A bearingless rotor hub central fatigue test design method

Abstract

The present application belongs to the field of fatigue test, and relates to a bearingless rotor central fatigue test design method. The method comprises the following steps: when characteristic load of the bearingless rotor central fatigue test is selected, the load distribution on the central body to be simulated and the important degree of the influence on the central strength are considered, the flapping bending moment and the edgewise bending moment are selected as the characteristic load, and the centrifugal force is selected as the environmental load; the bearingless rotor central is connected with the flapping arm section, and the section is taken as the load monitoring position, wherein the flapping bending moment, the edgewise bending moment and the centrifugal force of the section are consistent with the test design load; the bearingless central hub center is taken as the load monitoring position, and the spindle bending moment and the spindle torque of the load monitoring position are within the error range of 5% of the test design load in consideration of the control system accuracy and the implementability.

Description

Technical Field

[0001] This invention belongs to the field of fatigue testing and relates to a fatigue test design method for a bearingless rotor central component. Background Technology

[0002] The rotor system is the core component of helicopter design. Traditional metal articulated rotors have complex structures, a large number of parts, high weight, and high maintenance costs. In contrast, bearingless rotors eliminate the flapping, oscillating, and torsional hinges, replacing them with flexible structures. This simplifies the structure, reduces drag, reduces the number of parts, and lightens the weight. Furthermore, they offer advantages such as high maneuverability, good agility, high reliability, and ease of maintenance, making them one of the important indicators of advanced helicopter design.

[0003] The central component, located at the center of the rotor, is a critical part of the entire rotor system. Its strength is a key indicator of the success of the rotor system design. The central component is a typical example of a high- and low-cycle combined fatigue component, and currently, most helicopters still rely on fatigue testing to verify its strength. Therefore, conducting fatigue tests on the central component of a bearingless rotor during the engineering design phase is essential to ensure the safe operation of the helicopter.

[0004] To verify the strength of the central component of a bearingless rotor, the key lies in employing a well-designed fatigue test method to obtain accurate structural fatigue performance values. Traditional approaches, such as those for spherical flexible structures, decompose and synthesize the load at the hub center, using the flapping and tessellation hinges as application points. This load is then distributed to the flapping and tessellation hinges, transforming the load into forces in three directions at the hinge points of each arm. This load is then directly applied to the central component. While this method is mature and reliable, it is only suitable for structures where the flapping and tessellation hinges are located precisely on the central component, and is not applicable to bearingless rotors. As a novel rotor configuration, the hinge function of a bearingless rotor is replaced by a flexible structure. Since the equivalent hinge location is not on the central component, traditional methods are no longer suitable. Therefore, the fatigue test design method for its central component must differ from that of previous central components. Summary of the Invention

[0005] The purpose of this invention is to simulate the load distribution on the central component body by simulating the cross-sectional bending moment at the joint section between the loading central component and the swing arm, while ensuring that the load at the hub center is consistent with the test design load, thereby ensuring the accuracy of the fatigue test.

[0006] The technical solution of the present invention:

[0007] A fatigue test design method for a bearingless rotor central component includes:

[0008] When selecting characteristic loads for fatigue testing of the bearingless rotor central component, the load distribution on the central component body and the importance of its influence on the strength of the central component are considered. The flapping moment and the oscillation moment are selected as characteristic loads, while the applied centrifugal force is used as the environmental load.

[0009] The section where the bearingless rotor center component and the swing arm meet is used as the load monitoring position. The swing moment, oscillation moment and centrifugal force of this section are consistent with the test design load.

[0010] The center of the bearingless central component, the propeller hub, was used as the load monitoring location. Considering the accuracy and feasibility of the control system, the spindle bending moment and spindle torque at this load monitoring location were within 5% of the error range of the experimental design load.

[0011] The principle of moving test loading at the loading position of the actuator cylinder is designed so that the characteristic load at the load monitoring position and the characteristic load at the load monitoring position reach the design value.

