A tandem unmanned helicopter drive shaft and a design method thereof

Abstract

The application discloses a kind of longitudinal unmanned helicopter transmission shaft and its design method, it is related to unmanned helicopter transmission system design field.The design method includes: initial parameter is entered including the rotation inertia of each component of system and multi-working condition load spectrum;Transmission shaft structure design is carried out and stress intensity check is completed;Local resonance is avoided by regulating single shaft frequency;Eight degrees of freedom transmission system torsional vibration dynamics matrix is constructed to check whole chain coupling vibration;Torsional angle-transmission ratio coupling model is used to solve and compensate actual deviation of front and rear rotor phase;Fatigue damage value of transmission shaft is quantitatively calculated based on Miner theory;Finally, according to multi-dimensional convergence criterion, the final parameter is output.The application can accurately predict coupling vibration, control the deviation of rotor phase within 3°, and quantify fatigue life, effectively improve the stability and service durability of transmission system.

Description

Technical Field

[0001] This invention relates to the field of unmanned helicopter transmission system design, specifically to a tandem unmanned helicopter transmission shaft and its design method. Background Technology

[0002] The statements in this section are provided only as background information in connection with this disclosure and may not constitute prior art.

[0003] Tandem-type unmanned helicopters employ a longitudinal layout with two rotors, one in front and one behind, rotating in opposite directions. This eliminates the tail rotor, offering advantages such as high payload capacity, excellent hovering stability, and efficient use of fuselage space. They are widely used in cargo delivery, reconnaissance and inspection, emergency rescue, and agricultural operations. Their transmission system typically uses an engine-belt drive-front and rear driveshafts-front and rear reduction gears-twin rotors power transmission structure. The driveshafts, as core transmission components, are subjected to alternating torque, torsional vibration loads, and the coupling effects of assembly deviations over extended periods. Their structural strength, torsional vibration characteristics, critical speed, and influence on rotor phase directly determine the overall flight safety, service life, and handling quality of the aircraft.

[0004] However, the existing tandem drive shaft design for unmanned helicopters has significant flaws, mainly in the following three aspects: 1. Difficulty in predicting coupled vibrations across the entire drive train. Traditional designs typically only perform torsional vibration and critical speed analyses on a single drive shaft, without integrating series components such as the engine, belt drive, reducer, and rotor into a global dynamic model. This makes it impossible to identify coupled vibration modes of multiple components, which can easily lead to system resonance and excessive vibration amplitude during operation, severely shortening the service life of components.

[0005] 2. Lack of quantitative assessment and compensation methods for rotor phase deviation. The industry generally ignores the influence of the elastic torsion of the drive shaft and has not established a phase calculation model that links the torsion angle with the gearbox transmission ratio. After the drive shaft undergoes torsional deformation under load, it is amplified by the reduction mechanism, causing the front and rear rotors to deviate from the theoretical phase by 90°, resulting in helicopter shaking and a decrease in maneuverability. In severe cases, it can even cause interference between the front and rear rotor blades.

[0006] 3. Lack of a quantitative assessment system for fatigue life. Existing designs mostly rely on engineering experience for simple static strength checks, without conducting differentiated designs for asymmetric driveshafts that are long at the front with multiple supports and short at the rear with rigidity. Furthermore, there is a lack of life assessment based on alternating loads under full flight conditions, making it impossible to accurately predict the fatigue failure risk of driveshafts under long-term service, resulting in large structural redundancy or uncontrollable durability of products. Summary of the Invention

[0007] The purpose of this invention is to address the technical problems in the current design of tandem unmanned helicopter transmission systems, namely, the difficulty in predicting coupled vibrations across the entire transmission chain, the lack of quantitative assessment methods for rotor phase deviation, and the lack of quantitative control over fatigue life. This invention provides a tandem unmanned helicopter transmission shaft and its design method. Based on constructing a torsional vibration dynamics matrix of the transmission system across the entire domain to eliminate coupled resonance, establishing a torsional angle-transmission ratio coupled phase model to compensate for actual deviations, and employing Miner's linear cumulative damage theory to quantify fatigue life through a multi-dimensional convergence verification system, this invention achieves accurate analysis of the transmission system's global dynamics, ultra-high precision matching of rotor phase, and quantitative assessment of service life. It completely avoids the risks of system resonance and blade interference, and comprehensively improves the operational stability and service durability of the transmission system.

