A method for simplifying helicopter tail section damage tolerance test load spectrum

Abstract

The application 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 single test load spectrum block task profile as a unit, obtaining a simplified spectrum based on a rain flow counting method; attaching a landing state to each task profile, calculating the total cycle number of the single task profile after considering the landing state according to the time proportion of the single task profile in the test load spectrum and the total number of landing states; meanwhile, classifying the landing state into various landing working conditions, calculating the corresponding number of each landing working condition in the load spectrum block; determining the specific landing working condition corresponding to the single task profile, and recording the total number m of the jth flight state of the test spectrum block j ; j is any integer from 1 to the total number of flight states; simplifying and merging the task profiles of the test load spectrum block to which the landing state is attached; performing load balancing of each flight and landing state of the test load spectrum block to determine the loading load.

Description

Technical Field

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

[0002] Since the tail section structure is a critical structure for single-force transmission fatigue, according to relevant specifications, a damage tolerance test is generally required for the tail section structure.

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

[0004] For complex aircraft models with more than 10 typical mission profiles, the flight time of each mission profile is often more than several hours, and there are more than 20 flight states before refinement in each mission profile. The single test load spectrum block obtained by the rainflow simplification method in the previous mission profile is more than 1,000 lines, which no longer meets the requirements of the test implementation. Summary of the Invention

[0005] Purpose of the invention: To provide a simplified load spectrum method for damage tolerance tests of helicopter tail sections, to formulate the principle of load spectrum block simplification under complex mission profiles, to achieve the goal of simplifying load spectrum blocks under complex mission profiles, to obtain simplified load spectrum blocks that meet the test requirements, and to achieve load balancing in flight and landing states, thus providing a basis for subsequent simplification of load spectra for damage tolerance tests.

[0006] Technical solution:

[0007] A simplified method for load spectrum testing of damage tolerance in helicopter tail section is provided. The tail section of the helicopter includes tail landing gear, comprising:

[0008] Using the mission profile of a single test load spectrum block as a unit, the rainflow method is used for preliminary simplification to obtain a simplified spectrum. The simplified spectrum includes the rainflow count results of each mission profile. The rainflow count results include the load conditions, occurrence sequence and repetition number of each flight state within a mission profile.

[0009] The landing state is added as a new state to each mission profile. The total number of cycles for each mission profile after considering the landing state is calculated based on the time proportion of the individual mission profile within the test load spectrum and the total number of landing states. Simultaneously, the landing states are further refined 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 for each mission profile after considering the landing state and the corresponding numbers of various landing conditions in the load spectrum block, combinations and arrangements are made to determine the specific landing condition corresponding to a single mission profile. Finally, the total number of times m for flight state j in the test spectrum block is recorded. j j takes any integer from 1 to the total number of flight states;

[0010] The test load spectrum blocks with additional landing conditions are simplified and merged between mission profiles;

[0011] Using the equivalent control profile bending moment as the balancing principle, load balancing was performed on the test load spectrum blocks for each flight and landing state to determine the loading load.

[0012] Furthermore, the calculation of the total number of cycles for a single mission profile, considering the landing state, based on the rainflow counting results includes:

[0013] Assuming the payload spectrum is compiled in w flight hours, if the number of landings is n times per hour, then a single payload spectrum must contain wn 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 for the first mission profile in w flight hours is (a1%w / b1) times, and so on. If the time proportion of the last mission profile is a... m %, the time required to complete a single profile is b m If the number of hours is not considered, then without considering the number of merged landings, the number of cycles for the last mission profile in flight hours w is (a m %w / b m )Second-rate;

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

[0016] Furthermore, the landing states are further refined into various landing conditions, and the frequency of each landing condition in the corresponding load spectrum block is calculated, including:

[0017] Based on the known percentage of landing sinking velocity d i Pitch attitude percentage e iPercentage of quality status f i The landing states are further categorized into various landing conditions, and the frequency (wnd) of each landing condition in the corresponding load spectrum block is calculated. i e i f i .