[0012] Based on the load monitoring location, the load detection location, the characteristic loads at the two locations, and the principle of moving test loading, fatigue tests were conducted on the central component of the bearingless rotor.

[0013] The loading principle for the movement test of the actuator's loading position and loading force is as follows:

[0014] When the centrifugal force is an environmental load, all the following steps must be performed in an environment with centrifugal force:

[0015] Once a loading position is obtained, compare the current bending moment at the docking section with the design requirement value;

[0016] If the current bending moment of the docking section is greater than the design requirement, the loading position of the actuator remains unchanged, and the loading force of the actuator is reduced until the bending moment of the docking section is equal to the design requirement.

[0017] If the current bending moment of the docking section is less than the design requirement, the loading position of the actuator remains unchanged, and the loading force of the actuator is increased until the bending moment of the docking section is equal to the design requirement.

[0018] If the bending moment of the current docking section is equal to the design requirement, then compare the bending moment of the main shaft at the hub center with the main shaft torque.

[0019] If either the central spindle bending moment or the spindle torque exceeds its required value, then while ensuring that the bending moment of the docking section remains unchanged, reduce the loading force of the actuator cylinder and move the loading position of the actuator cylinder outward along the blade span.

[0020] If either the central spindle bending moment or the spindle torque is less than its required value, then while ensuring that the bending moment of the docking section remains unchanged, the loading force of the actuator cylinder is increased, and the loading position of the actuator cylinder is moved inward along the spanning direction.

[0021] If both the central spindle bending moment and the spindle torque are equal to the required values, the debugging is complete.

[0022] The fatigue test procedure for the bearingless rotor central component includes:

[0023] First, load adjustment is carried out according to the principle of moving test loading position of actuator cylinder. After adjusting to the low cycle load loading position, low cycle fatigue test is carried out.

[0024] After completing the low-cycle fatigue test, continue to adjust the load according to the principle of moving the actuator loading position. After adjusting to the loading position and loading force of the first level of high-cycle fatigue test, conduct the first level of high-cycle fatigue test. After completing the first level of high-cycle fatigue test, continue to adjust the load according to the principle of moving the actuator loading position. After adjusting to the loading position and loading force of the second level of high-cycle fatigue test, conduct the second level of high-cycle fatigue test. ... Repeat this process until the fatigue test termination conditions are met, and the test ends.

[0025] The loading position and loading force determined by the principle of moving and testing the loading position and loading force of the actuator cylinder are the final loading position and loading force of the actuator cylinder.

[0026] There is a load transfer relationship between the load at the joint section between the bearingless central component and the swing arm and the load at the center section of the propeller hub.

[0027] The high-cycle fatigue test for helicopters is an accelerated test. After multiple cycles, the load will be upgraded, with the static load remaining unchanged and the dynamic load increasing proportionally.

[0028] Each time the load is adjusted during the test, the loading position and loading force need to be readjusted to ensure the authenticity of the load distribution on the central component.

[0029] The beneficial effects of this invention are as follows: A fatigue test design method for a bearingless central component simulates the load distribution on the central component by controlling the flapping and oscillating bending moments at the joint section between the central component and the flapping arm / flexible beam, as well as the bending moment and torque at the rotor hub center. This allows for fatigue test verification of the bearingless central component. This method accurately simulates the actual load conditions of the bearingless central component, providing a practical and effective method for strength verification of bearingless rotor central components. It yields the structural fatigue performance of the central component, providing a strong basis for determining the safe service life of the rotor system, which is of great significance for the safe use of helicopters. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a single arm of a bearingless central component under load.

[0031] Figure 2This diagram shows the relationship between the bending moment distribution trend and the loading point location on the bearingless central component.

[0032] Figure 3 A schematic diagram for adjusting the swing load.

