helicopter

Abstract

To improve the detachable configuration of the helicopter. [Solution] The helicopter body is separated into a first part and a second part. The power unit is located in the first part. The tail rotor is located at the end of the second part opposite to the first part. The first shaft is located within the first part and transmits the rotational driving force of the power unit. The first adapter is connected to the first shaft. The second adapter is connected to the first adapter. The second shaft is connected to the second adapter and the tail rotor and is located within the second part. The first bearing is located radially outside the first adapter and rotatably supports the first adapter, or is located adjacent to the first adapter and rotatably supports the first shaft. The second bearing is located radially outside the second adapter and rotatably supports the second adapter, or is located adjacent to the second adapter and rotatably supports the second shaft.

Description

Technical Field

[0001] The present invention relates to a helicopter.

Background Art

[0002] In the field of helicopters, there is a need to compactify the aircraft by removing a part of the aircraft when it is not in use for easy storage and transportation of the aircraft. For example, Patent Document 1 below discloses a technique for connecting two shafts for transmitting power to a tail rotor using splines. The connecting portion of these two shafts is supported by one bearing. According to this technique, when the helicopter is not in use, such as during storage or transportation, the two shafts can be disconnected and the aircraft can be separated into two parts, thereby compactifying the aircraft.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the technique of Patent Document 1 still has room for improvement regarding the separable configuration.

Means for Solving the Problems

[0005] This specification discloses a helicopter comprising a body, a power unit, a tail rotor, a first shaft, a first adapter, a second adapter, a second shaft, a first bearing, and a second bearing. The body is separated into a first part and a second part. The power unit is located in the first part. The tail rotor is located at the end of the second part opposite to the first part. The first shaft has a first end located closer to the power unit and a second end located further away from the power unit, and is located within the first part, and transmits the rotational driving force of the power unit. The first adapter is connected to the second end of the first shaft. The second adapter is located on the opposite side of the first shaft from the first adapter and is connected to the first adapter. The second shaft has a third end connected to the second adapter and a fourth end connected to the tail rotor, and is located within the second part. The first bearing is positioned radially outward of the first adapter and rotatably supports the first adapter, or is positioned adjacent to the first adapter and rotatably supports the first shaft. The second bearing is positioned radially outward of the second adapter and rotatably supports the second adapter, or is positioned adjacent to the second adapter and rotatably supports the second shaft. [Brief explanation of the drawing]

[0006] [Figure 1] This is a perspective view of a helicopter according to the first embodiment, separated into two parts. [Figure 2] This is a magnified section of Figure 1. [Figure 3] This is a schematic cross-sectional view of a helicopter showing the arrangement of the shaft assembly. [Figure 4] This is a side view of the shaft assembly, where the first adapter and the second adapter are separated. [Figure 5] Figure 4 is a cross-sectional view of the shaft assembly along line AA, where the first adapter and the second adapter are separated. [Figure 6] Figure 4 is a cross-sectional view of the shaft assembly along line AA, where the first adapter and the second adapter are in the process of being connected. [Figure 7] Figure 4 is a cross-sectional view of the shaft assembly along line AA, where the first adapter and the second adapter are connected. [Figure 8] This is a partial cross-sectional view of a shaft assembly according to the second embodiment, in which the first adapter and the second adapter are connected. [Modes for carrying out the invention]

[0007] Referring to Figures 1-7, a helicopter 10 according to a non-limiting first embodiment will be described below. In this embodiment, the helicopter 10 is an unmanned aircraft, but it may be a manned aircraft. As shown in Figure 1, the helicopter 10 comprises a body 20, a main rotor 11, a tail rotor 12, and skids 15. The body 20 comprises a fuselage section 21 and a tail section 22 that extends elongated from the fuselage section 21. The fuselage section 21 is a structure that supports the main rotor 11. In the following description, the direction in which the fuselage section 21 and the tail section 22 are aligned is defined as the front-rear direction of the helicopter 10. Of the front-rear direction, the side where the fuselage section 21 is located is defined as the front side of the helicopter 10, and the side where the tail section 22 is located is defined as the rear side. In addition, the direction in which the rotor axis of the main rotor 11 extends is defined as the up-down direction of the helicopter 10. Of the vertical directions, the side where the main rotor 11 is located is defined as the upper side, and the side where the skid 15 is located is defined as the lower side of the helicopter 10. Also, the direction perpendicular to the longitudinal direction and the vertical direction is defined as the left-right direction of the helicopter 10. Of the left-right directions, the right side when viewed from the rear to the front is defined as the right side of the helicopter 10, and the opposite side is defined as the left side. The tail section 22 is a structure that supports the tail rotor 12 and the shaft assembly 30, which will be described later, and extends rearward from the fuselage section 21. The main rotor 11 is located above the fuselage section 21. In Figure 1, one of the three blades of the main rotor 11 is omitted from the illustration. The tail rotor 12 is located at the rear end of the tail section 22. The tail rotor 12 generates torque to counteract the counter torque that acts on the aircraft 20 when the blades of the main rotor 11 rotate.

[0008] As shown in Figure 1, the aircraft body 20 is separable in the middle of the tail section 22. The portion of the tail section 22 in front of the separation point is also called the front tail section 23, and the portion behind the separation point is also called the rear tail section 24. As shown in Figure 2, the front tail section 23 is provided with a first flange member 25. The first flange member 25 is attached to the rear end of the front tail section 23. The first flange member 25 comprises a first cylindrical portion 25a that surrounds the outer circumferential surface of the rear end portion of the front tail section 23, and a first flange portion 25b that extends radially outward from the rear edge of the first cylindrical portion 25a. The first cylindrical portion 25a is fixed to the front tail section 23 by a plurality of rivets 29. The rear tail section 24 is provided with a second flange member 26. The second flange member 26 is attached to the front end of the rear tail section 24. The second flange member 26 comprises a second cylindrical portion 26a surrounding the outer circumferential surface of the front end portion of the rear tail portion 24, and a second flange portion 26b extending radially outward from the front edge of the second cylindrical portion 26a. The second cylindrical portion 26a is fixed to the rear tail portion 24 by a plurality of rivets 29. The front tail portion 23 and the rear tail portion 24 are detachably connected by connecting the first flange portion 25b of the first flange member 25 and the second flange portion 26b of the second flange member 26 with a plurality of bolts 27 and nuts 28.

