Undercarriage variable stroke load calibration test device and calibration method

Abstract

The invention belongs to the field of aircraft flight tests, and relates to an undercarriage variable stroke load calibration test device and a calibration method. The device comprises a gas tank, a gas source, a four-way connector, a switch and a pressure gauge, the undercarriage buffer is connected with one connector of the four-way connector through a gas charging connector and a hose, the other three connectors of the four-way connector are connected with the gas tank, the pressure gauge and one end of the switch respectively, and the other end of the switch is connected with the gas source through the hose.

Description

Technical Field

[0001] This invention belongs to the field of aircraft flight testing and relates to a landing gear variable stroke load calibration test device and calibration method, particularly to a landing gear variable stroke load calibration method and test device using an external accumulator tank connected to the buffer and utilizing the internal friction of the buffer. Background Technology

[0002] Landing gear load measurement is a crucial aspect of aircraft development and flight testing, employing a strain gauge-based method. Load calibration involves applying a series of known loads (forces and moments) to the landing gear with attached strain gauges, measuring the corresponding strain gauge bridge response, and establishing a mathematical relationship (load equation) between the landing gear load and the strain gauge bridge response. Currently, this is typically done offline, by removing the landing gear from the aircraft and testing it separately. To address the issue of buffer expansion and contraction during loading, a common approach is graded calibration. This involves repeatedly loading the buffer at several fixed strokes (calibration strokes) after deflation and refilling, obtaining the mathematical relationship between the strain response and load at these calibration strokes. The strain response-load relationship at other non-calibration strokes is obtained through interpolation. Clearly, the number of calibration strokes affects both the load measurement accuracy and the workload of the calibration test. A compromise is usually reached, typically using 3 to 5 strokes based on the maximum range of change in the landing gear buffer stroke (structural stroke).

[0003] Furthermore, the deflation and oil filling process for a fixed buffer stroke is time-consuming and labor-intensive. To minimize changes in the landing gear configuration caused by variations in the buffer stroke during loading and to improve load calibration quality, it is essential to ensure the buffer is "completely purged of air and fully filled with oil." Since the buffer's internal cavity is typically divided into multiple interconnected chambers, its structure is complex, and some gas is often trapped in the oil as air bubbles, making direct removal difficult. Therefore, the deflation and oil filling process generally involves a complex cycle of "attitude adjustment - oil filling - settling - oil replenishment - load testing." Moreover, after load calibration, the buffer must be restored to the required filling state for installation, and static pressure curve plotting and airtightness checks must be performed to ensure that the requirements for reinstallation are met.

[0004] If the buffer stiffness can be altered by changing the buffer filling pressure, and then different load samples can be obtained under the same stroke through follow-up loading at several different filling pressures, the landing gear load calibration process can be comprehensively simplified in terms of test preparation, test implementation, and test recovery. However, because the relative change in air chamber volume during buffer compression is relatively large, the relative change in load is also large. Under the constraints of buffer pressure bearing capacity and the requirement for appropriate calibration load magnitude, the calibration load for short strokes needs to be obtained at a higher filling pressure, while the calibration load for long strokes needs to be obtained at a lower filling pressure. Therefore, loading at multiple filling pressures is required, and the test efficiency needs to be further improved. Summary of the Invention

[0005] Purpose of the invention: This invention provides a landing gear variable stroke load calibration test device and calibration method to improve the landing gear load calibration quality and test efficiency.

[0006] Technical solution: A landing gear variable stroke load calibration test device includes: an air tank, an air source, a four-way connector, a switch, and a pressure gauge. The landing gear buffer is connected to one port of a four-way connector via an air inlet and a hose. The other three ports of the four-way connector are respectively connected to one end of the air tank, the pressure gauge, and the switch. The other end of the switch is connected to the air source via a hose.

[0007] A landing gear variable stroke load calibration method, the method being performed using the aforementioned landing gear variable stroke load calibration test apparatus, the method comprising: Step 1: Determine the maximum travel of the landing gear buffer. S max Oil pressing area A air chamber volume V '; Step 2: Determine the load components of the landing gear axle load and the limiting loads of the load components of the landing gear axle load; Step 3: Determine the maximum travel value of the buffer to be calibrated S H-max The desired calibration target range and the relationship between the load components that can cause changes in the buffer travel and the resulting axial force on the landing gear buffer; Step 4: Based on the results of Steps 1 to 3, determine the minimum specified pressure value, the maximum specified pressure value, and the intermediate specified pressure value; Step 5: Conduct landing gear follow-up loading tests at the minimum specified pressure value, the maximum specified pressure value, and the intermediate specified pressure value respectively, and obtain the linear equations of each load component and each strain bridge response.

