Patent Publication Number: US-2023150655-A1

Title: Leaf spring type landing gear

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Korean Patent Application No. 10-2021-0157193 filed on Nov. 16, 2021. The entire contents of is the above-listed application are hereby incorporated by reference for all purposes. 
     TECHNICAL FIELD 
     The following disclosure relates to a leaf spring type landing gear, and more particularly, to a leaf spring type landing gear that is connected to a lower portion of a fuselage of an aircraft to absorb shocks generated during takeoff and landing. 
     BACKGROUND 
     A landing gear is disposed on a lower portion of a fuselage of an aircraft to absorb shocks generated during takeoff and landing on the ground. In addition, a load generated during landing is increased to several times the weight of the fuselage, and accordingly, the landing gear is disposed to prevent the fuselage from being destroyed due to energy transferred from the load to the fuselage. 
     The landing gear is implemented in various types of landing gears such as oleo-pneumatic type, hydraulic type, pneumatic type, and elastic body type landing gears, and is coupled to the fuselage of the aircraft. Referring to  FIG.  1   , the elastic body type landing gear is easy to design, manufacture, and assemble and is light as compared to other types of landing gears such as the oleo-pneumatic type landing gear. Therefore, the elastic body type landing gear has been widely used in a small craft, an unmanned aerial vehicle, a helicopter, and the like. The elastic body type landing gear receives a high impact load due to limitation in strain, and is vulnerable to absorption of shocks because dissipated energy due to friction or the like is smaller than that in the other types of landing gears. In the case of the elastic body type landing gear, when the aircraft lands at a relatively high speed, the aircraft bounces into the air due to the high impact load, which may lead to an accident. 
     In order to solve the problem of the elastic body type landing gear as described above, development such as forming a landing gear with various composite materials or changing a shape of a landing gear has been conducted. Accordingly, the present applicant has disclosed a landing gear for an aircraft with wheels having a shape including a plurality of landing members in Korean Patent Publication No. 10-1542806 (Landing gear for aircraft with wheels, method of determining shape of landing gear for aircraft with wheels, and program recording medium, hereinafter, referred to as the “related art”). Referring to  FIG.  2   , the landing gear for an aircraft with wheels of the related art includes a frame connecting a fuselage and wheels in a form in which a plurality of quadrants are combined, in which the frame includes three quadrants consisting of a first quadrant, a second quadrant, and a third quadrant from an upper portion to the ground. Therefore, in this case, an impact load and a bounce load may be significantly reduced while geometric restrictions are reduced, and thus, the problem of the elastic body type landing gear according to the related art is solved. 
     Furthermore, development has been conducted in various fields to further improve the performance of the aircraft, and research and development of a landing gear having higher efficiency than the landing gear disclosed in the related art have been conducted. In addition, development has been conducted to improve the performance of the aircraft while minimizing a weight of the landing gear so that the aircraft has higher performance and higher efficiency. 
     RELATED ART DOCUMENT 
     Patent Document 
     KR 10-1542806 B1 (published on Aug. 7, 2015) 
     SUMMARY 
     An embodiment of the present disclosure is directed to providing a landing gear having higher performance and higher efficiency, and an object of the present disclosure is to provide a leaf spring type landing gear including a frame having a shape with higher performance for mitigation and absorption of shocks. 
     In one general aspect, a leaf spring type landing gear mounted on a lower portion of a fuselage of an aircraft includes: a first frame connected to the fuselage and bent to have a circle center below; a second frame connected to the first frame; and a third frame connected to the second frame and at least partially bent to have a circle center below, wherein the second frame includes a 2-1st frame and a 2-2nd frame having circle centers formed in opposite directions and is formed to be bent in an S shape. 
     The first frame, the second frame, and the third frame may be integrally formed. 
     A pair of the second frame and the third frame may be disposed at each of both ends of the first frame to be formed in a spraddle-legged shape. 
     The third frame may include a 3-1st frame connected to the second frame and bent to have a circle center below and a 3-2nd frame connected to the 3-1st frame and bent to have a circle center above, and may be formed to be bent in an S shape. 
     The 3-2nd frame may come into contact with the ground when the aircraft lands. 
     The leaf spring type landing gear may further include a damper having both ends connected to the 2-1st frame and the 2-2nd frame, respectively. 
     The damper may be disposed so that the other end is inclined at a predetermined angle with respect to a lower side from one end connected to the 2-1st frame, and the predetermined angle may be formed at −10° to +15°. 
     A vertical height of the second frame may be greater than a vertical height of each of the first frame and the third frame. 
     The vertical height of the third frame may be greater than the vertical height of the first frame. 
     An inflection point between the 2-1st frame and the 2-2nd frame may be located at the center in both directions with respect to ends of the first frame and the third frame. 
     The circle centers of the 2-1st frame and the 2-2nd frame may be formed in the both directions, respectively. 
     The leaf spring type landing gear may further include a wheel connected to the other end of the third frame. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view illustrating comparisons of weight efficiency and gear efficiency according to types of landing gears. 
         FIG.  2    is a view illustrating a frame of a landing gear for an aircraft with wheels according to the related art. 
         FIG.  3    is a front view of an aircraft on which a leaf spring type landing gear according to the present disclosure is mounted. 
         FIG.  4    is a front view of a leaf spring type landing gear according to an exemplary embodiment of the present disclosure. 
