Abstract:
An engine attachment pylon for mounting an aircraft engine to an aircraft structure while minimizing vibrations induced into the engine attachment pylon during flight and operation of the engine. The engine attachment pylon comprises a rigid box like structure housing a resonator which is tuned to attenuate tension and compression vibrations experienced by the engine attachment pylon. The engine attachment pylon is primarily used in combination within another identical engine attachment pylon, both being linked together on a vertical plane within the fuselage by a hinge like junction, and each engine attachment pylon being raised approximately 30° from the horizontal axis of the fuselage.

Description:
RELATED APPLICATIONS 
     The present application claims priority to European Patent Application filed on Feb. 27, 2012 with application number 12157059.2, the entirety of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an engine attachment pylon for attaching an aircraft engine to a fuselage of an aircraft. 
     A known engine attachment pylon of this type is described in FR2943623 (U.S. Published Application 2012/0066937). It is an object of this invention to provide an improvement of an engine attachment pylon as described in FR2943623 (U.S. Published Application 2012/0066937). 
     SUMMARY OF THE INVENTION 
     According to the first aspect of the invention there is provided an engine attachment pylon, for mounting an aircraft engine to an aircraft structure, comprising a rigid structure housing a dynamic mass absorber which is tuned to absorb vibrations of the aircraft engine; the rigid structure substantially forming a box and comprising a first and a second attachment means to connect the engine and the fuselage respectively. 
     According to a second aspect of the invention there is provided an engine attachment assembly comprising a rear portion of an aircraft fuselage, two aircraft engines, and two engine attachment pylons wherein each engine attachment pylon connects each engine to the fuselage and wherein the engine attachment pylons according to any of the preceding claims are arranged such that the engine attachment pylons are joined on a vertical plane (P) within the aircraft fuselage by a junction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying drawings, of which: 
         FIG. 1  is a perspective view of a rear portion of a fuselage having two engines attached to it by means of two engine attachment pylons; 
         FIG. 2  is a similar view as  FIG. 1  showing a dynamic mass absorber located inside each engine attachment pylon according to the present invention; and 
         FIG. 3  is a detailed view of the resonator according to arrow F of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , there is shown a rear portion of a fuselage  10  of an aircraft having a central longitudinal axis (x). The description will be made using a conventional axis system, comprising a longitudinal (x), a horizontal (y), and a vertical (z) axis. The rear portion of the fuselage  10  comprises two engines  11 ,  12  each having a central longitudinal axis (a) parallel to the longitudinal axis (x) of the fuselage  10 . In this example, each engine comprises a nacelle  13 ,  14  for housing a compressor and combustion chamber, and a pair of counter rotating open fan blades  15 ,  16  providing thrust to the aircraft. Each engine is attached to the fuselage by means of an engine attachment pylon  17 ,  18 . Each engine attachment pylon comprises a rigid structure  19  covered by aerodynamic fairings, in particular a front fairing  20  which forms a leading edge and a rear fairing  21  which forms a trailing edge of the pylon. With reference to  FIG. 3 , the rigid structure  19  forms substantially a box, which comprises a front spar  22 , a rear spar  23 , connected together by a first plate attachment means  24  and a second plate attachment means  25  extending perpendicularly between each spar, and sealed with an upper  26  and a lower panel  27 . With reference to  FIG. 2 , both rigid structures  19  are joined together on a vertical plane (P) passing through the longitudinal (x) axis of the fuselage  10  by a junction  28 . Each rigid structure passes through openings in the fuselage, as explained in FR2943643 (U.S. Published Application 2012/0066937) and incorporated in the present description by reference. In this example, the rigid structures are raised by 30° from the horizontal (y) axis. The engine attachment pylons  17 ,  18  interface at the uppermost edge second structural members so as to form the junction  28  which is substantially a hinge. The first attachment means  24  is conventionally rigidly attached to the engine nacelle. The rigid structure  19  is attached to the fuselage  10  internally by means of struts, as explained in FR2943643 (U.S. Published Application 2012/0066937), but not shown in the figures. 