[0008] The technical solution of the present invention is as follows: A design method for a tandem unmanned helicopter drive shaft, the tandem unmanned helicopter comprising a transmission system, the transmission system including a front drive shaft, a rear drive shaft, a front reducer, a rear reducer, a belt drive, an engine, a front rotor, and a rear rotor; and both the front drive shaft and the rear drive shaft are provided with connecting holes at their ends; the design method includes the following steps: Step S1: Input the initial parameters of the transmission system. The initial parameters include material parameters, transmission shaft structure and arrangement parameters, transmission and load parameters, rotational inertia and stiffness parameters of each component of the system, reducer transmission ratio, and fatigue load and material SN characteristic parameters. Among them, the transmission and load parameters include the transmission shaft operating speed, extreme working condition load, and multi-working condition alternating load spectrum. Step S2: Based on the structure and arrangement parameters of the drive shaft, carry out the structural design and weight calculation of the front drive shaft and the rear drive shaft, and sequentially complete the strength verification of the shaft torsional stress and the extrusion stress of the connecting hole of the front drive shaft and the rear drive shaft to evaluate the static strength of the drive shaft. Step S3: Based on the material parameters and the structure and arrangement parameters of the drive shaft, calculate the uniaxial torsional stiffness, natural torsional frequency, and first-order critical speed of the front drive shaft and the rear drive shaft respectively, and calculate the uniaxial resonance isolation margin between the operating speed of the drive shaft and the first-order critical speed; at the same time, adjust the structure and arrangement parameters of the drive shaft according to the frequency isolation criterion so that the difference in natural torsional frequency between the front drive shaft and the rear drive shaft reaches a preset threshold to avoid local resonance range; Step S4: Integrate the rotational inertia and stiffness parameters of the front drive shaft, the rear drive shaft, the front reducer, the rear reducer, the belt drive device, the engine, the front rotor, and the rear rotor to construct the torsional vibration dynamics matrix of the eight-degree-of-freedom transmission system, conduct global vibration modal analysis, and calculate the global system resonance isolation margin to identify the risk of coupled vibration between all transmission chain components. Step S5: Calculate the static torsion angles of the front drive shaft and the rear drive shaft under the extreme working condition load. Combined with the transmission ratio of the reducer, use the torsion angle-transmission ratio coupled phase calculation model to solve the actual deviation of the phases of the front rotor and the rear rotor, and perform phase compensation on the transmission system based on the actual deviation. Step S6: Based on the multi-condition alternating load spectrum and the material SN characteristic curve, the fatigue life of the front drive shaft and the rear drive shaft is quantitatively calculated using Miner's linear cumulative damage theory, and the total fatigue damage value of the drive shaft is obtained. Step S7: Complete the design verification based on the multi-dimensional convergence criteria, and output the final design parameters of the drive shaft after all indicators meet the standards; wherein, the multi-dimensional convergence criteria include: the static strength of the drive shaft meets the standards, the single-axis resonance isolation margin and the global system resonance isolation margin both meet the standards, the actual deviation is within the preset deviation threshold, and the total fatigue damage value of the drive shaft is less than 1.

[0009] Furthermore, in step S2, the calculation formulas for the drive shaft weight, maximum torsional stress of the shaft body, and extrusion stress of the connecting hole of the front and rear drive shafts are as follows: Formula for calculating the weight of the drive shaft: ; Formula for calculating the maximum torsional stress of a shaft: ; Formula for calculating the extrusion stress of the connecting hole: ; in: This refers to the total mass of the drive shaft; Density of the drive shaft material; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. This refers to the effective length of the drive shaft; This represents the maximum torsional stress of the shaft. To transmit torque to its limit; This refers to the allowable torsional stress of the material. For the compressive stress of the flange connection hole; Number of connection holes; The diameter of the connecting hole; The thickness of the drive shaft; The radius of the flange hole pitch circle; This represents the allowable compressive stress of the material.

[0010] Furthermore, in step S3, the calculation formulas for the uniaxial torsional stiffness, the natural torsional frequency, and the first-order critical speed are as follows: Uniaxial torsional stiffness: ; The natural torsional vibration frequency corresponds to the natural torsional vibration angular frequency: ; First-order critical speed: ; in: It is the uniaxial torsional stiffness; Shear modulus of the material; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. This refers to the effective length of the drive shaft; This is the inherent torsional angular frequency; The moment of inertia of the drive shaft; This is the first-order critical speed; The elastic modulus of the material; The moment of inertia of the drive shaft section; Density of the drive shaft material; This refers to the cross-sectional area of ​​the drive shaft; The preset threshold is greater than 15%; the standard for the single-axis resonance isolation margin is: the isolation margin between the operating speed of the transmission shaft and the first-order critical speed is greater than ±20%.

[0011] Furthermore, in step S4, the dynamic equation corresponding to the torsional vibration dynamic matrix of the eight-degree-of-freedom transmission system is:

[0012] in: Here is the system's rotational inertia matrix; The system's overall damping matrix; Here is the torsional stiffness matrix of the system; This is the system's torsional angular acceleration vector; This is the system's torsional angular velocity vector; This is the system's torsional angular displacement vector; This is the external excitation torque vector.

