Abstract:
A propulsion assembly includes an engine surrounded by a nacelle, a means for draining the fluids from the engine and a means for guiding said fluids to a retention box. The retention box is arranged outside the engine and has a cavity for storing drained fluids. The retention box is fixed to a cowling of the nacelle and supported thereby.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a propulsion assembly comprising a box for retaining drained liquids, these liquids being, for example, oil, water and/or fuel. 
       PRIOR ART 
       [0002]    The prior art includes the document U.S. Pat. No. 5,285,636. 
         [0003]    An aeroplane propulsion assembly generally has means for draining liquids (oil, water and/or fuel) from the engine to prevent these liquids from collecting and disrupting the operation of the engine. The oil and fuel are drained owing to the fact that the dynamic seal technologies (pumps, AGBs, chokes, actuators, etc.) do not allow for perfect sealing. Therefore, the liquids that pass through the dynamic seals have to be drained to prevent them leaking into the engine. The water is drained to prevent water-retention areas, which often lead to corrosion. 
         [0004]    In the current state of the art, the drained liquids can be evacuated directly to the outside. The means for draining the liquids from the engine can also be connected by conveying means, such as ducts, to a retaining box comprising a cavity for storing the drained liquids. This retaining box is located within the propulsion assembly. It is attached to the engine and is generally located in the lower portion of the propulsion assembly so that the drained liquids flow into the conveying means and into the storage cavity as a result of gravity. 
         [0005]    The propulsion assembly further comprises a drainage mast for discharging the drained liquids to the outside. This mast is supported by the nacelle and protrudes towards the outside of the nacelle. Said mast is also located in the lower portion of the propulsion assembly, facing the retaining box, and collects liquids exiting the box. The mast comprises a lower end comprising an opening for discharging the liquids to the outside of the nacelle. When the storage cavity in the retaining box is emptied, the liquids are discharged as far as to the opening in the mast and then discharged to the outside of the propulsion assembly. 
         [0006]    In some propulsion assemblies, the opening kinematics of the cowls does not give manual access to the retaining box, nor does it allow for a leak-tight hydraulic connection between the conveying means and said box. It would be conceivable to not equip said propulsion assemblies with a retaining box, in which case the outlets of said conveying means would open directly opposite the mast and would dispense the drained liquids in the region of the mast as soon as said liquids are collected. However, some aircraft manufacturers want their propulsion assemblies to have boxes for retaining the drained liquids, in particular in order to have better control over the time at which said liquids are discharged to the outside. 
         [0007]    The present invention proposes a simple, effective and economical solution to this problem. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention proposes a propulsion assembly comprising an engine surrounded by a nacelle, means for draining liquids from the engine and means for conveying said liquids to a retaining box outside the engine, the retaining box comprising a mast having an aerodynamic profile which comprises an internal cavity for storing the liquids and at least one opening for discharging the liquids held in the cavity, characterised in that this retaining box is attached to a cowl of the nacelle and is supported thereby, and comprises, at one end of the mast, an attachment plate comprising means for attachment to the cowl of the nacelle and connection means that interact with said liquid conveying means. 
         [0009]    According to the invention, the retaining box is no longer carried by the engine, but is instead carried by the nacelle of the propulsion assembly. The retaining box thus takes up less space, and it is conceivable for said discharge mast to be rigidly connected to and integral with the box such that at least one portion of the cavity for storing the drained fluids can be housed within the mast. This invention is particularly, but not exclusively, suitable for turbine engines having less space between the nacelle and the engine. 
         [0010]    The mast preferably has a radial dimension which is such that the liquids are discharged outside of the boundary layer located on the outer surface of the nacelle during flight. In other words, the radial dimension of the profiled portion of the mast is preferably greater than the thickness of this boundary layer. 
         [0011]    The retaining box can be attached by its plate to a fixed or removable cowl of the nacelle. 
         [0012]    The plate can be covered by a heat protection sheet. 
         [0013]    The retaining box is always located at 6 o&#39;clock in terms of the dial of a clock. 