         FIG.  5    is a view illustrating a leaf spring type landing gear in which strain is generated due to landing according to an exemplary embodiment of the present disclosure. 
         FIG.  6    is a view illustrating a frame of a leaf spring type landing gear according to an exemplary embodiment of the present disclosure. 
         FIG.  7    is a view illustrating a frame of a leaf spring type landing gear according to another exemplary embodiment of the present disclosure. 
         FIG.  8    is a graph showing a comparison of the frame of the leaf spring type landing gear according to the present disclosure and the frame of the landing gear according to the related art. 
         FIGS.  9 A and  9 B  are graphs showing characteristics of the leaf spring type landing gear according to the present disclosure. 
         FIGS.  10 A to  10 D  and  FIGS.  11 A to  11 D  are graphs showing comparisons of displacements and the amounts of strain of the leaf spring type landing gear according to the present disclosure and the landing gear according to the related art. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a leaf spring type landing gear having the configuration as described above according to the present disclosure will be described in detail with reference to the accompanying drawings. 
       FIGS.  3  and  4    relate to the leaf spring type landing gear according to the present disclosure.  FIG.  3    is a front view of an aircraft on which the leaf spring type landing gear according to the present disclosure is mounted, and  FIG.  4    is a front view of a leaf spring type landing gear according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG.  3   , a leaf spring type landing gear  100  according to the present disclosure may be mounted on a lower portion of a fuselage  11  of an aircraft  10 , and the aircraft  10  may be any one of a variety of types such as a small aircraft, a light aircraft, a helicopter, and an unmanned aerial vehicle. In this case, one end of the leaf spring type landing gear  100  may be coupled to the fuselage  11 , and the leaf spring type landing gear  100  may be disposed to absorb shocks generated during takeoff and landing of the aircraft  10 . For instance, the leaf spring type landing gear  100  may absorb a high impact load generated when the aircraft  10  lands at a relatively high speed. Hereinafter, in the following description, a direction in which the aircraft  10  travels is defined as a front and rear direction, a distance between the air and the ground is defined as a vertical direction, and as a posture of the aircraft  10  may be changed during flight, a shape of the aircraft  10  in a state placed on the ground will be described as a reference. 
     Referring to  FIG.  4   , the leaf spring type landing gear  100  according to the present disclosure may include a first frame  110 , a second frame  120 , and a third frame  130  connected to each other. In this case, the leaf spring type landing gear  100  according to the present disclosure may be formed in a spraddle-legged shape, and a pair of the second frame  120  and the third frame  130  may be sequentially connected to each of left and right ends of the first frame  110 . In this case, the first frame  110  may be formed in an arc shape to have a circle center below, and the center of the first frame  110  may be formed in a different shape so as to be mounted on the fuselage  11  of the aircraft  10 . Alternatively, a pair of the first frame  110 , the second frame  120 , and the third frame  130  may be connected to each of left and right sides of the fuselage  11 . 
     The second frame  120  may include a 2-1st frame  121  and a 2-2nd frame  122  having circle centers formed in different directions. In this case, the 2-1st frame  121  and the 2-2nd frame  122  may be formed in arc shapes in which circle centers are formed right and left, respectively. Accordingly, the 2-1st frame  121  and the 2-2nd frame  122  may be bent in an S shape. In addition, the third frame  130  may be formed in an arc shape so that at least a part thereof is bent downward. In this case, the first frame  110 , the second frame  120 , and the third frame  130  may be integrally formed, and may be formed of a metal or a composite material according to the type of the aircraft  10  on which the leaf spring type landing gear  100  is mounted. 
     The leaf spring type landing gear  100  according to the present disclosure may further include a damper  140  disposed on the second frame  120 . In this case, both ends of the damper  140  may be connected to the 2-1st frame  121  and the 2-2nd frame  122 , respectively. An attachment position of the damper  140  may vary according to stroke characteristics, and may be implemented in various types of dampers such as an elastic body type damper, for example, a rubber or spring type damper, and hydraulic type, pneumatic type, and oleo-pneumatic type dampers. 
     The leaf spring type landing gear  100  according to the present disclosure may further include a wheel  150  disposed at an end of the third frame  130 . In addition, although not illustrated, a skid extending in the front and rear direction may be disposed at the end of the third frame  130 . 
       FIGS.  5  and  6    relate to the leaf spring type landing gear according to an exemplary embodiment of the present disclosure.  FIG.  5    is a front view illustrating a leaf spring type landing gear in which strain is generated due to landing, and  FIG.  6    is a view illustrating the frame of the leaf spring type landing gear. 
     Referring to  FIG.  5   , when the leaf spring type landing gear  100  according to the present disclosure lands on the ground, a predetermined strain may occur due to the weight of the fuselage  11 . The amount of strain (δ) generated at this time is a factor determining shock mitigation. Although if the amount of strain (δ) is larger, the aircraft may bounce into the air due to dissipated energy. The leaf spring type landing gear  100  according to the present disclosure may reduce the bounce of the aircraft by the structure of the first frame  110 , the second frame  120 , and the third frame  130 , and the damper  140  disposed on the second frame  120 . Therefore, the leaf spring type landing gear  100  may provide more comfort to an occupant while reducing energy transferred to the fuselage  11 . 
