Abstract:
Landing gear mount techniques for aircraft are described. The landing gear is mounted to composite structures of the aircraft in a manner that distributes landing loads, including out-of-plane loads, adequately so that the landing gear and its mounting to the aircraft is tough and can withstand variable landing loads. The landing gear is disposed between and fastened on each side to composite bulkheads. The composite bulkheads are also bonded to the outer skins of the aircraft. The described mounting distributes the loads into the composite bulkheads and from there into the outer skins. This distribution of the loading helps the landing gear withstand variable landing loads and helps maintain the integrity of the composite materials.

Description:
FIELD 
     This disclosure relates to aircraft with landing gear, in particular mounting of the landing gear to composite structure of the aircraft. 
     BACKGROUND 
     Composite materials do not typically perform well when loaded out-of-plane. This is not a problem when the loading situation is well known or constant. However, when the loading situation is highly variable, composites can perform poorly. 
     There is increasing use of composite materials in aircraft, including unmanned aerial vehicles (UAV&#39;s). UAV&#39;s are often provided with landing gear to facilitate landing, where the landing gear is connected to the composite material forming the UAV. When landing UAV&#39;s, they often land rough and are subject to high and variable loads. Since the landing gear is connected to the composite material, this can lead to failure, for example delamination, of the composite at or near the interface of the landing gear and the composite structure. 
     Thus, improvements in mounting landing gear of aircraft to composite structure of the aircraft is desirable. 
     SUMMARY 
     An improved landing gear mount for aircraft is described, where the landing gear is fixed to composite structures of the aircraft in a manner that distributes landing loads, including out-of-plane loads, adequately so that the landing gear and its mounting to the aircraft is tough and can withstand variable landing loads. The concepts described herein are applicable to any aircraft where the landing gear is to be connected to composite structures of the aircraft. One example of an aircraft that can employ the concepts described herein is a UAV which utilizes a skeleton structure formed from composite bulkheads and composite outer skins bonded to the bulkheads. 
     The landing gear is disposed between and fastened on each side to composite bulkheads. The composite bulkheads are also bonded to the outer skins of the aircraft. The disclosed mounting distributes the loads into the composite bulkheads and from there into the outer skins. This distribution of the loading helps the landing gear withstand variable landing loads and helps maintain the integrity of the composite materials. 
     In one embodiment, an aircraft landing gear mount includes first and second bulkhead panels formed of composite material, the bulkhead panels extending vertically and the bulkhead panels include facing side surfaces. Landing gear including a support rod and a wheel connected to an end of the support rod is also provided. The support rod includes a mounting end that is disposed between the facing side surfaces of the first and second bulkhead panels. The mounting end of the support rod is fastened to the facing side surfaces of the first and second bulkhead panels. 
     In another embodiment, an aircraft includes a plurality of bulkhead panels formed of composite material, with the bulkhead panels extending vertically and each bulkhead panel including side surfaces and a top surface. A plurality of landing gear are provided, with each landing gear including a support rod and a wheel connected to an end of the support rod. Each support rod includes a mounting end that is disposed between facing side surfaces of two of the bulkhead panels. The mounting end of each support rod is fastened to the facing side surfaces of two bulkhead panels. In addition, aircraft skins are disposed over the bulkhead panels and fastened to the top surfaces of the bulkhead panels using a bonding material. 
    
    
     
       DRAWINGS 
         FIG. 1  is a perspective view of an aircraft that employs the inventive concepts described herein. 
         FIG. 2  depicts the aircraft of  FIG. 1  with the outer skins removed to reveal the composite bulkhead panels. 
         FIG. 3  is a top view of  FIG. 2 . 
         FIG. 4  is a detailed view of the right wing illustrating details of how the landing gear is mounted to the wing. 
         FIG. 5  is a front view of  FIG. 2  showing details of the front landing gear mount. 
