Helicopter hub center load acquisition method

Abstract

The invention provides a helicopter propeller hub center load acquisition method, which comprises the following steps of: respectively pasting not less than three groups of strain gauges on an orthogonal section (0 degree and 90 degrees) on a rotor wing simulation shaft, and calibrating a proportional relation between strain output and actual bending moment through a cantilever beam loading method before a test; and then the bending moment (Mf) and the shearing force (T) at the center of the propeller hub can be obtained through a linear interpolation calculation method. According to the calculation method, the center bending moment (Mf) and the shearing force (T) of the propeller hub required by the test can be obtained by adjusting the three-way loading load of a plurality of support arms in the center part of the propeller hub.

Description

Technical Field

[0001] The present application belongs to the technical field of calculating the bending moment (Mf) and shear force (T) at the center of a helicopter hub, and specifically relates to a method for obtaining the center load of a helicopter hub. Background Art

[0002] As one of the core components of the helicopter rotor system, the helicopter hub is a key stress-bearing component on the helicopter. It bears the centrifugal force, lift, flapping force, swing force, and damper force transmitted by the blades, and its stress conditions are very complex. Therefore, the fatigue life of the central component directly affects the service life of the entire helicopter, and its performance directly affects the strength and flight safety of the helicopter.

[0003] The hub centerpiece fatigue test includes a variety of complex overall loads and local loads. Usually, centrifugal force loading points, swing loading points, flapping loading points, and damper force loading points are designed on each arm to achieve load application. f , T, due to space and shape limitations, it is not possible to arrange bending moment and torque measuring pieces, so the load M can only be measured through the extended rotor simulation shaft f , T. That is, by monitoring the strain value on the rotor simulation shaft, it is calculated whether the central test load of the hub center piece meets the design index requirements. Therefore, it is necessary to establish an accurate mathematical model method based on mechanical knowledge to decouple the central dynamic load M of the hub center piece. f 、T. Summary of the invention

[0004] Purpose of the invention: To provide a high-precision and high-reliability linear interpolation calculation method for the hub center load in response to the calculation requirements of the large-load loading test of the helicopter hub central component.

[0005] The present application provides a method for obtaining a helicopter hub center load, the method comprising:

[0006] Step 1: At different cross-sectional positions at the 0-degree cross-section on the simulated rotor axis, and at cross-sectional positions at a certain distance from the bottom and the top, arrange at least 3 sets of bending moment measurement strain gauges at appropriate intervals;

[0007] Step 2: Paste the strain gauge at the determined patch position, and the pasting process should comply with the strain gauge pasting process regulations;

[0008] Step 3: Use a cantilever beam method to load and calibrate the rotor simulation shaft, use an actuator to apply a calibration load, calibrate the relationship between the bending moment and strain of the corresponding section on the rotor simulation shaft, and use three calibration average data for processing to determine the relationship between the actual bending moment M and the strain output με on the rotor simulation shaft, and obtain the proportional coefficient k=με / M of each group of full-bridge strain;

[0009] Step 4: During the fatigue test of the central part, in order to obtain the bending moment (M f ) and shear force (T), and periodically apply loads to all arms of the hub through the three-way loading mechanism of the central part; during the load application process, the bending moment strain output on the rotor simulation shaft is the strain value με. Through the obtained proportional coefficient k, the actual bending moment at this location can be directly derived as M=με / k.

[0010] Step 5. One end of the rotor simulation shaft is fixed and the other end is loaded. This loading can be simplified into a cantilever beam. Therefore, as long as the bending moment at no less than two points in the middle is obtained, the bending moment values ​​at other positions can be obtained. The bending moment M obtained by the B01, B03, and B05 strains of the 0° section on the rotor simulation shaft is obtained by linear interpolation calculation method to obtain the bending moment at any point on the shaft, and thus the bending moment at the center of the hub (M) is obtained. f );

[0011] Step 6. Since the bending moment on the simulated shaft is a straight line of linear proportion, the shear force is a constant; the shear force (T) at the center of the hub is the shear force on the rotor simulation shaft. The slope of the curve can be calculated by linear interpolation, which is the shear force (T) on the rotor simulation shaft.