     Referring to  FIG.  6   , the first frame  110 , the second frame  120 , and the third frame  130  may have a standard width a in the front and rear direction and a standard height b in the vertical direction. In this case, the height of the second frame  120  may be greater than each of the heights of the first frame  110  and the third frame  130 . The height of the third frame  130  may be greater than the height of the first frame  110 . As an example, a height ratio of the first frame  110 , the second frame  120 , and the third frame  130  may be 1:3:2. 
     An inflection point between the 2-1st frame  121  and the 2-2nd frame  122  of the second frame  120  may be located at the central portion of the end of the first frame  110  and the end of the third frame  130 . In this case, when the inflection point is located at the center, a length from the inflection point of the second frame  120  to the end of the first frame  110  may correspond to a length from the inflection point of the second frame  120  to the end of the third frame  130 . In this case, the central portion may mean a portion corresponding to 0.4 to 0.6 of the standard width a. In addition, a width a′ of the 2-1st frame  121  or the 2-2nd frame  122  may be ⅛ or less of the standard height b. 
     Upper and lower ends of the damper  140  may be connected to the 2-1st frame  121  and the 2-2nd frame  122 , respectively. In this case, the damper  140  may be disposed so that the lower end is inclined at a predetermined angle (θ) with respect to the upper end. When it is assumed that a direction of the damper  140  adjacent to the third frame  130  is a positive (+) direction and a direction opposite to the direction is a negative (−) direction, the predetermined angle (θ) of the damper  140  may be formed at −10° to +15° according to stroke characteristics. 
       FIG.  7    relates to a leaf spring type landing gear according to another exemplary embodiment of the present disclosure, and  FIG.  7    is a view illustrating a frame of the leaf spring type landing gear. 
     Referring to  FIG.  7   , in the leaf spring type landing gear  100  according to the present disclosure, the third frame  130  may include a 3-1st frame  131  and a 3-2nd frame  132  and may be bent in an S shape. In this case, the 3-1st frame  131  may be connected to the second frame  120  and may be bent in an arc shape to have a circle center below, and the 3-2nd frame  132  may be connected to the 3-1st frame  131  and may be bent in an arc shape to have a circle center above. The circle center of the 3-1st frame  131  may be biased to the right and the circle center of the 3-2nd frame  132  may be biased to the left. In addition, an inflection point between the 3-1st frame  131  and the 3-2nd frame  132  may be located at the central portion of the left and right widths of the third frame  130 . 
     In  FIGS.  6  and  7   , a linear-shaped frame  21  and an arc-shaped frame  22  are illustrated together. In the following description, the leaf spring type landing gear  100  having the same standard width a and standard height b according to the present disclosure will be compared with the leaf spring type landing gear  100  including the linear-shaped frame  21  and the arc-shaped frame  22 . 
       FIG.  8    and  FIGS.  9 A and  9 B  relate to the leaf spring type landing gear according to the present disclosure.  FIG.  8    is a graph showing a comparison of the frame of the leaf spring type landing gear according to the present disclosure and the frame of the landing gear according to the related art, and  FIGS.  9 A and  9 B  are graphs showing characteristics of the leaf spring type landing gear according to the present disclosure. 
       FIG.  8    illustrates a friction force (μP) and a ground load at the time of landing. A moment (M) may be calculated according to the following equation. 
     In this case, the strain is large as the moment is large because the strain is proportional to the moment. As illustrated in  FIG.  8   , a magnitude of the moment applied to the arc-shaped frame  22  is smaller than that applied to the linear-shaped frame  21 , and thus, the amount of strain of the arc-shaped frame  22  is smaller than that of the linear-shaped frame  21  when the same load is applied. On the other hand, in the leaf spring type landing gear  100  according to the present disclosure, a large magnitude of the moment is applied to an outer leg portion based on the central portion. In addition, as a relatively small magnitude of the moment is applied to a root portion, the amount of strain is large at the root portion. Therefore, the root portion to which a maximum magnitude of the moment is applied may satisfy strength with a cross-sectional area such as a linear shape or an elliptical shape. Since strain of a leaf spring type landing gear  100   b  according to another exemplary embodiment of the present disclosure is larger than that of a leaf spring type landing gear  100   a  according to an exemplary embodiment of the present disclosure, a skid type landing gear may be suitable for the leaf spring type landing gear  100   b , and a wheel type landing gear may be suitable for the leaf spring type landing gear  100   a.    
     Referring to  FIG.  9 A , in the leaf spring type landing gear  100  according to the present disclosure, a length of a stroke may be changed according to a descent speed and a landing load. In addition, the standard height b, the standard width a, the skid type or the wheel type, and the like may be selectively designed based on the numerical values set at the time of design. In addition, when compared with the arc-shaped frame  22  according to the related art, as illustrated in  FIG.  9 B , it is possible to similarly implement an oleo-pneumatic type landing gear through a more stable landing and an elastic body. 
       FIGS.  10 A to  10 D  and  FIGS.  11 A to  11 D  relate to the leaf spring type landing gear according to the present disclosure.  FIGS.  10 A to  10 D  and  FIGS.  11 A to  11 D  are graphs showing comparisons of displacements and the amounts of strain of the leaf spring type landing gear according to the present disclosure and the landing gear according to the related art. 
       FIGS.  10 A to  10 D  and  FIGS.  11 A to  11 D  illustrate the results of the linear-shaped frame  21 , the arc-shaped frame  22 , the leaf spring type landing gear  100   a  according to an exemplary embodiment, and the leaf spring type landing gear  100   b  according to another exemplary embodiment analyzed by setting design variables shown in the table below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Classification 
                 Numerical value 
                 Unit 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Weight of aircraft 
                 600 
                 (kg) 
               
