A method for measuring and verifying the intersection load of a statically indeterminate engine

Abstract

The present invention establishes a method for measuring and verifying the intersection loads of statically indeterminate aircraft engines. First, a strain bridge is designed and installed, and separate load calibration tests are carried out on the engine's inner / outer thrust pins and vertical / horizontal tie rods. The strain-load equations for each intersection load component are established using a stepwise multivariate linear regression method. Then, onboard load calibration tests are carried out on the engine's inner / outer thrust pins and vertical / horizontal tie rods, and the calibration test data are used to establish a method for verifying the rationality and prediction accuracy of the aforementioned strain-load equations. The present invention avoids the problem of multicollinearity in the constructed load equations that affects robustness, improves the equation's prediction accuracy, and provides a technical path for verifying the rationality of constructing strain-load equations for statically indeterminate aircraft engines based on separate load calibration test data, providing reliable support for flight measurements of intersection loads on aircraft engines.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft engine mounting structure health monitoring, and in particular relates to a method for measuring and verifying the intersection load of a statically indeterminate engine. Background Art

[0002] Aircraft engine mounting support structures are critical components prone to fatigue fracture. Failure can lead to loss of effective engine support and loss of control, compromising flight safety. Therefore, obtaining the actual loads directly exerted by the engine on the aircraft structure during flight, verifying the strength design rationality of the engine mounting support structure, and conducting health monitoring of such structures are crucial to ensuring aircraft safety.

[0003] A lot of research and application have been carried out on the thrust measurement methods of aircraft engines at home and abroad, and two mature thrust measurement methods have been formed, namely the Gas Generator Method (GGM) and the direct measurement method, which have been successfully applied on many types of aircraft.

[0004] The GGM method requires the installation of numerous temperature, pressure, and flow sensors on the engine, resulting in complex calculation models and high costs, making it rarely used. The direct measurement method, which deploys a strain gauge bridge at the engine's mounting point, eliminates the need for complex calculation models, is relatively simple to modify and test, and offers high reliability.

[0005] Existing research applications primarily focus on three-point statically determinate engines, measuring only engine thrust. However, aircraft engines' primary mounting intersections are typically subjected to biaxial or triaxial loads, making engine thrust alone insufficient for strength verification and health monitoring of the engine's mounting support structures. In particular, for engines with four-point statically indeterminate mounting, accurate measurement of intersection loads and a robust verification methodology are currently lacking. Summary of the Invention

[0006] The purpose of the present invention: The present invention solves the problem of obtaining the intersection loads of engine installations during actual flight of in-service aircraft by establishing a method for measuring and verifying the intersection loads of statically indeterminately installed aircraft engines, and provides a more accurate load input for the strength verification and health monitoring of the engine installation support structure. The present invention draws on the idea of ​​direct thrust measurement to measure the intersection loads of four-point statically indeterminately installed engines. First, a strain bridge is designed, and a separate load calibration test of the engine installation section is carried out. The stepwise multivariate linear regression method is used to establish the strain-load equations of each intersection load component; then, using the on-board load calibration test data, a method for verifying the rationality and prediction accuracy of the load equation is established.

[0007] The technical solution of the present invention:

[0008] The statically indeterminate four-point engine mount described in this invention is mounted on an aircraft using an inboard thrust pin, an outboard thrust pin, a vertical tie rod, and a horizontal tie rod. The inboard and outboard thrust pins are each secured to the fuselage structure at one end via two mounting joints and hingedly connected to the engine at the other end, with their axes parallel to the ground and perpendicular to the heading. The inboard thrust pin constrains the engine's heading and vertical translational displacement, while the outboard thrust pin constrains the engine's lateral, heading, and vertical translational displacement.

[0009] One end of the vertical / horizontal tie rod is connected to the fuselage in a hinged manner, and the other end is connected to the engine in a hinged manner. The vertical tie rod constrains the vertical translation displacement of the engine, and the horizontal tie rod constrains the lateral translation displacement of the engine.

[0010] The coordinate system is established as follows: the origin is located 270 mm above the nose of the aircraft, the Y axis is the axis of symmetry of the aircraft and is located on the manufacturing horizontal plane of the fuselage, with the rearward direction being positive; the Z axis is perpendicular to the Y axis and is positive upward within the symmetry plane of the aircraft; the X axis is perpendicular to the YZ plane and is positive pointing towards the left wing.