[0013] Furthermore, in step S5, the calculation model for the torsion angle-transmission ratio coupling phase includes the following calculation formula: Drive shaft static torsion angle: The polar moment of inertia of the drive shaft section ; Equivalent twist angle at rotor tip: ; Actual deviation: ; in: This refers to the static torsion angle of the drive shaft. This refers to the effective length of the drive shaft; To transmit torque to its limit; Shear modulus of the material; The polar moment of inertia of the drive shaft section; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. The gear ratio of the reducer; This is the equivalent twist angle at the rotor tip; This is the equivalent torsion angle at the front rotor end corresponding to the front drive shaft; This is the equivalent torsion angle at the rear rotor end corresponding to the rear drive shaft; The actual deviation is defined as a preset deviation threshold of less than 3°.

[0014] Furthermore, in step S6, the formula for quantifying the fatigue life of the drive shaft using Miner's linear cumulative damage theory is as follows: Total fatigue damage value of drive shaft: ; Equivalent service life: ; in: This represents the total fatigue damage value of the drive shaft. For load condition levels; For the first Actual number of cycles for the load level; For the first Number of fatigue failure cycles of materials under level load; Equivalent service life; This refers to the working time corresponding to a single load cycle.

[0015] The present invention also proposes a tandem unmanned helicopter drive shaft, comprising: a front drive shaft and a rear drive shaft; The left end of the front drive shaft is used to connect to the belt drive device, and the right end is used to connect to the front reducer; the left end of the rear drive shaft is used to connect to the belt drive device, and the right end is used to connect to the rear reducer. Both the front drive shaft and the rear drive shaft are equipped with connecting flanges at their ends. Adjacent connecting flanges are connected by a diaphragm coupling. The connecting flanges and the diaphragm coupling are secured by connecting bolts, outer arc-shaped gaskets, and inner arc-shaped gaskets, and locked in place with nuts. The structural parameters of the front drive shaft and the rear drive shaft are determined using the above-mentioned design method, so that the difference in the natural torsional vibration frequency between the front drive shaft and the rear drive shaft is greater than 15%, and the actual deviation of the equivalent torsional phase at the rotor end of the two shafts is less than 3°.

[0016] Furthermore, both the front drive shaft and the rear drive shaft are hollow tubular structures; the length of the front drive shaft is greater than the length of the rear drive shaft, and the front drive shaft is a multi-support span structure.

[0017] Furthermore, the outer arc-shaped gasket and the inner arc-shaped gasket are arranged in pairs on the end faces of the connecting flange that contact the connecting bolts and nuts, in order to compensate for the assembly angle deviation of the flange mating part and to balance the preload of the connecting bolts.

[0018] Furthermore, the front drive shaft and the rear drive shaft are made of 7015-T651 aluminum alloy.

[0019] Compared with existing technologies, the advantages of this invention are: 1. Precise avoidance of full-domain coupling resonance: It breaks through the limitations of traditional single-component analysis, integrates the eight core physical entities of the transmission chain to construct an eight-degree-of-freedom torsional vibration dynamic matrix, realizes full modal analysis from the power output end to the load end, and predicts and thoroughly investigates the coupling vibration risks between all transmission chain components in advance.

[0020] 2. Ultra-high precision rotor phase matching: The first torsion angle-transmission ratio coupled phase calculation model accurately quantifies the phase shift caused by the elastic torsion of the long and short transmission shafts under load, and performs system compensation based on the actual deviation, strictly controlling the final rotor phase deviation within 3°, completely solving the problem of helicopter shaking and blade interference caused by phase misalignment.

[0021] 3. Quantitative and controllable fatigue throughout the entire life cycle: It changes the previous extensive mode of relying solely on static strength verification, divides the load spectrum of multiple real flight conditions such as cruise, maneuver, and extreme overload, and combines the material SN curve and Miner damage theory to quantitatively assess the service life of the drive shaft, eliminating the risk of fatigue fracture under long-term service from the design source.

