A landing gear fatigue test load spectrum equivalent conversion method

Abstract

This invention discloses an equivalent conversion method for landing gear fatigue test load spectrum, comprising: obtaining raw data from a preset landing gear design load spectrum file; simplifying the compression of the shock absorber strut and the tire compression to calculate the fixed compression of the shock absorber strut and the compression of the test tire; standardizing the vertical load under each working condition, keeping the vertical load amplitude and the load distribution ratio between the left and right wheels unchanged, and replacing the compression of the shock absorber strut under each working condition with the fixed compression of the shock absorber strut; establishing the moment balance equation of the main hinge point based on the fixed compression of the shock absorber strut, calculating the equivalent directional load and / or equivalent lateral load corresponding to each working condition, and obtaining the equivalent load spectrum; and correcting the equivalent load spectrum to obtain the test load spectrum. This method solves the problem that existing technologies cannot effectively simulate the load spectrum under various compressions of the landing gear, thus improving the accuracy of landing gear fatigue test assessment.

Description

Technical Field

[0001] This invention relates to the field of aircraft landing gear fatigue testing technology, and in particular to an equivalent conversion method for landing gear fatigue testing load spectrum. Background Technology

[0002] As a critical component of an aircraft, the fatigue performance of the landing gear directly affects the safety of the aircraft during takeoff and landing. By conducting fatigue tests using a specific load spectrum, the load conditions that the landing gear bears during actual use can be effectively simulated, thereby accurately assessing the fatigue life and reliability of the landing gear.

[0003] Landing gear fatigue testing typically employs two loading schemes: The first is the variable compression loading scheme, which simulates the variations in various compression values ​​within the landing gear's fatigue design load spectrum to accurately reflect the landing gear's fatigue performance under real-world conditions. However, considering the multiple compression values ​​in the load spectrum, the test process requires repeated filling and draining of the oil inside the buffer struts, increasing the loading difficulty and extending the test cycle. The second is the fixed compression loading scheme, which converts various compression values ​​into a fixed compression value based on the landing gear's fatigue design load spectrum, allowing the fatigue test to verify the landing gear's fatigue performance under a fixed compression value. Compared to the variable compression scheme, the fixed compression loading scheme eliminates the need for frequent oil filling and draining, significantly reducing the difficulty of the test operation and shortening the test cycle, making it the more mainstream implementation method for landing gear fatigue testing.

[0004] The equivalent conversion of the load spectrum for landing gear fatigue testing is a crucial step in the design process of fatigue tests for landing gear with fixed compression. It primarily involves selecting the compression of a fixed shock absorber strut and the tire compression as the fatigue test loading scheme. Currently, the main method for converting the test load spectrum is the bending moment equivalence method using a single section (with the principal hinge point as the equivalent reference). This conversion method can only guarantee the assessment of the equivalent bending moment locations of the landing gear section. Other non-equivalent sections may experience overload or underload, resulting in an inability to effectively simulate the load spectrum under various compression conditions of the landing gear. This can lead to discrepancies between the fatigue test results and the fatigue design performance, failing to achieve the goal of equivalent assessment of the main structural components of the landing gear.

[0005] Therefore, researching a load spectrum equivalent conversion method that can take into account the stress state of multiple sections of the landing gear is of great engineering application value for achieving a comprehensive and accurate assessment of the fatigue performance of each main load-bearing structural component of the landing gear. Summary of the Invention

[0006] The purpose of this invention is to provide an equivalent conversion method for landing gear fatigue test load spectrum. By constructing the moment balance equation of the main hinge point for various working conditions, the equivalent correction of the corresponding azimuth load and / or lateral load is completed, and the test load spectrum adapted to the fixed compression test conditions is output. This solves the problem that the existing technology, which relies only on the equivalent bending moment of a single section, cannot effectively simulate the load spectrum of the landing gear under various compression conditions, thus improving the accuracy of landing gear fatigue test assessment.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: an equivalent conversion method for landing gear fatigue test load spectrum, comprising the following steps: S1: Obtain raw data from the preset landing gear design load spectrum file. The raw data includes the compression of different buffer struts and tire compression under each load condition. S2: The compression of the buffer strut and the compression of the tire are simplified and calculated to obtain the fixed compression of the buffer strut and the compression of the test tire. S3: Standardize the vertical load under each working condition, keep the vertical load amplitude and the load distribution ratio between the left and right wheels unchanged, and replace the compression amount of the buffer support under each working condition with the fixed compression amount of the buffer support. S4: Based on the fixed compression of the buffer support, establish the moment balance equation of the main hinge point, calculate the equivalent heading load and / or equivalent lateral load corresponding to each working condition, and obtain the equivalent load spectrum; S5: Perform load correction on the equivalent load spectrum to obtain the test load spectrum after load correction. The load correction includes converting the vertical torque of the combined vertical and lateral load conditions into a couple at the left and right wheels.

[0008] This invention unifies the conversion of the compression of the buffer strut and tires within the landing gear design load spectrum, and uses this as a benchmark to construct the moment balance equation of the main hinge point for various working conditions. It completes the equivalent correction of the corresponding directional load and / or lateral load, and outputs a test load spectrum adapted to the fixed compression test conditions. Compared with the traditional single-section bending moment equivalent method, this invention can achieve equivalent matching of the stress of the entire landing gear structure, avoid the problem of local overload or underload in the test, accurately restore the real stress state under multiple compression values, and improve the accuracy of landing gear fatigue test assessment.

