A method for obtaining a hub center load of a helicopter

Abstract

The application provides a method for obtaining the hub center load of a helicopter, which comprises the following steps: pasting no less than three groups of strain gauges on the orthogonal cross sections (0 degree and 90 degree) of a rotor simulation shaft; calibrating the proportional relationship between the strain output and the actual bending moment before the test through a cantilever beam loading method; and then obtaining the bending moment (M f ) and the shear force (T) at the hub center through a linear interpolation calculation method. The calculation method can obtain the required hub center bending moment (M f ) and shear force (T) through adjusting the three-way loading load of the multiple supporting arms in the hub central part.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of the bending moment (Mf) and shear force (T) calculation of the hub center of a helicopter, and particularly relates to a method for obtaining the load of the hub center of a helicopter. BACKGROUND

[0002] The hub of a helicopter is one of the core components of the rotor system of the helicopter and is a key load-bearing component on the helicopter, which bears the centrifugal force, lift, flapping force, lead-lag force and damper force transmitted by the blades. The stress condition of the hub is very complex. Therefore, the fatigue life of the central part directly affects the service life of the entire helicopter, and the performance of the central part directly affects the strength of the helicopter and flight safety.

[0003] In the fatigue test of the hub central part, various complex overall loads and local loads are included. Centrifugal force loading points, lead-lag loading points, flapping loading points and damper force loading points are usually designed on each arm to achieve the application of loads. For the central dynamic load M f , T of the hub central part, due to the space and shape restrictions, bending moment and torque measuring pieces cannot be arranged, so the load M f , T can only be measured by the extended rotor simulation shaft. That is, by monitoring the strain value on the rotor simulation shaft, it is determined whether the central test load of the hub central part meets the design index requirements, so it is necessary to establish an accurate mathematical model method to decouple the central dynamic load M f , T of the hub central part by using mechanical knowledge. SUMMARY

[0004] The application aims to provide a high-precision and high-reliability linear interpolation calculation method for the central load of the hub of a helicopter.

[0005] The application provides a method for obtaining the central load of the hub of a helicopter, which comprises the following steps:

[0006] Step 1. At different cross-section positions on the 0-degree cross-section of the rotor simulation shaft, a certain distance from the bottom and the top, appropriate spacing is selected, and not less than 3 groups of bending moment measuring strain pieces are arranged;

[0007] Step 2. The strain pieces are pasted at the determined patch positions, and the pasting process should comply with the strain piece pasting process regulations;

[0008] Step 3. The rotor simulation shaft is loaded and calibrated in a cantilever beam mode, the actuator is used to apply a calibration load, the relationship between the bending moment and the strain of the corresponding cross-section on the rotor simulation shaft is calibrated, the calibration is processed by using the average value data of three calibrations, the relationship between the actual bending moment M and the strain output με of the rotor simulation shaft is determined, and the proportional coefficient k of each group of full-bridge strain is obtained. = με / M;

[0009] Step 4, in the process of fatigue test of the central part, in order to obtain the bending moment (M f ) and shear force (T) of the hub center, periodic load is applied to all the arms of the hub by the three-way loading mechanism of the central part; in the process of load application, the bending moment strain output of the rotor simulation shaft is strain value με, and the actual bending moment at the position can be directly obtained by the obtained proportional coefficient k, that is, M = με / k.

[0010] Step 5, one end of the rotor simulation shaft is fixed, and the other end is loaded, which can be simplified as a cantilever beam, so as to obtain the bending moment at other positions by obtaining the bending moment at any two or more points in the middle. The bending moment M obtained by the strain of B01, B03 and B05 of the 0° section of the rotor simulation shaft is obtained by linear interpolation calculation method, and the bending moment at any point on the shaft is obtained, that is, the bending moment (M f ) at the hub center is obtained.

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

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

[0013] Preferably, the distance away from the bottom arc transition and the top chamfer of the rotor simulation shaft is about 15-20 cm, so as to avoid abnormal and nonlinear strain data caused by local stress concentration of the structure.

