A coaxial dual-rotor helicopter shaft bending moment load calculation method

Abstract

The application belongs to the field of decoupling calculation of bending moment of rotating structure, and particularly relates to a coaxial dual-rotor helicopter shaft bending moment load calculation method, axial tension Fy, torque My, longitudinal bending moment Mx and transverse bending moment Mz calibration are carried out, inner and outer shaft strain-load conversion coefficient matrixes are obtained, the inner shaft and the outer shaft are combined, the top flange gap of the inner and outer shafts is aligned, the direction from the center of the top end face to the centerline of the gap is X direction, the inner shaft is subjected to static loading, the outer shaft strain coupling response is obtained, and then the inner shaft-outer shaft coupling response coefficient is obtained; the strain load measured in the inner and outer shaft rotating coordinate system is converted to the body coordinate system; in the body coordinate system, the shaft bending moment load of the inner shaft and the coupling shaft bending moment load of the inner shaft to the outer shaft are calculated; in the body coordinate system, the shaft bending moment load of the outer shaft is calculated, and the coupling shaft bending moment load of the inner shaft to the outer shaft is eliminated, and the real shaft bending moment load of the outer shaft is obtained.

Description

Technical Field

[0001] This invention belongs to the field of decoupled calculation of bending moment for rotating structural components in mechanics of materials, and particularly relates to a method for calculating the axial bending moment load of a coaxial twin-rotor helicopter. Background Technology

[0002] Compared to conventional single-rotor helicopters with a tail rotor, the control trim strategy for coaxial high-speed helicopters is more complex. Achieving good attitude sensitivity in the control trim strategy is an essential prerequisite for designing a control effectiveness strategy using coaxial dual rotors. The pitch and roll moments of the upper and lower rotors of a coaxial helicopter are key parameters for evaluating its control effectiveness. Currently, these four parameters are calculated using the following steps: ① Two sets of orthogonally distributed full-bridge moment strain gauges are attached to the inner and outer shafts of the coaxial dual rotors respectively; ② The sensitivity coefficients of the two sets of full-bridge moment strain gauges on the inner and outer shafts are obtained through loading and calibration on the inner and outer shafts; ③ The load response of the full-bridge moment strain gauges on the inner and outer shafts is measured under rotation; ④ Fourier series expansions are performed on the two sets of moment loads on the inner and outer shafts respectively, and the moment amplitudes in the 0°-180° azimuth are selected as the pitch moment and the moment amplitudes in the 90°-270° azimuth are selected as the roll moment.

[0003] However, the inner shaft bending moment (upper rotor pitch / roll moment) response and the outer shaft bending moment (lower rotor pitch / roll moment) response are coupled and dynamically rotate. Therefore, the current calculation method often has a large error when calculating the outer shaft bending moment. Summary of the Invention

[0004] The technical problem solved by this invention is that current calculation methods often have large errors when calculating the external shaft bending moment. This invention addresses the problem of large errors in external shaft bending moment calculation by providing a vector decomposition-based method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter. This method obtains the mapping matrix between the internal and external shaft bending moment loads and the corresponding strain gauges through static calibration. Furthermore, based on the mapping matrix, the bending moment load response results of the decoupled calculation of the internal and external shafts under rotational conditions are obtained. Further, the direction of the internal and external shaft bending moment vectors at the current azimuth is obtained through a 0-azimuth pulse signal. Based on the principle of vector decomposition, the bending moment loads of the upper and lower rotors in the hub coordinate system are transformed into the pitch and roll moment loads of the upper and lower rotors in the body coordinate system, thereby achieving high-precision calculation of the pitch and roll moments of the upper and lower rotors.

[0005] The technical solution of the present invention: A method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter, the method comprising: S1. After the inner and outer shafts are fitted with patches, they are fixed on the calibration bench. The point of application of the applied torque is set at the center of the lower rotor hub using the calibration fixture. The axial tension Fy, torque My, longitudinal bending moment Mx, and lateral bending moment Mz are calibrated to obtain the strain-load transformation coefficient matrix of the inner and outer shafts. , ; S2, combine the inner shaft and the outer shaft, align the notches on the top flanges of the inner and outer shafts, and apply static loading to the inner shaft in the direction X, from the center of the top end face to the centerline of the notch, to obtain the strain coupling response of the outer shaft, and thus obtain the inner shaft-outer shaft coupling response coefficient. ; S3, converts the strain load measured in the inner and outer axis rotating coordinate system to the body coordinate system; S4. In the body coordinate system, calculate the axial bending moment load of the inner shaft and the coupled axial bending moment load of the inner shaft to the outer shaft. S5. In the body coordinate system, calculate the axial bending moment load of the outer shaft and eliminate the coupled axial bending moment load of the inner shaft to the outer shaft to obtain the true axial bending moment load of the outer shaft.

