Helicopter tail section damage tolerance test load spectrum simplification method

Abstract

The invention belongs to the field of fatigue strength test design, and relates to a helicopter tail section damage tolerance test load spectrum simplification method. The method comprises the following steps: taking a task section of a single test load spectrum block as a unit, and obtaining a simplified spectrum based on a rain flow counting method; attaching a landing state to each mission profile, and calculating the total cycle index of the individual mission profile after the landing state is considered according to the time proportion of the individual mission profile in the test load spectrum and the total number of times of the landing state; meanwhile, the landing state is classified into various landing working conditions in a refined mode, and the corresponding frequency of each landing working condition in the load spectrum block is calculated; determining a specific landing condition corresponding to a single mission profile, and recording the total number mj of the jth flight state of the test spectrum block; j is any integer from 1 to the total number of flight states; simplifying and combining task profiles of the test load spectrum block with the additional landing state; and carrying out load balancing on the test load spectrum block in each flight state and each landing state, and determining a loading load.

Description

Technical Field

[0001] The invention belongs to the field of fatigue strength test design and relates to a method for simplifying a load spectrum of a helicopter tail section damage tolerance test. Background Art

[0002] Since the tail section structure is a key structure for single-force fatigue, it is generally necessary to conduct a damage tolerance test on the tail section structure in accordance with relevant specifications.

[0003] When conducting damage tolerance tests on the tail section structure, since the typical mission profiles of previous models were relatively simple and the flight actions of a single profile were also relatively simple, it was only necessary to adopt the damage equivalence principle and use the rain flow method to simplify the characteristic loads of each state in the mission profile to meet the test requirements.

[0004] For complex aircraft models that include more than 10 typical mission profiles, the flight time of a single mission profile is often more than several hours, and each mission profile has more than 20 flight states before refinement. The single test load spectrum block obtained by the previous rain flow simplification method in the mission profile is as many as more than 1,000 lines, which no longer meets the requirements of test implementation. Summary of the invention

[0005] Purpose of the invention: A method for simplifying the load spectrum of a helicopter tail section damage tolerance test is provided, a principle for simplifying load spectrum blocks under complex mission profiles is formulated, the goal of simplifying load spectrum blocks under complex mission profiles is achieved, simplified load spectrum blocks that meet the test requirements are obtained, load balancing in flight and landing states is achieved, and a basis is provided for the subsequent simplification of load spectra in damage tolerance tests.

[0006] Technical solution:

[0007] A method for simplifying a load spectrum for a damage tolerance test of a tail section of a helicopter is provided. The tail section of the helicopter includes a tail landing gear, and includes:

[0008] Taking the mission profile of a single test load spectrum block as a unit, the rain flow method is used for preliminary simplification to obtain a simplified spectrum. The simplified spectrum includes the rain flow counting results of each mission profile. The rain flow counting results include the load conditions, occurrence order and repetition times of each flight state in a mission profile.

[0009] The landing state is added as a new state to each mission profile. The total number of cycles of the individual mission profile after considering the landing state is calculated according to the time proportion of the individual mission profile in the test load spectrum and the total number of landing states. At the same time, the landing state is refined and classified into various landing conditions, and the number of times each landing condition corresponds to in the load spectrum block is calculated. Based on the total number of cycles of the individual mission profile after considering the landing state and the number of times various landing conditions correspond to in the load spectrum block, the specific landing condition corresponding to the individual mission profile is determined, and the total number of flight states No. j in the test spectrum block is recorded. j ; j is any integer from 1 to the total number of flight states;

[0010] Simplified merging between mission profiles for test load spectrum blocks with additional landing conditions;

[0011] The load spectrum block is tested based on the balancing principle of the equivalent bending moment of the control section to balance the loads in each flight and landing state and determine the loading load.

[0012] Furthermore, the total number of cycles of the individual mission profile after considering the landing state is calculated according to the rain flow counting result, including:

[0013] Assuming that the load spectrum block is compiled based on w flight hours, if the number of landings is n times per hour, a single load spectrum block needs to include w n landings;

[0014] If the time proportion of the first mission profile is a1%, and the time required to complete a single profile is b1 hours, then without considering the number of combined landings, the number of cycles of the first mission profile in w flight hours is (a1%w / b1). Similarly, if the time proportion of the last mission profile is a m %, the time required to complete a single section is b m hours, without considering the number of combined landings, the number of cycles of the last mission profile in w flight hours is (a m %w / b m )Second-rate;

[0015] Assign one landing state to each mission profile, and determine the magnification factor of the number of cycles of each mission profile: Then the total number of cycles of each mission profile after considering the landing state is determined to be c times the number of cycles of the mission profile.

