Identification and statistical analysis method of typical landing gear motion segments based on field measurement results

Abstract

This invention belongs to the field of aircraft design technology, specifically involving a method for identifying and statistically analyzing typical landing gear action segments based on measured results. The method includes the following steps: Step 1: Dividing the landing gear into action segments and establishing criteria for determining the action segment in which the measured landing gear load data is located; Step 2: Validating the measured landing gear load data; Step 3: Dividing the measured landing gear load data into stages according to the time-load history; extracting data within different stages based on the action segment criteria; Step 4: Performing rainflow statistics on the extracted data from different action segments sequentially.

Description

Technical Field

[0001] This invention belongs to the field of aircraft design technology, specifically relating to a method for identifying and statistically analyzing typical landing gear movement segments based on measured results. Background Technology

[0002] In structural fatigue life determination, the load spectrum is a prerequisite and foundation for durability, damage tolerance analysis, and fatigue testing. The accuracy of the load spectrum directly affects the results of durability, damage tolerance analysis, and fatigue testing, and consequently, the determination of aircraft service life. The landing gear ground load spectrum is the basis for landing gear structural life determination.

[0003] Fatigue durability assessments of aircraft structures are conducted during the prototyping and detailed design stages. Fatigue tests before type approval also utilize fatigue load spectra. Therefore, before obtaining measured load spectra, a design load spectrum representative of the aircraft's average operating conditions is essential for estimating the landing gear fatigue life. Load spectra can be obtained by analyzing measured statistical data from landing gear of similar aircraft, combined with the specific characteristics of the aircraft, such as differences in aircraft weight, landing gear cushioning characteristics, wheel braking torque, and structural stiffness. A thorough analysis is necessary, drawing on successful and unsuccessful experiences in determining the lifespan of landing gear structures from other aircraft models. This comprehensive analysis yields a fatigue design load spectrum representative of the expected operating conditions and characteristics of this aircraft model. Another method for obtaining the spectrum is to derive a design spectrum based on the standard spectrum provided by specifications, combined with existing theoretical analysis and experimental experience. Of course, the most accurate and reliable landing gear load spectrum is obtained through field measurements of this aircraft model followed by statistical analysis.

[0004] After the aircraft design is finalized, transitions to small-batch production, and a certain number of aircraft are in service with the military, the landing gear fatigue load spectrum should be measured and statistically analyzed, and recompiled after acquiring a large amount of data. The amount of measured load spectrum data is enormous, and most of the work, such as data screening, segmentation, interpretation, classification, processing, and damage equivalence, is done manually, which is time-consuming and labor-intensive. Summary of the Invention

[0005] The purpose of this invention is to address the time-consuming and labor-intensive nature of processing massive amounts of data in load spectrum processing. Given limited resources and engineering needs, this application proposes a method for identifying and statistically analyzing typical landing gear movement segments based on measured results. By establishing reasonable processes, methods, and criteria, it achieves data task segment division and automated movement segment identification. This method can process large amounts of measured data within two person-times per month and improves the accuracy of data processing.

[0006] The technical solution of this invention:

[0007] A method for identifying and statistically analyzing typical landing gear actuation segments based on measured results includes the following steps:

[0008] Step 1: Divide the landing gear mission phases and establish the criteria for determining the action phase in which the measured load data of the landing gear is located;

[0009] Step 2: Screen the validity of the measured load data of the landing gear;

[0010] Step 3: Divide the measured load data of the landing gear into stages according to the time load history; extract data in different stages according to the aforementioned action segment criteria;

[0011] Step 4: Perform rainflow statistics on the extracted data from different action segments.

[0012] Furthermore, in step one, based on the landing gear load characteristics, the takeoff mission segment is divided into: engine test segment on the takeoff line, turning segment, braking segment, and curved or straight taxiing segment.

[0013] The landing mission is divided into landing impact, left and right turns, braking, and curved or straight taxiing segments.

[0014] Furthermore, in step one, the criteria for each action segment include:

[0015] If the left and right main start brake pressures are greater than 19 MPa, it is determined that the engine test phase is underway on the takeoff line.