[0022] 4. Lightweight structure and extremely high reliability: Differentiated design and multi-support span adjustment for long and short drive shafts, while ensuring that the strength in both torsional stress and compressive stress meets the standards and that the single-axis modes are completely decoupled (natural frequency difference >15%), the overall ineffective load is greatly reduced; at the same time, the arc-shaped gasket and diaphragm coupling are equipped to effectively compensate for assembly angle deviation and absorb vibration. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0024] Figure 1 A flowchart illustrating a design method for a tandem unmanned helicopter drive shaft, as provided in an embodiment of the present invention; Figure 2 This is a partial structural assembly cross-sectional view of a tandem unmanned helicopter drive shaft provided in an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached figures: 1-Drive shaft, 2-Connecting flange, 3-Diaphragm coupling, 4-First bolt, 5-Outer arc-shaped gasket, 6-Inner arc-shaped gasket, 7-First nut, 8-Second bolt, 9-Adjusting washer, 10-Second nut. Detailed Implementation

[0026] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0027] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0028] Example 1 Please see Figure 1 This embodiment provides a design method for a tandem unmanned helicopter drive shaft. The tandem unmanned helicopter includes a transmission system, which includes a front drive shaft, a rear drive shaft, a front reducer, a rear reducer, a belt drive device, an engine, a front rotor, and a rear rotor; and the ends of the front drive shaft and the rear drive shaft are provided with connecting holes.

[0029] It should be noted that the tandem unmanned helicopter described in this embodiment adopts a longitudinal layout with two rotors, one in front and one behind. The rotors operate as follows: the front rotor rotates counterclockwise from a top-down view, and the rear rotor rotates clockwise from a top-down view. The theoretical phase angle between the front and rear rotors is 90°. This counter-rotation mechanism places extremely high demands on the dynamic torsional stability of each component of the transmission system.

[0030] The design method includes the following steps: Step S1: Input the initial parameters of the transmission system. The initial parameters include material parameters, transmission shaft structure and arrangement parameters, transmission and load parameters, rotational inertia and stiffness parameters of each component of the system, reducer transmission ratio, and fatigue load and material SN characteristic parameters. Among them, the transmission and load parameters include the transmission shaft operating speed, extreme working condition load, and multi-working condition alternating load spectrum.

[0031] Specifically, this step aims to build a high-precision, comprehensive basic database, avoiding the problems of coarse parameters and single operating conditions in traditional designs. Combining all flight conditions such as helicopter idling, cruise, extreme maneuvering, and short-term overload, the specific basic parameters entered in this embodiment are shown in Tables 1 to 5: Table 1. Material parameters of the drive shaft

[0032] Table 2 Transmission Shaft Structural Parameters

[0033] Table 3 Transmission and Load Parameters

[0034] Table 4 System Moment of Inertia

[0035] Table 5 Fatigue Load and Material SN Characteristic Parameters

[0036] Step S2: Based on the structure and arrangement parameters of the drive shaft, carry out the structural design and weight calculation of the front drive shaft and the rear drive shaft, and sequentially complete the strength verification of the shaft torsional stress and the extrusion stress of the connecting hole of the front drive shaft and the rear drive shaft to evaluate the static strength of the drive shaft. The calculation formulas for the drive shaft weight, maximum torsional stress of the shaft body, and extrusion stress of the connecting hole of the front and rear drive shafts are as follows: Formula for calculating the weight of the drive shaft: ; Formula for calculating the maximum torsional stress of a shaft: ; Formula for calculating the extrusion stress of the connecting hole: ; In the above formula: This refers to the total mass of the drive shaft; Density of the drive shaft material; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. This refers to the effective length of the drive shaft; This represents the maximum torsional stress of the shaft. To transmit torque to its limit; This refers to the allowable torsional stress of the material. For the compressive stress of the flange connection hole; Number of connection holes; The diameter of the connecting hole; The thickness of the drive shaft; The radius of the flange hole pitch circle; This represents the allowable compressive stress of the material.

[0037] Substitute the parameters from Tables 1 to 5 into the above formula: (a) Quantitative weight reduction calculation: front drive shaft mass Rear drive shaft mass By combining the structural characteristics of the two drive shafts, a differentiated design was carried out, which reduced the overall ineffective load while ensuring the matching of structural stiffness.

[0038] (b) Dual-dimensional strength check: maximum torsional shear stress of the drive shaft ; Calculate the compressive stress in the connection holes at the weak points of the flange bolt connection. It has sufficient static load-bearing capacity, effectively avoiding hole crushing, fretting wear and loosening failure under alternating loads.

[0039] Step S3: Based on the material parameters and the structure and arrangement parameters of the drive shaft, calculate the uniaxial torsional stiffness, natural torsional frequency, and first-order critical speed of the front drive shaft and the rear drive shaft respectively, and calculate the uniaxial resonance isolation margin between the operating speed of the drive shaft and the first-order critical speed; at the same time, adjust the structure and arrangement parameters of the drive shaft according to the frequency isolation criterion so that the difference in natural torsional frequency between the front drive shaft and the rear drive shaft reaches a preset threshold to avoid local resonance range; The calculation formulas for uniaxial torsional stiffness, the natural torsional frequency, and the first-order critical speed are as follows: Uniaxial torsional stiffness: ; The natural torsional vibration frequency corresponds to the natural torsional vibration angular frequency: ; First-order critical speed: ;(When calculating the first critical speed of the front drive shaft, the formula in Take the single-span support spacing of the front drive shaft as the bearing housing spacing. When calculating the first critical speed of the rear drive shaft, the formula contains... Take the total length of the rear drive shaft ) In the above formula, the symbols have the same meaning as above. The preset threshold is greater than 15%; the standard for the single-axis resonance isolation margin is: the isolation margin between the operating speed of the transmission shaft and the first-order critical speed is greater than ±20%.