[0009] The helicopter 10 includes a shaft assembly 30. As shown in Figure 3, the shaft assembly 30 extends in the longitudinal direction within the airframe 20. The direction of extension of the shaft assembly 30 coincides with the longitudinal direction of the airframe 20. The helicopter 10 includes an engine 13, which is a power unit, and a gearbox. The engine 13 is located within the fuselage section 21. The engine 13 is the power source that rotates the main rotor 11 and the tail rotor 12. The rotational force of the engine 13 is transmitted to the tail rotor 12 via the shaft assembly 30. The tail section 22 includes a support mechanism that rotatably supports the shaft assembly 30. The support mechanism includes a bearing 31, a first bearing 80, a first rubber sleeve 81, a second bearing 90, and a second rubber sleeve 91. In this embodiment, the shaft assembly 30 is rotatably supported by the bearing 31, the first bearing 80, and the second bearing 90. The front end of the shaft assembly 30 is connected to a gear shaft in a gearbox located between the engine 13 and the shaft assembly 30. The gear shaft is rotatably supported by bearings.

[0010] As shown in Figures 3 and 4, the shaft assembly 30 comprises a first shaft 40 and a second shaft 50. The first shaft 40 extends into the fuselage 21 and the front tail 23. In an alternative embodiment, the first shaft 40 may extend only into the front tail 23. The second shaft 50 extends into the rear tail 24. The first shaft 40 and the second shaft 50 are arranged coaxially, with the first shaft 40 located forward of the second shaft 50, i.e., closer to the engine 13. The first shaft 40 and the second shaft 50 are detachably connected at approximately the same position in the direction of shaft extension where the front tail 23 and the rear tail 24 separate.

[0011] The first shaft 40 has a first end 41 and a second end 42. The first end 41 is the end of the first shaft 40 located closer to the engine 13 in the longitudinal direction. The second end 42 is the end of the first shaft 40 located further away from the engine 13 in the longitudinal direction. A bearing 31 supports the first shaft 40. The second shaft 50 has a third end 51 and a fourth end 52. The third end 51 is the end of the second shaft 50 located further away from the tail rotor 12 in the longitudinal direction. The fourth end 52 is the end of the second shaft 50 located closer to the tail rotor 12 in the longitudinal direction and is connected to the tail rotor 12.

[0012] The configuration for detachably connecting the first shaft 40 and the second shaft 50 will be described below with reference to Figures 4 to 7. Figure 4 shows the shaft assembly 30 in a state where the first shaft 40 and the second shaft 50 are separated. As shown in Figure 4, the shaft assembly 30 further comprises a first adapter 60 and a second adapter 70. The first shaft 40 and the second shaft 50 are connected via the first adapter 60 and the second adapter 70. Specifically, the first adapter 60 is connected to the second end 42 of the first shaft 40. The second adapter 70 is positioned on the opposite side of the first shaft 40, with the first adapter 60 in between. The front end of the second adapter 70 is connected to the first adapter 60, and the rear end of the second adapter 70 is connected to the third end 51 of the second shaft 50. In this embodiment, the first adapter 60 and the second adapter 70 are connected by a spline coupling.

[0013] Figure 5 shows a cross-section of the shaft assembly 30 along line AA in Figure 4, where the first shaft 40 and the second shaft 50 are separated. Figure 6 shows a cross-section of the shaft assembly 30 along line AA in Figure 4, where the first shaft 40 and the second shaft 50 are in the process of being connected. In other words, Figure 6 shows the state in which the tip of the second adapter 70 is being inserted into the first adapter 60. Figure 7 shows a cross-section of the shaft assembly 30 along line AA in Figure 4, where the first shaft 40 and the second shaft 50 are fully connected. In this embodiment, as shown in Figure 5, each of the first shaft 40 and the second shaft 50 is a cylindrical aluminum alloy member. This reduces the weight of the shaft assembly 30. Each of the first adapter 60 and the second adapter 70 is a substantially cylindrical iron member. Because the first adapter 60 and the second adapter 70 are made of iron, the transmission of rotational driving force by spline coupling can be performed stably.

[0014] As shown in Figure 5, the first adapter 60 has a first connecting portion 64 on its front side. The first connecting portion 64 is connected to the second end 42 of the first shaft 40 by being inserted into the second end 42 of the first shaft 40. The rear end of the second end 42 abuts against the first step portion 67 of the first adapter 60, thereby positioning the first shaft 40 and the first adapter 60 in the extending direction of the shaft assembly 30. The first shaft 40 and the first adapter 60 are fixed together by a plurality of rivets 43 that pass radially through the second end 42 and the first connecting portion 64. The second adapter 70 has a second connecting portion 74 on its rear side. The second connecting portion 74 is connected to the third end 51 of the second shaft 50 by being inserted into the third end 51 of the second shaft 50. The front end of the third end 51 abuts against the second step portion 79 of the second adapter 70, thereby positioning the second shaft 50 and the second adapter 70 in the extending direction of the shaft assembly 30. The second shaft 50 and the second adapter 70 are fixed together by a plurality of rivets 53 that pass through the second shaft 50 and the second adapter 70 in the radial direction.

[0015] As shown in Figure 5, the first adapter 60 is provided with a spline hole 61. The second adapter 70 is provided with a spline shaft 71. The spline shaft 71 is an axial portion with multiple teeth formed along its circumference. The spline hole 61 is a cylindrical portion with multiple grooves formed therein that have a shape to fit the multiple teeth of the spline shaft 71. In this embodiment, the spline hole 61 and the spline shaft 71 are square splines, but they may also be involute splines. As shown in Figure 7, when the first adapter 60 and the second adapter 70 are connected, the spline hole 61 and the spline shaft 71 are spline-coupled, with the multiple teeth of the spline shaft 71 fitting into the multiple grooves of the spline hole 61. As a result, the rotational driving force transmitted from the engine 13 to the first shaft 40 is transmitted to the second shaft 50 via the spline coupling between the first adapter 60 and the second adapter 70. The rotational driving force transmitted to the second shaft 50 is further transmitted to the tail rotor 12.

[0016] As shown in Figure 5, the first adapter 60 has a first protrusion 62 extending along the circumferential direction on its inner circumference. In this embodiment, the first protrusion 62 extends in an annular shape along the circumferential direction. However, the first protrusion 62 may have a configuration in which a plurality of protrusions extending along the circumferential direction are arranged at intervals in the circumferential direction. In this embodiment, the first protrusion 62 is located in front of the spline hole 61 in the extending direction of the shaft assembly 30. In an alternative embodiment, the first protrusion 62 may be located behind the spline hole 61. The inner diameter of the first protrusion 62 is smaller than the spline diameter of the spline hole 61. The first protrusion 62 protrudes radially inward from the inner circumferential surface of the first adapter 60 such that the inner diameter of the first protrusion 62 is smaller than the spline diameter of the spline hole 61. In other words, the first protrusion 62 projects radially inward from the inner circumferential surface of the first adapter 60 to a height greater than half the difference between the small spline diameter and the large spline diameter of the spline hole 61. The small spline diameter of the spline hole 61 is the diameter of the spline hole 61 at the top of the multiple grooves of the spline hole 61, that is, the part that protrudes most radially inward. The large spline diameter of the spline hole 61 is the diameter of the spline hole 61 at the bottom of the multiple grooves of the spline hole 61, that is, the part that is recessed most radially outward. The first protrusion 62 projects radially inward even further than the part of the spline hole 61 that protrudes most radially inward.