[0016] If the absolute value of the turning actuator stroke is greater than 5mm and the absolute value of the main starter lateral load is greater than 1.5kN, then it is determined that it is in the turning stage;

[0017] If the left and right main starter brake pressures are greater than 1.5 MPa but less than 15 MPa, then the system is considered to be in the braking phase.

[0018] Furthermore, in step two, the validity of the measured landing gear load data for this takeoff and landing is screened based on the vertical load of the nose landing gear, the vertical load of the main landing gear, the lateral load of the main landing gear, and the number of takeoff turns, as follows:

[0019] If the sum of the vertical load of the front landing gear and the vertical load of the main landing gear during the takeoff phase differs from the total weight of the aircraft during the takeoff phase by more than 1%, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid.

[0020] If the sum of the vertical loads of the nose landing gear and the main landing gear during the landing phase exceeds 1% of the total weight of the aircraft during the landing phase, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid.

[0021] If the average value of the vertical load of the nose landing gear in the first second during the takeoff phase differs from the vertical load of the nose landing gear in the static stop state by more than 5%, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid.

[0022] If the average value of the main landing gear lateral load in the first second during the takeoff phase differs from the main landing gear lateral load in the static stop state by more than 5%, the measured landing gear load data for this takeoff and landing is deemed invalid; otherwise, it is valid.

[0023] If the number of turns during takeoff is less than the actual number of curves at the airport, the measured load data of the landing gear for this takeoff and landing is considered invalid; otherwise, it is valid.

[0024] If the vertical load of the nose landing gear or the vertical load of the main landing gear is negative throughout the entire flight path of the takeoff and landing missions, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid.

[0025] Furthermore, in step three, the steps for dividing the measured load data of the landing gear into stages are as follows:

[0026] Step a: Divide the measured load data of the landing gear in half according to the time load history;

[0027] Step b: Locate the point where the main landing gear signal disappears in the first half of the segment. The data in the time period before the main landing gear signal disappears is the takeoff mission segment data.

[0028] Step c: In the second half, find the main landing wheel load signal reproduction point. The data in the time period after the reproduction point is the landing mission segment data.

[0029] Furthermore, in step three, the data extraction process is as follows:

[0030] In the takeoff mission phase data, extract the data of the engine test section, turning section and braking section on the takeoff line in sequence according to the criteria in step one. The remaining data in the takeoff mission phase data are the data of the curve or straight taxiing section.

[0031] In the landing mission segment data, the data in the first 1 second is the landing impact segment data; then, in the landing mission segment data, the turning segment and braking segment data are extracted in sequence according to the criteria in step one; the remaining data in the landing mission segment data is the curve or straight-line taxiing segment data.

[0032] Furthermore, in step four, the mean and amplitude of the load data of the landing gear in three directions for different action segments are calculated and summarized in a table.

[0033] The beneficial effects of this invention are:

[0034] This invention will change the inefficient and intensive work status quo of traditional load spectrum measurement data, which requires manual reading and task segmentation. It will greatly improve the efficiency of load spectrum compilation, reduce manual labor intensity, and has good economic and engineering application value. The technical methods in this project can be applied to the analysis of aircraft landing gear load measurement data and load spectrum compilation, and can also provide a reference for the compilation of load spectra for other aircraft components. Attached Figure Description

[0035] Figure 1 Flowchart of the method for identifying and statistically analyzing typical landing gear action segments based on measured results;

[0036] Figure 2 This is a schematic diagram of the data interpretation and rainflow statistics process for each action segment. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] A method for identifying and statistically analyzing typical landing gear actuation segments based on measured results is described in [link to documentation]. Figure 1 The specific implementation steps are as follows:

[0039] Step 1: Summarize and classify the load characteristics of typical action segments

[0040] Landing gear load spectrum can be divided into takeoff taxiing, landing taxiing, landing gear retraction / extension, and ground maintenance segments according to the mission performed. Based on the landing gear load characteristics, the takeoff taxiing segment includes the following actions: engine test on the takeoff line, left and right turns, braking, curved or straight taxiing, and shimmy (generally not occurring); the landing taxiing segment includes the following actions: landing impact, left and right turns, braking, curved or straight taxiing, and shimmy; the landing gear retraction / extension segment includes retraction, in-flight maneuvering, and the load on the landing gear by the retraction / extension actuators, as well as wheel braking; the ground maintenance segment includes ground traction, engine scheduled maintenance, and jack lifting.