         FIG. 6  is a detailed view of the front landing gear mount. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an aircraft  10  that employs the inventive concepts described herein. The aircraft  10  is illustrated as being a UAV with an aircraft fuselage or main body  12 , wings  14 ,  16 , an engine  18  driving a propeller  20  at the rear of the fuselage, and landing gear including right and left rear landing gear  22   a ,  22   b  and front landing gear  24 . However, the aircraft is not limited to a UAV, and the inventive concepts can be employed on other types of aircraft, including manned aircraft. 
     Composite outer skins  26  form the exterior of the aircraft  10  to form a smooth, aerodynamic exterior surface.  FIG. 2  illustrates the aircraft  10  with the skins  26  removed. The composite material forming the skins  26  can be any suitable composite material, for example a carbon fiber composite or a glass fiber composite. 
     The fuselage  12  and wings  14 ,  16  of the aircraft  10  are formed by a composite substructure  30  created by a plurality of composite bulkhead panels  32 . The various panels  32  extend in the axial direction (i.e. in the front to back direction) of the aircraft and in a direction transverse to the axial direction (i.e. in the direction of the wings  14 ,  16 ). The composite panels  32  are formed of a suitable composite material to meet strength and weight requirements for the aircraft. An example of a suitable composite material is a carbon fiber composite. The panels  32  are preferably anisotropic with the fiber orientation in a single direction. 
     The panels  32  are bonded to each other where they adjoin using a suitable bonding material, such as an epoxy. In addition, the bulkhead panels  32  include generally planar edge surfaces  42  to which the skins  26  are bonded using a suitable bonding material, such as an epoxy. 
     With reference to  FIGS. 2-4 , the bulkhead panels  32  forming each wing  14 ,  16  include a front wing spar  34 , a rear wing spar  36 , a middle wing spar  38 , and axial wing ribs  40 . The right and left rear landing gear  22   a ,  22   b  are mounted to the wings  14 ,  16  in an identical manner. Therefore only the mounting of the landing gear  22   b  will be described in detail, it being understood that the landing gear  22   a  is mounted to the wing  14  in an identical manner. 
     The landing gear  22   b  includes a metal support rod  50  and a wheel  52  rotatably mounted to the lower end of the support rod  50  that allows the aircraft to roll on the ground during take-offs and landings. The upper end of the support rod  50  defines a mounting end that is disposed between facing side surfaces  54 ,  56  of the rear wing spar  36  and the middle wing spar  38 . 
     A metal support structure  60  (best seen in  FIGS. 3 and 4 ), for example an aluminum bracket, is fixed to the mounting end of the rod  50 . The support structure  60  includes a lower mount section that includes a first portion  62  that extends toward, and is designed to be closely adjacent to or abut, the side surface  54 , and a second portion  64  that extends toward, and is designed to be closely adjacent to or abut, the side surface  56 . The first and second portions  62 ,  64  are also closely adjacent to or abutting against the side surface  66  of the bulkhead panel  32  that extends between the spars  36 ,  38 . 
     The support structure  60  also includes an upper mount section disposed vertically above and connected to the lower mount section. The upper mount section includes a first portion  68  that extends toward, and is designed to be closely adjacent to or abut, the side surface  54 , and a second portion  70  that extends toward, and is designed to be closely adjacent to or abut, the side surface  56 . 
     As best seen in  FIG. 4 , the first and second portions  62 ,  64 ,  68 ,  70  are detachably fastened to the wing spars  36 ,  38  using suitable detachable fastening mechanisms  80 , for example bolts. The first and second portions  62 ,  64  of the lower mount section are also detachably fastened to the bulkhead panel  32  between the spars  36 ,  38  using similar fastening mechanisms  80 . To facilitate connection, grommets  82 , for example aluminum grommets, can be disposed within holes  84  formed in spars  36 ,  38  and panel  32 , with the fastening mechanisms  80  then being connected to the grommets  82 . 
