A tandem dual coaxial rotorcraft transmission system and rotorcraft

Abstract

The application relates to a tandem double coaxial double-rotor machine transmission system, which comprises a middle shaft unit connected in symmetry through multiple sections of parallel shafts, engine output reduction units connected in symmetry on the left and right sides of the middle shaft unit, and front-rotor reversing reduction units and rear-rotor reversing reduction units connected on the outer sides of the engine output reduction units; the transmission system adopts two front and rear engine outputs, transmits power to lower rotor shafts through first-stage bevel gears in the rotor reduction units and second-stage helical cylindrical gear reduction, and transmits power to upper rotors through third-stage helical cylindrical gear reduction, the upper rotor shafts and the lower rotor shafts are realized as coaxial counter-rotation through inner and outer shafts, power transmission of the front and rear coaxial double rotors is realized, and the remaining power is transmitted to fans through the front and rear first-stage bevel gears to realize ventilation cooling of the reversing bevel gears in the rotor machine reduction system; the design can greatly improve power utilization efficiency and helicopter hovering efficiency, and is favorable for reducing the weight of the system.

Description

Technical Field

[0001] This invention belongs to the field of aerospace technology and relates to a tandem twin-coaxial twin-rotor transmission system and a rotorcraft. Background Technology

[0002] In the aerospace field, conventional tandem helicopters can efficiently hover and perform vertical takeoff and landing (VTOL), but their maneuverability is relatively poor. Unlike conventional tandem helicopters, tandem coaxial twin-rotor helicopters use two counter-rotating rotors arranged front and rear to balance rotor torque and utilize the torque difference between the rotors to achieve directional control. Therefore, they have a higher rotor power consumption ratio, smaller blade diameter, more flexible VTOL characteristics, and are better able to resist interference from gusts. Tandem coaxial twin-rotor helicopters require less power during hovering and low-to-medium speed flight than conventional helicopters, resulting in a more compact structure and smaller fuselage dimensions. Structurally, the lift of a tandem coaxial twin-rotor helicopter is generated by two rotors, and compared to a tandem helicopter of the same mass, with the same rotor disk load, its rotor radius is smaller than that of a conventional helicopter. Tandem coaxial rotorcraft can reduce fuselage length, and helicopter components can be compactly mounted around the center of gravity, reducing the helicopter's pitch and roll moment of inertia, thus providing better maneuverability.

[0003] The transmission system is one of the key moving components of a tandem coaxial rotorcraft. Its main function is to transmit the engine's output power to the front and rear rotors and other accessory devices through a specific gear ratio, reducing speed and steering. It is a crucial power transmission system for tandem rotorcraft. To meet the carrying capacity requirements of tandem helicopters, the transmission system of a tandem coaxial rotorcraft must be more compact, lighter, and more reliable. Due to the conventional tandem helicopter rotor structure and long fuselage, the entire transmission system is heavy and large in size. Therefore, it is necessary to propose a tandem coaxial rotorcraft transmission system to avoid the problems existing in the above design. Summary of the Invention

[0004] In view of this, in order to solve the problem of poor overall aircraft handling caused by the long fuselage and heavy weight of the current tandem rotorcraft transmission system, the present invention provides a lightweight, compact, and highly efficient tandem coaxial rotorcraft transmission system and rotorcraft.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A tandem coaxial twin rotor transmission system includes an intermediate shaft unit symmetrically connected by multiple parallel shafts, an engine output reduction unit symmetrically connected on the left and right sides of the intermediate shaft unit, and a front rotor reversing reduction unit and a rear rotor reversing reduction unit respectively connected to the outside of the engine output reduction unit.

[0007] The engine output reduction unit includes an engine output shaft, a first-stage engine reduction input cylindrical gear mounted on the engine output shaft, and a first-stage engine reduction output cylindrical gear meshing with the first-stage engine reduction input cylindrical gear. The first-stage engine reduction output cylindrical gear is mounted on the parallel shafts at both ends.