[0018] Furthermore, based on the total number of cycles for each individual mission profile after considering landing conditions and the corresponding number of times for each landing condition in that load spectrum block, the specific landing conditions corresponding to a single mission profile are determined by combining and matching these factors, including:

[0019] Assign landing scenarios to each mission profile until the number of landing scenarios assigned equals the total number of cycles for that mission profile after considering landing scenarios.

[0020] Furthermore, record the total number of times the j-th flight state in this test spectrum block is recorded, including:

[0021] The number of times the j-th flight state in the mission profile is obtained;

[0022] Multiply the number of times the j-th flight state is called by the total number of cycles in the mission profile to get the total number of times the j-th flight state is called in the mission profile.

[0023] The total number of times each flight state j is counted in all mission segments is summed to obtain the total number of times each flight state j is counted in the test spectrum.

[0024] Furthermore, for flight state j, the test payload spectrum blocks for the additional landing state are simplified and merged between mission profiles, including:

[0025] Get the time taken to complete a flight state j and the proportion of time taken for flight state j to the total flight hours w.

[0026] The scaling correction ratio is determined based on the time taken to complete a flight state j, the proportion of flight state j to the total flight hours w, and the total number of flight states j in the test spectrum.

[0027] For the q-th mission profile, divide the total number of times the j-th flight state is divided by the scaling correction ratio, take the remainder of the quotient, and use the quotient as the number of cycles for the j-th flight state of the mission profile. Add the remainder to the total number of times the j-th flight state is in the (q+1)-th mission profile.

[0028] Repeat the previous step to simplify and merge all task profiles, and obtain the number of cycles and the state order within each profile in the test load spectrum.

[0029] Furthermore, using the equivalent control profile bending moment as the balancing principle, load balancing was performed on the test load spectrum blocks for various flight and landing states to determine the applied loads, including:

[0030] The main load-bearing joints of the tail section structure were selected as loading points. The load balancing principle was to control the bending moment of each frame of the tail section structure to be consistent. The bending moment of each main frame of the tail section structure was obtained based on the inertial balance load of the whole aircraft. The load of each loading point under each flight and landing state was obtained sequentially through load balancing.

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

[0032] Furthermore, when performing load balancing for landing, it is essential to first ensure that the load at the landing gear loading point matches the actual calculated load.

[0033] Beneficial effects:

[0034] This invention employs further simplification principles, specifically within specific mission profiles. The simplified spectra obtained above are merged based on post-rainflow results, merging profiles in similar states (those with minimal differences). Smaller dynamic load cycles (less than 5% of the maximum dynamic load within the profile) are eliminated due to less damage. Then, the number of cycles for each mission profile within a single load spectrum block is determined by combining the total number of landings and the time proportion of each mission profile. Finally, based on the time proportion of each flight state and the completion duration of a single flight state, the total number of cycles for a single flight state within the entire load spectrum block is obtained. Mission profiles are then merged to ensure the simplicity of the simplified load spectrum and the feasibility of the experiment. Ultimately, the experimental load spectrum block is simplified to approximately 300 lines. Detailed Implementation

[0035] This invention provides a simplified method for load spectrum testing of helicopter tail section damage tolerance, 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 within the profile, and considering the flight attitude combination under each state (such as sideslip during level flight and different bank angles during turns), the load conditions, occurrence sequence, and repetition frequency of each flight state within each mission profile can be obtained. The sum of the bending moments in the My and Mz directions at the docking frame between the tail section and the transition section is selected as the main characteristic loads. The damage equivalence principle is used, and the rainflow method is used to perform preliminary simplification of the mission profile.

[0037] [2] Based on the simplified spectrum obtained in the previous section, states with similar characteristics were merged according to the results after rainflow. Smaller dynamic load cycles (less than 5% of the maximum dynamic load in the profile) were eliminated based on the less damage. It is important to remember that the basic principle of merging is to merge range pairs with larger dynamic and static loads (dynamic load increase should not exceed 3% of the maximum dynamic load) and a more conservative approach.