[0017] As shown in FIG. 5, the second adapter 70 has an outer peripheral surface portion 72 facing outward on its outer peripheral portion. As shown in FIGS. 6 and 7, the outer peripheral surface portion 72 facing outward is radially opposed to the first convex portion 62 of the first adapter 60 during and after the connection of the first adapter 60 and the second adapter 70. The radial clearance between the first convex portion 62 and the outer peripheral surface portion 72 facing outward is smaller than the difference between the minor spline diameter of the spline hole 61 and the minor spline diameter of the spline shaft 71, and is also smaller than the difference between the major spline diameter of the spline hole 61 and the major spline diameter of the spline shaft 71. The minor spline diameter of the spline shaft 71 is the diameter of the spline shaft 71 at the bottom of the plurality of teeth of the spline shaft 71, that is, the portion that is the most inward in the radial direction. The major spline diameter of the spline shaft 71 is the diameter of the spline shaft 71 at the top of the plurality of teeth of the spline shaft 71, that is, the portion that protrudes the most outward in the radial direction.

[0018] According to this configuration, the first convex portion 62 and the outer peripheral surface portion 72 facing outward function as guides for regulating the radial positional relationship between the first adapter 60 and the second adapter 70 when inserting the second adapter 70 into the first adapter 60 for spline connection and when removing the second adapter 70 from the first adapter 60 to release the spline connection. Therefore, when attaching and detaching the first adapter 60 and the second adapter 70, it is possible to suppress the axes of the first adapter 60 and the second adapter 70 from tilting with respect to each other, and thus suppress the application of an excessive radial force to the spline hole 61 and the spline shaft 71. Accordingly, the attachment and detachment of the first adapter 60 and the second adapter 70 can be performed smoothly.

[0019] As shown in FIG. 5, the second adapter 70 includes a second convex portion 73 extending along the circumferential direction on its outer peripheral portion. In the present embodiment, the second convex portion 73 extends annularly along the circumferential direction. However, the second convex portion 73 may have a configuration in which a plurality of convex portions extending along the circumferential direction are arranged at intervals in the circumferential direction. In the present embodiment, the second convex portion 73 is located on the rear side of the spline shaft 71 in the extending direction of the shaft assembly 30. In an alternative embodiment, the second convex portion 73 may be located on the front side of the spline shaft 71. The outer diameter of the second convex portion 73 is larger than the major spline diameter of the spline shaft 71. In other words, the second convex portion 73 projects radially outward from the outer peripheral surface of the second adapter 70 at a height greater than half of the difference between the minor spline diameter of the spline shaft 71 and the major spline diameter of the spline shaft 71. That is, the second convex portion 73 projects further radially outward than the portion of the spline shaft 71 that projects most radially outward.

[0020] As shown in FIG. 5, the first adapter 60 includes an opposing inner peripheral surface portion 63 on its inner peripheral portion. As shown in FIGS. 6 and 7, the opposing inner peripheral surface portion 63 faces the second convex portion 73 of the second adapter 70 radially during and after the connection between the first adapter 60 and the second adapter 70. The clearance between the second convex portion 73 and the opposing inner peripheral surface portion 63 is smaller than the difference between the major spline diameter of the spline hole 61 and the major spline diameter of the spline shaft 71, and smaller than the difference between the minor spline diameter of the spline hole 61 and the minor spline diameter of the spline shaft 71.

[0021] The opposing inner circumferential surface portion 63 and the second protrusion portion 73 function as guides that restrict the radial positional relationship between the first adapter 60 and the second adapter 70 when inserting the second adapter 70 into the first adapter 60 to spline-couple it, and when removing the second adapter 70 from the first adapter 60 to release the spline coupling. Therefore, when attaching and detaching the first adapter 60 and the second adapter 70, it is possible to suppress the tilting of the axis of the first adapter 60 and the axis of the second adapter 70 relative to each other, and consequently, it is possible to suppress the acting of unnecessary radial forces on the spline hole 61 and the spline shaft 71. In particular, in this embodiment, the first protrusion portion 62 and the opposing outer circumferential surface portion 72, and the opposing inner circumferential surface portion 63 and the second protrusion portion 73 function as guides on both sides of the spline hole 61 and the spline shaft 71 in the extending direction of the shaft assembly 30. Therefore, it is possible to more effectively suppress the application of extra radial forces to the spline hole 61 and the spline shaft 71.

[0022] As shown in Figure 5, the first adapter 60 includes a first small-diameter portion 65 having an outer diameter smaller than the outer diameter of the first connecting portion 64. The first small-diameter portion 65 is located behind the first connecting portion 64, i.e., closer to the second adapter 70. The spline hole 61 is formed on the inner circumference of the first small-diameter portion 65. A first bearing 80 is positioned radially outward of the first small-diameter portion 65 to rotatably support the first adapter 60. In this embodiment, the first bearing 80 includes a radial ball bearing, but the type of bearing is not particularly limited as long as it can rotatably support the first adapter 60.

[0023] A substantially cylindrical first rubber sleeve 81 is positioned on the outer circumference of the first small-diameter portion 65. The first rubber sleeve 81 is a component manufactured using a material with appropriate elasticity and damping characteristics. For example, the first rubber sleeve 81 is a component manufactured using an elastic material such as fluororubber. The first rubber sleeve 81 is fitted onto the first small-diameter portion 65 so as to rotate integrally with the first adapter 60. The outer circumferential surface of the first rubber sleeve 81 is provided with an annular groove 82 extending in the circumferential direction. The first bearing 80 is partially housed within this annular groove 82. Specifically, the inner ring of the first bearing 80 is fitted into the annular groove 82 so as to rotate integrally with the first rubber sleeve 81. The outer ring of the first bearing 80 is supported by a first bearing support 83 fixed to the front tail portion 23. The first bearing support 83 may be supported by a first flange member 25. The first rubber sleeve 81 is positioned to abut against the stepped portion between the first connecting portion 64 and the first small-diameter portion 65. This allows for easy positioning of the first rubber sleeve 81 and the first bearing 80 in the extending direction of the shaft assembly 30. The position of the first bearing 80 in the extending direction of the shaft assembly 30 is fixed by an annular retaining ring 84 positioned on the rear side of the first rubber sleeve 81 so as to abut against the first rubber sleeve 81.