[0040] Based on the parameters of this embodiment, the torsional stiffness of the front drive shaft is calculated as follows: Rear drive shaft torsional stiffness Further, the natural torsional vibration angular frequency of the front drive shaft was obtained. The natural torsional angular frequency of the rear drive shaft ; and then the natural torsional vibration frequency of the front drive shaft can be calculated. The natural torsional vibration frequency of the rear drive shaft The difference between the two is much greater than 15%, achieving complete decoupling of the single-axis modes and avoiding localized coupled vibration between the two axes. Furthermore, the natural frequency of the front drive shaft (59.0Hz) has sufficient isolation margin from the operating excitation frequency (approximately 43.58Hz), eliminating the risk of torsional resonance; the natural frequency of the rear drive shaft (258.5Hz) is much higher than all operating excitation frequencies of the entire machine, ensuring absolute safety.

[0041] Regarding the first-order bending critical speed, the front drive shaft Rear drive shaft The rated operating speed of the drive shaft is 2614.6 r / min, and the isolation margin between it and the aforementioned critical speed is much greater than ±20%, completely avoiding the risk of bending resonance and torsional resonance in a single component.

[0042] Step S4: Integrate the rotational inertia and stiffness parameters of the front drive shaft, the rear drive shaft, the front reducer, the rear reducer, the belt drive device, the engine, the front rotor, and the rear rotor to construct the torsional vibration dynamics matrix of the eight-degree-of-freedom transmission system, conduct global vibration modal analysis, and calculate the global system resonance isolation margin to identify the risk of coupled vibration between all transmission chain components. The dynamic equation corresponding to the torsional vibration dynamic matrix of the eight-degree-of-freedom transmission system is:

[0043] in: Here is the system's rotational inertia matrix; The system's overall damping matrix; Here is the torsional stiffness matrix of the system; This is the system's torsional angular acceleration vector; This is the system's torsional angular velocity vector; This is the system's torsional angular displacement vector; This is the external excitation torque vector.

[0044] This step overcomes the limitations of traditional single-component analysis by constructing a model for the entire transmission chain. It employs lumped inertia modeling, with the rotational inertia matrix... This is an 8th-order diagonal matrix, with the diagonal elements being the rotational inertia values ​​entered in Table 4, as follows:

[0045] Construct an 8th-order symmetric stiffness matrix based on the series relationship of the transmission chain. Its construction rules are as follows: The off-diagonal elements represent the torsional stiffness of the connecting shaft segments of adjacent components, while the diagonal elements represent the sum of the stiffnesses at both ends of the corresponding nodes. The values ​​are assigned by combining the geometry and material parameters of the transmission shaft.

[0046] Using the commonly used proportional damping model in engineering (Pick Calculate the overall damping matrix.

[0047] Based on the above input parameters, an excitation vector is established. Its matrix elements correspond to the following 8 degrees of freedom: The plus or minus sign indicates the counter-rotating characteristic of the front and rear rotors, as detailed below:

[0048] Solve the characteristic equation The 8th natural frequency of the system is obtained: front drive shaft Rear drive shaft Front reducer Rear reducer Belt drive device ;engine Fore rotor rear rotor .

[0049] Because the rotational inertia of the twin rotors is much greater than that of the other components, the low-order modes of the system are mainly dominated by the inertia of the twin rotors. The operating excitation frequency of the drive shaft in this system is... Rotor operating excitation frequency The system's natural frequencies at each order are isolated from the two types of operating excitation ranges, and the overall system resonance isolation margin meets the standard, with no risk of coupled resonance.

[0050] Step S5: Calculate the static torsion angles of the front drive shaft and the rear drive shaft under the extreme working condition load. Combined with the transmission ratio of the reducer, use the torsion angle-transmission ratio coupled phase calculation model to solve the actual deviation of the phases of the front rotor and the rear rotor, and perform phase compensation on the transmission system based on the actual deviation. To address the operational requirement of tandem dual rotors rotating in opposite directions, and to resolve the phase misalignment problem caused by inconsistent elastic torsion of the major and minor shafts under load, the torsion angle-transmission ratio coupled phase calculation model includes the following calculation formulas: Drive shaft static torsion angle: The polar moment of inertia of the drive shaft section ; Equivalent twist angle at rotor tip: ; Actual deviation: ; Substituting the data, we obtain: Static torsion angle of the front drive shaft. Static torsion angle of rear drive shaft After calculation using the reducer, the equivalent torsional angle at the rotor end corresponding to the front drive shaft is... The rear drive shaft corresponds to .