[0009] Furthermore, in S2, the simplification process for the tire compression specifically includes: S2.1: Convert the bending moment corresponding to the heading load or lateral load in the design load spectrum from the wheel center point to the tire contact point to complete the force point correction under working conditions; S2.2: Based on the force point correction for each working condition, calculate the tire compression for each working condition with additional bending moment in the design load spectrum; S2.3: Select the tire compression value that appears most frequently as the test tire compression value.

[0010] By converting the bending moment at the wheel center point to the tire contact point, the stress point is corrected, restoring the true force transmission state of the tire. The tire compression values ​​of all working conditions with additional bending moments are statistically analyzed, and the highest frequency value is selected as the fixed tire compression value for the test. This not only simplifies the compression values ​​of various tire specifications and avoids repeated adjustments to the tire loading state during the test, but also ensures that the stress is equivalent in most working conditions, taking into account both the convenience of test operation and the accuracy of load conversion equivalence.

[0011] Furthermore, in S2, the simplification of the compression amount of the buffer support specifically includes: The compression amount and corresponding fatigue damage of the buffer support under each working condition in the design load spectrum are statistically analyzed. The compression amount range of the buffer support corresponding to the working condition where the fatigue damage exceeds the preset damage threshold is screened, and the median value of the range is taken as the fixed compression amount of the buffer support. This step determines a unified fixed compression amount of the buffer support, which provides a stable conversion benchmark for solving the torque balance equation for the subsequent full working condition and improves the damage matching accuracy of the subsequent load equivalent conversion.

[0012] Furthermore, the operating conditions include a combination of non-braking vertical and heading loads. In S4, the equivalent heading load corresponding to the combination of non-braking vertical and heading loads is calculated as follows: Establish the torque balance equation at the principal hinge point: ; The equivalent heading load distributed to the wheels was calculated as follows: ; Among them, M x To design the yaw moment at the wheel axle center under the load spectrum, P x The design load spectrum represents the yaw force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, λ is the difference between the load distribution ratio of the left wheel and the right wheel, and P... zo P represents the vertical force at the center of the wheel axle under the equivalent load spectrum, t is the half-wheel distance between the left and right wheels, and P is the vertical force at the center of the wheel axle. xo P represents the yaw force at the wheel axle center under the equivalent load spectrum, where ΔH is the fixed compression of the buffer strut; x1 P x2 Let these represent the center heading forces of the left and right engines under the equivalent load spectrum, respectively, satisfying... ;P 1x P 2x These represent the heading forces at the center of the left and right engines under the design load spectrum, respectively.

[0013] For the combined vertical and directional load conditions without braking, a moment balance equation for the main hinge point is established. The equivalent total directional load is solved by constraining the equality of the main hinge bending moments under the original and fixed compression load conditions. Then, the independent directional loads for the left and right wheels are obtained based on the wheel load distribution ratio. This solution method uses full moment vector equivalence as a constraint, rather than just single-section unidirectional moment matching, which can completely reproduce the comprehensive stress state at the main hinge under the original load condition. Simultaneously, it distinguishes the load distribution between the left and right wheels, accurately restoring the actual load distribution of the wheels, significantly improving the calculation accuracy of the equivalent directional load under fixed compression, and ensuring the equivalence of fatigue damage under the load conditions.

[0014] Furthermore, the operating condition includes a combination of braking vertical and heading loads. In S4, the equivalent heading load corresponding to the combination of braking vertical and heading loads is calculated as follows: Establish the torque balance equation at the principal hinge point: ; The equivalent heading load distributed to the wheels was calculated as follows: ; Among them, M x M y These represent the heading and lateral moment at the wheel axle center under the design load spectrum, respectively. x The design load spectrum represents the yaw force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, λ is the difference between the load distribution ratio of the left wheel and the right wheel, and P... zo F represents the vertical force at the center of the wheel axle under the equivalent load spectrum, t is the half-wheel distance between the left and right wheels, and F is the vertical force at the center of the wheel axle. xo The simplified contact point azimuth force at the wheel axle center under the equivalent load spectrum; L1 is the distance from the wheel center to the tire contact point in the test spectrum, ΔH is the fixed compression of the buffer strut; F x1 F x2 These are the heading forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... P 1x P 2x M represents the center heading force of the left and right wheels under the design load spectrum, respectively. 1y M 2y These represent the lateral moment at the center of the left and right wheels under the design load spectrum, respectively.

[0015] Under braking conditions, considering both directional and lateral bending moments, the equality of the vector resultant bending moment is used as an equivalent constraint, fully covering the bidirectional bending moment coupling force characteristics under braking conditions. The calculation process introduces the tire contact point offset distance and the additional lateral bending moments of the left and right wheels, distinguishes the tire contact position to correct the load arm, and then combines the wheel load distribution difference to separate the independent contact directional forces of the left and right tires. Compared with the solution method that only considers unidirectional bending moments in non-braking conditions, this calculation model fully restores the influence of the additional bending moment brought by the lateral force under braking conditions, corrects the arm deviation caused by the tire contact point position, accurately restores the real coupled force state under braking conditions, effectively avoids the load conversion deviation caused by ignoring lateral bending moments and contact point offsets, significantly improves the accuracy of equivalent load calculation for braking combination conditions, and ensures equivalent matching of fatigue damage in this type of high-damage braking condition.