[0011] The following invention scheme is proposed for the actual measurement and verification method of the intersection load of the hyperstatic four-point mounted engine, which includes the following steps:

[0012] Step 1: Design strain bridges on the inner / outer thrust pins and vertical / horizontal pull rods.

[0013] Ten sets of strain bridges are arranged on both the inner and outer thrust pins; one set of shear bridges is arranged on the front and rear surfaces of the area where the first section is located, one set of shear bridges and one set of tension-compression bridges are arranged on the upper and lower surfaces of the area where the first section is located, and one set of shear bridges is arranged on the front and rear surfaces of the area where the second section is located, and one set of shear bridges is arranged on the upper and lower surfaces of the area where the second section is located.

[0014] The first section is located between the two mounting sections, and the second section is located between the mounting section and the engine;

[0015] A group of tension and compression bridges are symmetrically arranged on both sides of the outer surface of the middle part of the cylinder of the vertical / horizontal pull rod.

[0016] Step 2: Conduct separate load calibration tests on the inner / outer thrust pins and vertical / horizontal tie rods;

[0017] The inner thrust pin and the outer thrust pin are fixed respectively by two mounting joints in the same manner as the inner / outer thrust pins are installed on the machine; the vertical / horizontal pull rods are fixed respectively by an axial force loading device.

[0018] For the thrust pin, unidirectional loading calibration tests are first carried out in various directions. The inner thrust pin includes four working conditions: heading tension, compression, and vertical tension and compression. The outer thrust pin includes six working conditions: lateral tension and compression, heading tension, compression, and vertical tension and compression. Then, bidirectional or tridirectional composite loading calibration tests are carried out. According to the angle between the resultant force of the heading and vertical loads and the positive direction of the Z-axis, the composite loading calibration test of the inner thrust pin includes the following five working conditions: 107.6°, 112.4°, 99.2°, 63.6°, and 224.4°. The composite loading calibration test of the outer thrust pin includes the following six working conditions: 126.8°, 158.0°, 187.5°, 314.8°, 37.0°, and 78.0°.

[0019] For vertical / horizontal tie rods, axial tension / compression loads are applied respectively through the actuator for calibration test.

[0020] Step 3: Conduct on-board load calibration tests on the inner / outer thrust pins and vertical / horizontal tie rods;

[0021] Design the engine dummy and install it on the aircraft through the inner / outer thrust pins and vertical / horizontal pull rods; the aircraft is fixed to the ground rails through the dummy landing gear wheels, among which the front landing gear constrains the vertical translation displacement of the aircraft, and the left / right main landing gear constrains the lateral, heading, and vertical translation displacement of the aircraft.

[0022] The engine dummy is provided with five loading points, namely, a first lateral loading point and a first vertical loading point located in the front direction and before the inner and outer thrust pins, a heading loading point and a second lateral loading point located in the rear direction, and a second vertical loading point located in the middle and after the vertical / horizontal tie rods;

[0023] The working conditions for on-board load calibration tests on inner / outer thrust pins and vertical / horizontal pull rods include: one pure heading loading, six compound loadings, and six compound loadings, specifically: one (lateral +, vertical +), three (lateral +, vertical -), and two (lateral -, vertical -). "+" indicates that the load is positive, and "-" indicates that the load is negative.

[0024] Step 4: Preprocess the test data of the individual load calibration tests of the inner / outer thrust pins, vertical / horizontal pull rods, and the on-board load calibration test, including: retaining the data in the strain bridge response linear segment between 50% and 100% of the loading ratio in the test data, and eliminating the other data. Under each working condition, the number of data eliminated from each group of strain bridges is the same.

[0025] Step 5: Divide the test data of the separate load calibration test into a regression data set and a verification data set. The principle of division is: first, according to the load size and direction of different load calibration conditions, the conditions are divided into regression conditions and verification conditions. Both the regression conditions and the verification conditions should cover the positive and negative directions of the load components. The load size of the regression condition covers the typical value, and the number of regression conditions is more than the number of verification conditions; then the corresponding load and bridge data of the regression condition are used as the regression data set, and the load and bridge data of the verification condition are used as the verification data set.