[0041] The landing gear loads in each maneuver segment have distinct characteristics. A careful analysis of the load characteristics of each typical maneuver segment is necessary to establish corresponding classification and statistical methods. Based on the actual aircraft measurements, for example, typical maneuvers during takeoff can be divided into engine test segment, turning segment, braking segment, and taxiing segment, while typical maneuvers during landing taxiing segment can be divided into landing impact segment, taxiing segment, braking segment, and turning segment. The data processing workflow framework is as follows: Figure 2 .

[0042] ① Engine test section identification

[0043] During engine testing, there is a large yaw load on the main landing gear. Under these conditions, the braking pressure of the main landing gear is at its maximum. Theoretically, the quasi-static component in the y-direction of each main wheel is the horizontal static thrust of the engine.

[0044] P y·z =-0.5P H (1)

[0045] In the formula P H This is the engine thrust.

[0046] During engine testing, the nose landing gear only bears the Z-axis force. However, the nose-down moment caused by the engine thrust significantly increases the vertical load on the nose landing gear. The Z-axis force on the nose landing gear is:

[0047]

[0048] In the formula, h is the height of the thrust line from the ground.

[0049] L is the distance between the front wheel and the main wheel.

[0050] Because modern aircraft brakes use electronic anti-lock braking systems (ABS), the hydraulic pressure does not reach the system's maximum pressure during normal taxiing and braking. It is typically only slightly more than half of the maximum pressure. When the maximum braking pressure is reached, the aircraft is already at a stop. Pilots, by practice, always use the stop brake pressure (21 MPa) to bring the aircraft to a stop on the takeoff line, then increase engine thrust until the brakes are released to allow for a shorter takeoff run.

[0051] Criterion setting: The left and right main starter brake pressures are greater than 19MPa.

[0052] ②Determination of turning sections

[0053] Turning is the condition under which the lateral force is greatest when an aircraft is being controlled on the ground. It is a combination and representation of the loading conditions of taxiing on curves and turning. Here, turning refers to low-speed stable turning.

[0054] Turning can be achieved through methods such as manipulating the nose wheel, differential braking, and differential thrust. The goal of turning is to generate a nose-swing moment. A rolling moment also exists during a turn, which is balanced by the increased vertical load on the left and right main wheels. Lateral forces are generated on each landing gear during a turn; the resultant force of these lateral forces is the centripetal force that propels the aircraft in a curved path. The corresponding centrifugal inertial force acts on the aircraft's center of gravity, and together they constitute a rolling moment. This moment causes the outer main wheels to load and the inner main wheels to unload.

[0055] Theoretically, the force acting on the main landing gear during a turn is:

[0056]

[0057] The force acting on the nose landing gear is:

[0058]

[0059] In the formula n x Lateral overload factor

[0060] H is the height of the aircraft's center of gravity above the ground when the aircraft is stationary.

[0061] t is the main wheel track

[0062] Criterion settings: Left turn criteria: Turning actuator stroke greater than 5mm and the absolute value (resultant force) of the main starter lateral load greater than 1.5kN.

[0063] Right turn criteria: the stroke of the turning actuator is less than -5mm and the absolute value (resultant force) of the main starter lateral load is greater than 1.5kN.

[0064] ③ Braking segment identification

[0065] The load acting on the landing gear during skidding and braking consists of two parts: a quasi-static component and a small vibration superimposed on the quasi-static force. Braking force F y The average value of the quasi-static component of the force depends on the braking torque, which is related to the braking pressure. The vertical force P acting on the main landing gear during braking... z The quasi-static component of the force is the static wheel load, and the incremental part is ΔP. z The main cause is the unloading on the main starter due to the nose-down torque caused by braking.

[0066] The number of braking cycles and braking duration vary depending on the aircraft type. Many aircraft braking patterns differ from US military specifications, and are mostly tailored to the specific characteristics and operating methods of each aircraft. Aircraft equipped with automatic braking systems brake more frequently but with relatively less braking force. Aircraft without automatic braking systems rely on intermittent braking by the pilot, resulting in a higher frequency and less braking force.

