Abstract:
A pylon for suspending an engine beneath an aircraft wing, capable of being attached by one end to a casing of the engine and by another end to the wing is disclosed. The pylon includes at least one articulation actuated by a actuator making it possible to change the height position of the engine on the ground and in flight.

Description:
The present invention relates to a pylon for suspending an engine under an aircraft wing, and an engine attached under a wing with a pylon of this type. 
     BACKGROUND OF THE INVENTION 
     In turbofan engines, the air entering the turbomachine is divided into a primary flow or hot flow passing through a compressor which supplies a combustion chamber arranged downstream and into a secondary flow or cold flow, providing a considerable portion of the thrust, which flows around the compressor and which is discharged with the hot gases. 
     In order to restrict the consumption of fuel and the noise level, the engine manufacturers seek to increase the rate of dilution which is equal to the ratio between the output flow of cold air and the output flow of hot air, which leads to an increase in the diameter of the turbomachine. Because these engines are installed under the wings, the increase in the rate of dilution is limited by the need to have a minimal distance between the nacelle, that is to say the outer envelope of the turbomachine, and the ground. 
     For safety reasons, the engine is usually positioned upstream of the wing in order that, in the event of a shattering of a rotor disk, for example, the debris is prevented from reaching the portions of the wing where the fuel is stored. For the same reason, the engines are not incorporated into the wing. 
     A first approach would consist in increasing the height of the landing gear in order to increase the distance between the turbomachine and the ground. However, this solution is not satisfactory because it leads to a substantial increase in the cost and weight of the aircraft. A second approach consists in bringing the turbomachine closer to the wing and therefore reducing the distance between the nacelle and the wing. The air circulating in this space is thus accelerated, which may cause the formation of shock waves inducing a considerable increase in aerodynamic drag. 
     It is however preferred, in the prior art, to maintain a sufficient ground clearance and bring the engine closer to the wing, despite the disadvantages that that comprises. 
     SUMMARY OF THE INVENTION 
     The subject of the present invention is a pylon for suspending an aircraft engine which avoids these disadvantages of the prior art in a simple, effective and economical manner. 
     Accordingly it proposes a pylon for suspending an engine beneath an aircraft wing, capable of being attached by one end to a casing of the engine and by another end to the wing, which comprises at least one articulation and a motorized means making it possible to change the height position of the engine between a “cruise” position and a takeoff/landing position. 
     The incorporation according to the invention of an articulation in the pylon allows a relative movement of the engine relative to the wing and relative to the ground. The invention therefore makes it possible to adapt the position of the engine relative to the wing according to the various phases of flight. When the aircraft is on the ground or in the takeoff or else landing phase, the engine is brought closer to the wing so that the distance between the nacelle and the ground is sufficient. In the cruise phase, the engine may be moved away from the wing, which makes it possible to limit the aerodynamic drag and therefore optimize fuel consumption. 
     In addition, such an articulated pylon makes it possible to make maintenance operations easier by allowing the engine to be lowered. 
     The motorized means for changing the height position of the engine may for example be an electric or hydraulic actuator. 
     This actuator makes it possible to control the movement of the engine relative to the wing. In the case of a hydraulic actuator, the latter may be connected to the hydraulic circuit of the landing gear for example, thereby allowing it to be supplied with power. 
     In addition, if a blade is lost, the hydraulic actuator may absorb a portion of the energy released by the separation of a blade from its attachment point. 
     Advantageously, the articulation comprises at least one deformable quadrilateral comprising two link rods whose ends are articulated about horizontal transverse axes on two portions of the pylon, of which one is attached to the engine casing and the other to the wing. 
     According to a feature of the invention, the two link rods are parallel and have identical lengths. 
     The two link rods may also have different lengths which makes it possible, by actuating the actuator, to incline the engine relative to the horizontal in the take off phase in order to optimize the intake of air into the turbomachine. 
     The invention also relates to an aircraft engine attached under a wing by a suspension pylon, wherein this pylon is of the type described above. 