[0014] Preferably, the method further comprises:

[0015] After the preliminary resistance measurement inspection of the pasted strain gauge, the Wheatstone full-bridge resistance is formed in full-bridge mode.

[0016] Preferably, in the process of cantilever beam loading calibration, a special device is 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 that the calibration load and the strain gauge and the axis of the simulation shaft do not coincide in a plane, and other directional components are generated, which leads to inaccurate calibration data; in the data processing process, the theoretical bending moment value of each step of the calibration load applied to the cross section is obtained by the calculation method of the cantilever beam, and then compared with the actual strain output data value, so as to obtain a proportional coefficient of strain value and bending moment value.

[0017] Preferably, the three-way loading mechanism truly simulates the force process of the central part in the flight process, and applies a variety of composite loads according to the phase, so that the circumferential load around the axis of the rotor simulation shaft is uniform rotation load.

[0018] Preferably, the linear proportion straight line is obtained by fitting the obtained multi-point bending moment values on the simulation shaft, and the bending moment curve variation law can be obtained, and the bending moment curve variation law can be defined by conversion into a formula.

[0019] Preferably, the method further comprises:

[0020] Step 7, in order to improve data reliability and calculation accuracy, the paddle hub linear interpolation calculation method adopts a dual-redundancy calculation method, that is, the same bending moment strain is arranged at the 90-degree orthogonal section of the simulation shaft, and 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, and the two groups of strain gauges B01, B03, B05 and B02, B04, B06 can be linearly interpolated and calculated respectively;

[0021] Step 8, as known from the foregoing, the bending moment (M f ) and the shear force (T) calculated by the 0-degree section and the 90-degree section respectively should be equal in theory;

[0022] Step 9, during the test, not only the bending moment (M f ) and the shear force (T) of the paddle hub center are monitored in time through the strain output values of each section on the simulation shaft, but also the three-way load applied by the paddle hub support arm is used to adjust the bending moment (M f ) and the shear force (T) required by the test in time, and the helicopter paddle hub center load linear interpolation calculation method is used to ensure that the paddle hub test is effectively carried out.

[0023] The application has the following technical effects:

[0024] The helicopter paddle hub center load linear interpolation calculation method can greatly simplify the calculation of the paddle hub center test load, improve the accuracy of the paddle hub center test load, shorten the test period and save costs. The helicopter paddle hub central fatigue test is carried out by using the method, the test load is stable and reliable, and the helicopter paddle hub center can meet the requirement of applying various complex test loads. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Central part schematic diagram;

[0026] Figure 2 Test load phase relationship schematic diagram;

[0027] Figure 3 Rotor simulation shaft patch diagram;

[0028] Figure 4 Bending moment and shear force linear difference diagram. DETAILED DESCRIPTION

[0029] Aiming at the calculation requirement of large load test of helicopter hub central part, a high-precision and high-reliability linear interpolation calculation method of hub center load is provided. The method is to paste not less than 3 groups of strain gauges on the orthogonal cross section (0 degree and 90 degree) of the rotor simulation shaft. Before the test, the proportional relationship between the strain output and the actual bending moment is calibrated through the cantilever beam loading method, and then the bending moment (M f ) and shear force (T) at the hub center can be obtained through the linear interpolation calculation method. The calculation method can obtain the required bending moment (M f ) and shear force (T) at the hub center by adjusting the three-way load of the multiple arms in the hub central part.

[0030] The test shows that the calculation method can meet the load calculation requirement of helicopter central fatigue test, and has the advantages of simple calculation, low environmental requirement, fast processing speed, high measurement accuracy, etc., which can shorten the test period, speed up the test efficiency, save the test cost, and well meet the load calculation requirement of helicopter hub fatigue test.

[0031] Please refer to Figures 1-4 , a linear interpolation calculation method for the bending moment (M f ) and shear force (T) at the hub center of the helicopter is invented according to the load characteristics and structural characteristics of the helicopter.