[0038] [3] Merging landing states into the load spectrum. For aircraft with tail section structures including tail landing gear, the landing state needs to be added as a separate condition to the ground condition of each mission profile. First, let's 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 needs to contain 1000n landings. Assuming 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 merging of landing times, the number of cycles of the first mission profile in 1000fh is (1000a1% / b1) times, and so on, with the time proportion of the last mission profile being a m %, the time required to complete a single profile is b m If the number of hours is not considered, then without considering the number of merged landings, the number of loops for the last mission profile in 1000fh is (1000a) m % / b m ( ) times. To ensure a consistent total number of landings, one landing state is assigned to each completed mission profile, and the amplification factor for the number of cycles for each mission profile is found to be . The total number of cycles for each mission profile, considering the landing state, is the number of cycles calculated above multiplied by the amplification factor c. That is, the total number of cycles for the first mission profile in the 1000fh load block, considering the landing state, is (1000a1% / b1)*c times. Then, according to the landing sinking velocity percentage d... i Pitch attitude percentage e i Percentage of quality status f i If the landing conditions are proportionally refined into various landing scenarios, then each landing scenario corresponds to 1000 times in a single load spectrum block. i e i f i Based on the above results, the total number of cycles for each mission profile after considering landing states and the corresponding number of times each landing state occurs in a single payload spectrum block are combined and matched to finally determine the specific landing state corresponding to a single mission profile. Let m be the total number of times the p-th flight state occurs in the payload spectrum block at this point. p .

[0039] Where, m pThe acquisition method includes: obtaining the number of times the j-th flight state in the mission profile; multiplying the number of times the j-th flight state by the total number of cycles in the mission profile to obtain the total number of times the j-th flight state in the mission profile; and summing the total number of times the j-th flight state in all mission profiles to obtain the total number of times the j-th flight state in the test spectrum.

[0040] [4] The single load spectrum obtained in the previous section is simplified and merged between mission profiles. Based on the load spectrum after merging the landing states 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. Therefore, it is necessary to calculate the total number of tests for each flight state in the current single load spectrum and reduce the number of flight states for each mission profile. According to the time ratio of each flight state in the flight spectrum and combined with the completion time of each flight state in previous models, the total number of calculations n for each flight state under 1000fh of a single load spectrum is calculated. s The number of times m for each flight state in the experimental load spectrum obtained in the previous step. p Scaling and adjusting to n according to the ratio s If the number of times for each flight state within a single mission profile is not an integer after scaling, the remaining non-integer times can be carried over to the next mission profile to be rounded up. The ultimate goal of simplification is to ensure that the total number of tests for each flight and landing state within a single load spectrum block is consistent with the total number of calculations. This completes the simplification and merging between profiles, resulting in the number of cycles for each profile in the test load spectrum and the state order within the profile.

[0041] [5] Finally, load balancing for each flight and landing state was performed based on the principle of equivalent control section bending moment to determine the loading load. The main load-bearing joints of the tail section structure were selected as loading points. The principle of load balancing was to ensure that the bending moments of each frame of the tail section structure were consistent. The bending moments of each main frame of the tail section structure were calculated based on the inertial balance load of the entire aircraft. The loads of each loading point in each flight and landing state were obtained sequentially through load balancing. During the load balancing process, it is necessary to consider that the test load of each loading joint should not exceed the bearing capacity of the loading point and its surrounding structure. The loading loads for each flight and landing state should be further verified through a virtual experimental finite element model. Note that when performing load balancing for the landing state, it is necessary to first ensure that the loads at the landing gear loading points are consistent with the actual calculated loads.