[0008] Furthermore, in step three, the maximum travel value of the buffer is to be calibrated. S H-max for S max Reduce by 5mm.

[0009] Furthermore, in step three, the target range for calibration loading is 10% to 60% of the load limit for each load component of the landing gear.

[0010] Furthermore, in step three, the relationship between the load component that can cause changes in the buffer stroke and the resulting axial force on the landing gear buffer is determined by the static equilibrium relationship based on the landing gear structure.

[0011] Further, in step four, determining the maximum specified pressure value specifically involves: determining the minimum value among the maximum values ​​of the target calibration load range for each load component that can cause changes in the buffer stroke, such that the buffer stroke reaches the maximum stroke to be calibrated under this minimum load. S H-max The requirements were determined to ensure that the buffer compression stroke reached the specified value. S H-max Pressure value and initial filling pressure value before loading ;

[0012] in, To calibrate the axial force of the buffer corresponding to the minimum value among the maximum values ​​of each load component that can cause changes in the buffer stroke, the following parameters are required: V0 is the coefficient of friction for the expansion and contraction of the buffer, and V0 is the volume of the buffer's air chamber. V 'The sum of the gas cylinder volume;' If the pressure value at the maximum travel of the buffer is within the allowable filling pressure range of the buffer, select the initial filling pressure value. Set the maximum specified pressure value; otherwise, reduce the proportion of the maximum value of the load component that can cause changes in the buffer travel to its corresponding limit load, and redetermine the maximum specified pressure value until the pressure value at the maximum buffer travel is within the allowable filling pressure range of the buffer.

[0013] Further, in step four, the minimum specified pressure value is determined, specifically as follows: The minimum value among the minimum values ​​of the target calibration load range for each load component that can cause changes in the buffer travel is selected, such that the buffer travel under this minimum load exactly reaches the maximum travel to be calibrated. S H-max The requirements were determined to ensure that the buffer compression stroke reached the specified value. S H-max Pressure value and initial filling pressure value before loading ;

[0014] in: To calibrate the axial force of the buffer corresponding to the minimum value among the minimum values ​​within the target loading range for each load component that can cause changes in the buffer travel, The initial filling pressure value is selected as the friction coefficient for the expansion and contraction of the buffer. Specify the minimum pressure value.

[0015] Furthermore, in step four, the intermediate specified pressure value is determined by taking several equal divisions of the minimum specified pressure value and the maximum specified pressure value as the intermediate specified pressure value.

[0016] Further, step five specifically involves: Record the buffer travel value, the applied load value, and the strain bridge response values, which are no less than the number of load components; Select several buffer travel values ​​within the recorded buffer travel value range; Under the same selected buffer stroke value, the response coefficients of each strain bridge to each load component are linearly regressed based on each load component value and the response values ​​of multiple strain bridges. For different selected buffer travel values ​​and the corresponding response coefficients of each strain bridge, a polynomial fitting is used to derive the functional relationship between the response coefficients of each strain bridge to each load component and the buffer travel value. Based on the relationship between the response of each strain gauge bridge and each load component, a set of linear equations is established for each load component and each strain gauge bridge response. The coefficients of the linear equations are the functional relationship between the response coefficient of each strain gauge bridge to each load component and the buffer travel value. The system of linear equations is in the form of: ,in, For the response of the i-th strain bridge, For the buffer travel, Let be the response coefficient of the j-th load component to the i-th strain bridge, where the coefficient is the buffer travel. The function.

[0017] Furthermore, the gas tank volume is 5 times the volume of the buffer air chamber.