     The engine attachment pylon  18  further comprises a dynamic mass absorber  29 , or resonator, as shown in  FIGS. 2 and 3 , according to the present invention, housed within the rigid structure  19 . The terms dynamic mass absorber and resonator may be used interchangeably. With reference to  FIG. 3 , the resonator  29  comprises a damping member  30  attached at one end to the second attachment means  25  and movably attached at the other end to a load transfer means  31 . The load transfer means comprises  31  a lever  32  pivotally mounted around a pivot  33  and attached at one end to the damping member  30  and a fitting  34  at the other end. The fitting  34  attaches the lever  32  to the first attachment means  24 . The damping member  30  has a narrow width compared to its length and extends, in-use, in the direction between the engine  11  and the fuselage  10 . The damping member  30  comprises a lumped mass  35 , or suspended ring mass, which is preferably located in the vicinity of the first attachment means  24 . The pivot  33  is preferably a ball joint attaching the lever  32  to the end of a fixed member  36 , having a narrow width compared to its length and which is attached at its other end to the second attachment means  25 . 
     During flight and operation of the engines, vibrations comprising bending (B), torsion (TO), and tension (TE) and compression (C), as illustrated in  FIG. 1 , will be induced and transferred to the fuselage. The bending and torsion vibrations are attenuated by an arrangement of struts, which are not illustrated in the figure but are explained in FR2943643 (U.S. Published Application 2012/0066937). The struts serve to support the engine attachment pylons  17 ,  18  and reduce bending and torsion vibrations induced into the engine attachment pylon by the operation of the engine  11 ,  12  and during flight. The tension and compression vibrations in this example are attenuated by the resonator  29 . Tension and compression vibrations are experienced by the fitting  34 , and subsequently transferred to the damping member  30  by inducing oscillatory rotations in the lever  32  around the pivot  33 . Then, the amplitude of the displacements at the attachment point of the damping member  30  to the lever  32  is attenuated by the inertia of the lumped mass  35 , or ring mass, mounted onto the damping member  30 , thus acting altogether as a damping force. The size of the ring mass  35  is chosen so that the dynamic mass absorber  29  can dissipate or absorb the vibration of the engine  11 ,  12 . In particular, the weight of the lumped mass  35  is determined as a function of the amount of force required to react against the frequency of the vibrations seen at the location of the fitting  34 . 
     The principal advantage of this invention is to provide an engine attachment pylon  17 ,  18  which prevents tension and compression vibration from the engines  11 ,  12  from propagating into the cabin area of the fuselage. Also, the use of the junction  28  in the present invention minimizes any vibrations from one engine attachment pylon  17  from propagating into the other engine attachment pylon  18 . This is achieved because the junction  28  forms a hinge which isolates the movement from one engine attachment pylon  17  to the other  18 . 
     Another advantage of this invention is that the position of the lumped mass  35  being located in the vicinity of the first attachment means  24  prevents bending vibrations from being induced into the engine attachment pylon  17  due to the existence of the resonator  29 . Also, by implementing a lumped mass  35  as the means of damping, there is a reduced maintenance burden due to there being no moving parts and no hydraulic leakage. 
     Alternatively, the lumped mass  35  could be replaced by a hydraulic damper. The pivot  33  may also be changed such that it is not a fixed member  36  having a narrow width compared to its length and extending to the second structural member  25 , but takes the form of a rigid strut attached between the upper  26  and lower panels  27 , at the location of the pivot  33 . 
     It will be appreciated that engine attachment configurations other than a rear mounted configuration with two engines mounted on engine attachment pylons  17 ,  18  raised by 30° from the horizontal (y) axis of an aircraft fuselage are possible. The engine attachment pylon according to the present invention could easily be adapted for other configurations. One such configuration would be to attach the second structural member to the fuselage. In this case, there is no need for a junction connecting the two engine attachment pylons and it would be appreciated that there would be a reduction in structural mass as a result. The engine attachment pylon could also be relocated to beneath the wing. In this case, the resonator within the engine attachment pylon would extend vertically in the direction between the engine and the wing. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.