[0008] Both the front rotor reversing reduction unit and the rear rotor reversing reduction unit include a second-stage bevel gear input shaft, a second-stage bevel gear output shaft that is driven by the second-stage bevel gear input shaft, and a second-stage bevel gear accessory shaft that is driven by the second-stage bevel gear output shaft. The second-stage bevel gear input shaft is installed on the outer side of both ends of the parallel shaft. A third-stage helical cylindrical gear input shaft is driven by the second-stage bevel gear output shaft. A lower rotor shaft is driven by the third-stage helical cylindrical gear input shaft. An upper rotor shaft is connected above the lower rotor shaft.

[0009] Furthermore, a synchronizing clutch is installed on the central parallel shaft of the intermediate shaft unit, and brake discs are installed on the parallel shafts at both ends. Deep groove ball bearings are also installed on the parallel shafts. By connecting or disconnecting from the engine through the synchronizing clutch, engine power is transmitted to the entire system, effectively controlling the on / off state of power transmission.

[0010] Furthermore, a deep groove ball bearing is installed on the engine output shaft to provide support.

[0011] Furthermore, an overrunning clutch is installed on the engine output shaft. The overrunning clutch connects to or disconnects from the engine, and the engine power is transmitted to the entire system through the overrunning clutch, which can effectively control the on and off of power transmission.

[0012] Furthermore, a second-stage reversing reduction input bevel gear is mounted on the second-stage bevel gear input shaft, and a second-stage reversing reduction output bevel gear meshing with the second-stage reversing reduction input bevel gear is mounted on the second-stage bevel gear output shaft. A second-stage reversing reduction output accessory bevel gear meshing with the second-stage reversing reduction output bevel gear is mounted on the second-stage bevel gear accessory shaft. A third-stage reduction input helical cylindrical gear is mounted on the second-stage bevel gear output shaft. A third-stage reduction output helical cylindrical gear I, meshing with the third-stage reduction input helical cylindrical gear, is mounted on the lower rotor shaft. A fourth-stage reduction output helical cylindrical gear is mounted on the lower rotor shaft. A third-stage reduction output helical cylindrical gear II and a fourth-stage reduction input helical cylindrical gear, both meshing with the third-stage reduction input helical cylindrical gear, are mounted on the third-stage helical cylindrical gear input shaft. The fourth-stage reduction input helical cylindrical gear mounted on the third-stage helical cylindrical gear input shaft meshes with the fourth-stage reduction output helical cylindrical gear mounted on the lower rotor shaft.

[0013] Furthermore, the second-stage bevel gear input shaft and the second-stage reversing reduction bevel gear are integrated into one structure, and the second-stage bevel gear accessory shaft and the second-stage accessory bevel gear are integrated into one structure.

[0014] Furthermore, the second-stage bevel gear input shafts on both sides of the second-stage reversing reduction bevel gear are equipped with back-to-back tapered roller bearings and cylindrical roller bearings for support; the second-stage bevel gear output shaft is equipped with cylindrical roller bearings and four-point contact ball bearings for support; the second-stage bevel gear accessory shaft is equipped with cylindrical roller bearings and four-point contact ball bearings for support; the third-stage helical cylindrical gear output shaft is equipped with cylindrical roller bearings and four-point contact ball bearings for support; and the upper rotor shaft and lower rotor shaft are equipped with cylindrical roller bearings and four-point contact ball bearings for support.

[0015] Furthermore, the engine output shaft is connected to the first-stage engine reduction gear via a spline connection, and the second-stage bevel gear input shaft is connected to the engine reduction gear via a spline connection.

[0016] Furthermore, in the front rotor reversing reduction unit and the rear rotor reversing reduction unit, the output shaft of the second-stage bevel gear is splinedly connected to the output bevel gear of the second-stage reversing reduction and the input helical cylindrical gear of the third-stage reduction; the output shaft of the third-stage helical cylindrical gear is splinedly connected to the output helical cylindrical gear II of the third-stage reduction and the input helical cylindrical gear of the fourth-stage reduction; the lower rotor shaft is splinedly connected to the output helical cylindrical gear of the fourth-stage reduction; and the upper rotor shaft is splinedly connected to the output helical cylindrical gear I of the third-stage reduction.