[0016] Furthermore, the landing state is subdivided into various landing conditions, and the number of times each landing condition corresponds to the load spectrum block is calculated, including:

[0017] According to the known landing sinking speed percentage d i , pitch attitude percentage e i, quality status percentage f i The landing state is subdivided into various landing conditions, and the number of times each landing condition corresponds to the load spectrum block is calculated as wnd i e i f i .

[0018] Furthermore, based on the total number of cycles of the individual mission profile after considering the landing state and the corresponding number of various landing conditions in the load spectrum block, the specific landing condition corresponding to the individual mission profile is determined, including:

[0019] Landing conditions are assigned to each mission profile until the number of assigned landing conditions is equal to the total number of cycles of the mission profile after considering the landing state.

[0020] Furthermore, the total number of flight states of the test spectrum block No. j is recorded, including:

[0021] Get the number of times the jth flight state occurs in the mission profile;

[0022] Multiply the number of times of the j-th flight state by the total number of cycles of the mission profile to obtain the total number of times of the j-th flight state in the mission profile;

[0023] Add up the total number of flight states No. j in all mission profiles to obtain the total number of flight states No. j in the test spectrum block.

[0024] Furthermore, for the jth flight state, the test load spectrum block of the additional landing state is simplified and merged between mission profiles, including:

[0025] Get the time taken to complete a j-th flight state and the time ratio of the j-th flight state to w flight hours;

[0026] Determine the scaling correction ratio according to the time taken to complete a j-th flight state, the proportion of the j-th flight state to the w flight hours, and the total number of the j-th flight state of the test spectrum block;

[0027] For the qth mission profile, divide the total number of the jth flight state by the scaling correction ratio, and take the remainder as the number of cycles of the jth flight state of the mission profile. Add the remainder to the total number of the jth flight state of the q+1th mission profile.

[0028] Repeat the previous step to complete the simplified merging of all mission profiles and obtain the number of cycles of each profile in the test load spectrum and the state sequence within the mission profile.

[0029] Furthermore, the load spectrum block is tested to balance the loads of each flight and landing state by controlling the equivalent bending moment of the section as the balancing principle, and the loading load is determined, including:

[0030] The main load-bearing joint position of the tail section structure is selected as the loading point, and the load balancing principle is to control the bending moment of each frame position of the tail section structure to be consistent. The bending moment of each main frame position of the tail section structure is obtained according to the inertial balance load of the whole aircraft. The load of each loading point in each flight and landing state is obtained in turn through load balancing.

[0031] At the same time, considering that the test load at each loading point cannot exceed the bearing capacity of the loading point and its surrounding structures, the loading loads for each flight and landing state must be further verified through a virtual test finite element model.

[0032] Furthermore, when load balancing for the landing state, it is necessary to first ensure that the load at the landing gear loading point is consistent with the actual calculated load.

[0033] Beneficial effects:

[0034] The present invention formulates further simplification principles and further simplifies the profile. The simplified spectra obtained above are merged in the same state (states with little difference) according to the results after rain flow, and the smaller dynamic load cycles (less than 5% of the maximum dynamic load in the profile) are eliminated according to the smaller damage. Then, the number of cycles of each mission profile in a single load spectrum block is determined in combination with the total number of landings and the time ratio of each mission profile. Finally, based on the time ratio of each flight state and the completion time of a single flight state, the total number of single flight states in the entire load spectrum block is obtained, and the mission profiles are merged to ensure the simplicity of the simplified load spectrum and the feasibility of the test. Finally, the test load spectrum block is simplified to more than 300 lines. DETAILED DESCRIPTION

[0035] The present invention provides a method for simplifying a load spectrum of a helicopter tail section damage tolerance test, comprising the following steps:

[0036] [1] The damage equivalence principle is used for preliminary simplification. First, based on the load characteristics, occurrence sequence, and time proportion in the section, and considering the flight attitude combination in each state (such as sideslip in level flight and different bank angles in turning, etc.), the load conditions, occurrence sequence, and number of repetitions in each flight state in each mission section can be obtained. The sum of the bending moments in the My and Mz directions of the frame station at the docking frame of the tail section and the transition section is selected as the main characteristic load, and the damage equivalence principle is used to make a preliminary simplification of the mission section using the rain flow method.