[0018] Technical effects of the present invention: On the one hand, this invention, by expanding the buffer capacity, mitigates the pressure changes of the landing gear buffer during stroke variations, thus making the changes in the external load required for the buffer throughout its extension and retraction smoother (see...). Figure 2 This allows for the acquisition of calibration load samples with a single filling pressure that satisfies both short and long stroke conditions, avoiding the drawback of requiring a higher filling pressure for short strokes and a lower filling pressure for long strokes without expansion. It also reduces the number of filling pressure changes and test conditions (see [link]). Figure 3 (a) and Figure 3 (b)); On the other hand, the present invention utilizes the characteristic that the internal friction of the buffer is in opposite directions during the expansion and contraction processes, thereby causing the calibration load value corresponding to a certain stroke value to be different during the compression and expansion processes (see Figure 4 (a) and Figure 4 (b) ) , achieving the same number of calibration load samples with half the number of filling pressure changes (see Figure 5 (a) and Figure 5 (b) greatly improves the efficiency of calibration tests. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the method of the present invention; Figure 2 This is a schematic diagram comparing the pressure change of the buffer before and after the expansion of the present invention with the change of stroke; Figure 3 The diagram shows the number of filling pressure changes before and after capacity expansion, where (a) is the number of filling pressure changes before capacity expansion; and (b) is the number of filling pressure changes after capacity expansion. Figure 4 It is a schematic diagram of the direction of friction force during the compression and extension process of the buffer and the axial force required to balance the air pressure inside the buffer, wherein (a) is a schematic diagram of the direction of friction force during the compression process of the buffer and the axial force required to balance the air pressure inside the buffer, and (b) is a schematic diagram of the direction of friction force during the extension process of the buffer and the axial force required to balance the air pressure inside the buffer. Figure 5 These are schematic diagrams showing the number of filling pressure changes with and without considering the internal friction of the buffer. (a) shows the number of filling pressure changes without considering the internal friction of the buffer, and (b) shows the number of filling pressure changes with considering the internal friction of the buffer. Figure 6 This is a schematic diagram illustrating the calibration principle of the calibration method of the present invention; Figure 7 This is a schematic diagram of the experimental apparatus of the present invention; Among them: 1-landing gear wheel, 2-landing gear shock absorber, 3-air tank, 4-hose, 5-air source, 6-switch, 7-four-way connector, 8-pressure gauge. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0022] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0023] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0025] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0027] This invention, on the one hand, expands the landing gear buffer using a accumulator tank to stabilize the pressure and required axial force of the buffer during stroke changes; on the other hand, it utilizes the property that the internal friction force is opposite in direction during the buffer's expansion and contraction to increase the load samples under the same filling pressure, reduce the number of filling pressure changes, thereby reducing the number of calibration conditions and significantly improving test efficiency.

[0028] like Figure 7The present invention provides a landing gear variable stroke load calibration test device, comprising: an air tank 3, an air source 5, a four-way connector 7, a switch 6, and a pressure gauge 8. The landing gear buffer 2 is connected to one interface of a four-way connector via an air inlet and a hose 4. The other three interfaces of the four-way connector are respectively connected to one end of the air tank, the pressure gauge, and the switch. The other end of the switch is connected to the air source via a hose.

[0029] The present invention provides a landing gear variable stroke load calibration method, comprising: Determine the maximum travel (structural travel) of the landing gear buffer. S max Oil pressing area A air chamber volume V 'Structural design parameters;' Determine the load components of the landing gear axle load (typically including three forces and three moments acting on the wheel center, parallel to the aircraft's longitudinal, vertical, and lateral directions; these are the three force load components). and 3 torque load components The load limits for the load components of the landing gear wheel axle loads; The landing gear should remain upright and stationary for at least 5 minutes, then deflate the buffers through the buffer inflation nozzle; inflate the buffer chambers using a hose through the inflation nozzle to approximately 5 times the buffer chamber volume. V The gas tank is connected; by S max Subtract 5mm as the maximum travel value (maximum travel) of the shock absorber to be calibrated. S H-max .

[0030] Take 10% to 60% of the limiting load of each load component of the landing gear as the target range for calibration loading; Determine the load component that can cause changes in the buffer travel, and determine the relationship between the load component that can cause changes in the buffer travel and the resulting axial force on the landing gear buffer based on the static equilibrium relationship of the landing gear structure. Determine the minimum value among the maximum values ​​of the target calibration load range for each load component that can cause changes in the buffer travel. The buffer travel should be such that, under this minimum load, the buffer travel exactly reaches the maximum travel to be calibrated. S H-max The requirements were determined to ensure that the buffer compression stroke reached the specified value. S H-max Pressure value and initial filling pressure value before loading ;

[0031] In the formula: To calibrate the axial force of the buffer corresponding to the minimum value among the maximum values ​​of each load component that can cause changes in the buffer stroke, the following parameters are required: V0 is the coefficient of friction for the expansion and contraction of the buffer, and V0 is the volume of the buffer's air chamber. V The sum of the pressure and the gas tank volume. If the pressure value at the maximum stroke of the buffer is within the allowable filling pressure range of the buffer, select the initial filling pressure value. Set the maximum specified pressure value; otherwise, reduce the proportion of the maximum value of the load component that can cause changes in the buffer stroke to its corresponding limit load, and redetermine the maximum specified pressure value until the pressure value at the maximum buffer stroke is within the allowable filling pressure range of the buffer. The minimum value among the minimum values ​​of the target calibration load range for each load component that can cause changes in the buffer travel is selected, such that the buffer travel under this minimum load exactly reaches the maximum travel to be calibrated. S H-max The requirements were determined to ensure that the buffer compression stroke reached the specified value. S H-max Pressure value and initial filling pressure value before loading ;