[0024] According to the above configuration, the first bearing 80 is positioned radially outward of the first small-diameter portion 65 of the first adapter 60, which has a relatively smaller outer diameter. Therefore, compared to the case where the first bearing 80 is positioned radially outward of the first connecting portion 64, the diameters of the first adapter 60 and the first bearing 80 can be reduced, and consequently, the helicopter 10 can be made lighter. Furthermore, the first bearing 80 rotatably supports the first adapter 60 via the first rubber sleeve 81. Therefore, even if misalignment occurs between the first adapter 60 and the second adapter 70 due to distortion of the aircraft body 20 or the like, the misalignment can be absorbed by the elastic deformation of the first rubber sleeve 81.

[0025] In an alternative embodiment, the first bearing 80 may be positioned radially outward of the first connecting portion 64. In a further alternative embodiment, the first adapter 60 may have a constant outer diameter from its front end to its rear end. In a further alternative embodiment, the first bearing 80 may be positioned adjacent to the first adapter 60 and in front of the first adapter 60, and may rotatably support the first shaft 40. In this case, the first bearing 80 may support the first shaft 40 via an iron sleeve instead of the first rubber sleeve 81. In a further embodiment, the first bearing 80 may directly support the first adapter 60 or the first shaft 40 without the first rubber sleeve 81.

[0026] As shown in Figure 5, the second adapter 70 includes a second small-diameter portion 75 having an outer diameter smaller than the outer diameter of the second connecting portion 74, and a third small-diameter portion 76 having an outer diameter smaller than the outer diameter of the second small-diameter portion 75. The second small-diameter portion 75 is located in front of the second connecting portion 74, that is, closer to the first adapter 60. The third small-diameter portion 76 is located in front of the second small-diameter portion 75. The spline shaft 71 and the second protrusion 73 are formed on the outer circumference of the third small-diameter portion 76. A second bearing 90 is positioned radially outward of the second small-diameter portion 75 to rotatably support the second adapter 70. In this embodiment, the second bearing 90 includes a radial ball bearing, but the type of bearing is not particularly limited as long as it can rotatably support the second adapter 70.

[0027] A substantially cylindrical second rubber sleeve 91 is positioned on the outer circumference of the second small-diameter portion 75. The second rubber sleeve 91 is a component manufactured using a material with appropriate elasticity and damping characteristics. For example, the second rubber sleeve 91 is a component manufactured using an elastic material such as fluororubber. The second rubber sleeve 91 is fitted into the second small-diameter portion 75 so as to rotate integrally with the second adapter 70. The outer circumferential surface of the second rubber sleeve 91 is provided with an annular groove 92 extending in the circumferential direction. The second bearing 90 is partially housed within this annular groove 92. More specifically, the inner ring of the second bearing 90 is fitted into the annular groove 92 so as to rotate integrally with the second rubber sleeve 91. The outer ring of the second bearing 90 is supported by a second bearing support 93 fixed to the rear tail portion 24. The bearing support 93 may be supported by a second flange member 26. Since no retaining ring is used in the second rubber sleeve 91, the second bearing 90 and the second adapter 70 can move relative to each other in the extending direction of the shaft assembly 30. Therefore, even if misalignment occurs between the first adapter 60 and the second adapter 70 due to distortion of the machine body 20, the misalignment can be absorbed by the relative displacement between the second adapter 70 and, consequently, between the second shaft 50 and the second bearing 90.

[0028] According to the above configuration, the second bearing 90 is positioned radially outward of the second small-diameter portion 75 of the second adapter 70, which has a smaller outer diameter than the second connecting portion 74. Therefore, compared to the case where the second bearing 90 is positioned radially outward of the second connecting portion 74, the second adapter 70 and the second bearing 90 can be made smaller in diameter, and consequently, the helicopter 10 can be made lighter. Furthermore, the spline shaft 71 and the second protrusion 73 are formed on the third small-diameter portion 76 of the second adapter 70, which has a smaller outer diameter than the second small-diameter portion 75. Therefore, the spline shaft 71 and the second protrusion 73 can be made smaller in diameter, and consequently, the helicopter 10 can be made even lighter. Furthermore, the second bearing 90 rotatably supports the second adapter 70 via the second rubber sleeve 91. Therefore, even if misalignment occurs between the first adapter 60 and the second adapter 70 due to distortion of the aircraft body 20, the misalignment can be absorbed by the elastic deformation of the second rubber sleeve 91.

[0029] In an alternative embodiment, the second bearing 90 may be positioned radially outward of the second connecting portion 74 or the third small-diameter portion 76. In a further alternative embodiment, the second adapter 70 may have a constant outer diameter from its front end to its rear end, or the second small-diameter portion 75 and the third small-diameter portion 76 may have the same outer diameter. In a further alternative embodiment, the second bearing 90 may be positioned adjacent to the second adapter 70 and on the rear side of the second adapter 70 to rotatably support the second shaft 50. In this case, the second bearing 90 may support the second shaft 50 via an iron sleeve instead of the second rubber sleeve 91. In a further embodiment, the second bearing 90 may directly support the second adapter 70 or the second shaft 50 without the second rubber sleeve 91.

[0030] As shown in Figure 5, an annular groove extending in the circumferential direction is formed on the outer circumferential surface of the second protrusion 73. An annular O-ring 78 is housed in this groove. As shown in Figure 7, when the first adapter 60 and the second adapter 70 are connected, the O-ring 78 seals the space between the first adapter 60 and the second adapter 70 behind the spline hole 61 and the spline shaft 71. Furthermore, a sealing rubber 66 having a shape and size that conforms to the inner circumferential surface of the first adapter 60 is arranged inside the first adapter 60. The sealing rubber 66 is located in front of the spline hole 61. Also, a sealing rubber 77 having a shape and size that conforms to the inner circumferential surface of the second adapter 70 is arranged on the inner circumferential part of the second adapter 70. With this configuration, as shown in Figure 7, the area 68 where the grease used in the spline hole 61 and the spline shaft 71 is located is isolated from the outside air. Area 68 is the internal space of the first adapter 60 and the second adapter 70, which is sealed by the O-ring 78 and the sealing rubber 77 and the sealing rubber 66.