[0006] Furthermore, the upper rotor telemetry data acquisition unit is installed on the upper rotor blade and the lower rotor telemetry data acquisition unit respectively; and strain gauges are attached to the upper and lower rotor shafts respectively; the upper rotor telemetry data acquisition unit and the lower rotor telemetry data acquisition unit are two sets of blade strain load acquisition units that are synchronously acquired, and are used to acquire the strain signals of the upper rotor blade with attached strain gauges and the lower rotor blade with attached strain gauges respectively; the photoelectric pulse sensor is arranged at a preset position on the top of the fuselage, and the photoelectric pulse sensor is installed vertically upward, and the upper and lower rotor shafts are respectively referred to as the inner and outer shafts.

[0007] Furthermore, S1 specifically refers to: After the outer shaft is patched, it is fixed on the calibration stand, and the point of application of the applied torque is set at the center of the lower rotor hub by the calibration fixture. The axial tensile force Fy, torque My, longitudinal bending moment Mx, and lateral bending moment Mz were calibrated. The loading directions included both positive and negative directions, and the calibration load amounts in each direction were divided into m levels, where m≥5. The tension of the outer shaft was then obtained for the full-bridge combination. Torque axle combination Longitudinal bending moment full bridge combination and lateral bending moment full bridge combination Based on the 4×(m+1) group of load and strain responses under various loading conditions, the external shaft strain-load transformation coefficient matrix is ​​obtained. ; The inner shaft was statically calibrated by applying a load, and the point of application of the loading torque was fixed at the center of the rotor hub using a calibration fixture. The loading direction, magnitude, and number of load stages were exactly the same as those for the outer shaft. Based on 4×(m+1) sets of calibration loads and strain responses, the strain-load transformation coefficient matrix of the inner shaft was obtained. .

[0008] Furthermore, S2 specifically refers to: Combine the inner and outer shafts, aligning the notches on the top flanges of the inner and outer shafts. The direction from the center of the top end face to the centerline of the notch is defined as the X-axis. The loading position, load, and direction are the same as in the inner shaft calibration process. Perform static loading on the inner shaft to obtain the strain coupling response of the outer shaft. Multiply by the external axis strain-load transformation coefficient matrix The coupled load response of the outer shaft is obtained, and then divided by the rated load. Obtain the inner-axis-outer-axis coupling response coefficients .

[0009] Furthermore, S3 specifically refers to: Record the average response of the entire strain bridge of the inner and outer shafts at low speeds for no less than 10 revolutions as the initial dynamic reading, and obtain the combined response value of the entire strain bridge of the inner and outer shafts after deducting the initial dynamic reading in all subsequent rotational states. and ; The inner and outer shafts are mounted on a coaxial helicopter. The rotor blades are rotated in a static state to trigger the photoelectric pulse sensor, and the initial azimuth angles of the top flange notches of the inner and outer shafts are measured. and ; The rotor telemetry data acquisition unit and the lower rotor telemetry data acquisition unit are set to the same sampling rate S for fixed-frequency acquisition. When the rotor speed is stable at N, the photoelectric pulse sensor acquires the phase of the sampling point between two consecutive pulse rising edges, which is uniformly distributed. The phase angle of each sampling point in one revolution is obtained by calculating the sampling point between the two pulse rising edges. The specific method is as follows: Based on the rising edge of the continuous pulse signal acquired by the photoelectric pulse sensor, the combined strain values ​​of the inner shaft and the outer shaft are extracted in whole cycles. The first sampling point after exceeding the first rising edge threshold is the initial azimuth angle of the flange notch at the top of the inner shaft and the outer shaft. and Since the inner axis rotates in the positive direction, the phase of the full-bridge strain values ​​on the inner axis increases point by point. The outer shaft rotates in the opposite direction, therefore the phase of the full-bridge strain values ​​on the outer shaft decreases point by point. By analogy, the phase angle corresponding to the nth strain full-bridge numerical point of the inner axis and the outer axis in a series of sampling points is obtained. and

[0010]

[0011] .