[0012] Preferably, the cross section includes an A cross section, a B cross section, and a C cross section.

[0013] Preferably, a certain distance of about 15-20 cm is avoided from the bottom arc transition and the top chamfer of the rotor simulation shaft to avoid abnormal and nonlinear strain data due to local stress concentration in the structure.

[0014] Preferably, the method further comprises:

[0015] After a preliminary resistance measurement and inspection of the pasted strain gauges, a Wheatstone full-bridge resistor is formed in a full-bridge manner.

[0016] Preferably, the cantilever beam loading calibration requires that during the calibration process, a special device be used to make the loading load perpendicular to the pasting section of the calibration strain gauge and the axis of the simulation shaft, so as to avoid the calibration load and the strain gauge and the axis of the simulation shaft not coinciding in the same plane, generating components in other directions, and causing inaccurate calibration data; during the data processing process, the cantilever beam calculation method needs to be used to obtain the theoretical bending moment value applied to the cross section at each step of the calibration load, and then compared one by one with the actual strain output data value to obtain a proportional coefficient between the strain value and the bending moment value.

[0017] Preferably, the three-way loading mechanism realistically simulates the stress process of the central component during flight, and applies a variety of composite loads loaded in phase, so that the load on the rotor simulation shaft in the circumferential direction around the axis is a uniformly distributed rotational load.

[0018] Preferably, the linear proportional straight line is obtained by fitting the multi-point bending moment values ​​obtained on the simulation axis, so that the variation law of the bending moment curve can be obtained, and it can also be defined by converting it into a formula.

[0019] Preferably, the method further comprises:

[0020] Step 7. In order to improve data reliability and calculation accuracy, the hub linear interpolation calculation method adopts the double redundancy calculation method, that is, the same bending moment strain is arranged at 90 degrees of the orthogonal section of the simulated shaft. Through theoretical analysis, it can be obtained that the strain values ​​B01 and B02 at the same position on the shaft are equal, B03 and B04 are equal, and B05 and B06 are equal. The two groups of strain gauges B01, B03, B05 and B02, B04, B06 can be linearly interpolated respectively.

[0021] Step 8: As mentioned above, the bending moments (M) calculated for the 0-degree section and the 90-degree section are f ) and shear force (T) should be equal in theory;

[0022] Step 9: During the test, the bending moment (M) at the hub center is monitored in real time by simulating the strain output values ​​of each section on the shaft. f ) and shear force (T), and also adjust the bending moment (M) required for the test in time through the three-way load applied by the hub support arm f ) and shear force (T), and the helicopter hub center load linear interpolation calculation method is used to ensure the hub test is carried out effectively.

[0023] This application has the following technical effects:

[0024] The invention discloses a method for calculating the central load of a helicopter hub by linear interpolation, which can greatly simplify the calculation of the central test load of the hub, improve the accuracy of the central test load of the hub, shorten the test cycle, and save costs. The method of the invention is used to perform fatigue tests on the central parts of the helicopter hub, and the test load is stable and reliable, which can meet the application of various complex test loads on the center of the helicopter hub. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the central piece;

[0026] Figure 2 Schematic diagram of the phase relationship of the test load;

[0027] Figure 3 Rotor simulation axis patch diagram;

[0028] Figure 4 Linear difference plot of bending moment and shear force. DETAILED DESCRIPTION

[0029] Aiming at the requirements of large load test calculation of helicopter hub center, a high-precision and high-reliability linear interpolation calculation method for hub center load is provided. This method pastes at least 3 sets of strain gauges on the orthogonal sections (0 degrees and 90 degrees) on the rotor simulation axis, calibrates the proportional relationship between strain output and actual bending moment by cantilever beam loading method before the test, and then obtains the bending moment (M) at the hub center by linear interpolation calculation method. f ) and shear force (T). This calculation method can obtain the hub center bending moment (M) required for the test by adjusting the three-way loading loads of multiple arms in the hub centerpiece. f ) and shear force (T).