Claims

1. A simplified method for load spectrum testing of damage tolerance in helicopter tail section, wherein the tail section of the helicopter includes tail landing gear, characterized in that, include: Using the mission profile of a single test load spectrum block as a unit, the rainflow method is used for preliminary simplification to obtain a simplified spectrum. The simplified spectrum includes the rainflow count results of each mission profile. The rainflow count results include the load conditions, occurrence sequence and repetition number of each flight state within a mission profile. The landing state is added as a new state to each mission profile. The total number of cycles for each mission profile considering the landing state is calculated based on the time proportion of the individual mission profile within the test load block and the total number of landing states. Simultaneously, the landing states are further refined into various landing conditions, and the number of times each landing condition corresponds to within the test load block is calculated. Based on the total number of cycles for each mission profile considering the landing state and the corresponding numbers of various landing conditions within the test load block, combinations and arrangements are made to determine the specific landing condition corresponding to a single mission profile. Finally, the total number of times m for flight state j within the test load block is recorded. j j takes any integer from 1 to the total number of flight states; The test load spectrum blocks with additional landing conditions are simplified and merged between mission profiles; Using the equivalent control profile bending moment as the balancing principle, load balancing was performed on the test load spectrum blocks for each flight and landing state to determine the loading load; For flight state j, the test payload spectrum blocks for the additional landing state are simplified and merged between mission profiles, including: Get the time taken to complete a flight state j and the proportion of time taken for flight state j to the total flight hours w. The scaling correction ratio is determined based on the time taken to complete a flight state j, the proportion of flight state j to the total flight hours w, and the total number of flight states j in the test payload spectrum block. For the q-th mission profile, divide the total number of times the j-th flight state is divided by the scaling correction ratio, take the remainder of the quotient, and use the quotient as the number of cycles for the j-th flight state of the mission profile. Add the remainder to the total number of times the j-th flight state is in the (q+1)-th mission profile. Repeat the previous step to complete the simplification and merging of all task profiles, and obtain the number of cycles and the state order within each profile in the test load spectrum block. The load balancing for each flight and landing state of the test load spectrum block was performed based on the principle of equivalent control profile bending moment, and the applied loads were determined, including: The load-bearing joint of the tail section structure was selected as the loading point. The load balancing principle was to control the bending moment of each frame of the tail section structure to be consistent. The bending moment of each frame of the tail section structure was obtained based on the inertial balance load of the whole aircraft. The load of each loading point in each flight and landing state was obtained in turn through load balancing. Meanwhile, considering that the test load at each loading point cannot exceed the bearing capacity of the loading point and its surrounding structure, the loading loads for each flight and landing state should be further verified through a virtual test finite element model.

2. The method according to claim 1, characterized in that, The calculation of the total number of cycles for a single mission profile, taking landing states into account, based on the proportion of time for that single mission profile within the test load spectrum and the total number of landing states includes: Assuming the test payload spectrum is compiled in w flight hours, if the number of landings is n times per hour, then a single payload spectrum block must contain wn 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 for the first mission profile in w flight hours is (a1%w / b1) times, and so on. If the time proportion of the last mission profile is a... m %, the time required to complete a single profile is b m If the number of hours is not considered, then without considering the number of merged landings, the number of cycles for the last mission profile in flight hours w is (a m %w / b m )Second-rate; Assign one landing state to each mission profile and determine the amplification factor for the number of cycles for each mission profile as follows: Then, the total number of loops for each mission profile, after considering the landing state, is determined to be c times the number of loops for the mission profile.

3. The method according to claim 2, characterized in that, The landing conditions are further categorized into various landing scenarios, and the frequency of each landing scenario in the test load spectrum is calculated, including: Based on the known percentage of landing sinking velocity d i Pitch attitude percentage e i The mass state percentage fi further categorizes the landing state into various landing conditions, and calculates the corresponding number wnd for each landing condition in the test load spectrum block. i e i f i .

4. The method according to claim 3, characterized in that, Based on the total number of cycles for each individual mission profile after considering landing conditions, and the corresponding number of cycles for various landing scenarios in the test load spectrum, the specific landing scenarios corresponding to a single mission profile are determined by combining and matching these factors, including: Assign landing scenarios to each mission profile until the number of landing scenarios assigned equals the total number of cycles for that mission profile after considering landing scenarios.

5. The method according to claim 4, characterized in that, Record the total number of times the j-th flight state of this test load spectrum block is recorded, including: Get the number of times the j-th flight state appears in the mission profile; multiply the number of times the j-th flight state appears by the total number of cycles in the mission profile to get the total number of times the j-th flight state appears in the mission profile. The total number of times for flight state j in all mission profiles is summed to obtain the total number of times for flight state j in the test payload spectrum block.

6. The method according to claim 1, characterized in that, When performing load balancing for landing, it is essential to first ensure that the load at the landing gear loading point matches the actual calculated load.