[0033] Figure 4 This is a schematic diagram showing the patch and loading position on the propeller dummy. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] To ensure accurate service life testing results for bearingless rotors and the safe and reliable operation of helicopter rotors, it is necessary to research a fatigue testing method for the central component of a bearingless rotor. This method can accurately simulate the load-bearing conditions of the central component of a bearingless rotor, correctly derive its structural fatigue performance values, and thus provide the true safe fatigue life of the central component.

[0036] 1. Experimental Methods

[0037] Main shaft bending moment M at the center of the propeller hub f and spindle torque M z The fatigue load is caused by the aerodynamic load on the blades, which is transmitted to the central component through the flapping arm and combined at the center of the rotor hub. These loads are correlated. Therefore, as long as the load at the joint section between the bearingless central component and the flapping arm, as well as the load at the center of the rotor hub, are consistent with the actual load on the central component, then the fatigue loading simulation of the bearingless rotor central component is correct.

[0038] When selecting characteristic loads for fatigue testing of the bearingless rotor central component, the load distribution on the central component body and its importance to the strength of the central component are considered. Swinging moment and oscillation moment are selected as characteristic loads, and centrifugal force is applied as an environmental load.

[0039] The section where the bearingless rotor center component and the swing arm meet is designated as the load monitoring point. The swinging moment, oscillation moment, and centrifugal force at this section must be consistent with the experimental design load. A dummy swing arm component (such as...) is connected to the center component. Figure 1 As shown), a swinging force F is applied at a suitable position on the dummy via an actuator. B , pendulum force F r and centrifugal force F CSince the monitoring load cannot be directly measured, it is necessary to attach two or more sets of strain gauges at appropriate positions on the swing arm dummy and interpolate the values ​​to ensure that the monitoring load meets the requirements. The center of the bearingless central component, the hub, is used as the load monitoring location. Considering the accuracy and feasibility of the control system, the spindle bending moment and spindle torque at this location do not need to be consistent with the design load, but they must be within a 5% error range of the experimental design load.

[0040] The characteristic loads of the fatigue test monitoring profile and the loads at the monitoring positions of the bearingless rotor central component can be determined based on the load spectrum used in helicopter flight. However, the loading position and the magnitude of the loading force of the actuator cylinder need to be determined through debugging using the moving loading method.

[0041] The initial flapping shear force magnitude and loading position are defined by the relationship between the lever arm and bending moment. Adjustments are then made based on the bending moment trends formed by the bending moment at the rotor hub center and the flapping dynamic bending moment at the docking section. The oscillation bending moment at the rotor hub center cancels out due to phase relationship; therefore, adjustments are needed based on the bending moment trends formed by the rotor hub center torque and the oscillation static bending moment. Commissioning includes adjusting the magnitude and position of the loading force. The relationship between the bending moment distribution trend and the loading position on the bearingless rotor's central component is as follows: Figure 2 As shown.

[0042] Fatigue testing of the bearingless rotor's central component requires two parts: low-cycle fatigue testing and high-cycle fatigue testing. After a certain number of cycles in the high-cycle fatigue test, the load needs to be increased, typically by increasing the load every 500,000 cycles. Each time the load is adjusted during the test, the loading position needs to be readjusted to ensure the accuracy of the load distribution on the central component.

[0043] 2. Test equipment and layout

[0044] The bearingless rotor center component test involved phase-coordinated loading of multiple outriggers. The test equipment included a coordinated loading control system, loading actuators, force sensors, and a data acquisition system. The swinging and oscillating force loading fixtures on the swinging outrigger dummy were designed for sliding loading, and the actuators were adjustable along the spanwise direction.

[0045] The bearingless rotor central component is fixed on the test bench. Swinging arm dummy components are installed on the mating sections of each arm, each dummy having a movable loading fixture interface. Two or more sets of strain gauges are attached to appropriate positions on the swinging arm dummy components to measure and monitor the load. Centrifugal force actuators, swinging force actuators, and pendulum force actuators are installed sequentially. The data acquisition system collects data, and the loading system coordinates to adjust the loading force values, thus forming a complete test system.