[0026] Step 6: Construct the strain-load equations for the inner / outer thrust pins and vertical / horizontal tie rods based on their respective regression data sets. The equations for the vertical / horizontal tie rods are constructed using traditional linear regression methods, while the equations for the inner / outer thrust pins are constructed using the following methods and steps:

[0027] Step 6A: Calculate the covariance correlation coefficient between the load vector and each set of bridge strain response vectors in the regression data set, and eliminate the strain bridges with a covariance correlation coefficient less than r1; r1 ranges from [0.3 to 0.5];

[0028] Step 6B: Calculate the covariance correlation coefficient between the response data of any two groups of strain bridges in the remaining strain bridges, and select all strain bridge combinations whose covariance correlation coefficient between any two groups is less than r2, where r2 ranges from [0.9 to 0.95];

[0029] Step 6C: For all strain bridge combinations selected in step 6B, construct the strain-load equation for each bridge combination based on the stepwise linear regression method to calculate the goodness of fit (R 2 ) is the maximum criterion, and the optimal equations in the strain-load equations containing bn=2~k groups of bridges are determined respectively, where k represents the number of bridges in the combination containing the most bridges found in step 6B.

[0030] Step 7: Substitute the bridge data in the verification data set into the k-1 sets of strain-load equations established in step 6, predict the load value, and compare it with the load in the verification data set. Calculate the relative error between the two and select the equation with the smallest predicted relative error as the optimal strain-load equation.

[0031] Step 8: Substitute the test data of the on-board load calibration test pre-processed in step 4 into the optimal strain-load equations of the inner / outer thrust pins and vertical / horizontal tie rods, respectively, and solve the following intersection loads (i.e., internal forces) acting on the engine dummy components: The intersection load components F of the outer thrust pin along the X, Y, and Z directions x外 、F y外 、F z外 , the intersection load component F of the inner thrust pin along the Y and Z directions y内 、Fz内 , vertical load P of the vertical tie rod z垂直 , the lateral load P of the horizontal tie rod x水平 ;

[0032] Step 9: Using the intersection loads (internal forces) obtained in step 8, calculate their resultant force and torque on the engine in the specified direction; using the external loads on the engine loading point (external forces), calculate their resultant force and torque on the engine in the specified direction. The steps are as follows:

[0033] Step 9A: Use formulas (1) to (3) to calculate the resultant axial load Py, the resultant vertical load Pz, and the resultant moment Mz on the inner thrust pin hinge point of the engine dummy caused by the internal forces;

[0034] Py= F y外 + F y内 (1)

[0035] Pz= F z外 + F z内 +P z垂直 (2)

[0036] Mz=P x水平 ×L1+ F y外 ×L2 (3)

[0037] Wherein, L1 is the Y-direction distance between the horizontal tie rod and the inner thrust pin, and L2 is the X-direction distance between the load application point of the outer thrust pin intersection and the inner thrust pin hinge point;

[0038] Step 9B: Use (4) to (6) to calculate the resultant axial load Py', the resultant vertical load Pz', and the resultant moment Mz' on the inner thrust pin hinge point caused by the external force.

[0039] Py'= P y9015 (4)

[0040] Pz'= P z9012 +P z9013 (5)

[0041] Mz'= P x9011 ×L3+ P z9014 ×L4+ P y9015 ×L5 (6)

[0042] L3 is the Y-distance between the first lateral loading point and the inner thrust pin, L4 is the Y-distance between the second lateral loading point and the inner thrust pin, and L5 is the X-distance between the heading loading point and the inner thrust pin.