[0016] Furthermore, the working condition includes a combination of vertical and lateral loads. In S4, the equivalent lateral load corresponding to the combined vertical and lateral load working condition is calculated as follows: Establish the torque balance equation at the principal hinge point: ; The equivalent heading load distributed to the wheels was calculated as follows: ; Among them, M x To design the yaw moment at the wheel axle center under the load spectrum, P y The design load spectrum represents the lateral force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, F yo The simplified lateral force at the wheel axle center contact point under the equivalent load spectrum; L1 is the distance from the wheel center to the tire contact point in the test spectrum; ΔH is the fixed compression of the buffer support; λ is the difference between the load distribution ratio of the left wheel and the right wheel; P zo F represents the vertical force at the center of the wheel axle under the equivalent load spectrum, where t is the half-wheel distance between the left and right wheels; y1 F y2 These are the lateral forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... M 1x M 2x These are the center-heading moments of the left and right rotor wheels under the design load spectrum, respectively; P 1y P 2y These represent the lateral forces at the center of the left and right rotor wheels under the design load spectrum.

[0017] For combined vertical and lateral load conditions, the equations combine the directional bending moment and the additional bending moment generated by the lateral loads into the equivalent constraint of the resultant bending moment, fully restoring the comprehensive moment formed by the bidirectional load coupling in this type of condition. The calculation introduces a tire contact offset distance correction lever arm, while integrating the independent bending moment of a single wheel and the lateral load term. Then, based on the difference in the left and right wheel distribution ratios, the left and right tire contact lateral forces are obtained. This solution model fully considers the additional bending moment derived from the lateral load and the lever arm changes caused by the tire contact point offset, fully reproducing the composite force characteristics of pure lateral combined conditions. It compensates for the deficiency of neglecting the lateral coupling effect in the single unidirectional bending moment equivalent, significantly improving the calculation accuracy of the equivalent lateral load in laterally dominant conditions, and ensuring the equivalent effect of fatigue damage in laterally stressed conditions such as turning and sideslip.

[0018] Furthermore, the operating conditions include three-dimensional combined operating conditions. In S4, the equivalent heading load and equivalent lateral load corresponding to the combined vertical and lateral load operating conditions are calculated as follows: Establish the torque balance equation at the principal hinge point: ; The equivalent heading load and equivalent lateral load distributed to the wheels were calculated: ; Among them, M x To design the yaw moment at the wheel axle center under the load spectrum, P y The design load spectrum represents the lateral force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... x To design the yaw force at the wheel axle center under the load spectrum, P z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, F yo To simplify the lateral force at the wheel axle center contact point under the equivalent load spectrum, L1 is the distance from the wheel center to the tire contact point in the test spectrum, ΔH is the fixed compression of the buffer support, λ is the difference between the load distribution ratio of the left wheel and the right wheel, and P zo P represents the vertical force at the wheel axle center under the equivalent load spectrum, where t is the half-wheel distance between the left and right wheels; xo P represents the yaw force at the wheel axle center under the equivalent load spectrum. x1 P x2 Let these represent the center heading forces of the left and right engines under the equivalent load spectrum, respectively, satisfying... ;F y1 F y2 These are the lateral forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... ; k This is a fixed ratio coefficient between lateral load and heading load.

[0019] The moment balance equations simultaneously consider the directional bending moment, the lateral load-added bending moment, and the directional load-added bending moment, using the complete equality of the principal hinge vector resultant bending moments as an equivalent constraint to fully cover the composite moment effect generated by the coupling of three loads. During the solution process, the total equivalent directional and lateral loads are solved uniformly, and the independent directional and lateral ground contact loads of each wheel are obtained based on the difference in the left and right wheel distribution ratios. This fully recreates the complex composite force state of taxiing, turning, and braking, while also taking into account tire ground contact offset arm correction and left and right wheel load distribution, avoiding the loss of coupling moments caused by separate directional equivalences. This comprehensively improves the calculation accuracy of bidirectional equivalent loads under multi-load coupling conditions, ensuring the equivalent matching effect of fatigue damage under high-damage composite conditions.

[0020] Furthermore, S4 also includes establishing an equivalent equation for braking torque for in-flight braking conditions: ; The equivalent heading load distributed to the tire contact point is calculated as follows: ; Among them, M 1y M 2y F represents the center lateral moment of the left and right rotor wheels under the design load spectrum, respectively. xo The simplified contact point heading force at the wheel axle center under the equivalent load spectrum; L1 is the distance from the wheel center to the tire contact point in the test spectrum, λ is the difference between the load distribution ratio of the left wheel and the right wheel, F x1 F x2 These are the heading forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... .

[0021] An independent moment equation is established for the special forces of in-flight braking without ground vertical load. The equivalent heading load is solved only by the braking lateral bending moment and the grounding arm. Irrelevant moment interference is eliminated, the solution logic is simplified, the single wheel load distribution of in-flight braking is accurately restored, and the conversion accuracy of this special condition is improved.

[0022] Furthermore, the equivalent load spectrum is corrected according to the following formula to obtain the vertical force P at the center loading points of the left and right wheels under the test load spectrum. o1x P o2x : ; ; Among them, P 1x P 2x P represents the center heading force of the left and right wheels under the design load spectrum, respectively. x1 P x2 M represents the center heading force of the left and right engines under the equivalent load spectrum, respectively. 1z M2z These represent the center vertical moments of the left and right wheels under the design load spectrum, respectively, where t is the half-wheel distance between the left and right wheels, and M is the torque at the center of the wheel. 1y M 2y These represent the lateral moment at the center of the left and right wheels under the design load spectrum, respectively.