[0017] A rotorcraft includes a fuselage and the aforementioned tandem coaxial rotor transmission system, wherein the aforementioned tandem coaxial rotor transmission system is disposed within the fuselage.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The tandem coaxial twin-rotor transmission system disclosed in this invention employs two engines, one at the front and one at the rear. The power is reversed and reduced in speed by a first-stage bevel gear in the rotor reversing and reduction unit. Then, the power is transmitted to the lower rotor by a second-stage helical cylindrical gear and to the upper rotor by a third-stage helical cylindrical gear, thus achieving coaxial reversal of the upper and lower rotor shafts. Compared with the traditional tandem transmission system, this structure is more compact, has higher power utilization efficiency, and can greatly reduce system weight and structural size.

[0020] 2. The tandem coaxial twin-rotor transmission system disclosed in this invention features an overrunning clutch mounted on the engine output shaft. This overrunning clutch enables the engine to engage and disengage when one engine fails. An automatic synchronizing clutch is mounted on the intermediate shaft unit. This automatic synchronizing clutch enables simultaneous high-speed transmission of enormous torque while maintaining synchronized rotational speeds, automatically disengaging and engaging.

[0021] 3. The tandem coaxial twin rotor transmission system disclosed in this invention adopts a single-stage bevel gear pair and a two-stage cylindrical gear pair; the bevel gear pair is used for deceleration and reversal, and the cylindrical gear pair is used for deceleration and to realize the coaxial reversal of the rotor shaft. It has a compact structure and high transmission efficiency.

[0022] 4. The tandem coaxial twin rotorcraft transmission system disclosed in this invention has a fan installed on the shaft of the first-stage bevel gear in the front and rear rotor reversing reduction units. The fan can realize ventilation and cooling of the reversing bevel gear in the rotorcraft reduction system.

[0023] 5. The tandem coaxial twin-rotor transmission system disclosed in this invention features a second-stage bevel gear input shaft and a second-stage reversing reduction input bevel gear integrated into the front and rear rotor reversing reduction units, and a second-stage bevel gear accessory shaft and a second-stage accessory bevel gear integrated into the front and rear rotor reversing reduction units. The input shaft is equipped with back-to-back tapered roller bearings, which helps to counteract the axial force generated by the meshing of the transmission system. The second-stage reduction reversing output bevel gear, the third-stage helical cylindrical gear, and the fourth-stage helical cylindrical gear are connected by splines, which helps to reduce the misalignment rate and improve the stability of the transmission system.

[0024] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0026] Figure 1 This is a schematic diagram of the tandem coaxial twin-rotor transmission system of the present invention;

[0027] Figure 2 This is a front view of the tandem coaxial twin-rotor transmission system of the present invention;

[0028] Figure 3 This is a schematic diagram of the transmission principle of the tandem coaxial twin rotorcraft transmission system of the present invention.

[0029] Reference numerals: First-stage engine reduction gear 1, overrunning clutch 3, engine output shaft 4, synchronizing clutch 5, first-stage engine reduction gear 8, brake disc 10, second-stage reversing reduction gear 13, second-stage bevel gear output shaft 15, second-stage reversing reduction gear 17, second-stage reversing reduction gear 18, second-stage bevel gear accessory shaft 21, third-stage reduction gear 24, third-stage reduction gear I, second-stage reduction gear 26, fourth stage... The system includes a reduction gear 29 (helical cylindrical gear), a lower rotor shaft 32, an upper rotor shaft 33, a third-stage helical cylindrical gear input shaft 34, a fourth-stage reduction gear input helical cylindrical gear 36, a third-stage reduction gear II 38, a second-stage bevel gear input shaft 40, deep groove ball bearings 2, 41, 6, 7, and 9, tapered roller bearings 11 and 12, cylindrical roller bearings 14, 16, 19, 22, 25, 28, 31, 35, and 39, and four-point contact ball bearings 20, 23, 27, 30, and 37. Detailed Implementation

[0030] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0031] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures, and should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0032] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0033] like Figures 1-3 The tandem coaxial twin-rotor transmission system shown includes an intermediate shaft unit symmetrically connected by four parallel shafts, an engine output reduction unit symmetrically connected to the left and right sides of the intermediate shaft unit, and a front rotor reversing reduction unit and a rear rotor reversing reduction unit respectively connected to the outside of the engine output reduction unit. The front rotor reversing reduction unit and the rear rotor reversing reduction unit have the same structure.