[0037] [2] Based on the simplified spectrum obtained in the previous section, the states with little difference are merged according to the results after rain flow. Smaller dynamic load cycles (less than 5% of the maximum dynamic load in the section) are eliminated according to the smaller damage. Remember that the basic principle of merging is to merge the ranges with large dynamic and static loads (the dynamic load increase cannot be greater than 3% of the maximum dynamic load) and tend to be conservative.

[0038] [3] Merge the landing state into the load spectrum. For aircraft with a tail section structure that includes a tail landing gear, the landing state needs to be added as a separate operating condition to the ground operating condition of each mission profile. First, take a single load spectrum block 1000fh as an example for compilation. If the number of landings is n times per hour, then a single load spectrum block must include 1000n landings. Assuming that the time proportion of the first mission profile is a1%, and the time required to complete a single profile is b1 hours, then without considering the number of merged landings, the number of cycles of the first mission profile in 1000fh is (1000a1% / b1) times, and so on. The time proportion of the last mission profile is a m %, the time required to complete a single section is b m hours, without considering the number of combined landings, the number of cycles of the last mission profile in 1000fh is (1000a m % / b m ) times. In order to ensure the consistency of the total number of landings, a landing state is assigned according to the completion of a single mission profile, and the magnification factor of the number of cycles of each mission profile is found to be The total number of cycles of each mission profile after considering the landing state is the number of cycles calculated above multiplied by the magnification factor c, that is, the total number of cycles of the first mission profile in the 1000fh load spectrum block after considering the landing state is (1000a1% / b1)*c times. Then according to the landing sinking speed percentage d i , pitch attitude percentage e i , quality status percentage f i The landing state is divided into various landing conditions in equal proportion, and the number of times each landing condition corresponds to a single load spectrum block is 1000nd. i e i f i According to the above results, the total number of cycles of each mission profile after considering the landing state and the number of corresponding landing states in a single load spectrum block are combined and matched, and finally the specific landing state corresponding to a single mission profile is determined. The total number of the pth flight state in the load spectrum block at this time is recorded as m p .

[0039] Among them, m pThe acquisition method includes: acquiring the number of flight states No. j in the mission profile; multiplying the number of flight states No. j by the total number of cycles of the mission profile to obtain the total number of flight states No. j in the mission profile; adding the total number of flight states No. j in all mission profiles to obtain the total number of flight states No. j in the test spectrum block.

[0040] [4] Simplify and merge the mission profiles of the single load spectrum block obtained in the previous section. Based on the load spectrum after merging the landing state obtained in the previous section, in order to ensure the total number of landings, the number of cycles of each profile is actually amplified by a factor of c. To this end, it is necessary to calculate the total number of tests for each flight state in the current single load spectrum block and delete the number of flight states of each mission profile. According to the time ratio of each flight state in the flight spectrum and the completion time of each flight state in previous model experience, the total number of calculations of each flight state under a single load spectrum block of 1000fh is calculated. s . The number m of each flight state in the test load spectrum obtained in the previous step p , scaled and corrected to n s If the number of flight states in a single mission profile is not an integer after scaling, the remaining non-integer number can be left to the next mission profile to round up. The ultimate goal of simplification is to make the total number of tests for each flight and landing state in a single load spectrum block consistent with the total number of calculations. At this point, the simplified merger between profiles is completed, and the number of cycles of each profile in the test load spectrum and the state order within the profile are obtained.

[0041] [5] Finally, the loads of each flight and landing state are balanced based on the balancing principle of controlling the equivalent bending moment of the section to determine the loading load. The main load-bearing joint position of the tail section structure is selected as the loading point, and the load balancing principle is to control the bending moment of each frame station of the tail section structure to be consistent. The bending moment of each main frame station of the tail section structure is obtained according to the inertial balance load calculation of the whole aircraft, and the load of each loading point in each flight and landing state is obtained in turn through load balancing. During the load balancing process, it is necessary to consider that the test load of each loading joint cannot exceed the bearing capacity of the loading point and its surrounding structures. The loading loads of each flight and landing state must be further verified through a virtual test finite element model. Note that when performing load balancing for the landing state, it is necessary to first determine that the load at the landing gear loading point is consistent with the actual calculated load.