[0032] The bending moment M f and shear force T at the hub center can be accurately calculated through the calculation method. The calculation method greatly simplifies the load loading method, so that the bending moment and shear force at the hub center can be obtained by the conventional three-way loading mechanism of the hub arm. The calculation method improves the test load loading and measurement accuracy, shortens the test period, and meets the load loading requirement of the helicopter hub central part.

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

[0034] Step 1, on the 0 degree cross section of the rotor simulation shaft, select appropriate spacing at the cross section position at a certain distance from the bottom and top, and arrange not less than 3 groups of bending moment measurement strain gauges. For example, A cross section, B cross section, C cross section, see Figure 3 Rotor simulation shaft patch diagram.

[0035] Among them, the certain distance should avoid the bottom arc transition and top chamfer of the rotor simulation shaft by about 15-20 cm, so as to avoid 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 be evenly distributed on the effective length of the simulation shaft, so that the force arm is equal multiple increment, and the linear error is avoided due to the different spacing.

[0036] Step 2: Attach the strain gauges to the designated locations, following the strain gauge attachment process. After a preliminary resistance measurement and inspection of the attached strain gauges, a full-bridge Wheatstone resistor is constructed. This bridge configuration offers high sensitivity, excellent strain resistance, and eliminates the effects 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 for each group of full-bridge strain.

[0038] Cantilever beam loading calibration requires a dedicated device to ensure that the load is perpendicular to the cross-section of the calibration strain gauge and the axis of the simulation shaft during the calibration process. This prevents the calibration load, strain gauge, and simulation shaft axes from being aligned, which could generate force components in other directions and lead to inaccurate calibration data. During data processing, the cantilever beam calculation method is used to determine the theoretical bending moment value applied to the cross-section at each calibration load step. This is then compared with the actual strain output data 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), cyclically applying loads to all hub arms via the central component's three-dimensional loading mechanism. During the load application process, the bending moment and strain output on the rotor simulation shaft is a strain value με. Using the resulting proportionality factor k, the actual bending moment at that location can be directly calculated 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 multiple composite loads loaded in phase, so that the load on the rotor simulation axis around the axis is a uniformly distributed rotational load. Figure 2 As shown in the figure, the bending moment cannot be calculated for this complex load. In this case, the strain value of each section can be obtained by measuring equipment. Adding the proportional coefficient K obtained in step 3 above, the actual bending moment of the section can be calculated using the formula.

[0041] Step 5: One end of the rotor simulation shaft is fixed and the other end (test piece mounting end) is loaded. This loading can be simplified into a cantilever beam form. Therefore, as long as the bending moment of at least 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 hub center (M f ).

[0042] Step 6, since the bending moment on the simulation shaft is a linear proportion straight line, the shear force is a constant value. The shear force (T) at the center of the hub is the shear force on the simulation shaft of the rotor, which can be calculated by linear interpolation method to calculate the slope of the curve, that is, the shear force (T) on the simulation shaft of the rotor.

[0043] Wherein, the linear proportion straight line is obtained by fitting the bending moment values obtained on the simulation shaft, that is, the bending moment curve variation law can be obtained, and the formula can be defined by transformation.

[0044] Step 7, in order to improve the data reliability and calculation accuracy, the hub linear interpolation calculation method adopts double redundancy calculation method. That is, the same bending moment strain is arranged at the 90-degree orthogonal section of the simulation 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 (see Figure 3 ), and two groups of strain gauges (B01, B03, B05) and (B02, B04, B06) can be calculated by linear interpolation respectively.

[0045] Step 8, as known from the foregoing, the bending moment (M f ) and shear force (T) calculated by the 0-degree section and the 90-degree section respectively should be equal in theory. Due to the installation error of the test piece, the machining error of the test fixture, the measurement error of the control system, the measurement error of the strain gauge and the like, there is a certain difference between the theoretically calculated load and the feedback combined load, and the error is controlled to be within 3% according to the design requirement.