[0030] The experiments show that the calculation method can meet the load calculation requirements of helicopter hub fatigue test. It has the advantages of simple and convenient calculation, low environmental requirements, fast processing speed and high measurement accuracy. It can shorten the test cycle, speed up the test efficiency and save the test cost, and well meet the requirements of helicopter hub fatigue test loading calculation.

[0031] See also Figure 1-Figure 4 According to the load characteristics and structural characteristics of helicopters, a method for measuring the central bending moment (M f ) and shear force (T) are calculated by linear interpolation.

[0032] This calculation method can accurately calculate the bending moment M at the center of the hub. f This calculation method greatly simplifies the load loading method, so that the bending moment and shear force of the hub center can be obtained through the conventional hub support arm three-way loading mechanism. This calculation method improves the test load loading and measurement accuracy, shortens the test cycle, and meets the load loading requirements of the helicopter hub centerpiece.

[0033] The steps of the method provided in this application are as follows:

[0034] Step 1: At different cross-sectional positions at the 0-degree section on the rotor simulation axis, at cross-sectional positions at a certain distance from the bottom and top, choose appropriate spacing and arrange no less than 3 sets of bending moment measurement strain gauges. For example, section A, section B, section C, see Figure 3 Rotor simulation axis patch diagram.

[0035] Among them, a certain distance should be avoided from the bottom arc transition and the top chamfer of the rotor simulation shaft by about 15-20cm, so as to avoid the abnormal and nonlinear strain data caused by local stress concentration of the structure. The appropriate spacing means that the spacing between each group of strain gauges should evenly divide the effective length on the simulation shaft, so that the force arm increases in equal multiples, avoiding the linear error caused by different spacing sizes.

[0036] Step 2: Paste the strain gauge to the determined patch position, and the pasting process should comply with the strain gauge pasting process regulations. After preliminary resistance measurement and inspection of the pasted strain gauge, form a Wheatstone full-bridge resistor in a full-bridge manner. The advantages of this bridge circuit are high sensitivity, good strain resistance, and can eliminate the influence of ambient temperature.

[0037] Step 3: Use a cantilever beam method to load and calibrate the rotor simulation shaft. Use the actuator to apply the calibration load and calibrate the relationship between the bending moment and strain of the corresponding section on the rotor simulation shaft. The calibration is processed using the average data of three calibrations to determine the relationship between the actual bending moment M and the strain output με on the rotor simulation shaft, and obtain the proportional coefficient k=με / M of each group of full-bridge strain.

[0038] Among them, the cantilever beam loading calibration requires that the loading load be perpendicular to the pasting section of the calibration strain gauge and the axis of the simulation shaft through a special device during the calibration process to avoid the calibration load and the strain gauge and the simulation shaft axis not coinciding in the same plane, generating components in other directions, and causing inaccurate calibration data. In the data processing process, the cantilever beam calculation method is required to obtain the theoretical bending moment value applied to the cross section at each step of the calibration load, and then compare it with the actual strain output data value one by one to obtain a proportional coefficient between the strain value and the bending moment value.

[0039] Step 4: During the fatigue test of the central part, in order to obtain the bending moment (M f ) and shear force (T), and periodically load all the hub arms through the central component three-way loading mechanism. During the load application process, the bending moment strain output on the rotor simulation shaft is the strain value με. Through the obtained proportionality coefficient k, the actual bending moment at this location can be directly obtained as M = με / k.