[0043] Step 10: Compare the resultant forces and moments calculated from the intersection loads and external loads to see if they are balanced. If they are balanced, it means that the strain-load equation established based on the test data from the separate load calibration test is reasonable and has sufficient accuracy, and can be used to predict the intersection loads of the inner / outer thrust pins and vertical / horizontal tie rods in actual flight. This includes the following steps:

[0044] Step 10A: Combine Py with Py', Pz with Pz', and Mz with Mz', and use least squares regression to fit their linear relationships. If the absolute value of the fitting slope is within the range of 1±0.03 and the goodness of fit (R 2 ) is greater than 0.99, indicating that Py and Py', Pz and Pz', and Mz and Mz' are highly consistent and balanced, which indirectly proves that the optimal strain-load equation established through the independent load calibration test data can accurately predict the thrust pin load on the aircraft, and the optimal strain-load equation can be used for subsequent engine installation intersection load flight measurement;

[0045] Otherwise, the optimal strain-load equation is not applicable. In this case, find the unbalanced term and execute step 10B.

[0046] Step 10B: Return to step 7. For the unbalanced terms of the resultant force or moment in step 10A, eliminate the corresponding strain-load equations in step 10A, select the set of equations with the highest prediction accuracy from the remaining set, and execute steps 8, 9, and 10A again.

[0047] Beneficial effects of the present invention:

[0048] The present invention proposes a method for measuring and verifying the intersection load of an over-statically-determined aircraft engine, which avoids the multicollinearity problem of the constructed load equation that affects the robustness, improves the prediction accuracy of the equation, and establishes a technical method for verifying the rationality and accuracy of the load equation based on on-board load calibration test data, providing reliable support for the flight measurement of the engine installation intersection load. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A technical flow chart of the method of the present invention;

[0050] Figure 2 This is a schematic diagram of the engine installation structure;

[0051] Figure 3 This is a schematic diagram of the connection between the thrust pin and the fuselage structure. Letters C and D in the figure represent the first and second sections of the thrust pin bridge installation respectively.

[0052] Figure 4This is a schematic diagram of the distribution of loading points of the dummy engine parts in the onboard load calibration test. In the figure, 1 is the inner thrust pin, 2 is the outer thrust pin, 3 is the vertical tie rod, 4 is the horizontal tie rod, 9011 is the first lateral loading point, 9012 is the first vertical loading point, 9013 is the second vertical loading point, 9014 is the second lateral loading point, and 9015 is the heading loading point.

[0053] Figure 5 Create a flow chart for the load equations;

[0054] Figure 6 Validation flow chart for load equations;

[0055] Figure 7 This is a comparison diagram of the resultant force and torque caused by the internal and external forces on the engine dummy, where: Figure 7 (a) is the comparison of the resultant directional load caused by internal and external forces. Figure 7 (b) Comparison of the resultant vertical loads caused by internal and external forces, Figure 7 (c) Comparison of the Z-direction resultant moments caused by internal and external forces. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0057] A method for measuring and verifying the intersection load of an over-determined engine. Figure 1 One of the possible specific implementations includes the following steps:

[0058] The first step is to adopt Figure 2 The aircraft engine with four-point hyperstatic installation shown in the figure takes into account the installation effect and the transverse axis effect. Ten sets of strain bridges are arranged on the inner and outer thrust pins, of which five sets are backup bridges. The bridges are located as shown in the figure. Figure 3 The first and second sections, C and D, are shown. Section C is between the two mounting sections, while Section D is between the mounting section and the engine. Section C features two sets of shear bridges on the forward and aft surfaces, two sets of shear bridges on the upper and lower surfaces, and two sets of tension-compression bridges. Section D features two sets of shear bridges on the forward and aft surfaces, and two sets of shear bridges on the upper and lower surfaces. Two sets of tension-compression bridges are arranged on the outer surface of the central portion of the cylindrical body of the vertical and horizontal tie rods. All electrical bridges are full bridges.

[0059] The second step is to carry out separate load calibration tests on the inner / outer thrust pins and vertical / horizontal pull rods. The inner / outer thrust pins and vertical / horizontal pull rods are fixed separately using mounting joints in the same way as they are installed on the machine. The vertical / horizontal pull rods are fixed separately using an axial force loading device.

