 
     The flow E is next taken by the outer side of the wall  24  and accelerated at  29 . The role of wall  24  is to take this flow to prevent it from penetrating into the drain  10 . 
     The angle formed between the tangent to the wall  26  and the outer face of the wall  24  is on the order of about 30 degrees. 
     Tests showed that in the zones  28  of the louvers  12  low-pressure regions are created corresponding to negative pressure coefficients K P  on the order of approximately −0.34 in comparison with low-pressure regions with a K P  coefficient of approximately −0.19 at the outlet of the conventional drain  5  with the same drainage capacity. The drains tested had profiles identical to those from  FIG. 8 . 
       FIGS. 10  show a practical method of making the drain  10  according to which the part of the drain  10  properly called  10 ′ is extended in its part plugging into the stem post made up by the trailing edge  6  of the structure  3  and two symmetric parts  10 ″ intended to come flush with the wails of the two sides of the structure  3 , the stem post of the latter consequently being cut to receive the unit  10 ′– 10 ″. 
     Generally the louvers  12  are parallel to the trailing edge  6  and in the immediate area of this edge, and on both sides. 
     The dimensions and the shape of the louvers  12  can of course vary depending, for example, on the desired drainage capacity. 
     In the embodiment described, the ratio between the length  13  ( FIG. 5 ) and the width  22  ( FIG. 6 ) of each louver  12  is about 20, but it could be different according to the applications, specifically depending on the desired drainage capacity, the flow cross-section of the louvers  12  depending on this capacity. The width  22  must preferably on the order of about 10 to 20 mm to avoid the intrusion of wild fowl. 
     Generally, the aggregate flow cross-section of the two louvers  12  will be slightly greater than the internal cross-section of the drain conduit  10  upstream from the louvers  12 . 
     The shape of the external cross-section of the drain  10  shown with a rectangular contour  15  in  FIG. 8  can also vary, with it understood that the width  1  will be slightly less than the minor axis  7  of the drain  5  with an elliptical cross-section of equivalent drainage capacity. The ratio of the length L of the cross-section  15  to the width  1  is preferably on the order of about 2.8 as shown in the example from  FIG. 8 . This ratio can vary in the range from about 1 to about 10. 
     The sides  11   a  and  11   b  of the drain  10  are preferably generally flat, but could potentially be slightly convex. 
     Beyond the aspiration capacity of a drain like  10 , noticeably greater than that of a conventional drain  5  not only in flight but also taxiing on the ground, the aerodynamic behavior of drain  10  in flight is very favorable in comparison with that of drain  5 . In fact, the resulting drag is significantly reduced notably because of the fact of the creation of the aspiration zone on the sides of the drain  10 , near the louvers  12 , and not right at the rear nose  19  of the drain  10  which is profiled, whereas in the conventional drain  5 , the aspiration is created behind the drain  5 , the low pressure thereby formed downstream directly and more amply contributes to the creation of drag. 
     As an example and for the embodiment described, the drain  10  projects on the trailing edge  6 , axially to the aerodynamic flow, a distance on the order of about 120 mm equivalent to distance  9  of drain  5 .