[0051] Actual deviation between front and rear rotors This value is less than the preset deviation threshold of 3°, meeting the requirements. This completely solves the problem of blade interference and reduced control accuracy caused by neglecting elastic torsion in the theoretical design.

[0052] Step S6: Based on the multi-condition alternating load spectrum and the material SN characteristic curve, the fatigue life of the front drive shaft and the rear drive shaft is quantitatively calculated using Miner's linear cumulative damage theory, and the total fatigue damage value of the drive shaft is obtained. The calculation formula is as follows: Total fatigue damage value of drive shaft: ; Equivalent service life: ; The symbols in the above formula have the same meaning as above. Based on a single-hour rotation cycle count of 156,876 times / h, the total number of cycles of the drive shaft over 2000h is... Specifically, the actual number of cycles for each load level is as follows: , , Combining the material torsional fatigue SN curve formula (where m=9), fatigue limit With the cyclic base in Table 5 The fatigue failure cycle numbers corresponding to each load level were obtained by solving the problem as follows: Second-rate, Second-rate, Second-rate.

[0053] The final calculation yielded the total fatigue damage value. .because This proves that the drive shaft will not experience fatigue fracture within the designed flight time of 2000h, and quantitatively predicts its reliability under long-term service.

[0054] Step S7: Complete the design verification based on the multi-dimensional convergence criteria, and output the final design parameters of the drive shaft after all indicators meet the standards; wherein, the multi-dimensional convergence criteria include: the static strength of the drive shaft meets the standards, the single-axis resonance isolation margin and the global system resonance isolation margin both meet the standards, the actual deviation is within the preset deviation threshold, and the total fatigue damage value of the drive shaft is less than 1.

[0055] This step establishes a closed-loop verification system encompassing "weight, strength, uniaxial mode, system dynamics, phase accuracy, and fatigue life." Once all parameters meet the requirements as measured above, the iteration is deemed converged. The output finalized data can directly support component processing, assembly, and complete machine testing, eliminating the reliance on experience in traditional design.

[0056] Example 2 Please see Figure 2 , Figure 2 This image shows a partial structural assembly cross-sectional view of a tandem unmanned helicopter drive shaft provided by an embodiment of the present invention. The core structural parameters, geometric dimensions, and dynamic characteristics of the solid drive shaft provided in this embodiment are all obtained strictly using the design method described in Embodiment 1, forming an inseparable design and manufacturing closed loop.

[0057] Specifically, a tandem driveshaft for an unmanned helicopter includes a front driveshaft and a rear driveshaft (labeled 1 in the figure). To minimize the ineffective load on the airframe while ensuring strength, both the front and rear driveshafts are hollow tubular structures made of aerospace-grade 7015-T651 aluminum alloy. Considering the overall layout characteristics of the helicopter, the length of the front driveshaft (e.g., 2.8m) is greater than the length of the rear driveshaft (e.g., 0.5m), and due to the larger span of the front driveshaft, it is configured as a multi-span structure (the spacing between supports per span is adjusted to 0.905m).

[0058] In terms of transmission connections, the left end of the front driveshaft is used to connect to the belt drive device, and the right end is used to connect to the front reducer; the left end of the rear driveshaft is used to connect to the belt drive device, and the right end is used to connect to the rear reducer. Because helicopters deform under complex operating conditions, the transmission system is prone to assembly deviations and dynamic misalignment. Therefore, this embodiment employs a special flexible structure design for the driveshaft docking nodes: Both the front drive shaft and the rear drive shaft are integrally machined or securely assembled with connecting flanges 2 at their ends. A diaphragm coupling 3 is provided between two adjacent connecting flanges 2 to achieve transmission connection. The connecting flanges 2 and the diaphragm coupling 3 are connected by first bolts 4 and second bolts 8, and are locked in place by first nuts 7, second nuts 10, and adjusting washers 9.

[0059] More preferably, at the contact point between the connecting flange 2 and the head of the bolt or the end face of the nut, a pair of outer arc-shaped gaskets 5 and inner arc-shaped gaskets 6 are provided. In actual assembly and operation, the diaphragm coupling 3 mainly transmits large torque and compensates for radial / axial deviations through the elastic deformation of its diaphragm; while the paired outer arc-shaped gaskets 5 and inner arc-shaped gaskets 6 can undergo slight relative sliding like spherical bearings, specifically used to precisely compensate for the assembly angle deviation at the flange mating point, and to balance the preload on each connecting bolt, preventing fatigue fracture of a single bolt under alternating loads.