[0060] The single load calibration test is carried out for the thrust pin. First, unidirectional loading calibration tests are carried out in all directions. The inner thrust pin includes four working conditions: axial tension, compression and vertical tension and compression. The outer thrust pin includes six working conditions: lateral tension and compression, axial tension, compression and vertical tension and compression. Then, a bidirectional or tridirectional composite loading calibration test is carried out. The test is divided according to the angle between the resultant force of the axial and vertical loads and the positive direction of the Z axis. The composite loading calibration test of the inner thrust pin is designed with five different resultant angles in the YZ plane (107.6°, 112.4°, 129.8° and 130.9°). The composite loading conditions of the outer thrust pin are 99.2°, 63.6°, and 224.4°. Six composite loading conditions with different resultant angles (126.8°, 158.0°, 187.5°, 314.8°, 37.0° and 78.0°) are designed in the YZ plane to cover the typical stress forms of the thrust pin. For the vertical / horizontal pull rod, it is fixed on the axial force loading device and axial loading is performed through the actuator to carry out calibration tests under tension and compression loads.

[0061] The third step is to design a dummy engine part, and install it on the aircraft using the same connection method as the real engine part through the inner / outer thrust pins and vertical / horizontal tie rods, and design 5 loading points on the dummy part, such as Figure 4 As shown, lateral, heading, and vertical loads are applied in combination; the aircraft is fixed to the ground rail through the landing gear dummy wheels, wherein the front landing gear constrains the vertical translation displacement of the aircraft, and the left / right main landing gear constrains the lateral, heading, and vertical translation displacement of the aircraft.

[0062] The engine dummy is provided with five loading points, such as Figure 4 As shown, there are respectively a first lateral loading point 9011 and a first vertical loading point 9012 located in the forward direction and before the inner and outer thrust pins, a heading loading point 9015 and a second lateral loading point 9014 located in the rear direction, and a second vertical loading point 9013 located in the middle and after the vertical / horizontal tie rods;

[0063] Calibration conditions include one pure azimuth loading condition and six combined lateral and vertical loading conditions: one (lateral +, vertical +), three (lateral +, vertical -), and two (lateral -, vertical -). "+" indicates a positive load, and "-" indicates a negative load. The forces and moments exerted by the external loads on the aircraft are balanced by applying trim loads to a main load-bearing frame on the forward fuselage and to the drag chute connector above the engine.

[0064] The fourth step is to preprocess the test data of the individual load calibration tests of the inner / outer thrust pins, vertical / horizontal pull rods, and the on-board load calibration tests, including: in the test data, retaining the data in the linear segment of the strain bridge response between 50% and 100% of the loading ratio, and eliminating the other data. Under each working condition, the number of data eliminated from each group of strain bridges is the same.

[0065] In the fifth step, the test data from the individual load calibration tests was divided into a regression dataset and a verification dataset. Five conditions for the inner thrust pin were used as regression conditions, and the remaining four conditions were used as verification conditions. Eight conditions for the outer thrust pin were used as regression conditions, and four conditions were used as verification conditions. The corresponding load and bridge data for the regression conditions served as the regression dataset, while the load and bridge data for the verification conditions served as the verification dataset.

[0066] The sixth step is to construct the axial strain-load equation of the inner thrust pin containing 2 or 3 groups of bridges and the vertical load equation containing 2 groups of bridges; the lateral strain-load equation of the outer thrust pin containing 2 or 3 groups of bridges, the axial strain-load equation of the outer thrust pin containing 2 or 3 groups of bridges, and the vertical load equation containing 2 or 3 groups of bridges; the strain-load equation of the vertical pull rod and the horizontal pull rod containing one group of bridges.

[0067] The strain-load equation is of the form:

[0068] Load=c1×bridge1+c2×bridge2+c3×bridge3+….

[0069] Where c1, c2, c3, ... represent coefficients, bridge1, bridge2, bridge3, ... represent the response values ​​of the bridge, and Load is the predicted load value.

[0070] In the seventh step, the corresponding bridge data in the verification data set are substituted into the strain-load equation group established in step six to predict the load value. By calculating the relative error with the load in the verification data set, the optimal strain-load equations for the heading and vertical directions of the inner thrust pin are selected, both of which contain two sets of bridges. The optimal strain-load equations for the lateral, heading, and vertical directions of the outer thrust pin are equations containing three, two, and two sets of bridges, respectively.