[0067] The recommended load for the main starting and braking spectrum in the national military standard is:

[0068] Maximum braking

[0069] Medium braking

[0070] The front wheel of a certain model has no brake device, while the main wheel uses a brake device equipped with an electronic anti-skid system. The brake pressure is 9MPa and the residual brake fluid pressure is about 1.5MPa.

[0071] Criterion setting: The left and right main starter brake pressures are greater than 1.5MPa and less than 15MPa.

[0072] ④ Gliding segment identification

[0073] Taxiing load refers to the load on the landing gear during takeoff, landing, and towing. Ground taxiing load is mainly caused by the unevenness of the runway. Its magnitude is related to the unevenness and also closely related to the taxiing speed. The rougher the runway, the greater the load, and the higher the taxiing speed, the greater the load.

[0074] The taxiing load can be obtained through dynamic response analysis using a runway surface shape with specified power spectral density characteristics. The vertical load acting on the landing gear during taxiing is a quasi-static stopping load superimposed with an increment. Theoretically, the formula for calculating the vertical load during taxiing is:

[0075]

[0076] When the wheels encounter an obstacle, in addition to the vertical load, a directional load is also generated.

[0077] Step 2: Filtering Payload Data

[0078] The main parameters included in the measured load spectrum results of the landing gear are shown in Table 1.

[0079]

[0080]

[0081] Payload data screening mainly involves the following steps:

[0082] ① Compare the total weight of the aircraft during takeoff with the sum of the vertical loads of the nose landing and the main landing. If the difference between the two is within 1%, it is considered normal. Otherwise, all data for this takeoff and landing is considered abnormal, and the data for this takeoff and landing is invalid.

[0083] ② Compare the total aircraft weight and the sum of the nose landing vertical load and the main landing vertical load during the landing phase. If the difference between the two is within 1%, it is considered normal; otherwise, all data for this takeoff and landing are considered abnormal, and the data for this takeoff and landing is invalid.

[0084] ③ Average the results of the vertical load data collected in the first second during the takeoff phase, and compare the obtained data with the static stop load. If the difference between the vertical load and the static stop load of the front landing exceeds 5%, it is determined that the initial sampling segment of this takeoff and landing has entered the engine test, the data collection is incomplete, and the takeoff and landing data is invalid.

[0085] ④ Average the results of the main landing lateral load data collected in the first second during the takeoff phase. Compare the obtained data with the lateral load under the static shutdown state of the main landing. If the difference exceeds 5%, it means that the initial sampling phase has entered the turning or other actions, the data collection is incomplete, and the takeoff and landing data is invalid.

[0086] ⑤ Determine the number of turns during takeoff. Based on the actual situation of the airport, if the number of turns in the collected data is less than the number of curves in the airport, then the takeoff and landing data is incomplete and the data for this takeoff and landing is invalid.

[0087] ⑥ Perform a full-process scan of all vertical loads of the nose landing and main landing during the takeoff and landing phases. If a negative vertical load is found, the takeoff and landing data is considered abnormal and the data is invalidated.

[0088] Step 3: Develop a program to automatically divide tasks into segments, identify action segments, and perform rainflow statistics.

[0089] The measured load data was divided into task segments and extracted using Fortran software programming in the following steps: Step a, the measured landing gear load data was divided in half according to the time history; Step b, in the first half, the disappearance point of the main landing gear load signal was found, and the data in the time period before the disappearance point of the main landing gear load signal was the takeoff task segment data; Step c, in the second half, the recurrence point of the main landing gear load signal was found, and the data in the 1 second after the recurrence point was the landing impact segment, and the data in the remaining time period was the landing task segment data.

[0090] The test maneuvers revealed that the typical maneuvers included in the takeoff phase are: engine test on the takeoff line, turning, braking, and taxiing on a curve or straight line. The typical maneuvers included in the landing phase are: left and right turns, braking, and taxiing on a curve or straight line.

[0091] Using the typical motion segment load characteristics and classification statistics methods determined in Step 1, a process analysis and design for automatic identification of measured loads was conducted. In the takeoff mission segment data identification, the engine test segment, turning segment, and braking segment were identified sequentially; the remaining data were for the taxiing segment. In the landing mission segment data identification, the turning segment and braking segment were identified sequentially; the remaining data were for the taxiing segment. A self-developed program was used to automate the load identification process, enabling automatic identification of measured loads for each motion segment and statistical counting of landing gear three-dimensional load rainflow. The rainflow counting statistics objects were the landing gear lateral load, azimuth load, and vertical load in typical motion segments. The statistical results of the vertical load rainflow counting for a certain takeoff and landing taxiing segment are shown in Table 2.