         [0014]    The present invention also relates to a box for retaining drained liquids for a propulsion assembly as described above, the retaining box comprising a mast having an aerodynamic profile, said mast comprising an internal cavity for storing the liquids and at least one opening for discharging the liquids held in the cavity, characterised in that it comprises, at one end of the mast, an attachment plate comprising means for attachment to a nacelle cowl of said propulsion assembly and connection means for interacting with means for conveying drained liquids. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will be better understood and other details, features and advantages of the invention will become more apparent upon reading the following description given by way of non-limiting example and with reference to the accompanying drawings, in which: 
           [0016]      FIG. 1  is a schematic perspective view of an aircraft propulsion assembly according to the invention; 
           [0017]      FIG. 2  is a schematic enlarged view in perspective and in axial section of part of the propulsion assembly of  FIG. 1 ; 
           [0018]      FIG. 3  is another schematic perspective view of part of the propulsion assembly of  FIG. 1 ; 
           [0019]      FIGS. 4 and 5  are schematic perspective views of the discharge mast according to the invention; and 
           [0020]      FIG. 6  is a schematic axial cross section of the discharge mast according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Reference is first made to  FIG. 1 , which shows an aircraft propulsion assembly  10  comprising an engine  12  (such as a bypass turbojet engine, shown schematically by dashed lines) fitted inside a nacelle  14 . 
         [0022]    The engine  12  comprises, from upstream to downstream in the direction of flow of the gases (from left to right in the drawing), a fan, a compressor, a combustion chamber, a turbine, and an exhaust nozzle for ejecting the combustion gases. The nacelle  14  comprises an air inlet, cowls and an inverter, the cowls defining the outer surface of the propulsion assembly. 
         [0023]    The propulsion assembly  10  comprises a mast  16  for discharging drained liquids, said mast being oriented substantially radially and protruding on the outer surface of the nacelle. Said mast is located in the lower portion of the propulsion assembly, at 6 o&#39;clock in terms of the dial of a clock. 
         [0024]    Many types of liquid flow into the propulsion assembly  10 , in particular fuel, oil for lubricating the bearings of the rotating parts, and water, which can be drawn in by the ventilation scoops or formed by the condensation on the engine. 
         [0025]    During operation, said liquids are drained so that they do not collect and disrupt the operation of the propulsion assembly. The propulsion assembly comprises means for draining said liquids (such as drainage tubes), which are connected to a box for retaining said liquids by means for conveying liquids, such as ducts. According to the invention, said retaining box is carried by the nacelle  14  of the propulsion assembly. 
         [0026]      FIGS. 2 to 6  show an embodiment of the retaining box  17  according to the invention, which is incorporated in the discharge mast  16  and which comprises, on its radially outer end, a plate  22  for attachment to the nacelle  14 . 
         [0027]    In the example shown, the plate  22  has a substantially parallelepiped shape and is attached to cowls of the nacelle  14 . Said plate comprises openings  24  which are aligned with openings  26  in the nacelle for passing through nut and bolt-type means. The mast  16  has an aerodynamic profile and passes through a radial opening  28  in the nacelle. The retaining box  17  is fitted in this opening by being radially translated from the inside of the nacelle until the plate  22  abuts the inner surface of the nacelle. A seal can be provided and intended to be compressed between the plate and the nacelle. 
         [0028]    The plate  22  further comprises studs  30  for attaching a heat protection shield (not shown) and means  32 ,  34  for connecting the outlets  20  of the ducts  18  for conveying the drained fluids. 
         [0029]    These connection means firstly comprise channels  32 ,  34  in which the outlet ducts  18  are fitted, the radially outer ends of said channels  32 ,  34  opening onto the radially outer surface of the plate  22 . The channels  32  (four in the example shown) have a circular cross section and their radially outer outlets form openings that are aligned one behind the other, the peripheral edges of these openings being chamfered or having a rounded convex cross section. One duct  18  is designed to be fitted in each of said openings. 
         [0030]    The channel  34  has an elongate cross section and its radially outer outlet forms a clearance for receiving at least two other ducts  18 . The radially external end of said channel  34  forms a radially outer pipe, which protrudes on the radially outer surface of the plate  22 . 
         [0031]    The radially inner ends of the channels  32 ,  34  are in fluid communication with the inner cavity  36  of the retaining box  17 , which is in turn in fluid communication with one or more channels  38  for discharging the liquids ( FIG. 6 ), each of these channels  38  being able to have means for the controlled release of the liquids. 
         [0032]    In this case, there are two channels  38  and they are formed on the radially outer end portion of the mast. Their radially outer outlets form two circular openings, which are located upstream and downstream of the mast  16 , respectively. 
         [0033]    The profiled portion of the mast  16 , which protrudes on the outer surface of the nacelle, has a height H or a radial dimension that is greater than the thickness of the boundary layer on the nacelle during operation, such that the liquids discharged from the cavity  36  are ejected by the channels  38  outside of said boundary layer.