[0031] In this embodiment, the first bearing 80 and the second bearing 90 have the same size. Specifically, the first bearing 80 and the second bearing 90 have the same inner diameter and the same outer diameter. In this embodiment, the first bearing 80 and the second bearing 90 have the same structure by adjusting the thickness of the first rubber sleeve 81 and the second rubber sleeve 91. By using the first bearing 80 and the second bearing 90 of the same size, the procurement and management of parts becomes easier.

[0032] According to the helicopter 10 described above, when not in use, the connection between the first adapter 60 and the second adapter 70 can be released, separating the front tail section 23 and the rear tail section 24. By separating the helicopter 10 into two parts, the helicopter 10 can be made smaller, and the size of the container housing the helicopter 10 can also be reduced. Moreover, when not separated, the shaft assembly 30 is rotatably supported by the first and second bearings on both sides near the connection point between the first adapter 60 and the second adapter 70. Therefore, the deflection of both the first shaft 40 and the second shaft 50 is suppressed compared to the case where the shaft assembly 30 is supported by a single bearing near the connection point. Consequently, the rotational driving force of the engine 13 is smoothly transmitted to the tail rotor 12 via the shaft assembly 30.

[0033] Furthermore, when separated, the first shaft 40 and the first adapter 60 are supported by the first bearing 80 near the connection point, and the second shaft 50 and the second adapter 70 are supported by the second bearing 90 near the connection point. Therefore, when the front tail section 23 and the rear tail section 24 are separated and the first adapter 60 and the second adapter 70 are unconnected, the first shaft 40 and the first adapter 60 do not undergo large radial displacement near the connection point, nor do the second shaft 50 and the second adapter 70 undergo large radial displacement near the connection point. Thus, the handling of the two separated parts is improved.

[0034] The second embodiment will now be described with reference to Figure 8. The second embodiment differs from the first embodiment only in that a shaft assembly 130 is used instead of a shaft assembly 30. The following description will focus only on the differences between the shaft assembly 130 and the first embodiment. Figure 8 is a partial cross-sectional view of the shaft assembly 130 according to the second embodiment and corresponds to Figure 7. In Figure 8, components identical to those in the first embodiment are denoted by the same reference numerals. As shown in Figure 8, the shaft assembly 130 includes a first adapter 160 and a second adapter 170 instead of the first adapter 60 and the second adapter 70.

[0035] As shown in Figure 8, the first adapter 160 is equipped with a spline shaft 161. The second adapter 170 is equipped with a spline hole 171 that is spline-coupled to the spline shaft 161. The first adapter 160 is equipped with a first protrusion 162 extending along the circumferential direction on its outer circumference. In this embodiment, the first protrusion 162 extends in an annular shape along the circumferential direction. However, the first protrusion 162 may have a configuration in which a plurality of protrusions extending along the circumferential direction are arranged at intervals in the circumferential direction. The first protrusion 162 is located in front of the spline shaft 161. The outer diameter of the first protrusion 162 is larger than the spline diameter of the spline shaft 161. The first protrusion 162 protrudes radially outward from the outer circumferential surface of the first adapter 160 to a height greater than half the difference between the spline diameter of the spline shaft 161 and the spline diameter of the spline shaft 161. The first protrusion 162 protrudes radially further outward than the most radially outwardly protruding portion of the spline shaft 161. The second adapter 170 is provided with an opposing inner circumferential surface portion 172 on its inner circumference. The opposing inner circumferential surface portion 172 faces the first protrusion 162 radially during and after the connection between the first adapter 160 and the second adapter 170. The radial clearance between the first protrusion 162 and the opposing inner circumferential surface portion 172 is smaller than the difference between the large spline diameter of the spline hole 171 and the large spline diameter of the spline shaft 161, and smaller than the difference between the small spline diameter of the spline hole 171 and the small spline diameter of the spline shaft 161.

[0036] The second adapter 170 has a second protrusion 173 on its inner circumference that extends along the circumferential direction. The inner diameter of the second protrusion 173 is smaller than the small spline diameter of the spline hole 171. The second protrusion 173 projects radially inward from the inner surface of the second adapter 170 to a height greater than half the difference between the small spline diameter and the large spline diameter of the spline hole 171. The second protrusion 172 projects radially inward even further than the part of the spline hole 171 that protrudes most radially inward. The first adapter 160 has an opposing outer peripheral surface portion 163 on its outer circumference. The opposing outer peripheral surface portion 163 faces the second protrusion 173 radially during and after the connection between the first adapter 160 and the second adapter 170. The radial clearance between the second protrusion 173 and the opposing outer peripheral surface 163 is smaller than the difference between the small spline diameter of the spline hole 171 and the small spline diameter of the spline shaft 161, and smaller than the difference between the large spline diameter of the spline hole 171 and the large spline diameter of the spline shaft 161.

[0037] The first adapter 160 includes a first connecting portion 164 connected to the second end 42 of the first shaft 40, a first small-diameter portion 165 having an outer diameter smaller than the outer diameter of the first connecting portion 164, and a second small-diameter portion 166 having an outer diameter smaller than the outer diameter of the first small-diameter portion 165. The first small-diameter portion 165 is located behind the first connecting portion 164. The second small-diameter portion 166 is located behind the first small-diameter portion 165. A spline shaft 161 is formed on the outer circumference of the second small-diameter portion 166. A first bearing 180 that rotatably supports the first adapter 160 is positioned radially outward of the first small-diameter portion 165. Similar to the first embodiment, the first bearing 180 supports the first adapter 160 via a first rubber sleeve 181 having an annular groove 182 and is supported by a bearing support 183 fixed to the front tail portion 23. The bearing support 183 may be supported by the first flange member 25.

[0038] The second adapter 170 comprises a second connecting portion 174 connected to the third end 51 of the second shaft 50, and a third small-diameter portion 175 having an outer diameter smaller than the outer diameter of the second connecting portion 174. The third small-diameter portion 175 is located in front of the second connecting portion 174. A spline hole 171 is formed on the inner circumference of the third small-diameter portion 175. A second bearing 190 is positioned radially outward of the third small-diameter portion 175 to rotatably support the second adapter 170. Similar to the first embodiment, the second bearing 190 supports the second adapter 170 via a second rubber sleeve 191 having an annular groove 192 and is supported by a bearing support 193 fixed to the rear tail portion 24. The bearing support 193 may be supported by a second flange member 26. Similar to the first bearing 80 in the first embodiment, the position of the second bearing 190 in the extending direction of the shaft assembly 30 is fixed by the retaining ring 194. Also, similar to the second bearing 90 and second adapter 70 in the first embodiment, the first bearing 180 and the first adapter 160 can move slightly relative to each other in the extending direction of the shaft assembly 30.