[0032] In the formula: To calibrate the axial force of the buffer corresponding to the minimum value among the minimum values ​​within the target loading range for each load component that can cause changes in the buffer travel, V0 is the coefficient of friction for the expansion and contraction of the buffer, and V0 is the volume of the buffer's air chamber. V 'The sum of the gas tank volume and the initial filling pressure value.' Specify the minimum pressure value; The minimum and maximum specified pressure values ​​are divided into several equal parts to form the intermediate specified pressure value.

[0033] During the landing gear follow-up loading test at each specified pressure value, record the buffer stroke value, the loaded load value, and the strain bridge response values ​​of no less than the number of load components. Select several buffer travel values ​​within the recorded buffer travel value range; Under the same selected buffer stroke value, the response coefficients of each strain bridge to each load component are linearly regressed based on each load component value and the response values ​​of multiple strain bridges. For different selected buffer travel values ​​and the corresponding response coefficients of each strain bridge, a polynomial fitting is used to derive the functional relationship between the response coefficients of each strain bridge to each load component and the buffer travel value. Based on the relationship between the response of each strain gauge bridge and each load component, a set of linear equations is established for each load component and each strain gauge bridge response. The coefficients of the linear equations are the functional relationship between the response coefficient of each strain gauge bridge to each load component and the buffer travel value. The general form of a system of linear equations is: ,in, For the response of the i-th strain bridge, For the buffer travel, Let be the response coefficient of the j-th load component to the i-th strain bridge, where the coefficient is the buffer travel. The function.

[0034] By substituting the measured buffer travel value and the corresponding strain bridge response value during flight into the linear equation system, the actual load on the landing gear during flight can be obtained.

[0035] Example Figure 1 This is a flowchart illustrating the method of the present invention. Figure 1 As shown, after the start, the buffer is first deflated and expanded; secondly, the buffer filling pressure is adjusted to a specified pressure value; then, at at least two different specified pressure values, the landing gear is subjected to a stepless variable stroke follow-up loading test, and the load applied to the landing gear, the strain bridge response, and the buffer stroke value are recorded simultaneously in each follow-up loading test; finally, the landing gear buffer filling pressure is restored to the aircraft design value. Throughout the entire landing gear loading test, the oil volume in the landing gear buffer remains unchanged, consistent with that before the test.

[0036] Figure 6 This is a schematic diagram illustrating the calibration principle of the calibration method of this invention. (See diagram below.) Figure 6 and Figure 7 As shown, when a calibration load that causes compression of the buffer stroke is applied to the maximum calibration stroke under a certain buffer filling pressure P1, and then the buffer is gradually extended, a curve showing the change of the buffer stroke with the calibration load will be obtained. Figure 6 In the above diagram, curve P1 represents compression / extension. Therefore, during a certain buffer stroke S in the landing gear... i At this point, loads L1 and L2, and strain bridge response data ε1 and ε2 under these loads are obtained. Plotting the data pairs (L1, ε1) and (L2, ε2) in a graph yields... Figure 6 In the diagram below, point A1 is at coordinates (L1, ε1), and point A2 is at coordinates (L2, ε2). Similarly, under filling pressure P2, points A3 and A4 are at coordinates (L3, ε3) and (L4, ε4), respectively.

[0037] Performing linear regression on these four sets of data (L1, ε1), (L2, ε2), (L3, ε3), and (L4, ε4) will yield regression lines for points A1, A2, A3, and A4. The slope of these regression lines represents the landing gear's travel distance from the buffer to the specified value (S). i The response coefficient of the strain bridge to the load component under the given condition.

[0038] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A landing gear variable stroke load calibration test device, characterized in that, include: The system includes an air tank, an air source, a four-way connector, a switch, and a pressure gauge. The landing gear shock absorber is connected to one port of a four-way connector via an air nozzle and a hose. The other three ports of the four-way connector are connected to one end of the air tank, the pressure gauge, and the switch, respectively. The other end of the switch is connected to the air source via a hose.