[0023] Based on the existence of lateral bending moment, a differentiated correction logic is established: when lateral bending moment exists, the vertical loading force of the left and right wheels is directly set to zero to match the force characteristics of the lateral working condition without additional vertical moment superposition; when there is no lateral bending moment, according to the amplitude relationship between the original total heading load and the equivalent total heading load, an additional vertical bending moment is introduced and distributed in half to the left and right wheels to complete the vertical force compensation correction, accurately compensating for the vertical moment difference caused by the conversion of fixed compression amount, so that the final vertical loading force at the center of the left and right wheels can completely restore the original working condition vertical moment.

[0024] Furthermore, after S5, by comparing the load amplitudes of the test load spectrum and the design load spectrum acting on the main structure of the landing gear, the rationality of the equivalent conversion of the test load spectrum is verified. The load amplitude of the main structure is compared and verified on the converted test load spectrum to form a complete closed-loop verification logic, timely identify and correct conversion deviations, ensure that the force amplitude of the test load spectrum matches the original design conditions, and improve the overall reliability of the load equivalent conversion scheme.

[0025] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention obtains the test load spectrum under a fixed compression by uniformly converting the buffer struts and tire compression, establishing the main hinge vector moment balance equation under different working conditions, and correcting the heading / lateral load. This avoids the problem of incomplete and unreasonable assessment of multiple buffer strut compressions and multiple tire compressions under design conditions in fatigue tests with fixed compression, and achieves equivalent matching of the stress of the entire structure. Specifically, differentiated modeling is performed for different working conditions: the braking condition couples the heading and lateral bidirectional bending moments to eliminate the error of the lateral additional moment; the three-dimensional composite condition integrates the three-dimensional load coupling moment to avoid the deviation of losing the coupling effect in the separate directional equivalence; the in-flight braking condition independently establishes the moment equation to eliminate the calculation interference caused by the redundant terms of the ground vertical load. Considering the correction of the tire ground contact offset arm and the load distribution of the left and right wheels, the true stress of various working conditions is restored, avoiding local overload or underload assessment, and greatly improving the load equivalence accuracy and reliability of the fatigue test results. Attached Figure Description

[0026] To more clearly illustrate the technical method 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 one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1This is a flowchart of the equivalent conversion method of landing gear fatigue test load spectrum in an embodiment of the present invention; Figure 2 This is a simplified schematic diagram of the landing gear structure according to an embodiment of the present invention; Figure 3 This is a diagram showing the connection relationship of the landing gear structural components according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the left and right landing gear wheels according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the compression of the landing gear buffer strut according to an embodiment of the present invention; Figure 6 This is a distribution diagram of the compression amount of the landing gear design load spectrum buffer strut in an embodiment of the present invention.

[0028] In the figure 1. Outer cylinder; 2. Locking arm; 3. Retraction and extension mechanism; 4. Lower lock; 5. Piston rod; 6. Lower torque arm; 7. Upper torque arm; 8. Tire contact point; 9. Wheel and tire; 10. Upper support; 11. Fully extended upper support; 12. Lower support; 13. Compression amount. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. For ease of description, the terms "upper," "lower," "left," and "right" used below only indicate that they correspond to the upper, lower, left, and right directions in the accompanying drawings and do not limit the structure.

[0030] The technical methods of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The technical methods of this application will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0032] Figure 1The flowchart illustrates the equivalent conversion method for landing gear fatigue test load spectrum provided in this embodiment of the invention. First, the distribution of the compression amounts of the buffer strut and tires in the landing gear design load spectrum is analyzed. Based on the distribution of load, frequency, and buffer strut compression amounts under various working conditions in the design load spectrum, the fixed compression amounts of the buffer strut and tires during the fatigue test are determined. Then, an equivalent conversion of the load spectrum is performed according to the conversion principles, including the principle of constant vertical load, the principle of equivalent bending moment, the principle of equivalent braking moment, and the principle of shear force correction. The equivalent load spectrum is obtained by establishing equilibrium equations and then correcting it to obtain the landing gear fatigue test load spectrum. The rationality of the test load spectrum is verified by analyzing the performance of the main structural components of the landing gear.

[0033] This conversion method transforms the compression values ​​of multiple shock absorbers and multiple tires in the landing gear design load spectrum into fixed compression values. Based on the conversion principle and corrections, a fatigue test load spectrum is obtained. Furthermore, the fatigue test load spectrum is verified by combining the equivalent assessment of weak points in major structural components. This avoids the shortcomings of fixed compression value fatigue tests, which are incomplete and unreasonable in assessing the compression values ​​of multiple shock absorbers and multiple tires under design conditions. It is suitable for fixed compression value fatigue tests of landing gear. Figure 1 As shown, the method includes the following steps: S1: Obtain raw data from the preset landing gear design load spectrum file. This raw data includes the compression of different shock absorber struts and tires under various load conditions. The landing gear design load spectrum has converted the directional and lateral loads at the tire contact point to the wheel center point and provides the additional bending moment. The landing gear structure is as follows: Figure 2 and Figure 3 As shown.