[0071] In the eighth step, the bridge data of the on-board load calibration test pre-processed in the fourth step are respectively substituted into the optimal strain-load equations of the inner / outer thrust pins and vertical / horizontal tie rods in the seventh step to solve the following intersection loads (i.e., internal forces) acting on the engine dummy parts: the intersection load components F of the outer thrust pin along the X, Y, and Z directions x外 、F y外 、F z外 , the intersection load component F of the inner thrust pin along the Y and Z directions y内 、Fz内 , vertical load P of the vertical tie rod z垂直 , the lateral load P of the horizontal tie rod x水平 .

[0072] The ninth step is to use the intersection load (internal force) acting on the engine dummy and the external load (external force) on the loading point of the engine dummy to calculate their resultant force and moment in the specified direction of the engine dummy. The values ​​of the two are as follows: Figure 7 shown.

[0073] The tenth step is to calculate the slope of the resultant moment Mz of the axial load, the vertical load, the hinge point of the inner thrust pin, and the goodness of fit R of the two. 2 ,like Figure 7 As shown, the absolute values ​​of the slopes are 0.9948, 1.0073, and 1.0229, respectively, all within the range of 1±0.03; the goodness of fit R 2 The values ​​are 0.9998, 0.9986, and 0.9952, respectively, all greater than 0.995. This indicates a high degree of agreement between the two, and the balance of the engine's net force and torque caused by internal and external forces. This proves that the load equation established using data from separate load calibration tests on the inner / outer thrust pins and vertical / horizontal tie rods can accurately predict the intersection loads of a four-point hyperstatically mounted aircraft engine, and can be used for subsequent actual measurements of engine installation intersection loads.

[0074] The above is merely one specific embodiment of the present invention, and the present invention is described in detail. Any unspecified portion represents conventional technology. However, the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope 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 based on the scope of protection of the claims.

Claims

1. A method for measuring and verifying the intersection load of a statically indeterminate engine, characterized by: The engine is mounted on the fuselage structure using inboard / outboard thrust pins and vertical / horizontal tie rods. The inboard / outboard thrust pins are fixed to the fuselage structure at one end via two mounting joints, and are hingedly connected to the engine at the other end, with their axes parallel to the ground and perpendicular to the heading. The inboard thrust pin constrains the engine's heading and vertical translational displacement, while the outboard thrust pin constrains the engine's lateral, heading, and vertical translational displacement. One end of the vertical / horizontal tie rod is connected to a fuselage frame in an articulated manner, and the other end is connected to the engine in a hinged manner, wherein the vertical tie rod constrains the vertical translation displacement of the engine, and the horizontal tie rod constrains the lateral translation displacement of the engine; The coordinate system is established as follows: the origin is located 270 mm above the nose of the aircraft. The Y axis is the aircraft's symmetry axis and is located on the manufacturing horizontal plane of the fuselage, with the rearward direction being positive. The Z axis is perpendicular to the Y axis and is positive upward within the aircraft's symmetry plane. The X axis is perpendicular to the YZ plane and is positive toward the left wing. The method comprises the following steps: Step 1: Design strain bridges on the inner / outer thrust pins and vertical / horizontal pull rods; Step 2: Conduct separate load calibration tests on the inner / outer thrust pins and vertical / horizontal tie rods; Step 3: Conduct on-board load calibration tests on the inner / outer thrust pins and vertical / horizontal tie rods; Step 4: Pre-process the test data of the individual load calibration tests of the inner / outer thrust pins, vertical / horizontal tie rods, and the onboard load calibration test; Step 5: Divide the pre-processed test data of the single load calibration test into a regression data set and a verification data set according to the load size and direction; the regression data set and the verification data set both contain the load and the corresponding bridge response data; Step 6: Construct the strain-load equations based on the regression data sets of the inner / outer thrust pins and vertical / horizontal tie rods respectively; Step 7: Verify the load equation group in step 6 based on the verification data set and select the optimal "strain-load" equation with the highest prediction accuracy; Step 8: Substitute the pre-processed onboard load calibration data from Step 4 into the optimal "strain-load" equation from Step 7 to calculate the intersection loads at the connections between the inner / outer thrust pins, vertical / horizontal tie rods, and the engine; Step 9: Using the intersection loads obtained in step 8, which are internal forces, calculate the resultant force and torque on the engine in the specified direction; using the external loads on the engine loading point, which are external forces, calculate the resultant force and torque on the engine in the specified direction; Step 10: Compare the resultant forces and moments calculated from the intersection loads and external loads to see if they are balanced. If they are, the strain-load equation established based on the test data from the separate load calibration test is reasonable and accurate enough to be used for predicting the intersection loads of the inner / outer thrust pins and vertical / horizontal tie rods in actual flight.

2. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 1, characterized in that: In the step 1, ten sets of strain bridges are arranged on both the inner and outer thrust pins; one set of shear bridges is arranged on the front and rear surfaces of the area where the first cross section is located, one set of shear bridges and one set of tension-compression bridges are arranged on the upper and lower surfaces of the area where the first cross section is located, one set of shear bridges is arranged on the front and rear surfaces of the area where the second cross section is located, and one set of shear bridges is arranged on the upper and lower surfaces of the area where the second cross section is located; The first section is located between the two mounting sections, and the second section is located between the mounting section and the engine; A group of tension and compression bridges are symmetrically arranged on both sides of the outer surface of the middle part of the cylinder of the vertical / horizontal pull rod.

3. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 2, characterized in that: In the second step, the inner thrust pin and the outer thrust pin are fixed respectively using two mounting joints in the same manner as the inner / outer thrust pins are installed on the machine; and the vertical / horizontal pull rods are fixed respectively using an axial force loading device; For the thrust pin, firstly, unidirectional loading calibration tests are carried out in each direction respectively. The inner thrust pin includes 4 working conditions, namely, heading tension, compression, and vertical tension and compression. The outer thrust pin includes 6 working conditions, namely, lateral tension and compression, heading tension, compression, and vertical tension and compression. Then, bidirectional or tridirectional composite loading calibration tests are carried out. According to the angle between the resultant force of the heading and vertical loads and the positive direction of the Z axis, the composite loading calibration test of the inner thrust pin includes the following five working conditions: 107.6°, 112.4°, 99.2°, 63.6°, and 224.4°. The composite loading calibration test of the outer thrust pin includes the following six working conditions: 126.8°, 158.0°, 187.5°, 314.8°, 37.0°, and 78.0°. For vertical / horizontal tie rods, axial tension / compression loads are applied respectively through the actuator for calibration test.

4. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 3, characterized in that: In step 3, the engine dummy is designed and installed on the aircraft through inner / outer thrust pins and vertical / horizontal tie rods; The aircraft is fixed to the ground rails by the landing gear dummy wheels, wherein the front landing gear constrains the vertical translation displacement of the aircraft, and the left / right main landing gear constrains the lateral, heading, and vertical translation displacement of the aircraft; The engine dummy is provided with five loading points, namely, a first lateral loading point and a first vertical loading point located in the front direction and before the inner and outer thrust pins, a heading loading point and a second lateral loading point located in the rear direction, and a second vertical loading point located in the middle and after the vertical / horizontal tie rods; The working conditions for on-board load calibration tests on inner / outer thrust pins and vertical / horizontal tie rods include: one pure heading loading and six compound loading conditions, specifically: one type of lateral + and vertical +, three types of lateral + and vertical -, and two types of lateral - and vertical -. "+" indicates a positive load, and "-" indicates a negative load.

5. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 4, characterized in that: In step 4, the preprocessing includes: retaining the data in the test data where the strain bridge response is in the linear segment of the loading ratio of 50% to 100%, and eliminating the other data. Under each working condition, the number of data eliminated from each group of strain bridges is the same.

6. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 5, characterized in that: In the step five, the test data of the separate load calibration test is divided into a regression data set and a verification data set. The principle of division is: first, according to the load size and direction of different load calibration conditions, the conditions are divided into regression conditions and verification conditions. The regression conditions and verification conditions should both cover the positive and negative directions of the load components. The load size of the regression condition covers the typical value, and the number of regression conditions is more than the number of verification conditions; then the corresponding load and bridge data of the regression condition are used as the regression data set, and the load and bridge data of the verification condition are used as the verification data set.

7. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 6, characterized in that: In step 6, a strain-load equation group is constructed based on the regression data set. The equation group for the vertical / horizontal tie rod is constructed using a traditional linear regression method, and the equation group for the inner / outer thrust pin is constructed according to the following method and steps: Step 6A: Calculate the covariance correlation coefficient between the load vector and each set of bridge strain response vectors in the regression data set, and eliminate the strain bridges with a covariance correlation coefficient less than r1; r1 ranges from [0.3 to 0.5]; Step 6B: Calculate the covariance correlation coefficient between the response data of any two groups of strain bridges in the remaining strain bridges, and select all strain bridge combinations whose covariance correlation coefficient between any two groups is less than r2, where r2 ranges from [0.9 to 0.95]; Step 6C: For all strain bridge combinations selected in step 6B, construct the strain-load equation for each bridge combination based on the stepwise linear regression method to obtain the goodness of fit R 2 Taking the maximum as the criterion, determine the optimal equation in the strain-load equation containing bn=2~k groups of bridges, where k represents the number of bridges in the combination with the most bridges found in step 6B.

8. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 7, characterized in that: In step 7, the bridge data in the verification data set is substituted into the k-1 sets of strain-load equations established in step 6 to predict the load value, which is compared with the load in the verification data set, and the relative error between the two is calculated. The equation with the smallest relative error is selected as the optimal strain-load equation; In step eight, the test data of the on-board load calibration test pre-processed in step four are substituted into the optimal strain-load equations of the inner / outer thrust pins and vertical / horizontal tie rods, respectively, to solve the following intersection loads acting on the engine dummy: the intersection load components F of the outer thrust pin along the X, Y, and Z directions x外 、F y外 、F z外 , the intersection load component F of the inner thrust pin along the Y and Z directions y内 、F z内 , vertical load P of the vertical tie rod z垂直 , the lateral load P of the horizontal tie rod x水平 .

9. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 1, characterized in that: In step nine, the specific method and steps for calculating the resultant force and resultant moment using the intersection load and external load on the engine dummy component are as follows: Step 9A: Use formulas (1) to (3) to calculate the resultant axial load Py, the resultant vertical load Pz, and the resultant moment Mz on the inner thrust pin hinge point of the engine dummy caused by the internal forces; Py= F y外 + F y内 (1) Pz= F z外 + F z内 +P z垂直 (2) Mz=P x水平 ×L1+ F y外 ×L2(3) Wherein, L1 is the Y-direction distance between the horizontal tie rod and the inner thrust pin, and L2 is the X-direction distance between the load application point of the outer thrust pin intersection and the inner thrust pin hinge point; Step 9B: Use (4) to (6) to calculate the resultant axial load Py', the resultant vertical load Pz', and the resultant moment Mz' on the inner thrust pin hinge point caused by the external force. Py'= P y9015 (4) Pz'= P z9012 +P z9013 (5) Mz'= P x9011 ×L3+ P z9014 ×L4+ P y9015 ×L5(6) L3 is the Y-distance between the first lateral loading point and the inner thrust pin, L4 is the Y-distance between the second lateral loading point and the inner thrust pin, and L5 is the X-distance between the heading loading point and the inner thrust pin.

10. The method for measuring and verifying the intersection load of a statically indeterminate engine according to claim 1, characterized in that: In step 10, the following methods and steps are used to compare whether the resultant force and moment calculated from the intersection load and the external load are balanced: Step 10A: Combine Py with Py', Pz with Pz', and Mz with Mz', and use least squares regression to fit their linear relationships. If the absolute value of the fitting slope is within the range of 1±0.03 and the goodness of fit R 2 If the value is greater than 0.995, it indicates that Py and Py', Pz and Pz', and Mz and Mz' are highly consistent and balanced, which indirectly proves that the optimal strain-load equation established based on the independent load calibration test data can accurately predict the thrust pin load on the aircraft. The optimal strain-load equation can be used for subsequent actual flight measurements of engine installation intersection loads. Otherwise, the optimal strain-load equation is not applicable. In this case, find the unbalanced term and execute step 10B. Step 10B: Return to step 7. For the unbalanced terms of the resultant force or moment in step 10A, eliminate the corresponding strain-load equations in step 10A, select the set of equations with the highest prediction accuracy from the remaining set, and execute steps 8, 9, and 10A again.

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