[0060] Through the above structural design, and relying on the core algorithms such as "eight-degree-of-freedom dynamic matrix investigation" and "phase coupling model compensation" in Example 1, the physical driveshaft provided in this embodiment achieves two key breakthroughs in physical characteristics: First, it ensures that the inherent torsional vibration frequency difference between the front and rear driveshafts is greater than 15%, completely decoupling the physical modes and eliminating local resonance; second, it strictly controls the actual deviation of the equivalent torsional phase at the rotor end of the front and rear driveshafts to within a range of less than 3°. Thus, at the hardware level, it perfectly solves the industry-wide common problems of coupled vibration of the entire helicopter drivetrain and blade phase misalignment.

[0061] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0062] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A design method for a tandem unmanned helicopter drive shaft, characterized in that, The tandem unmanned helicopter includes a transmission system comprising a front drive shaft, a rear drive shaft, a front reduction gear, a rear reduction gear, a belt drive, an engine, a front rotor, and a rear rotor; and both the front and rear drive shafts are provided with connecting holes at their ends; the design method includes the following steps: Step S1: Input the initial parameters of the transmission system. The initial parameters include material parameters, transmission shaft structure and arrangement parameters, transmission and load parameters, rotational inertia and stiffness parameters of each component of the system, reducer transmission ratio, and fatigue load and material SN characteristic parameters. Among them, the transmission and load parameters include the transmission shaft operating speed, extreme working condition load, and multi-working condition alternating load spectrum. Step S2: Based on the structure and arrangement parameters of the drive shaft, carry out the structural design and weight calculation of the front drive shaft and the rear drive shaft, and sequentially complete the strength verification of the shaft torsional stress and the extrusion stress of the connecting hole of the front drive shaft and the rear drive shaft to evaluate the static strength of the drive shaft. Step S3: Based on the material parameters and the structure and arrangement parameters of the drive shaft, calculate the uniaxial torsional stiffness, natural torsional frequency, and first-order critical speed of the front drive shaft and the rear drive shaft respectively, and calculate the uniaxial resonance isolation margin between the operating speed of the drive shaft and the first-order critical speed; at the same time, adjust the structure and arrangement parameters of the drive shaft according to the frequency isolation criterion so that the difference in natural torsional frequency between the front drive shaft and the rear drive shaft reaches a preset threshold to avoid local resonance range; Step S4: Integrate the rotational inertia and stiffness parameters of the front drive shaft, the rear drive shaft, the front reducer, the rear reducer, the belt drive device, the engine, the front rotor, and the rear rotor to construct the torsional vibration dynamics matrix of the eight-degree-of-freedom transmission system, conduct global vibration modal analysis, and calculate the global system resonance isolation margin to identify the risk of coupled vibration between all transmission chain components. Step S5: Calculate the static torsion angles of the front drive shaft and the rear drive shaft under the extreme working condition load. Combined with the transmission ratio of the reducer, use the torsion angle-transmission ratio coupled phase calculation model to solve the actual deviation of the phases of the front rotor and the rear rotor, and perform phase compensation on the transmission system based on the actual deviation. Step S6: Based on the multi-condition alternating load spectrum and the material SN characteristic curve, the fatigue life of the front drive shaft and the rear drive shaft is quantitatively calculated using Miner's linear cumulative damage theory, and the total fatigue damage value of the drive shaft is obtained. Step S7: Complete the design verification based on the multi-dimensional convergence criteria, and output the final design parameters of the drive shaft after all indicators meet the standards; wherein, the multi-dimensional convergence criteria include: the static strength of the drive shaft meets the standards, the single-axis resonance isolation margin and the global system resonance isolation margin both meet the standards, the actual deviation is within the preset deviation threshold, and the total fatigue damage value of the drive shaft is less than 1.

2. The design method for the tandem unmanned helicopter drive shaft according to claim 1, characterized in that, In step S2, the calculation formulas for the drive shaft weight, maximum torsional stress of the shaft body, and extrusion stress of the connecting hole of the front and rear drive shafts are as follows: Formula for calculating the weight of a drive shaft: ; Formula for calculating the maximum torsional stress of a shaft: ; Formula for calculating the extrusion stress of the connecting hole: ; in: This refers to the total mass of the drive shaft; Density of the drive shaft material; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. This refers to the effective length of the drive shaft; This represents the maximum torsional stress of the shaft. To transmit torque to the limit; This refers to the allowable torsional stress of the material. For the compressive stress of the flange connection hole; Number of connection holes; The diameter of the connecting hole; The thickness of the drive shaft; The radius of the flange hole pitch circle; This represents the allowable compressive stress of the material.