[0034] S2: The compression values ​​of the buffer struts and tires are simplified to calculate the fixed compression value of the buffer struts and the test tire compression value. The compression value simplification is based on the fact that the landing gear design load spectrum consists of multiple buffer strut compression value load segments, including different buffer strut compression values ​​under various load conditions such as traction, ground turning, braking taxiing, takeoff run, and landing run. Considering the frequency of each load segment in the design load spectrum, the multiple buffer strut compression values ​​and tire compression values ​​are simplified to a fixed compression value. Figure 4 This diagram illustrates the points of application and directions of ground loads during landing gear fatigue testing. Figure 4 The simplification of the tire compression specifically includes: S2.1: Considering that the directional load and lateral load corresponding to the actual landing gear braking and bearing lateral loads are both applied to the tire contact point, and in order to facilitate the application of loads during fatigue testing, the bending moment corresponding to the directional load or lateral load in the design load spectrum is converted from the wheel center point to the tire contact point to complete the correction of the stress point position under working conditions.

[0035] S2.2: Based on the force point correction for each working condition, calculate the tire compression for each working condition with additional bending moment in the design load spectrum.

[0036] S2.3: Select the tire compression value that occurs most frequently as the test tire compression value δ.

[0037] The landing gear design load spectrum provides a load spectrum composed of multiple shock absorber strut compression load segments, such as the landing gear shock absorber strut compression. Figure 5 As shown, to facilitate the cyclic loading implementation of the landing gear fatigue test load spectrum, the landing gear design load spectrum for multiple strut compression values ​​needs to be uniformly converted to an equivalent value for a single strut compression value, thus compiling a fatigue test load spectrum for a single strut compression value. The distribution of strut compression values ​​in the landing gear design load spectrum is as follows: Figure 6 As shown. The simplification of the compression amount of the buffer support specifically includes: The compression amount and corresponding fatigue damage of the buffer support under each working condition in the design load spectrum are statistically analyzed. The compression amount range of the buffer support corresponding to the working condition where the fatigue damage exceeds the preset damage threshold is screened, and the median value of the range is taken as the fixed compression amount ΔH of the buffer support.

[0038] S3: Vertical load conversion principle: The magnitude of the vertical load remains unchanged before and after conversion. The vertical loads under various operating conditions are standardized, converting the center point loads of the left and right wheels in the landing gear design load spectrum to the center point loads of the wheel axles. (1) Vertical loads distributed to the wheel: (2) When the landing gear is subjected to the same vertical load, the additional bending moment caused by the difference in directional deformation due to the compression of different shock absorber struts is negligible. Therefore, when converting the vertical loads of traction, ground turning, braking taxiing, takeoff run, and landing run conditions in the landing gear design load spectrum into the fatigue test spectrum, the magnitude of the vertical load remains unchanged. Only the compression of the corresponding shock absorber strut is adjusted to the compression of the fixed shock absorber strut in the test, and the load distribution ratio between the left and right wheel centers remains unchanged.

[0039] S4: Based on the load characteristics of the fatigue design load spectrum, establish the moment balance equation of the main hinge point based on the fixed compression of the buffer strut, calculate the equivalent directional load and / or equivalent lateral load corresponding to each working condition, and obtain the equivalent load spectrum. According to the principle of equivalent bending moment at the main hinge point, the lateral load acts at the tire contact point to ensure that the lateral load is transmitted to the landing gear main hinge point with equivalent bending moment, and convert the lateral load of the landing gear equivalent load spectrum. Under non-ground braking conditions, the converted directional load acts at the wheel center to ensure that the directional load is transmitted to the landing gear main hinge point with equivalent bending moment, and convert the directional load of the landing gear equivalent load spectrum. Under ground braking conditions, the converted directional load acts at the contact point to ensure that the directional load is transmitted to the landing gear main hinge point with equivalent bending moment, and convert the directional load of the landing gear equivalent load spectrum.

[0040] The fatigue load conditions include combined vertical and yaw load conditions, combined vertical and lateral load conditions, and combined three-dimensional (vertical, yaw, and lateral) load conditions.

[0041] The following section will detail the process of establishing the moment balance equations for the main hinge point under various working conditions, as well as the solution process.

[0042] First, consider the combined vertical and directional loads without braking (My=0). When the landing gear is subjected to vertical and directional loads without braking, based on the fact that the equivalent moments of the ground loads about the main hinge point are equal before and after the transition, the following equation can be obtained: (3) The equivalent benchmark is that the vector resultant bending moment of the ground load on the main hinge point is completely equal before and after the conversion. The resultant bending moment of the landing gear main hinge is the core control quantity for fatigue damage of each load-bearing structure. Only by ensuring that the amplitude of the resultant bending moment is consistent before and after the conversion can the equivalent fatigue damage of the structure be achieved. The left side of the equation is the original design spectrum bending moment, and the right side is the test spectrum bending moment with a fixed compression amount. The test uses a fixed compression amount ΔH. The difference between the half wheel track t and the load distribution λ is introduced to reflect the lateral additional moment generated by the vertical load of the left and right wheels. Combined with the moment terms of the equivalent heading force and vertical force, the vector resultant bending moment of the main hinge under the fixed compression amount condition is obtained.

[0043] Traditional single-section methods only constrain one component of the directional bending moment or the vertical bending moment to be equal, without applying vector coupling constraints to the bidirectional bending moments. During the conversion of fixed compression, the bending moment in the other direction will shift, and the magnitude and direction of the final resultant bending moment of the principal hinge vector are inconsistent with the original working condition. The embodiment of this invention establishes an equivalent equation to vector superimpose the bending moments generated in the directional and vertical directions, ensuring that the magnitude and direction of the resultant bending moment are the same.