[0039] An annular groove formed on the outer circumferential surface of the first protrusion 162 houses an annular O-ring 168. Inside the first adapter 160, a seal rubber 167 is positioned, having a shape and size that conforms to the inner circumferential surface of the first adapter 160. Inside the second adapter 170, a seal rubber 176 is positioned, having a shape and size that conforms to the inner circumferential surface of the second adapter 170. The seal rubber 176 is positioned behind the spline hole 171. With this configuration, as shown in Figure 8, the area 169 where the grease used in the spline shaft 161 and spline hole 171 is located is isolated from the outside air. Area 169 is the internal space of the first adapter 160 and the second adapter 170, which is sealed by the O-ring 168, the seal rubber 167, and the seal rubber 176.

[0040] With a shaft assembly 130 having such a configuration, the same effects as the shaft assembly 30 of the first embodiment can be obtained.

[0041] Although several embodiments have been described above, these embodiments are provided to facilitate understanding of this teaching and do not limit the present invention. The present invention can be modified and improved without departing from its spirit, and its equivalents are included. Furthermore, any combination or omission of the components described in the claims and specification is possible to the extent that at least some of the above-mentioned problems can be solved or at least some of the effects can be achieved.

[0042] For example, the helicopter 10 and the shaft assemblies 30,130 may be separable at any point along the extension of the shaft assemblies 30,130 in the direction of extension of the shaft assemblies 30,130. For example, if the shaft assembly 30 extends from the tail section 22 to the fuselage section 21, the helicopter 10 may be separable at the boundary between the fuselage section 21 and the tail section 22. The fuselage section 21 and the front tail section 23 are non-limiting examples of the first part of the claims, and the rear tail section 24 is a non-limiting example of the second part of the claims.

[0043] Furthermore, the first adapter 60 and the second adapter 70 can be connected in a separable manner in any manner, not limited to spline connections. For example, the first adapter 60 and the second adapter 70 may be connected by serration connections. Alternatively, the first adapter 60 and the second adapter 70 may be connected by flange members and fasteners, similar to the first flange member 25 and the second flange member 26 shown in Figure 2.

[0044] The present invention can also be realized in the following embodiments. The various embodiments described below are not essential to the present invention and can be arbitrarily combined with any other embodiments.

[0045] According to a first embodiment, a helicopter is provided. This helicopter comprises a body, a power unit, a tail rotor, a first shaft, a first adapter, a second adapter, a second shaft, a first bearing, and a second bearing. The body is separated into a first part and a second part. The power unit is located in the first part. The tail rotor is located at the end of the second part opposite to the first part. The first shaft has a first end located closer to the power unit and a second end located further away from the power unit, and is located within the first part, through which the rotational driving force of the power unit is transmitted. The first adapter is connected to the second end of the first shaft. The second adapter is located on the opposite side of the first shaft from the first adapter and is connected to the first adapter. The second shaft has a third end connected to the second adapter and a fourth end connected to the tail rotor, and is located within the second part. The first bearing is positioned radially outward of the first adapter and rotatably supports the first adapter, or is positioned adjacent to the first adapter and rotatably supports the first shaft. The second bearing is positioned radially outward of the second adapter and rotatably supports the second adapter, or is positioned adjacent to the second adapter and rotatably supports the second shaft.

[0046] According to the first embodiment of the helicopter, when not in use, the connection between the first adapter and the second adapter can be released, separating the first and second parts of the aircraft. This allows for miniaturization of the helicopter and the container housing it. Furthermore, when not separated, the shaft assembly, which connects the first shaft, the first adapter, the second adapter, and the second shaft, is rotatably supported by the first and second bearings on both sides near the connection point between the first and second adapters (hereinafter also referred to as the adapter connection point). As a result, deflection of both the first and second shafts is suppressed compared to the case where the shaft assembly is supported by a single bearing near the adapter connection point. Consequently, the rotational driving force of the power unit is transmitted more smoothly to the tail rotor via the shaft assembly. Moreover, when separated, the first shaft and the first adapter are supported by the first bearing near the adapter connection point, and the second shaft and the second adapter are supported by the second bearing near the adapter connection point. Therefore, when the first and second parts of the aircraft are separated and the first and second adapters are disconnected, the first shaft and first adapter do not undergo significant radial displacement near the adapter connection point, nor do the second shaft and second adapter undergo significant radial displacement near the adapter connection point. Consequently, the handling of the two separated parts is improved.

[0047] According to a second aspect, in the first aspect, the first adapter includes a spline hole. The second adapter includes a spline shaft that is spline-coupled to the spline hole. The first adapter includes a first projection extending circumferentially on the inner circumference of the first adapter, which protrudes radially to a height greater than half the difference between the small spline diameter of the spline hole and the large spline diameter of the spline hole. The second adapter includes an opposing outer circumferential surface portion that is radially opposite to the first projection. The radial clearance between the first projection and the opposing outer circumferential surface portion is smaller than the difference between the small spline diameter of the spline hole and the small spline diameter of the spline shaft, and smaller than the difference between the large spline diameter of the spline hole and the large spline diameter of the spline shaft. According to the second embodiment, when the first shaft and the first adapter are connected, and the second shaft and the second adapter are connected, when attaching or detaching the first adapter and the second adapter, it is possible to suppress the tilting of the axes of the first adapter and the second adapter relative to each other. Therefore, it is possible to suppress the application of extra radial force to the spline hole and spline shaft due to the tilting between the axes of the first adapter and the second adapter.

[0048] According to the third embodiment, in the first or second embodiment, the first adapter includes a spline hole. The second adapter includes a spline shaft that is spline-coupled to the spline hole. The second adapter includes a second projection extending circumferentially on its outer circumference, projecting radially to a height greater than half the difference between the small spline diameter of the spline shaft and the large spline diameter of the spline shaft. The first adapter includes an opposing inner circumferential surface portion radially opposite to the second projection. The radial clearance between the second projection and the opposing inner circumferential surface portion is smaller than the difference between the large spline diameter of the spline hole and the large spline diameter of the spline shaft, and smaller than the difference between the small spline diameter of the spline hole and the small spline diameter of the spline shaft. According to the third embodiment, the same effects as the second embodiment can be obtained. In particular, when the second and third embodiments are combined, the application of unnecessary force to the spline teeth can be suppressed more effectively.