     Typically, the variation in the height position of the engine beneath the wing is approximately 20 cm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other details, advantages and features of the invention will appear on reading the following description made as a nonlimiting example with reference to the appended drawings in which: 
         FIG. 1  is a schematic view in axial section of a suspension pylon according to the invention, the engine being in the high position; 
         FIG. 2  is a schematic view in axial section of this pylon, the engine being in the low position. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is first of all made to  FIG. 1  which schematically represents a turbojet  10  coupled by a pylon  12  upstream of and under the wing  14  of an aircraft. 
     The turbojet comprises a nacelle (not shown) attached to a casing  18  of cylindrical shape which surrounds the front portion of the engine of which only the downstream portion is visible and a fan wheel (not visible) mounted inside the casing  18 . This fan wheel is rotated by the turbine of the turbojet in a manner well known to those skilled in the art. 
     When the engine operates, the air entering upstream, represented by the arrows E, is divided into a primary flow and a secondary flow respectively. The primary flow supplies an intake compressor, then is mixed with fuel and burned in the combustion chamber. The combustion gases pass through a turbine in order subsequently to be discharged into an exhaust casing  20  around an exhaust cone  22  as shown by the arrow P. The secondary flow (arrow S), flows around the body of the engine and represents most of the thrust in a high dilution rate engine. 
     The suspension pylon  12  is formed in this example of two portions, upstream  24  and downstream  26 , the downstream portion  26  being attached under the wing  14  of the aircraft and the upstream portion  24  being attached to the turbomachine  10 . The upstream portion comprises an upstream arm  28  extending obliquely downward and attached at its upstream end to a high-pressure compressor casing  30 . The arm  28  is connected at its downstream end to a portion  32  whose downstream end is attached to the exhaust casing  20 . The upstream portion  24  and downstream portion  26  are connected at their downstream and upstream ends by link rods  42  whose ends are articulated on the upstream portion  24  and downstream portion  26  about horizontal transverse axes  34 ,  36  and  38 ,  40 , respectively, so as to form an articulated quadrilateral. In the embodiment shown in the drawings, the link rods  42  have the same length and therefore form a deformable parallelogram. 
     A hydraulic or electric actuator  44  comprising a cylinder  46  and a piston rod  48  is mounted between the opposite articulation axes  34 ,  40  of the parallelogram, one end of the cylinder being articulated on the articulation axis  40  of the downstream portion  26  of the pylon  12  while one end of the piston rod  48  is articulated on the articulation axis  34  of the upstream portion  24  of the pylon  12 , this installation making it possible to change the position of the engine relative to the wing, on the ground and in flight. 
     During the operation of the turbomachine  10 , there are several flight phases during which the distance between the turbomachine  10  and the wing  14  must be changed. When stationary and during takeoff, the actuator makes it possible to keep the turbomachine  10  in a high position in order to maintain a maximal turbomachine/ground distance, the turbomachine  10  then being close to the wing  14 . During a cruise phase, the actuator  44  makes it possible to move the turbomachine  10  away from the wing  14  in order to limit the effects of aerodynamic drag and therefore reduce fuel consumption. Finally, on landing, the turbomachine  10  is returned to the high position corresponding to take off in order to resume sufficient ground clearance. The actuator makes it possible for example to move the turbomachine  10  over a height of approximately 20 cm. 
     It should be noted that the increase in aerodynamic drag and therefore the increase in fuel consumption due to the closeness of the turbomachine  10  relative to the wing  14  during the takeoff and landing phases is largely compensated by the reduced consumption achieved during the cruise phase thanks to moving the turbomachine  10  away in order to limit drag and to the use of a high dilution rate turbomachine  10 . In addition, the take off and landing phases are phases which do not last very long compared with the cruise phase. 
     As a variant, the ends of the actuator may be attached to the other two opposite articulation axes  36 ,  38  of the parallelogram, the actuator working in a reverse direction relative to the configuration represented in the drawings. 
     In another variant, it is possible to provide a quadrilateral articulated on either side of the actuator  44  in order to ensure a better hold of the turbomachine  10  and to better distribute the thrust of the turbomachine  10  over the whole of the pylon  12 . 
     In yet another variant, the link rods  42  have different lengths, which makes it possible to change the inclination of the axis  50  of the turbomachine relative to the wing while moving the turbomachine further away or closer to the wing, in order in particular to improve the performance of the turbomachine  10  on take off. 
     In other variants of the invention, the articulation of the pylon may be provided between the pylon and the engine, or between the pylon and the wing.