[0040] Among them, the three-way loading mechanism truly simulates the force process of the central component during flight, and applies a variety of composite loads loaded in phase, so that the load on the rotor simulation axis around the axis is a uniformly distributed rotating load, see Figure 2 As shown. This complex load cannot be used to calculate the bending moment. At this time, the strain value of each section can be obtained through the measuring equipment, plus the proportional coefficient K obtained in step 3 above, and the actual bending moment of the section can be calculated through the formula.

[0041] Step 5: One end of the rotor simulation shaft is fixed, and the other end (the test piece installation end) is loaded. This loading can be simplified into a cantilever beam form. Therefore, as long as the bending moment of any two points in the middle is obtained, the bending moment values ​​at other positions can be obtained. The bending moment M obtained by the strains of B01, B03, and B05 of the 0° section on the rotor simulation shaft is used. Figure 4 The linear interpolation method can be used to obtain the bending moment at any point on the shaft, and the bending moment at the center of the hub (M f ).

[0042] Step 6. Since the bending moment on the simulated shaft is a linearly proportional straight line, the shear force is a constant. The shear force (T) at the center of the hub is the shear force on the simulated rotor shaft. The slope of the curve can be calculated by linear interpolation, which is the shear force (T) on the simulated rotor shaft.

[0043] Among them, the linear proportional straight line is obtained by fitting the multi-point bending moment values ​​obtained on the simulation axis, and the change law of the bending moment curve can be obtained, which can also be defined by converting it into a formula.

[0044] Step 7: In order to improve data reliability and calculation accuracy, the hub linear interpolation calculation method adopts the double redundancy calculation method. That is, at the 90-degree orthogonal section of the simulated shaft, the same bending moment strain is arranged. Through theoretical analysis, it can be obtained that the strain values ​​B01 and B02 at the same position on the shaft are equal, B03 and B04 are equal, and B05 and B06 are equal (see Figure 3 ), the two groups of strain gauges (B01, B03, B05) and (B02, B04, B06) can be subjected to linear interpolation calculations respectively.

[0045] Step 8: As mentioned above, the bending moments (M) calculated for the 0-degree section and the 90-degree section are f ) and shear force (T) should be equal in theory. Due to the installation error of the test piece, the processing error of the test fixture, the measurement error of the control system, the measurement error of the strain gauge, etc., there will be a certain gap between the theoretically calculated load and the feedback composite load. The error is controlled within 3% according to the design requirements.

[0046] Step 9: During the test, the bending moment (M) at the hub center can be monitored in real time by simulating the strain output values ​​of each section on the shaft. f ) and shear force (T), and the bending moment (M) required for the test can be adjusted in time through the three-way load applied by the hub support arm. f ) and shear force (T). The helicopter hub center load linear interpolation calculation method is used to ensure that the hub test is carried out effectively.

[0047] The invention discloses a method for calculating the central load of a helicopter hub by linear interpolation, which can greatly simplify the calculation of the central test load of the hub, improve the accuracy of the central test load of the hub, shorten the test cycle, and save costs. The method of the invention is used to perform fatigue tests on the central parts of the helicopter hub, and the test load is stable and reliable, which can meet the application of various complex test loads on the center of the helicopter hub.