Claims

1. A method for simplifying the load spectrum of a damage tolerance test of a helicopter tail section, wherein the tail section of the helicopter includes a tail landing gear, characterized in that: include: Taking the mission profile of a single test load spectrum block as a unit, the rain flow method is used for preliminary simplification to obtain a simplified spectrum. The simplified spectrum includes the rain flow counting results of each mission profile. The rain flow counting results include the load conditions, occurrence order and repetition times of each flight state in a mission profile. The landing state is added as a new state to each mission profile, and the total number of cycles of the single mission profile after considering the landing state is calculated according to the time proportion of the single mission profile in the test load spectrum and the total number of landing states; at the same time, the landing state is subdivided into various landing conditions, and the number of times each landing condition corresponds to in the load spectrum block is calculated; Based on the total number of cycles of a single mission profile after considering the landing state and the corresponding number of various landing conditions in the load spectrum block, the specific landing condition corresponding to the single mission profile is determined, and the total number of flight states No. j in the test spectrum block is recorded. j ; j is any integer from 1 to the total number of flight states; Simplified merging between mission profiles for test load spectrum blocks with additional landing conditions; The load spectrum block is tested based on the balancing principle of the equivalent bending moment of the control section to balance the loads in each flight and landing state and determine the loading load.

2. The method according to claim 1, characterized in that The calculating of the total number of cycles of the individual mission profile after considering the landing state according to the rain flow counting result comprises: Assuming that the load spectrum block is compiled based on w flight hours, if the number of landings is n times per hour, a single load spectrum block needs to include w n landings; If the time proportion of the first mission profile is a1%, and the time required to complete a single profile is b1 hours, then without considering the number of combined landings, the number of cycles of the first mission profile in w flight hours is (a1%w / b1). Similarly, if the time proportion of the last mission profile is a m %, the time required to complete a single section is b m hours, without considering the number of combined landings, the number of cycles of the last mission profile in w flight hours is (a m %w / b m )Second-rate; Assign one landing state to each mission profile, and determine the magnification factor of the number of cycles of each mission profile: Then the total number of cycles of each mission profile after considering the landing state is determined to be c times the number of cycles of the mission profile.

3. The method according to claim 2, characterized in that The landing state is subdivided into various landing conditions, and the number of times each landing condition occurs in the load spectrum block is calculated, including: According to the known landing sinking speed percentage d i , pitch attitude percentage e i , quality status percentage f i The landing state is subdivided into various landing conditions, and the number of times each landing condition corresponds to the load spectrum block is calculated as wnd i e i f i .

4. The method according to claim 3, characterized in that Based on the total number of cycles of a single mission profile after considering the landing state and the corresponding number of various landing conditions in the load spectrum block, the specific landing conditions corresponding to a single mission profile are determined, including: Landing conditions are assigned to each mission profile until the number of assigned landing conditions is equal to the total number of cycles of the mission profile after considering the landing state.

5. The method according to claim 4, characterized in that Record the total number of flight states No. j of the test spectrum block, including: Get the number of times the jth flight state occurs in the mission profile; Multiply the number of times of the j-th flight state by the total number of cycles of the mission profile to obtain the total number of times of the j-th flight state in the mission profile; Add up the total number of flight states No. j in all mission profiles to obtain the total number of flight states No. j in the test spectrum block.

6. The method according to claim 5, characterized in that For the jth flight state, the test load spectrum block of the additional landing state is simplified and merged between mission profiles, including: Get the time taken to complete a j-th flight state and the time ratio of the j-th flight state to w flight hours; Determine the scaling correction ratio according to the time taken to complete a j-th flight state, the proportion of the j-th flight state to the w flight hours, and the total number of the j-th flight state of the test spectrum block; For the qth mission profile, divide the total number of the jth flight state by the scaling correction ratio, and take the remainder as the number of cycles of the jth flight state of the mission profile. Add the remainder to the total number of the jth flight state of the q+1th mission profile. Repeat the previous step to complete the simplified merging of all mission profiles and obtain the number of cycles of each profile in the test load spectrum and the state sequence within the mission profile.

7. The method according to claim 6, characterized in that The load balance of each flight and landing state of the test load spectrum block is carried out based on the balancing principle of the equivalent bending moment of the control section, and the loading load is determined, including: The main load-bearing joint position of the tail section structure is selected as the loading point, and the bending moment of each frame position of the tail section structure is controlled to be consistent as the load balancing principle. The bending moment of each main frame position of the tail section structure is obtained according to the inertial balance load calculation of the whole aircraft, and the load of each loading point in each flight and landing state is obtained in turn through load balancing; At the same time, considering that the test load at each loading point cannot exceed the bearing capacity of the loading point and its surrounding structures, the loading loads for each flight and landing state must be further verified through a virtual test finite element model.

8. The method according to claim 7, characterized in that When load balancing for landing conditions, first ensure that the load at the landing gear loading point is consistent with the actual calculated load.

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