[0044] The solution yields the heading loads distributed to the wheels: (4) The operating conditions include a combination of vertical and directional braking loads (My≠0). When the landing gear is subjected to vertical and directional loads during braking, based on the fact that the equivalent moments of the ground loads about the main hinge point are equal before and after the transition, the following formula can be obtained: (5) The equivalent heading load distributed to the wheels was calculated as follows: (6) The operating conditions include a combination of vertical and lateral loads. When the landing gear is subjected to both vertical and lateral loads, based on the fact that the equivalent moments of the ground loads about the main hinge point are equal before and after the conversion, the following formula can be obtained: (7) The equivalent heading load distributed to the wheels was calculated as follows: (8) The operating conditions include three-dimensional combined operating conditions. When the landing gear is subjected to vertical, directional, and lateral loads, based on the fact that the equivalent moments of the ground loads about the main hinge point are equal before and after the conversion, the following formula can be obtained: (9) Considering that Fyo and Pxo, Py and Px are all proportional to the vertical load, let: (10) P xo The load is: (11) The equivalent heading load and equivalent lateral load distributed to the wheels were calculated: (12) In one embodiment, S4 further includes applying the principle of equivalent braking torque for in-flight braking conditions to ensure equivalent braking torque at the wheel axle, and calculating the landing gear wheel contact point load. When the landing gear is only subjected to the lateral torque of wheel braking, based on the fact that the equivalent torque of the ground load on the wheel axle before and after the conversion is equal, the following formula can be obtained: (13) The equivalent heading load distributed to the tire contact point is calculated as follows: (14) S5: Perform load correction on the equivalent load spectrum to obtain the test load spectrum after load correction. The load correction includes converting the vertical torque of the combined vertical and lateral load conditions into a couple at the left and right wheels.

[0045] The test load spectrum is modified to the equivalent load spectrum. To ensure that bending moment and shear force are assessed simultaneously, the test load spectrum uses the larger value between the equivalent load spectrum and the design load spectrum. The vertical torque is converted into a pair of force couples applied to the center of the left and right wheels, thus generating the directional load at the center points of the left and right landing gear wheels. This achieves an equivalent assessment of the shear force of the landing gear structure. Since the directional loads in the design load spectrum are all at the center points of the wheels, and the directional loads in the test spectrum are at the center points of the wheels in non-braking conditions and at the tire contact points in braking conditions, under ground turning conditions, the left and right landing gear wheels bear the vertical torque exerted by the ground on the landing gear. To facilitate the test loading, the vertical torque in the design load spectrum is converted into a pair of force couples applied to the left and right wheels, i.e., the applied force couples are the directional force at the center of the left wheel and the directional force at the center of the right wheel.

[0046] Corrected P o1x P o2x for: (15) (16) In one embodiment, after S5, the rationality of the equivalent conversion of the test load spectrum is verified by comparing the load amplitudes of the test load spectrum and the design load spectrum acting on the main landing gear structure. The test load spectrum verification is demonstrated by evaluating the performance of the lower landing gear lock, outer cylinder, and piston rod main structure.

[0047] The lower lock mainly bears the balancing force generated by the bending moment at the main hinge point. Since the test load spectrum is converted by the bending moment at the main hinge point and corrected, the bending moment at the main hinge point in the test load spectrum is larger than the design load spectrum, and the balancing force transmitted to the lower lock is larger. Therefore, it can meet the test requirements for the fatigue performance of the lower lock structure.

[0048] The outer cylinder is analyzed in two parts: upper and lower. The load on the upper main hinge point is obtained by the balancing force of the lower lock and the load on the ground. Since the balancing force of the lower lock is too large, the load on the upper main hinge point is also too large. Therefore, it can meet the fatigue performance test of the upper structure of the outer cylinder. Considering the correction by the test load spectrum, the test load spectrum is not less than the design load spectrum, which can be used to evaluate the lower part of the outer cylinder. Therefore, it can meet the fatigue performance test of the outer cylinder structure.

[0049] The piston rod directly bears the ground load, and the test load spectrum is not less than the design load spectrum, thus meeting the requirements for evaluating the fatigue performance of the piston rod structure.

[0050] This invention ensures the equivalent performance of each part of the landing gear by using the principles of constant vertical load, equivalent bending moment, equivalent landing gear torque, equivalent braking torque, and shear force correction. Finally, the rationality of the converted test spectrum is verified by the converted test load spectrum.