[0034] A synchronizing clutch 5 is installed on the central parallel shaft of the intermediate shaft unit. The synchronizing clutch 5 connects to or disconnects from the engine, and the engine power is transmitted to the entire system through the synchronizing clutch 5, which can effectively control the on and off of power transmission. Brake discs 10 are installed on the parallel shafts at both ends, and deep groove ball bearings 6, 7, and 9 are installed on the parallel shafts.

[0035] The engine output reduction unit includes an engine output shaft 4, a first-stage engine reduction input cylindrical gear 1 mounted on the engine output shaft 4, and a first-stage engine reduction output cylindrical gear 8 meshing with the first-stage engine reduction input cylindrical gear 1. The first-stage engine reduction output cylindrical gear 8 is mounted on parallel shafts at both ends. Deep groove ball bearings 2 and 41 are mounted on the engine output shaft 4 for support. An overrunning clutch 3 is mounted on the engine output shaft 4, which connects to or disconnects from the engine. Engine power is transmitted to the entire system through the overrunning clutch 3, effectively controlling the on / off state of power transmission.

[0036] Both the front rotor reversing reduction unit and the rear rotor reversing reduction unit include a second-stage bevel gear input shaft 40, a second-stage bevel gear output shaft 15 connected to the second-stage bevel gear input shaft 40, and a second-stage bevel gear accessory shaft 21 connected to the second-stage bevel gear output shaft 15. The second-stage bevel gear input shaft 40 is mounted on the outer sides of both ends of the parallel shaft. A third-stage helical cylindrical gear input shaft 34 is connected to the second-stage bevel gear output shaft 15. A lower rotor shaft 32 is connected to the third-stage helical cylindrical gear input shaft 34. An upper rotor shaft 33 is connected above the lower rotor shaft 32. Specifically, a second-stage reversing reduction input bevel gear 13 is mounted on the second-stage bevel gear input shaft 40, a second-stage reversing reduction output bevel gear 17 meshing with the second-stage reversing reduction input bevel gear 13 is mounted on the second-stage bevel gear output shaft 15, and a second-stage reversing reduction output accessory bevel gear 18 meshing with the second-stage reversing reduction output bevel gear 17 is mounted on the second-stage bevel gear accessory shaft 21. The second-stage bevel gear output shaft 15 is equipped with a third-stage reduction helical gear 24. The upper rotor shaft 33 is equipped with a third-stage reduction output helical gear I 26 that meshes with the third-stage reduction input helical gear 24. The lower rotor shaft 32 is equipped with a fourth-stage reduction output helical gear 29. The third-stage helical gear input shaft 34 is equipped with a third-stage reduction output helical gear II 38 and a fourth-stage reduction input helical gear 36 that mesh with the third-stage reduction input helical gear 24. The fourth-stage reduction input helical gear 36 installed on the third-stage helical gear input shaft 34 meshes with the fourth-stage reduction output helical gear 29 installed on the lower rotor shaft 32.

[0037] The second-stage bevel gear input shaft 40 and the second-stage reversing reduction input bevel gear 13 are integrated into one structure, and the second-stage bevel gear accessory shaft 21 and the second-stage accessory bevel gear 18 are integrated into one structure.