Claims

1. A method for obtaining the center load of a helicopter hub, characterized in that: The method comprises: Step 1: At different cross-sectional positions at the 0-degree cross-section on the simulated rotor axis, and at cross-sectional positions at a certain distance from the bottom and the top, arrange at least 3 sets of bending moment measurement strain gauges at appropriate intervals; Step 2: Paste the strain gauge at the determined patch position, and the pasting process should comply with the strain gauge pasting process regulations; Step 3: Use a cantilever beam method to load and calibrate the rotor simulation shaft, use an actuator to apply a calibration load, calibrate the relationship between the bending moment and strain of the corresponding section on the rotor simulation shaft, and use three calibration average data for processing to determine the relationship between the actual bending moment M and the strain output με on the rotor simulation shaft, and obtain the proportional coefficient k=με / M of each group of full-bridge strain; Step 4: During the fatigue test of the central part, in order to obtain the bending moment (M f ) and shear force (T), and periodically apply loads to all arms of the hub through the three-way loading mechanism of the central part; during the load application process, the bending moment strain output on the rotor simulation shaft is the strain value με. Through the obtained proportional coefficient k, the actual bending moment at this location can be directly derived as M=με / k. Step 5. One end of the rotor simulation shaft is fixed and the other end is loaded. This loading can be simplified into a cantilever beam. Therefore, as long as the bending moment at no less than two points in the middle is obtained, the bending moment values ​​at other positions can be obtained. The bending moment M obtained by the B01, B03, and B05 strains of the 0° section on the rotor simulation shaft is obtained by linear interpolation calculation method to obtain the bending moment at any point on the shaft, and thus the bending moment at the center of the hub (M) is obtained. f ); Step 6. Since the bending moment on the simulated shaft is a straight line of linear proportion, the shear force is a constant; the shear force (T) at the center of the hub is the shear force on the rotor simulation shaft. The slope of the curve can be calculated by linear interpolation, which is the shear force (T) on the rotor simulation shaft.

2. The method according to claim 1, characterized in that The cross sections include A section, B section and C section.

3. The method according to claim 2, characterized in that Keep a certain distance of about 15-20cm away from the arc transition at the bottom and the chamfer at the top of the rotor simulation shaft to avoid abnormal and nonlinear strain data due to local stress concentration in the structure.

4. The method according to claim 3, characterized in that The method further comprises: After a preliminary resistance measurement and inspection of the pasted strain gauges, a Wheatstone full-bridge resistor is formed in a full-bridge manner.

5. The method according to claim 4, characterized in that The cantilever beam loading calibration requires that a special device be used during the calibration process to make the loading load perpendicular to the pasting section of the calibration strain gauge and the axis of the simulation shaft to avoid the calibration load and the strain gauge and the axis of the simulation shaft not coinciding in the same plane, generating components in other directions, and causing inaccurate calibration data; during the data processing process, the cantilever beam calculation method needs to be used to obtain the theoretical bending moment value applied to the cross section at each step of the calibration load, and then compared one by one with the actual strain output data value to obtain a proportional coefficient between the strain value and the bending moment value.

6. The method according to claim 5, characterized in that The three-way loading mechanism realistically simulates the stress process of the central component during flight, and applies a variety of composite loads loaded in phase, so that the load on the rotor simulation shaft around the axis is a uniformly distributed rotational load.

7. The method according to claim 6, characterized in that The linear proportional straight line is obtained by fitting the multi-point bending moment values ​​obtained on the simulation axis, and the variation law of the bending moment curve can be obtained, which can also be defined by converting it into a formula.

8. The method according to claim 1, characterized in that The method further comprises: Step 7. In order to improve data reliability and calculation accuracy, the hub linear interpolation calculation method adopts the double redundancy calculation method, that is, the same bending moment strain is arranged at 90 degrees of the orthogonal section of the simulated shaft. Through theoretical analysis, it can be obtained that the strain values ​​B01 and B02 at the same position on the shaft are equal, B03 and B04 are equal, and B05 and B06 are equal. The two groups of strain gauges B01, B03, B05 and B02, B04, B06 can be linearly interpolated respectively. Step 8: As mentioned above, the bending moments (M) calculated for the 0-degree section and the 90-degree section are f ) and shear force (T) should be equal in theory; Step 9: During the test, the bending moment (M) at the hub center is monitored in real time by simulating the strain output values ​​of each section on the shaft. f ) and shear force (T), and also adjust the bending moment (M) required for the test in time through the three-way load applied by the hub support arm f ) and shear force (T), and the helicopter hub center load linear interpolation calculation method is used to ensure the hub test is carried out effectively.

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