[0049] According to the fourth embodiment, in any of the first to third embodiments, the first adapter includes a spline shaft. The second adapter includes a spline hole that is spline-coupled to the spline shaft. The first adapter includes a first projection extending circumferentially on its outer circumference, projecting radially to a height greater than half the difference between the small spline diameter of the spline shaft and the large spline diameter of the spline shaft. The second adapter includes an opposing inner circumferential surface portion radially opposite to the first projection. The radial clearance between the first projection and the opposing inner circumferential surface portion is smaller than the difference between the large spline diameter of the spline hole and the large spline diameter of the spline shaft, and smaller than the difference between the small spline diameter of the spline hole and the small spline diameter of the spline shaft. According to the fourth embodiment, the same effect as in the third embodiment can be obtained.

[0050] According to the fifth embodiment, in any of the first to fourth embodiments, the first adapter includes a spline shaft. The second adapter includes a spline hole that is spline-coupled to the spline shaft. The second adapter includes a second protrusion extending circumferentially on its inner circumference, projecting radially to a height greater than half the difference between the small spline diameter of the spline hole and the large spline diameter of the spline hole. The first adapter includes an opposing outer circumferential surface portion radially opposite to the second protrusion. The radial clearance between the second protrusion and the opposing outer circumferential surface portion is smaller than the difference between the small spline diameter of the spline hole and the small spline diameter of the spline shaft, and smaller than the difference between the large spline diameter of the spline hole and the large spline diameter of the spline shaft. According to the fifth embodiment, the same effects as the second embodiment can be obtained. In particular, when the fourth embodiment and the fifth embodiment are combined, the application of unnecessary force to the spline teeth can be suppressed more effectively.

[0051] According to the sixth embodiment, in any of the first to fifth embodiments, the first adapter includes a first connecting portion connected to the second end of the first shaft, and a first small-diameter portion having an outer diameter smaller than the outer diameter of the first connecting portion. The first bearing is positioned radially outward of the first small-diameter portion. According to the sixth embodiment, the diameters of the first adapter and the first bearing can be reduced, and consequently, the weight of the helicopter can be reduced.

[0052] According to the seventh embodiment, in any of the first to sixth embodiments, the second adapter includes a second connecting portion connected to the third end of the second shaft, and a second small-diameter portion having an outer diameter smaller than the outer diameter of the second connecting portion. The second bearing is positioned radially outward of the second small-diameter portion. According to the seventh embodiment, the second adapter and the second bearing can be made smaller in diameter, and consequently, the helicopter can be made lighter.

[0053] According to the eighth aspect, in any of the first to seventh aspects, the first adapter includes a splined hole. The second adapter includes a splined shaft that is splined to the splined hole. The first adapter includes a first connecting portion connected to the second end of the first shaft, and a first small-diameter portion having an outer diameter smaller than the outer diameter of the first connecting portion. The first bearing is positioned radially outward of the first small-diameter portion. The first small-diameter portion includes a splined hole. The second adapter includes a second connecting portion connected to the third end of the second shaft, a second small-diameter portion having an outer diameter smaller than the outer diameter of the second connecting portion, and a third small-diameter portion having an outer diameter smaller than the outer diameter of the second small-diameter portion. The second bearing is positioned radially outward of the second small-diameter portion. The third small-diameter portion includes a splined shaft. According to the eighth aspect, the diameters of the first adapter, the second adapter, the first bearing and the second bearing can be reduced, and consequently, the helicopter can be made lighter.

[0054] According to the ninth aspect, in any of the first to eighth aspects, the first adapter includes a spline shaft. The second adapter includes a spline hole that spline-couples to the spline shaft. The first adapter includes a first connecting portion connected to the second end of the first shaft, a first small-diameter portion having an outer diameter smaller than the outer diameter of the first connecting portion, and a second small-diameter portion having an outer diameter smaller than the outer diameter of the first small-diameter portion. The first bearing is positioned radially outward of the first small-diameter portion. The second small-diameter portion includes the spline shaft. The second adapter includes a second connecting portion connected to the third end of the second shaft, and a third small-diameter portion having an outer diameter smaller than the outer diameter of the second connecting portion. The second bearing is positioned radially outward of the third small-diameter portion. The third small-diameter portion includes the spline hole. According to the ninth aspect, the same effect as in the eighth aspect can be obtained.

[0055] According to the tenth embodiment, in any of the first to ninth embodiments, the helicopter comprises a first rubber sleeve having a circumferentially extending annular groove, the annular groove partially housing a first bearing. The first bearing rotatably supports a first adapter or a first shaft via the first rubber sleeve. According to the tenth embodiment, misalignment between the first adapter and the second adapter can be absorbed by the elastic deformation of the first rubber sleeve.

[0056] According to the eleventh embodiment, in any of the first to tenth embodiments, the helicopter includes a second rubber sleeve having a circumferentially extending annular groove in which a second bearing is partially housed. The second bearing rotatably supports a second adapter or a second shaft via the second rubber sleeve. According to the eleventh embodiment, misalignment between the first adapter and the second adapter can be absorbed by the elastic deformation of the second rubber sleeve. [Explanation of symbols]

[0057] 10...Helicopter, 11...Main rotor, 12...Tail rotor, 13...Engine, 15...Skid, 20...Airframe, 21...Body section, 22...Tail section, 23...Front tail section, 24...Rear tail section, 25...First flange member, 26...Second flange member, 27...Bolt, 28...Nut, 29...Rivet, 30...Shaft assembly, 31...Bearing, 40...First shaft, 41...First end, 42...Second end, 43...Rivet, 50...Second shaft T, 51...Third end, 52...Fourth end, 53...Rivet, 60...First adapter, 61...Spline hole, 62...First protrusion, 63...Opposite inner circumferential surface, 64...First connecting part, 65...First small diameter part, 66...Seal rubber, 67...First step part, 68...Grease presence area, 70...Second adapter, 71...Spline shaft, 72...Opposite outer circumferential surface, 73...Second protrusion, 74...Second connecting part, 75...Second small diameter part, 76...Third small diameter part, 77...Seal rubber, 78...O-ring, 79... Second stage section, 80...First bearing, 81...First rubber sleeve, 82...Annular groove, 83...First bearing support, 84...Retaining ring, 90...Second bearing, 91...Second rubber sleeve, 92...Annular groove, 93...Second bearing support, 130...Shaft assembly, 160...First adapter, 161...Spline shaft, 162...First protrusion, 163...Opposite outer surface section, 164...First connecting section, 165...First small diameter section, 166...Second small diameter section, 167...Sealing ring 168...O-ring, 169...Grease area, 170...Second adapter, 171...Spline hole, 172...Opposite inner circumferential surface, 173...Second protrusion, 174...Second connecting part, 175...Third small diameter part, 176...Seal rubber, 180...First bearing, 181...First rubber sleeve, 182...Annular groove, 183...Bearing support, 190...Second bearing, 191...Second rubber sleeve, 192...Annular groove, 193...Bearing support, 194...Retaining ring

Claims

1. It is a helicopter, The aircraft separates into a first part and a second part, A power unit arranged in the first part, A tail rotor is positioned at the end of the second portion opposite to the first portion, A first shaft having a first end located near the power unit and a second end located far from the power unit, disposed within the first portion, and through which the rotational driving force of the power unit is transmitted, A first adapter connected to the second end of the first shaft, A second adapter is positioned on the opposite side of the first shaft, with the first adapter in between, and is connected to the first adapter. A second shaft having a third end connected to the second adapter and a fourth end connected to the tail rotor, and disposed within the second portion, A first bearing is positioned radially outward of the first adapter and rotatably supports the first adapter, or is positioned adjacent to the first adapter and rotatably supports the first shaft, A second bearing is positioned radially outward of the second adapter and rotatably supports the second adapter, or is positioned adjacent to the second adapter and rotatably supports the second shaft. A helicopter equipped with [a specific feature / equipment].