3. The design method for the tandem unmanned helicopter drive shaft according to claim 1, characterized in that, In step S3, the calculation formulas for uniaxial torsional stiffness, the natural torsional frequency, and the first-order critical speed are as follows: Uniaxial torsional stiffness: ; The natural torsional vibration frequency corresponds to the natural torsional vibration angular frequency: ; First-order critical speed: ; in: It is the uniaxial torsional stiffness; Shear modulus of the material; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. This refers to the effective length of the drive shaft; This is the inherent torsional angular frequency; The moment of inertia of the drive shaft; This is the first-order critical speed; The elastic modulus of the material; The moment of inertia of the drive shaft section; Density of the drive shaft material; This refers to the cross-sectional area of ​​the drive shaft; The preset threshold is greater than 15%; the standard for the single-axis resonance isolation margin is: the isolation margin between the operating speed of the transmission shaft and the first-order critical speed is greater than ±20%.

4. The design method for the tandem unmanned helicopter drive shaft according to claim 1, characterized in that, In step S4, the dynamic equation corresponding to the torsional vibration dynamic matrix of the eight-degree-of-freedom transmission system is: in: Here is the system's rotational inertia matrix; The system's overall damping matrix; Here is the torsional stiffness matrix of the system; Let be the system's torsional angular acceleration vector; This is the system's torsional angular velocity vector; This is the system's torsional angular displacement vector; This is the external excitation torque vector.

5. The design method for the tandem unmanned helicopter drive shaft according to claim 1, characterized in that, In step S5, the calculation model for the torsion angle-transmission ratio coupling phase includes the following calculation formula: Drive shaft static torsion angle: The polar moment of inertia of the drive shaft section ; Equivalent twist angle at rotor tip: ; Actual deviation: ; in: This refers to the static torsion angle of the drive shaft. This refers to the effective length of the drive shaft; To transmit torque to the limit; Shear modulus of the material; The polar moment of inertia of the drive shaft section; The outer diameter of the drive shaft; This refers to the inner diameter of the drive shaft. The gear ratio of the reducer; This is the equivalent twist angle at the rotor tip; This is the equivalent torsion angle at the front rotor end corresponding to the front drive shaft; This is the equivalent torsion angle at the rear rotor end corresponding to the rear drive shaft; The actual deviation is defined as a preset deviation threshold of less than 3°.

6. The design method for the tandem unmanned helicopter drive shaft according to claim 1, characterized in that, In step S6, the formula for quantifying the fatigue life of the drive shaft using Miner's linear cumulative damage theory is as follows: Total fatigue damage value of drive shaft: ; Equivalent service life: ; in: This represents the total fatigue damage value of the drive shaft; For load condition levels; For the first Actual number of cycles for the load level; For the first Number of fatigue failure cycles of materials under level load; Equivalent service life; This represents the working time corresponding to a single load cycle.

7. A tandem type unmanned helicopter drive shaft, characterized in that, include: Front drive shaft and rear drive shaft; The left end of the front drive shaft is used to connect to the belt drive device, and the right end is used to connect to the front reducer; the left end of the rear drive shaft is used to connect to the belt drive device, and the right end is used to connect to the rear reducer. Both the front drive shaft and the rear drive shaft are equipped with connecting flanges at their ends. Adjacent connecting flanges are connected by a diaphragm coupling. The connecting flanges and the diaphragm coupling are secured by connecting bolts, outer arc-shaped gaskets, and inner arc-shaped gaskets, and locked in place with nuts. The structural parameters of the front drive shaft and the rear drive shaft are determined by the design method described in any one of claims 1 to 6, so that the difference in the natural torsional vibration frequency between the front drive shaft and the rear drive shaft is greater than 15%, and the actual deviation of the equivalent torsional phase at the rotor end of the two shafts is less than 3°.

8. The tandem unmanned helicopter drive shaft according to claim 7, characterized in that, Both the front drive shaft and the rear drive shaft are hollow tubular structures; the length of the front drive shaft is greater than the length of the rear drive shaft, and the front drive shaft is a multi-support span structure.

9. The tandem unmanned helicopter drive shaft according to claim 7, characterized in that, The outer arc-shaped gasket and the inner arc-shaped gasket are arranged in pairs on the end face of the connecting flange that contacts the connecting bolts and nuts, in order to compensate for the assembly angle deviation of the flange mating part and to balance the preload of the connecting bolts.

10. The tandem unmanned helicopter drive shaft according to claim 8, characterized in that, The front drive shaft and the rear drive shaft are made of 7015-T651 aluminum alloy.

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