[0046] 3. Loading location debugging work

[0047] The loading location is determined according to the following principles:

[0048] Centrifugal force is an environmental load, and all the following steps must be performed in an environment with centrifugal force.

[0049] First, an initial loading position is determined by the relationship between bending moment and force in the load spectrum. Then, the magnitude and position of the actuator load are adjusted based on the monitored profile load and its changes. During this process, priority is given to ensuring the monitored profile load while minimizing its error. Adjustments are made first to the loading position, followed by the magnitude of the loading force. Load commissioning is considered successful only when the monitored profile bending moment matches the experimental design and the error between the monitored profile spindle load and the experimental design load is within 5%.

[0050] like Figure 3 As shown, taking a swinging load as an example, the specific steps are as follows:

[0051] According to the formula, at the joint section between the bearingless rotor center component and the dummy swing arm component: M B =F B ×L, to obtain the initial loading position A. Apply F at point A. B By comparing the feedback values ​​from the data acquisition system with the docking profile M B If M B If the force is too large, the position of the waving actuator remains unchanged, and the waving force is reduced until the docking section M is reached. B Meets the requirements; if M B If the force is too small, the position of the waving actuator remains unchanged, and the waving force is increased until the docking section M is reached. B Meets the requirements; if M B If the load is equal to the characteristic load of the experimental design, then continue to compare the bending moment M of the main shaft at the hub center. f If M f If the force is too large, the dynamic flapping force needs to be reduced, and the loading position should be moved along the spanwise direction towards the blade tip (during this process, the docking profile M must be maintained). B (Unchanged); if the hub center M f If the force is too small, the dynamic waving force needs to be increased, and the loading position needs to be moved towards the center along the spanwise direction (during this process, the docking section M needs to be maintained). B (Unchanged); when the center of the propeller hub M f If the load is within 5% of the test design load, the debugging is complete, and the position of the swinging actuator and the load value at this time are taken as the formal loading position and load of the test.

[0052] The adjustment steps for the oscillation load are similar to those described above.

[0053] 4. Experimental process and result processing

[0054] For fatigue testing of the bearingless rotor's central component, load adjustment is performed first. After adjusting to a suitable low-cycle load application position, a low-cycle fatigue test is conducted. Following the low-cycle fatigue test, adjustment continues until the application position and force of the first stage of high-cycle fatigue testing are reached, at which point the first stage of high-cycle fatigue testing is conducted. High-cycle fatigue testing for helicopters is an accelerated test, typically involving 300,000 to 500,000 cycles. Then, the load is increased, with the static load remaining unchanged while the dynamic load is increased proportionally. Therefore, adjustment continues until the application position and force of the second stage of high-cycle fatigue testing are reached, at which point the second stage of high-cycle fatigue testing is conducted… This process is repeated until the fatigue test termination conditions are met, at which point the test ends.

[0055] During fatigue testing, the magnitude of the loading force at the loading position needs to be readjusted every time the load changes to ensure the authenticity of the load distribution on the bearingless central component.

[0056] Analysis and comparison of the debugging loading data showed that all loading cycles meeting the error requirements were valid. Designers can evaluate the structural fatigue performance of the bearingless central component based on the number of valid test cycles according to the safe life assessment method, and finally give the safe fatigue life of the bearingless central component.

[0057] To ensure experimental accuracy, this invention proposes a moving test loading method with a non-fixed loading position, which can accurately simulate the load distribution on the bearingless central component and solve the problem of engineering test load simulation for bearingless central components.

[0058] like Figure 4 As shown, 01 is the center of the propeller hub, 02 is the cross-section of the central component and the dummy swing arm component, 03 is the cross-section of the first group of strain gauge patches, 04 is the cross-section of the nth group of strain gauge patches, 05 is the connection position of the movable swing force joint, and 06 is the connection position of the movable swing force joint.