[0046] Step 9, during the test, not only the bending moment (M f ) and shear force (T) at the center of the hub can be monitored in time through the strain output values of each section on the simulation shaft, but also the three-way load applied by the hub support arm can be adjusted in time to adjust the bending moment (M f ) and shear force (T) required by the test. Through the linear interpolation calculation method of the helicopter hub center load, the hub test can be effectively carried out.

[0047] The helicopter hub center load linear interpolation calculation method can greatly simplify the calculation of the hub center test load, improve the hub center test load accuracy, shorten the test period and save the cost. The helicopter hub central fatigue test is carried out by using the method, the test load is stable and reliable, and the helicopter hub center can meet the requirement of applying various complex test loads.

Claims

1. A method for obtaining helicopter hub center load, characterized in that: The method comprises: Step 1: Arrange at least three sets of bending moment measurement strain gauges at appropriate intervals at different cross-sectional positions at the 0-degree cross-section on the rotor simulation axis and at cross-sectional positions at a certain distance from the bottom and top. 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 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. The proportional coefficient k = µε / M for each group of full-bridge strain is obtained. Step 4, in the process of fatigue test of the central piece, in order to get the bending moment M of the hub center f and shear T, all the arms of the hub are subjected to periodic load by the three-way loading mechanism of the central piece; in the process of load application, the bending moment strain output on the rotor simulation shaft is strain value µε, and through the obtained proportional coefficient k, the actual bending moment at the place can be directly obtained as M=µε / k; Step 5, one end of the rotor simulation shaft is fixed, and the other end is loaded, which can be simplified as a cantilever beam, so as to obtain the bending moment value at other positions as long as the bending moment of any not less than two points in the middle is obtained; the bending moment M obtained through the strain of B01, B03 and B05 of the 0° section of the rotor simulation shaft is used to obtain the bending moment at any point on the shaft by using linear interpolation calculation method, and the bending moment M at the center of the hub is obtained f ; Step 6. Since the bending moment on the simulated shaft is a linearly proportional straight line, the shear force is a constant value. The shear force T at the hub center is the shear force on the rotor simulated shaft. The slope of the curve can be calculated by linear interpolation, which is the shear force T on the rotor simulated shaft. The arc transition at the bottom and the chamfer at the top of the rotor simulation shaft should be kept at a certain distance of about 15-20 cm to avoid abnormal and nonlinear strain data due to local stress concentration in the structure. The method further comprises: After preliminary resistance measurement and inspection of the pasted strain gauges, a Wheatstone full-bridge resistor is formed in full-bridge mode; Among them, the cantilever beam loading calibration requires that during the calibration process, a special device is used to ensure that the loading load is perpendicular to the bonding section of the calibration strain gauge and the axis of the simulation shaft. This prevents the calibration load from not coinciding with the strain gauge and the axis of the simulation shaft in the same plane, generating components in other directions and causing inaccurate calibration data. During the data processing process, the cantilever beam calculation method is used to obtain the theoretical bending moment value applied to the cross section at each step of the calibration load, and then a one-to-one comparison is made with the actual strain output data value to obtain a proportional coefficient between the strain value and the bending moment value. The three-way loading mechanism realistically simulates the stress process of the centerpiece during flight, applying multiple phased composite loads so that the load on the rotor simulation shaft around the axis is a uniformly distributed rotational load. 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.

2. The method of claim 1, wherein, The sections include section A, section B, and section C.

3. The method of claim 1, wherein, The method further comprises: Step 7. 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 sets of strain gauges B01, B03, B05 and B02, B04, B06 can be linearly interpolated respectively. Step 8, the bending moment M calculated by the 0 degree profile in Step 5 and the 90 degree profile in Step 7, respectively f and the shear force T, the bending moment M f and the shear force T should be theoretically equal; Step 9, during the test, not only through the simulation of the strain output value of each profile on the shaft to monitor the bending moment M f and shear T of the hub center in time, but also through the three-way load applied by the hub arm, the bending moment M f and shear T required for the test are adjusted in time to ensure the effective performance of the hub test through the linear interpolation calculation method of the helicopter hub center load.

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