Abstract:
A main landing gear for aircraft having a fuselage, a wing and a jet engine on opposite sides of the fuselage and housed in a nacelle attached to the wing. The main landing gear includes a landing gear at each side of the wing having wheels coupled to a driving device that moves the wheels between stowed and deployed positions. The engine nacelles each include a well located laterally with respect to the jet engines and configured as a housing space for stowing the wheels of the landing gears.

Description:
RELATED APPLICATION 
     This application claims priority to and incorporates by reference European Patent Application No. 14382071.0 filed on Feb. 27, 2014 
     FIELD OF THE INVENTION 
     This invention relates to commercial aircraft and more particularly to aircraft having a wing-mounted main landing gear (MLG). 
     BACKGROUND OF THE INVENTION 
     Most turbofan-powered commercial aircraft favor body or wing-mounted main landing gear arrangements. In both cases, the choice implies the provision of a wheel well large enough to fit the wheels and a driving device comprising a strut joined to the wheels and ancillary elements for moving the wheels from the deployed position to the stowed position and vice versa. 
     In the former case, the installation of an aerodynamic fairing that covers the MLG in its stowed position may be required in order to minimize drag. 
     In the latter, the wheel well compromises the sizing and manufacturing of the wing torsion box. In the early stages of commercial jet development, this situation was palliated by the introduction of the “Yehudi”, a kink in the wing planform trailing edge that increases the wing root chord and hence, the available volume for MLG stowage. 
     Regardless of where the MLG is mounted, the wheel well is commonly covered and sealed in cruise by the landing gear doors. These doors may or may not entirely cover the MLG from the flow, e.g. B737, but have an impact on the wing/fuselage skin and on the airframe noise during approach and landing configurations. 
     Common to both scenarios is the complex kinematics needed to achieve efficient movement of the wheel bogie/truck. Needless to say, these elements undergo high loads during landing, taxi and static conditions, which make said components large and heavy. 
     Therefore a reduction of the weight and complexity of the MLG attachment is highly sought after by the aeronautic industry. 
     This invention is addressed to the attention of that demand. 
     SUMMARY OF THE INVENTION 
     The invention refers to a MLG arrangement for aircraft comprising a fuselage, a wing and at least one jet engine at each side of the wing housed in a nacelle attached to the wing. 
     The MLG comprises a landing gear at each side of the wing having one or more wheels coupled to a driving device arranged for moving them from a stowed position to a deployed position and vice versa. The engine nacelles include wells located laterally with respect to the jet engines and configured as a housing space of the one or more wheels of each landing gear in its stowed position. Each driving device comprises a strut attached by one end to the load-bearing structure of the wing in a rotatory manner and by the other end to the one or more wheels. 
     Each landing gear may be configured with a single wheel or with a wheel truck including two or more wheels and the MLG may be configured with one or two landing gears at each side of the wing. 
     Advantageously the jet engines are turbofan engines. The large diameter of their nacelles, particularly in turbofan engines having a bypass ratio greater than 10, facilitates the housing of the wheels of the landing gears inside them. 
     Advantageously the driving device of each landing gear is arranged for moving the one or more wheels in a direction parallel to the X-Z plane of the aircraft. 
     In a first embodiment for an aircraft where the load-bearing structure of each side of the wing is a torsion box, the driving device of each landing gear comprises a strut configured with a fixed length and a first guiding element of fixed length having one end attached to the rear spar of the torsion box and the other end attached to the strut in an sliding manner. 
     In a second embodiment, the driving device of each landing gear comprises a strut configured with a variable length and a second guiding element of variable length having one end attached to the nacelle and the other end fixedly attached to the strut. 
     Other characteristics and advantages of the present invention will be clear from the following detailed description of embodiments illustrative of its object in relation to the attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 a  and 1 b    are frontal views of an aircraft with a nacelle-housed MLG illustrating two embodiments of the invention. 
         FIG. 2  is a plan view of an aircraft having in its left side (assuming that the reference axis is the flight direction) a conventional MLG and in its right side a MLG according to the invention for comparative purposes. 
         FIGS. 3 a  and 3 b    are schematic side views of the arrangement of a nacelle-housed MLG in an aircraft illustrating a first embodiment of the MLG kinematics. 
         FIGS. 4 a  and 4 b    are schematic side views of the arrangement of a nacelle-housed MLG in an aircraft illustrating a second embodiment of the MLG kinematics. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In reference to a commercial aircraft of a typical configuration comprising, as shown in  FIGS. 1 a  and 1 b   , a fuselage  11 , a wing  13 , a horizontal tail plane  17 , a vertical tail plane  19  and two wing-mounted jet engines  21  housed in nacelles  23 , the basic feature of the invention is that the MLG is arranged with the wheels  27  housed in wells located in the sides of the aft section of the nacelles  23  when they are in their stowed positions. 
     For a better illustration the wheels  27  of the MLG are shown in  FIGS. 1 a  and 1 b    in their deployed position in the left side and in their stowed position in the right side. 
     In the embodiment shown in  FIG. 1 a    the wheel wells are located at both sides of the jet engines  21 , in a vertically centered position with respect to them and the nacelles  23  have an oval aerodynamic shape enclosing the wheel wells. 
     In the embodiment shown in  FIG. 1 b    the wheel wells are located at both sides of the jet engines  21  in a low position with respect to them and the nacelles  23  have a bulged oval aerodynamic shape enclosing the wheel wells. 