[0051] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0052] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

[0053] Symbol Explanation O—Center point of piston rod wheel axle; O1, O2 — Center points of the left and right wheels; K1, K2 — left and right tire contact points; R—Wheel radius; δ—Test tire compression; SAT – Design spectrum buffer support compression amount; ΔH — Fixed compression of the buffer support in the test spectrum; t — the distance between the left and right wheel halves; k —A fixed proportionality coefficient between lateral load and heading load; L—Vertical distance from the wheel axle center to the main hinge point when the landing gear buffer strut is fully extended; L1—Distance from the center of the test wheel to the tire contact point; L2—Landing gear stabilizer moment; λ — the difference between the load distribution ratio of the left wheel and the load distribution ratio of the right wheel; P 1x —The heading force at the center of the left engine wheel under the design load spectrum; P 1y — Lateral force at the center of the left wheel under the design load spectrum; P 1z —Vertical force at the center of the left wheel under the design load spectrum; M 1x —The yaw moment at the center of the left engine wheel under the design load spectrum; M1y —The lateral moment at the center of the left wheel under the design load spectrum; M 1z —Vertical moment at the center of the left wheel under the design load spectrum; P 2x —The heading force at the center of the right engine wheel under the design load spectrum; P 2y —The lateral force at the center of the right wheel under the design load spectrum; P 2z —Vertical force at the center of the right wheel under the design load spectrum; M 2x —The heading moment at the center of the right engine wheel under the design load spectrum; M 2y —The lateral moment at the center of the right wheel under the design load spectrum; M 2z —Vertical moment at the center of the right wheel under the design load spectrum; P x —The yaw force at the wheel axle center under the design load spectrum; P y — Lateral force at the wheel axle center under the design load spectrum; P z —Vertical force at the wheel axle center under the design load spectrum; M x —The yaw moment at the wheel axle center under the design load spectrum; M y — Lateral moment at the wheel axle center under the design load spectrum; M z —Vertical moment at the wheel axle center under the design load spectrum; P xo —The yaw force at the wheel axle center under the equivalent load spectrum; P zo —Vertical force at the wheel axle center under the equivalent load spectrum; F xo —The directional force at the simplified ground contact point of the wheel axle center under the equivalent load spectrum; F yo —Simplified lateral force at the center grounding point of the wheel axle under the equivalent load spectrum; P x1 —The heading force at the center of the left engine wheel under the equivalent load spectrum; P z1 —Vertical force at the center of the left wheel under the equivalent load spectrum; F x1 —The heading force at the contact point of the left tire under the equivalent load spectrum; F y1 — Lateral force at the contact point of the left tire under the equivalent load spectrum; P x2—The heading force at the center of the right engine wheel under the equivalent load spectrum; P z2 —Vertical force at the center of the right wheel under the equivalent load spectrum; F x2 —The heading force at the right tire contact point under the equivalent load spectrum; F y2 —The lateral force at the contact point of the right tire under the equivalent load spectrum; P o1x —The heading force at the center loading point of the left engine wheel under the test load spectrum; P o1z —Vertical force at the center loading point of the left wheel under the test load spectrum; F k1x —The heading force at the left tire contact loading point under the test load spectrum; F k1y — Lateral force at the contact loading point of the left tire under the test load spectrum; P o2x —The heading force at the center loading point of the right engine wheel under the test load spectrum; P o2z —Vertical force at the center loading point of the right wheel under the test load spectrum; F k1x —The heading force at the right tire contact loading point under the test load spectrum; F k1y — Lateral force at the contact loading point of the right tire under the test load spectrum.

Claims

1. A method for equivalent conversion of load spectrum in landing gear fatigue testing, characterized in that, Includes the following steps: S1: Obtain raw data from the preset landing gear design load spectrum file. The raw data includes the compression of different buffer struts and tire compression under each load condition. S2: The compression of the buffer strut and the compression of the tire are simplified and calculated to obtain the fixed compression of the buffer strut and the compression of the test tire. S3: Standardize the vertical load under each working condition, keep the vertical load amplitude and the load distribution ratio between the left and right wheels unchanged, and replace the compression amount of the buffer support under each working condition with the fixed compression amount of the buffer support. S4: Based on the fixed compression of the buffer support, establish the moment balance equation of the main hinge point, calculate the equivalent heading load and / or equivalent lateral load corresponding to each working condition, and obtain the equivalent load spectrum; S5: Perform load correction on the equivalent load spectrum to obtain the test load spectrum after load correction. The load correction includes converting the vertical torque of the combined vertical and lateral load conditions into a couple at the left and right wheels.

2. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, In S2, the simplification of the tire compression specifically includes: S2.1: Convert the bending moment corresponding to the heading load or lateral load in the design load spectrum from the wheel center point to the tire contact point to complete the force point correction under working conditions; S2.2: Based on the force point correction for each working condition, calculate the tire compression for each working condition with additional bending moment in the design load spectrum; S2.3: Select the tire compression value that appears most frequently as the test tire compression value.

3. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, In S2, the simplification of the compression amount of the buffer support specifically includes: The compression amount and corresponding fatigue damage of the buffer support under each working condition in the design load spectrum are statistically analyzed. The compression amount range of the buffer support corresponding to the working condition where the fatigue damage exceeds the preset damage threshold is screened, and the median value of the range is taken as the fixed compression amount of the buffer support.

4. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, The operating conditions include a combination of non-braking vertical and heading loads. In S4, the equivalent heading load corresponding to the combination of non-braking vertical and heading loads is calculated as follows: Establish the torque balance equation at the principal hinge point: ； The equivalent heading load distributed to the wheels was calculated as follows: ； Among them, M x To design the yaw moment at the wheel axle center under the load spectrum, P x The design load spectrum represents the yaw force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, λ is the difference between the load distribution ratio of the left wheel and the right wheel, and P... zo P represents the vertical force at the center of the wheel axle under the equivalent load spectrum, t is the half-wheel distance between the left and right wheels, and P is the vertical force at the center of the wheel axle. xo P represents the yaw force at the wheel axle center under the equivalent load spectrum, where ΔH is the fixed compression of the buffer strut; x1 P x2 Let these represent the center heading forces of the left and right engines under the equivalent load spectrum, respectively, satisfying... ;P 1x P 2x These represent the heading forces at the center of the left and right engines under the design load spectrum, respectively.

5. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, The operating conditions include a combination of braking vertical and heading loads. In S4, the equivalent heading load corresponding to the combination of braking vertical and heading loads is calculated as follows: Establish the torque balance equation at the principal hinge point: ； The equivalent heading load distributed to the wheels was calculated as follows: ； Among them, M x M y These represent the heading and lateral moment at the wheel axle center under the design load spectrum, respectively. x The design load spectrum represents the yaw force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, λ is the difference between the load distribution ratio of the left wheel and the right wheel, and P... zo F represents the vertical force at the center of the wheel axle under the equivalent load spectrum, t is the half-wheel distance between the left and right wheels, and F is the vertical force at the center of the wheel axle. xo The simplified contact point azimuth force at the wheel axle center under the equivalent load spectrum; L1 is the distance from the wheel center to the tire contact point in the test spectrum, ΔH is the fixed compression of the buffer strut; F x1 F x2 These are the heading forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... P 1x P 2x M represents the center heading force of the left and right wheels under the design load spectrum, respectively. 1y M 2y These represent the lateral moment at the center of the left and right wheels under the design load spectrum, respectively.

6. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, The working condition includes a combination of vertical and lateral loads. In S4, the equivalent lateral load corresponding to the combined vertical and lateral load condition is calculated as follows: Establish the torque balance equation at the principal hinge point: ； The equivalent heading load distributed to the wheels was calculated as follows: ； Among them, M x To design the yaw moment at the wheel axle center under the load spectrum, P y The design load spectrum represents the lateral force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, F yo The simplified lateral force at the wheel axle center contact point under the equivalent load spectrum; L1 is the distance from the wheel center to the tire contact point in the test spectrum; ΔH is the fixed compression of the buffer support; λ is the difference between the load distribution ratio of the left wheel and the right wheel; P zo F represents the vertical force at the center of the wheel axle under the equivalent load spectrum, where t is the half-wheel distance between the left and right wheels; y1 F y2 These are the lateral forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... M 1x M 2x These are the center-heading moments of the left and right rotor wheels under the design load spectrum, respectively; P 1y P 2y These represent the lateral forces at the center of the left and right rotor wheels under the design load spectrum.

7. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, The operating conditions include a three-dimensional combined operating condition. In S4, the equivalent heading load and equivalent lateral load corresponding to the combined vertical and lateral load operating condition are calculated as follows: Establish the torque balance equation at the principal hinge point: ； The equivalent heading load and equivalent lateral load distributed to the wheels were calculated: ； Among them, M x To design the yaw moment at the wheel axle center under the load spectrum, P y The design load spectrum represents the lateral force at the axle center, where L is the vertical distance from the axle center to the main hinge point in the fully extended state of the landing gear strut, SAT is the design spectrum strut compression, and P... x To design the yaw force at the wheel axle center under the load spectrum, P z To design the vertical force at the wheel axle center under the load spectrum, L2 is the landing gear stabilizing moment, F yo To simplify the lateral force at the wheel axle center contact point under the equivalent load spectrum, L1 is the distance from the wheel center to the tire contact point in the test spectrum, ΔH is the fixed compression of the buffer support, λ is the difference between the load distribution ratio of the left wheel and the right wheel, and P zo P represents the vertical force at the wheel axle center under the equivalent load spectrum, where t is the half-wheel distance between the left and right wheels; xo P represents the yaw force at the wheel axle center under the equivalent load spectrum. x1 P x2 Let these represent the center heading forces of the left and right engines under the equivalent load spectrum, respectively, satisfying... ;F y1 F y2 These are the lateral forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... k is a fixed proportionality coefficient between lateral load and heading load.

8. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, S4 also includes establishing an equivalent equation for braking torque for in-flight braking conditions: ； The equivalent heading load distributed to the tire contact point is calculated as follows: ； Among them, M 1y M 2y F represents the center lateral moment of the left and right rotor wheels under the design load spectrum, respectively. xo The simplified contact point heading force at the wheel axle center under the equivalent load spectrum; L1 is the distance from the wheel center to the tire contact point in the test spectrum, λ is the difference between the load distribution ratio of the left wheel and the right wheel, F x1 F x2 These are the heading forces at the contact points of the left and right tires under the equivalent load spectrum, respectively, satisfying... .

9. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, The equivalent load spectrum is corrected according to the following formula to obtain the vertical force P at the center loading points of the left and right wheels under the test load spectrum. o1x P o2x : ； ； Among them, P 1x P 2x P represents the center heading force of the left and right wheels under the design load spectrum, respectively. x1 P x2 M represents the center heading force of the left and right engines under the equivalent load spectrum, respectively. 1z M 2z These represent the center vertical moments of the left and right wheels under the design load spectrum, respectively, where t is the half-wheel distance between the left and right wheels, and M is the torque at the center of the wheel. 1y M 2y These represent the lateral moment at the center of the left and right wheels under the design load spectrum, respectively.

10. The method for equivalent conversion of landing gear fatigue test load spectrum according to claim 1, characterized in that, After S5, the rationality of the equivalent conversion of the test load spectrum is verified by comparing the load amplitudes of the test load spectrum and the design load spectrum acting on the main landing gear structure.

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