[0038] Back-to-back tapered roller bearings 11 and 12 and cylindrical roller bearings 14 are installed on the input shaft 40 of the second-stage reversing reduction bevel gear 13 on both sides to provide support. Cylindrical roller bearings 16, 22, 25 and four-point contact ball bearings 23 are installed on the output shaft 15 of the second-stage bevel gear to provide support. Cylindrical roller bearings 19 and four-point contact ball bearings 20 are installed on the accessory shaft 21 of the second-stage bevel gear to provide support. Cylindrical roller bearings 35 and 39 and four-point contact ball bearings 37 are installed on the output shaft 34 of the third-stage helical cylindrical gear to provide support. Cylindrical roller bearings 28 and 31 and four-point contact ball bearings 27 and 30 are installed on the upper rotor shaft 33 and the lower rotor shaft 32 to provide support.

[0039] The engine output shaft 4 is splinedly connected to the first-stage engine reduction input cylindrical gear 1; the second-stage bevel gear input shaft 40 is splinedly connected to the engine reduction output cylindrical gear 8; in the front rotor reversing reduction unit and the rear rotor reversing reduction unit, the second-stage bevel gear output shaft 15 is splinedly connected to the second-stage reversing reduction output bevel gear 17 and the third-stage reduction input helical cylindrical gear 24; the third-stage helical cylindrical gear output shaft 34 is splinedly connected to the third-stage reduction output helical cylindrical gear II 38 and the fourth-stage reduction input helical cylindrical gear 36; the lower rotor shaft 32 is splinedly connected to the fourth-stage reduction output helical cylindrical gear 29; and the upper rotor shaft 33 is splinedly connected to the third-stage reduction output helical cylindrical gear I 26.

[0040] The tandem coaxial rotorcraft transmission system consists of an engine output reduction unit and a front and rear rotor reversing reduction unit. Power (on one side) is input from the engine output shaft 4, transmitted through the first-stage engine reduction input cylindrical gear 1 and the first-stage engine reduction output cylindrical gear 8 to the second-stage bevel gear input shaft 40. Then, through the second-stage reversing reduction input bevel gear 13 and the second-stage reversing reduction output bevel gear 17, power is transmitted to the second-stage bevel gear output shaft 15. The third-stage reduction input helical cylindrical gear 24 transmits power to the third-stage reduction output helical cylindrical gear I 26 and the third-stage reduction output helical cylindrical gear II 38. The third-stage reduction output helical cylindrical gear I 26 and the third-stage reduction output helical cylindrical gear II 38 transmit power to the upper rotor shaft 33 and the lower rotor shaft 32, respectively. The power transmission route on the other side is the same. The remaining power is transmitted to the fan via the second-stage reversing reduction output accessory bevel gear 18 to achieve ventilation and cooling of the reversing bevel gears in the rotorcraft's reduction system. The brake disc 10 is mounted on the parallel shaft of the intermediate shaft unit to brake the transmission system when it needs to decelerate.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A tandem twin-coaxial twin-rotor aircraft transmission system, characterized in that, It includes an intermediate shaft unit symmetrically connected by multiple parallel shafts, an engine output reduction unit symmetrically connected on the left and right sides of the intermediate shaft unit, and a front rotor reversing reduction unit and a rear rotor reversing reduction unit respectively connected to the outside of the engine output reduction unit. The engine output reduction unit includes an engine output shaft (4), a first-stage engine reduction input cylindrical gear (1) mounted on the engine output shaft (4), and a first-stage engine reduction output cylindrical gear (8) meshing with the first-stage engine reduction input cylindrical gear (1). The first-stage engine reduction output cylindrical gear (8) is mounted on the parallel shafts at both ends. Both the front rotor reversing reduction unit and the rear rotor reversing reduction unit include a second-stage bevel gear input shaft (40), a second-stage bevel gear output shaft (15) that is driven by the second-stage bevel gear input shaft (40), and a second-stage bevel gear accessory shaft (21) that is driven by the second-stage bevel gear output shaft (15). The second-stage bevel gear input shaft (40) is installed on the outer side of both ends of the parallel shaft. A third-stage helical cylindrical gear input shaft (34) is driven by the second-stage bevel gear output shaft (15). A lower rotor shaft (32) is driven by the third-stage helical cylindrical gear input shaft (34). An upper rotor shaft (33) is connected above the lower rotor shaft (32). The second-stage bevel gear input shaft (40) is equipped with a second-stage reversing reduction input bevel gear (13), the second-stage bevel gear output shaft (15) is equipped with a second-stage reversing reduction output bevel gear (17) meshing with the second-stage reversing reduction input bevel gear (13), the second-stage bevel gear accessory shaft (21) is equipped with a second-stage reversing reduction output accessory bevel gear (18) meshing with the second-stage reversing reduction output bevel gear (17), the second-stage bevel gear output shaft (15) is equipped with a third-stage reduction input helical cylindrical gear (24), and the upper rotor shaft (33) is equipped with a third-stage reduction input helical cylindrical gear. The third-stage reduction helical gear I (26) meshes with the wheel (24), and the fourth-stage reduction helical gear (29) is installed on the lower rotor shaft (32). The third-stage reduction helical gear II (38) and the fourth-stage reduction helical gear (36) mesh with the third-stage reduction helical gear (24) on the input shaft (34) of the third-stage reduction helical gear. The fourth-stage reduction helical gear (36) installed on the input shaft (34) of the third-stage reduction helical gear meshes with the fourth-stage reduction helical gear (29) installed on the lower rotor shaft (32).