2. A helicopter according to claim 1, The first adapter includes a spline hole, The second adapter includes a spline shaft that is spline-coupled to the spline hole, The first adapter includes a first protrusion extending circumferentially on the inner circumference of the first adapter, which protrudes radially to a height greater than half the difference between the small diameter of the spline of the spline hole and the large diameter of the spline of the spline hole. The second adapter includes an opposing outer peripheral surface portion that is radially opposite to the first protrusion, The radial clearance between the first protrusion and the opposing outer peripheral surface is The difference between the small diameter of the spline in the spline hole and the small diameter of the spline shaft is smaller than the difference between the small diameter of the spline in the spline hole and the small diameter of the spline shaft. Smaller than the difference between the large spline diameter of the spline hole and the large spline diameter of the spline shaft. Helicopter.

3. A helicopter according to claim 1, The first adapter includes a spline hole, The second adapter includes a spline shaft that is spline-coupled to the spline hole, The second adapter includes a second protrusion extending circumferentially on its outer circumference, which protrudes radially to a height greater than half the difference between the small diameter of the spline shaft and the large diameter of the spline shaft. The first adapter includes an opposing inner circumferential surface portion that is radially opposite to the second protrusion, The radial clearance between the second protrusion and the opposing inner circumferential surface is The difference between the large diameter of the spline in the spline hole and the large diameter of the spline shaft is smaller than the difference between the two. Smaller than the difference between the small diameter of the spline in the spline hole and the small diameter of the spline shaft. Helicopter.

4. A helicopter according to claim 1, The first adapter includes a spline shaft, The second adapter includes a spline hole that is spline-coupled to the spline shaft, The first adapter includes a first protrusion extending circumferentially on its outer circumference, which protrudes radially to a height greater than half the difference between the small diameter of the spline shaft and the large diameter of the spline shaft. The second adapter includes an opposing inner circumferential surface portion that is radially opposite to the first protrusion, The radial clearance between the first protrusion and the opposing inner circumferential surface is The difference between the large diameter of the spline in the spline hole and the large diameter of the spline shaft is smaller than the difference between the two. Smaller than the difference between the small diameter of the spline in the spline hole and the small diameter of the spline shaft. Helicopter.

5. A helicopter according to claim 1, The first adapter includes a spline shaft, The second adapter includes a spline hole that is spline-coupled to the spline shaft, The second adapter includes a second protrusion extending circumferentially on the inner circumference of the second adapter, which protrudes radially to a height greater than half the difference between the small diameter of the spline of the spline hole and the large diameter of the spline of the spline hole. The first adapter includes an opposing outer peripheral surface portion that is radially opposite to the second protrusion, The radial clearance between the second protrusion and the opposing outer peripheral surface is The difference between the small diameter of the spline in the spline hole and the small diameter of the spline shaft is smaller than the difference between the small diameter of the spline in the spline hole and the small diameter of the spline shaft. Smaller than the difference between the large spline diameter of the spline hole and the large spline diameter of the spline shaft. Helicopter.

6. A helicopter according to any one of claims 1 to 5, The first adapter includes a first connecting portion connected to the second end of the first shaft, and a first small-diameter portion having an outer diameter smaller than the outer diameter of the first connecting portion. The first bearing is positioned radially outward of the first small diameter portion. Helicopter.

7. A helicopter according to any one of claims 1 to 5, The second adapter includes a second connecting portion connected to the third end of the second shaft, and a second small-diameter portion having an outer diameter smaller than the outer diameter of the second connecting portion. The second bearing is positioned radially outward of the second small-diameter portion. Helicopter.

8. A helicopter according to claim 1, The first adapter includes a spline hole, The second adapter includes a spline shaft that is spline-coupled to the spline hole, The first adapter includes a first connecting portion connected to the second end of the first shaft, and a first small-diameter portion having an outer diameter smaller than the outer diameter of the first connecting portion. The first bearing is positioned radially outward of the first small diameter portion. The first small diameter portion includes the spline hole, The second adapter includes a second connecting portion connected to the third end of the second shaft, a second small-diameter portion having an outer diameter smaller than the outer diameter of the second connecting portion, and a third small-diameter portion having an outer diameter smaller than the outer diameter of the second small-diameter portion. The second bearing is positioned radially outward of the second small diameter portion. The third small diameter portion includes the spline shaft. Helicopter.

9. A helicopter according to claim 1, The first adapter includes a spline shaft, The second adapter includes a spline hole that is spline-coupled to the spline shaft, The first adapter includes a first connecting portion connected to the second end of the first shaft, a first small-diameter portion having an outer diameter smaller than the outer diameter of the first connecting portion, and a second small-diameter portion having an outer diameter smaller than the outer diameter of the first small-diameter portion. The first bearing is positioned radially outward of the first small diameter portion. The second small diameter portion includes the spline shaft, The second adapter includes a second connecting portion connected to the third end of the second shaft, and a third small-diameter portion having an outer diameter smaller than the outer diameter of the second connecting portion. The second bearing is positioned radially outward of the third small diameter portion. The third small diameter portion includes the spline hole. Helicopter.

10. A helicopter according to any one of claims 1 to 5, 8 and 9, The first rubber sleeve comprises an annular groove extending in the circumferential direction, the annular groove having which the first bearing is partially housed. The first bearing rotatably supports the first adapter or the first shaft via the first rubber sleeve. Helicopter.

11. A helicopter according to any one of claims 1 to 5, 8 and 9, The second rubber sleeve comprises an annular groove extending in the circumferential direction, the annular groove having which the second bearing is partially housed. The second bearing rotatably supports the second adapter or the second shaft via the second rubber sleeve. Helicopter.

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