[0092] Table 2. Statistical results of rainflow counting for vertical loads in a certain takeoff and landing taxiing section. Note: The first column in the table represents the mean load, the first row represents the load amplitude, and the rest represent the frequency of occurrence of the corresponding mean and amplitude.

[0093] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for identifying and statistically analyzing typical landing gear actuation segments based on measured results, characterized in that: The method includes the following steps: Step 1: Divide the landing gear into mission segments and establish criteria for determining the action segment in which the measured load data of the landing gear is located; Step 2: Screen the validity of the measured load data of the landing gear, as follows: If the sum of the vertical load of the front landing gear and the vertical load of the main landing gear during the takeoff phase differs from the total weight of the aircraft during the takeoff phase by more than 1%, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid. If the sum of the vertical load of the nose landing gear and the vertical load of the main landing gear during the landing phase differs from the total weight of the aircraft during the landing phase by more than 1%, then the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid. If the average value of the vertical load of the nose landing gear in the first second during the takeoff phase differs from the vertical load of the nose landing gear in the static stop state by more than 5%, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid. If the average value of the main landing gear lateral load in the first second during the takeoff phase differs from the main landing gear lateral load in the static stop state by more than 5%, the measured landing gear load data for this takeoff and landing is deemed invalid; otherwise, it is valid. If the number of turns during takeoff is less than the actual number of curves at the airport, the measured load data of the landing gear for this takeoff and landing is considered invalid; otherwise, it is valid. If the vertical load of the nose landing gear or the vertical load of the main landing gear is negative throughout the entire process of the takeoff and landing missions, the measured load data of the landing gear for this takeoff and landing is deemed invalid; otherwise, it is valid. Step 3: Divide the measured load data of the landing gear into stages according to the time load history; extract data in different stages according to the action segment criteria; extract the data of the engine test segment, turning segment and braking segment on the takeoff line in sequence according to the criteria in Step 1 in the takeoff mission segment data; the remaining data in the takeoff mission segment data are the data of the curve or straight taxiing segment. In the landing mission segment data, the data in the first 1 second is the landing impact segment data; then, in the landing mission segment data, the turning segment and braking segment data are extracted in sequence according to the criteria in step one; the remaining data in the landing mission segment data is the data of the curve or straight-line skidding phase. Step 4: Perform rainflow statistics on the extracted data from different action segments in sequence.

2. The method according to claim 1, characterized in that: In step one, the landing gear mission phases are divided into: takeoff mission phase, landing mission phase, landing gear retraction and extension mission phase, and ground maintenance mission phase.

3. The method according to claim 2, characterized in that: In step one, the takeoff mission segment is divided into the following segments based on the landing gear load characteristics: engine test segment on the takeoff line, turning segment, braking segment, and curved or straight taxiing segment. The landing mission is divided into the landing impact phase, left and right turning phases, braking phase, and curved or straight taxiing phase.

4. The method according to claim 3, characterized in that: In step one, the action segment criteria include: If the left and right main start brake pressures are greater than 19 MPa, it is determined that the engine test phase is underway on the takeoff line. If the absolute value of the turning actuator stroke is greater than 5mm and the absolute value of the main starter lateral load is greater than 1.5kN, then it is determined that it is in the turning stage; If the left and right main starter brake pressures are greater than 1.5 MPa but less than 15 MPa, then the system is considered to be in the braking phase.

5. The method according to claim 1, characterized in that: In step three, the steps for dividing the measured load data of the landing gear into stages are as follows: Step a: Divide the measured load data of the landing gear into half according to the time load history; Step b: Locate the point where the main landing gear signal disappears in the first half of the segment. The data in the time period before the main landing gear signal disappears is the takeoff mission segment data. Step c: In the second half, find the main landing wheel load signal reproduction point. The data in the time period after the reproduction point is the landing mission segment data.

6. The method according to claim 1, characterized in that: In step four, the mean and amplitude of the load data of the landing gear in three directions for different action segments are calculated and summarized in a table.

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