2. The tandem twin-coaxial twin-rotor transmission system as described in claim 1, characterized in that, The intermediate shaft unit is equipped with a synchronous clutch (5) on the central parallel shaft, and brake discs (10) are installed on the parallel shafts at both ends. Deep groove ball bearings are installed on the parallel shafts.

3. The tandem twin-coaxial twin-rotor transmission system as described in claim 2, characterized in that, A deep groove ball bearing is installed on the engine output shaft (4) to provide support.

4. The tandem twin-coaxial twin-rotor transmission system as described in claim 3, characterized in that, An overrunning clutch (3) is mounted on the engine output shaft (4).

5. The tandem twin-coaxial twin-rotor transmission system as described in claim 1, characterized in that, The second-stage bevel gear input shaft (40) and the second-stage reversing deceleration input bevel gear (13) are integrated into one structure, and the second-stage bevel gear accessory shaft (21) and the second-stage reversing deceleration output accessory bevel gear (18) are integrated into one structure.

6. The tandem twin-coaxial twin-rotor transmission system as described in claim 5, characterized in that, Back-to-back tapered roller bearings and cylindrical roller bearings are installed on the second-stage bevel gear input shaft (40) on both sides of the second-stage reversing reduction input bevel gear (13) to provide support. Cylindrical roller bearings and four-point contact ball bearings are installed on the second-stage bevel gear output shaft (15), the second-stage bevel gear accessory shaft (21), the third-stage helical cylindrical gear input shaft (34), the upper rotor shaft (33), and the lower rotor shaft (32) to provide support.

7. The tandem twin-coaxial twin-rotor transmission system as described in claim 6, characterized in that, The engine output shaft (4) is splinedly connected to the first-stage engine reduction input cylindrical gear (1), and the second-stage bevel gear input shaft (40) is splinedly connected to the first-stage engine reduction output cylindrical gear (8).

8. The tandem twin-coaxial twin-rotor transmission system as described in claim 7, characterized in that, In the front rotor reversing reduction unit and the rear rotor reversing reduction unit, the output shaft (15) of the second-stage bevel gear is splinedly connected to the output bevel gear (17) of the second-stage reversing reduction and the input helical cylindrical gear (24) of the third-stage reduction; the input shaft (34) of the third-stage helical cylindrical gear is splinedly connected to the output helical cylindrical gear II (38) of the third-stage reduction and the input helical cylindrical gear (36) of the fourth-stage reduction; the lower rotor shaft (32) is splinedly connected to the output helical cylindrical gear (29) of the fourth-stage reduction; and the upper rotor shaft (33) is splinedly connected to the output helical cylindrical gear I (26) of the third-stage reduction.

9. A rotary-wing aircraft, characterized in that, The aircraft includes a fuselage and a tandem coaxial twin-rotor transmission system as described in any one of claims 1 to 8, wherein the tandem coaxial twin-rotor transmission system is disposed within the fuselage.

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