2. A method for calibrating landing gear variable stroke load, characterized in that, The method is performed using the landing gear variable stroke load calibration test apparatus of claim 1, and the method includes: Step 1: Determine the maximum travel of the landing gear buffer. S max Oil pressing area A air chamber volume V '; Step 2: Determine the load components of the landing gear axle load and the limiting loads of the load components of the landing gear axle load; Step 3: Determine the maximum travel value of the buffer to be calibrated S H-max The desired calibration target range and the relationship between the load components that can cause changes in the buffer travel and the resulting axial force on the landing gear buffer; Step 4: Based on the results of Steps 1 to 3, determine the minimum specified pressure value, the maximum specified pressure value, and the intermediate specified pressure value; Step 5: Conduct landing gear follow-up loading tests at the minimum specified pressure value, the maximum specified pressure value, and the intermediate specified pressure value respectively, and obtain the linear equations of each load component and each strain bridge response.

3. The landing gear variable stroke load calibration method according to claim 2, characterized in that, In step three, the maximum travel value of the buffer is to be calibrated. S H-max for S max Reduce by 5mm.

4. The landing gear variable stroke load calibration method according to claim 3, characterized in that, In step three, the target range for calibration loading is 10% to 60% of the load limit for each load component of the landing gear.

5. The landing gear variable stroke load calibration method according to claim 4, characterized in that, In step three, the relationship between the load component that causes the change in the buffer stroke and the resulting axial force on the landing gear buffer is determined by the static equilibrium relationship based on the landing gear structure.

6. The landing gear variable stroke load calibration method according to claim 5, characterized in that, In step four, the maximum specified pressure value is determined. Specifically, the minimum value among the maximum values ​​of the target calibration load range for each load component that can cause a change in the buffer stroke is determined, so that the buffer stroke reaches the maximum stroke to be calibrated under this minimum load. S H-max The requirements were determined to ensure that the buffer compression stroke reached the specified value. S H-max Pressure value and initial filling pressure value before loading ; in, To calibrate the axial force of the buffer corresponding to the minimum value among the maximum values ​​of each load component that can cause changes in the buffer stroke, the following parameters are required: V0 is the coefficient of friction for the expansion and contraction of the buffer, and V0 is the volume of the buffer's air chamber. V 'The sum of the gas cylinder volume;' If the pressure value at the maximum travel of the buffer is within the allowable filling pressure range of the buffer, select the initial filling pressure value. Set the maximum specified pressure value; otherwise, reduce the proportion of the maximum value of the load component that can cause changes in the buffer travel to its corresponding limit load, and redetermine the maximum specified pressure value until the pressure value at the maximum buffer travel is within the allowable filling pressure range of the buffer.

7. The landing gear variable stroke load calibration method according to claim 6, characterized in that, In step four, the minimum specified pressure value is determined, specifically as follows: The minimum value among the minimum values ​​of the target calibration load range for each load component that can cause changes in the buffer travel is selected, such that the buffer travel under this minimum load exactly reaches the maximum travel to be calibrated. S H-max The requirements were determined to ensure that the buffer compression stroke reached the specified value. S H-max Pressure value and initial filling pressure value before loading ; in: To calibrate the axial force of the buffer corresponding to the minimum value among the minimum values ​​within the target loading range for each load component that can cause changes in the buffer travel, The initial filling pressure value is selected as the friction coefficient for the expansion and contraction of the buffer. Specify the minimum pressure value.

8. The landing gear variable stroke load calibration method according to claim 7, characterized in that, In step four, the intermediate specified pressure value is determined by taking several equal divisions of the minimum and maximum specified pressure values ​​as the intermediate specified pressure value.

9. The landing gear variable stroke load calibration method according to claim 8, characterized in that, Step five, specifically: Record the buffer travel value, the applied load value, and the strain bridge response values, which are no less than the number of load components; Select several buffer travel values ​​within the recorded buffer travel value range; Under the same selected buffer stroke value, the response coefficients of each strain bridge to each load component are linearly regressed based on each load component value and the response values ​​of multiple strain bridges. For different selected buffer travel values ​​and the corresponding response coefficients of each strain bridge, a polynomial fitting is used to derive the functional relationship between the response coefficients of each strain bridge to each load component and the buffer travel value. Based on the relationship between the response of each strain gauge bridge and each load component, a set of linear equations is established for each load component and each strain gauge bridge response. The coefficients of the linear equations are the functional relationship between the response coefficient of each strain gauge bridge to each load component and the buffer travel value. The system of linear equations is in the form of: ,in, For the response of the i-th strain bridge, For the buffer travel, Let be the response coefficient of the j-th load component to the i-th strain bridge, where the coefficient is the buffer travel. The function.

10. The landing gear variable stroke load calibration method according to claim 9, characterized in that, The air tank volume is 5 times the air chamber volume of the buffer.

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