     In both cases the nacelles  23  includes a door (not shown) to be opened when the wheels  27  are deployed and to be closed when they are stowed. 
     In the embodiments shown in  FIGS. 1 a  and 1 b   , the MLG comprises four single landing gears  25  each of them comprising a wheel  27  and a driving device  29 . 
     In other embodiments (not shown) the MLG comprises two single landing gears  25  arranged in the lateral side of the nacelles  23  closer to the fuselage  11 . 
     In similar embodiments to the aforementioned, the single wheel  27  can be substituted by a truck wheel. 
     The different arrangement of the MLG of the invention with respect to a conventional MLG arrangement is illustrated in  FIG. 2 . In the former the wheels (referenced with the number  27 ′) are stowed in the engine nacelle  23  while in the latter they are stowed in a ventral fairing  32 . In the former the wheels (referenced with the number  27 ″) are deployed at a position not so close to the fuselage  11  as the deployed position of the wheels  31  of the latter. 
       FIGS. 3 a  and 3 b    show the arrangement of an embodiment of a single landing gear  25  comprising a wheel (referenced with the number  27 ′ in the stowed position and with the number  27 ″ in the deployed position) and a driving device comprising a kinematic mechanism formed by a strut  41  and a first guiding element  43 .  FIG. 3 a    shows the strut  41  attached to the wheel  27 ′ in the stowed position inside the nacelle  23 .  FIG. 3 b    shows the strut  41  attached to the wheel  27 ″ in the deployed position on the ground. The strut  41 , having a fixed length, is attached by one end to the forward spar  51  of the torsion box  50  (the load bearing structure of the wing  13 ) in a rotatory manner and by the other end to the wheel. The first guiding element  43 , also having a fixed length, is attached by one end to the rear spar  53  of the torsion box  50  and by the other end to the strut  41  in a sliding manner so that it can be displaced from the point  61  to the point  63  of the strut  41  during a deploying operation of the wheel or vice versa in a stowing operation. 
       FIGS. 4 a  and 4 b    show the arrangement of another embodiment of a single landing gear  25  comprising a wheel—referenced with the number  27 ′ in the stowed position and with the number  27 ″ in the deployed position—and a driving device including a kinematic mechanism formed by a strut  42  and a second guiding element  44 .  FIG. 4 a    shows the strut  42  attached to the wheel  27 ′ in the stowed position inside the nacelle  23 .  FIG. 3 b    shows the strut  42  attached to the wheel  27 ″ in the deployed position on the ground. The strut  42 , having a variable length (by means of, for example, a telescopic arrangement) is attached by one end to the forward spar  51  of the torsion box  50  (the load bearing structure of the wing  13 ) in a rotatory manner and by the other end to the wheel. The second guiding element  44 , also having a variable length, is attached by one end to a fixed point  46  of the nacelle  23  and by the other end to the strut  42  to control its movement in a deploying/stowage operation of the wheel. 
     The kinematic mechanisms shown in  FIGS. 3 a   - 3   b,    4   a - 4   b  assume that the displacement of the driving device takes place in a direction parallel to the X-Z plane of the aircraft (X and Z being, respectively the longitudinal and vertical axis) to avoid as much as possible interaction with the hot engine exhaust plume as well as to simplify the MLG architecture. More complex solutions, however, are possible with the introduction of skewed and out-of-pane rotation/retraction mechanisms. 
     The invention is particularly advantageous for aircraft provided with turbofans of high bypass ratio (BPR) which are increasingly used in the aeronautic industry to improve fuel consumption and reduce noise. This trend involves a significant increase of the fan diameter. For example, while the fan diameter of the turbofans of the A320 Neo is 81″, very high bypass ratio (VHBPR) turbofans having fan diameters of up to 174″ are envisaged for the near future. 
     The invention takes advantage of the large fan diameters of turbofans of high bypass ratio, particularly of turbofans of BPR greater than 10, to house the MLG wheels inside the turbofan nacelles. The wheel wells need a small volume in comparison with the engine volume so that the required modification of a typical turbofan nacelle to house a wheel well does not involve significant aerodynamic costs. 
     Aircraft of conventional configuration provided with the MLG of the invention allow the integration of turbofans of high bypass ratio because they can keep a conventional wing dihedral and suitable angle A (see  FIGS. 1 a -1 b   ). 
     In addition, the invention has the following advantages.
         Reduced MLG weight.   Drag reduction through removal of the belly fairing.   Shorter MLG stroke.   Improvement of wing-fuselage junction, including high-lift systems, because of the placement of the landing gears far from it.   Increased fuel tank volume because of the small interference of the MLG with the wing torsion box.   Relief of engine loads on the wing while on ground (landing &amp; taxi) thanks to the position of the MLG.   Reduced fatigue of the wing structure because the landing manoeuvre will not have nacelles acting as cantilever-mass system as the main ground reaction will pass through them avoiding vibrations and heavy unsteady loads.   Integration of load entry points into hard points on the wing (combine engine and MLG).   Removal of tip-over criterion (improved X-wind performance) due to larger wheel track.   Enables negatively scarfed engine.   Enables over-the-wing engine location.   OEI (“One Engine Inoperative”) event improved if engines are placed more inboard, limited by an UERF (“Uncontained Engine Rotor Failure”) event.       

     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.