               
                 Landing load 
                 4 
                 (g) 
               
               
                 Standard width a 
                 700 
                 (mm) 
               
               
                 Standard height b 
                 500 
                 (mm) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Load 
                 P 
                 1,200 
                 (kg) 
               
               
                   
                 conditions 
                 μ 
                 0.3 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     In addition, the results analyzed by inputting the thickness t and the width of each frame as 24 mm and 150 mm, respectively, are illustrated in  FIGS.  10 A to  10 D  and  FIGS.  11 A to  11 D . 
       FIGS.  10 A to  10 D  and  FIGS.  11 A to  11 D  illustrate that the stroke of the amount of strain (δ) is 110 mm for the linear-shaped frame  21 , 87 mm for the arc-shaped frame  22 , 176 mm for the leaf spring type landing gear  100   a  according to an exemplary embodiment, and 177 mm for the leaf spring type landing gear  100   b  according to another exemplary embodiment. As described above, it may be appreciated that the amount of strain (δ) of the leaf spring type landing gear  100  according to the present disclosure is significantly different from that of the shape of the leaf spring type landing gear according to the related art. In addition, it may be appreciated that the performance for mitigation and absorption of shocks is enhanced as the amount of strain (δ) is increased. 
     As set forth above, the leaf spring type landing gear according to the present disclosure may significantly mitigate and absorb shocks by the configuration described above even at a high landing descent speed, and thus may have higher safety and comfort. 
     Further, since the leaf spring type landing gear according to the present disclosure satisfies both rigidity and strength, a size of a strut may be smaller, such that the weight efficiency may be increased. 
     Further, the leaf spring type landing gear according to the present disclosure may come into contact with the ground together with the skid to which a part of the third frame is connected during landing. Accordingly, the moment energy to be transferred may be reduced. 
     Further, in the leaf spring type landing gear according to the present disclosure, even when the descent speed exceeds the designed speed due to engine failure or turbulence, a large concentrated load is applied to the inner contact point and the damper attachment point, and damage to these points occurs, such that the energy transferred to the fuselage is significantly reduced and there is no overturning or damage to the fuselage. As a result, the safety may be further improved. 
     The present disclosure is not limited to the exemplary embodiments described above, but may be variously applied. In addition, the present disclosure may be variously modified by those skilled in the art to which the present disclosure pertains without departing from the gist of the present disclosure.