     This mounting of the right and left rear landing gear  22   a ,  22   b  distributes landing loads, including out-of-plane loads, into each of the wing spars  36 ,  38  as well as the bulkhead panel  32  between the wing spars  36 ,  38 . The load is then distributed into the skins  26  which are bonded to the panels  32 /wing spars. Because the load is distributed in this manner, the landing gear  22   a ,  22   b  is able to withstand greater landing loads, and the composite bulkhead panels are less likely to suffer failure, such as delamination, resulting from out-of-plane loads. 
     The right and left rear landing gear  22   a ,  22   b  are described as being fixed (i.e. non-retractable). However, the concepts described herein could also be applied where the landing gear  22   a ,  22   b  are designed to retract. 
     With reference now to  FIGS. 5 and 6 , the mounting of the front landing gear  24  will now be described. The bulkhead panels  32  include a pair of nose bulkhead panels  90 ,  92  having facing side surfaces  94 ,  96 . The front landing gear  24  includes a metal support rod  100  and a pair of wheels  102  rotatably mounted to the lower end of the support rod  100  that allow the aircraft to roll on the ground during take-offs and landings. The upper end of the support rod  100  defines a mounting end that is disposed between the facing side surfaces  94 ,  96 . 
     The front landing gear  24  is designed to be pivotally mounted so that it is retractable. In particular, a pair of metal support structures  110  (only one is visible in  FIG. 6 ), for example L-shaped aluminum brackets, are fixed to the facing side surfaces  94 ,  96 . The top end of the support rod  100  includes a collar  112  fixed thereto, with the collar including opposite flanges  114  (only one flange  114  is visible in  FIG. 6 ) that extend toward the respective side surfaces  94 ,  96 . The ends of the flanges  114  are positioned closely adjacent the side surfaces  94 ,  96 . Pivot shafts  116  (shown in dashed lines in  FIG. 6 ) extend from each flange  114  and are pivotally received within pivot receiving holes  118  formed in the panels  90 ,  92 . The pivot shafts  116  are pivotable within the holes  118 , allowing the collar  112  and the support rod  100  to pivot relative to the panels  90 ,  92 . 
     A second collar  120  is connected to the rod  100  below the collar  112 . The collar  120  includes a pair of ears  122  between which is secured the end of an actuating shaft  124 . The opposite end  126  of the shaft  124  is rigidly secured to a pivotable shaft  128  the opposite ends of which are pivotally retained within pivot holes  130  formed in the panels  90 ,  92 . A pair of links  132 ,  134  are fixed to the shaft  128  and to an actuator shaft  136 . A pair of actuators  138 ,  140  are secured to the shaft  136 , with each actuator being pivotally connected to the panels  90 ,  92 . 
     As suggested by the description, the front landing gear  24  is retractable via actuation of the actuators  138 ,  140 . The actuation force of the actuators  138 ,  140  is transmitted via the shaft  136 , links  132 ,  134 , shaft  128 , shaft  124 , and the collar  120  to the rod  100 . Because the rod is pivotally mounted, the front landing gear  24  can be extended and retracted from the aircraft  10  as appropriate. 
     Because the front landing gear  24  is mounted on each side to the panels  90 ,  92 , landing loads, including out-of-plane loads, are distributed into each of the panels  90 ,  92 . The load is then distributed into the skins  26  which are bonded to the panels  90 ,  92 . Because the load is distributed in this manner, the landing gear  24  is able to withstand greater landing loads, and the composite bulkhead panels are less likely to suffer failure, such as delamination, resulting from out-of-plane loads. 
     The front landing gear  24  is described as being retractable. However, the concepts described herein could also be applied where the landing gear  24  is designed to be fixed (i.e. non-retractable). 
     This bulkhead panel mounting of the front landing gear  24  also allows the mounting of the front landing gear to be disposed with a compartment  150  at the nose of the aircraft. The compartment  150  contains various sensitive electronics and avionics used by the aircraft. The compartment  150  provides an enclosure around the upper end of the landing gear  24  that is electromagnetic interference (EMI) shielded and environmentally shielded to prevent dust and other contaminants from entering the compartment and coming into contact with the electronics and avionics. 
     The embodiments disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.