[0059] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fatigue test design method for a bearingless rotor central component, characterized in that, include: When selecting characteristic loads for fatigue testing of the bearingless rotor central component, the load distribution on the central component body and the importance of its influence on the strength of the central component are considered. The flapping moment and the oscillation moment are selected as characteristic loads, while the applied centrifugal force is used as the environmental load. The section where the bearingless rotor center component and the swing arm meet is used as the load monitoring position. The swing moment, oscillation moment and centrifugal force of this section are consistent with the test design load. The center of the bearingless central component, the propeller hub, was used as the load monitoring location. Considering the accuracy and feasibility of the control system, the spindle bending moment and spindle torque at this load monitoring location were within the 5% error range of the experimental design load. The loading principle for moving the actuator cylinder loading position and loading force is designed so that the characteristic load at the load monitoring position and the characteristic load at the load detection position reach the design value. Based on the load monitoring location, the load detection location, the characteristic loads at the two locations, and the principle of moving test loading, fatigue tests were conducted on the central component of the bearingless rotor. The loading principle for the movement test of the actuator's loading position and loading force is as follows: When the centrifugal force is an environmental load, all the following steps must be performed in an environment with centrifugal force: Once a loading position is obtained, compare the current bending moment at the docking section with the design requirement value; If the current bending moment of the docking section is greater than the design requirement, the loading position of the actuator remains unchanged, and the loading force of the actuator is reduced until the bending moment of the docking section is equal to the design requirement. If the current bending moment of the docking section is less than the design requirement, the loading position of the actuator remains unchanged, and the loading force of the actuator is increased until the bending moment of the docking section is equal to the design requirement. If the bending moment of the current docking section is equal to the design requirement, then compare the bending moment of the main shaft at the hub center with the main shaft torque. If either the central spindle bending moment or the spindle torque exceeds its required value, then while ensuring that the bending moment of the docking section remains unchanged, reduce the loading force of the actuator cylinder and move the loading position of the actuator cylinder outward along the blade span. If either the central spindle bending moment or the spindle torque is less than its required value, then while ensuring that the bending moment of the docking section remains unchanged, the loading force of the actuator cylinder is increased, and the loading position of the actuator cylinder is moved inward along the spanning direction. If both the central spindle bending moment and the spindle torque are equal to the required values, the debugging is complete.

2. The method according to claim 1, characterized in that, The fatigue test procedure for the bearingless rotor central component includes: First, load adjustment is carried out according to the principle of moving test loading position of actuator cylinder. After adjusting to the low cycle load loading position, low cycle fatigue test is carried out. After completing the low-cycle fatigue test, continue to adjust the load according to the principle of moving the actuator loading position. After adjusting to the loading position and loading force of the first level of high-cycle fatigue test, conduct the first level of high-cycle fatigue test. After completing the first level of high-cycle fatigue test, continue to adjust the load according to the principle of moving the actuator loading position. After adjusting to the loading position and loading force of the second level of high-cycle fatigue test, conduct the second level of high-cycle fatigue test. ... Repeat this process until the fatigue test termination conditions are met, and the test ends.

3. The method according to claim 1, characterized in that, The loading position and loading force determined by the principle of moving and testing the loading position and loading force of the actuator cylinder are the final loading position and loading force of the actuator cylinder.

4. The method according to claim 1, characterized in that, There is a load transfer relationship between the load at the joint section between the bearingless central component and the swing arm and the load at the center section of the propeller hub.

5. The method according to claim 2, characterized in that, The high-cycle fatigue test for helicopters is an accelerated test. After multiple cycles, the load will be upgraded, with the static load remaining unchanged and the dynamic load increasing proportionally.

6. The method according to any one of claims 1-5, characterized in that, Each time the load is adjusted during the test, the loading position and loading force need to be readjusted to ensure the authenticity of the load distribution on the central component.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-6.

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