[0012] Furthermore, in S4, the axial bending moment load of the inner shaft is calculated in the body coordinate system, specifically as follows: Since the loads in all directions on the outer shaft will not cause a coupled response to the strain full-bridge combination on the inner shaft, the loads on the inner shaft are calculated first. The strain full-bridge combination value of the nth sampling point of the inner axis in a ring of sampling points. Multiply by the inner axis strain-load transformation coefficient matrix The longitudinal and transverse axial bending moment loads under the rotational coordinates of the propeller hub are obtained. ; Based on the azimuth angle of the inner axis By performing a transformation from the rotating coordinate system to the body coordinate system, the longitudinal and transverse bending moment loads of the inner shaft 4 in the body coordinate system are obtained. .

[0013] Furthermore, in S4, in the body coordinate system, the coupled axial bending moment load of the inner shaft to the outer shaft is calculated, specifically as follows: Multiply the axial bending moment load of the inner shaft by the inner shaft-outer shaft coupling response coefficient. Longitudinal and transverse axis bending moment coupled response coefficient elements The coupled longitudinal and transverse axial bending moment loads of the inner shaft to the outer shaft in the body coordinate system are obtained. .

[0014] Furthermore, S5 specifically refers to: The strain full-bridge combination value of the nth sampling point of the outer axis in a ring of sampling points. Multiply by the external axis strain-load transformation coefficient matrix The longitudinal and transverse axial bending moment loads in the rotational coordinates of the lower rotor hub are obtained. Based on the azimuth angle of the outer axis A transformation from the rotating coordinate system to the body coordinate system is performed to obtain the longitudinal and transverse bending moment loads of the outer shaft in the body coordinate system. Then, the coupled longitudinal and transverse bending moment loads of the inner shaft on the outer shaft in the body coordinate system are subtracted. Obtain the longitudinal and transverse bending moment loads of the outer shaft in the body coordinate system. .

[0015] This method solves the system of linear equations relating tension, torque, longitudinal axial bending moment, and transverse axial bending moment to obtain the external shaft strain-load transformation coefficient matrix. and the inner axis strain-load transformation coefficient matrix The linear fit is higher, which significantly improves the measurement accuracy of longitudinal and transverse bending moment loads. This method considers the coupling response of the inner shaft longitudinal and transverse bending moment loads to the outer shaft longitudinal and transverse bending moment loads, further improving the measurement accuracy of the outer shaft longitudinal and transverse bending moment loads. Attached Figure Description

[0016] Figure 1 Schematic diagram of inner and outer shaft patch; Figure 2 This is a schematic diagram of single-axis loading calibration for both inner and outer shafts. Figure 3 This is a schematic diagram of the loading calibration of the inner and outer shafts. Figure 4 This is a schematic diagram showing the initial orientation of the inner and outer shaft flange notches (X-axis) when the TOP signal is triggered; Figure 5 This is a schematic diagram showing the decoupled calculation results of pitching moment and rolling moment. Detailed Implementation

[0017] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] The technical solution of this invention is based on two sets of full-bridge bending moment load strain signals and 0-azimuth pulse signals that are orthogonally distributed and pasted on the inner and outer shafts of a coaxial dual-rotor helicopter. It has invented a method for calculating the shaft bending moment load of a coaxial dual-rotor helicopter based on vector decomposition, which significantly improves the calculation accuracy of the pitching moment and rolling moment of the inner and outer shafts of the coaxial dual-rotor.

[0019] The hardware system involved in the coaxial twin-rotor helicopter shaft bending moment load calculation method provided in this embodiment of the invention includes: an upper rotor telemetry acquisition device 1, a lower rotor telemetry acquisition device 2, a photoelectric pulse sensor 3, an inner shaft (upper rotor) 4, and an outer shaft (lower rotor) 5.

[0020] The upper rotor telemetry data acquisition unit 1 and the lower rotor telemetry data acquisition unit 2 are two sets of blade strain load data acquisition units that are synchronized. They are used to acquire strain signals from the inner shaft 4 of the upper rotor and the outer shaft 5 of the lower rotor, respectively. The installation positions are selected at the hubs of the upper and lower rotors, the closer to the center of rotation the better. The nonlinearity error of the data acquisition unit is no higher than 0.1%, and the clock error between the two sets of data acquisition units is no more than 100 microseconds.

[0021] like Figure 1As shown, the inner shaft 4 of the (upper rotor) has its centerline at the missing tooth of the top spline as 0°. Parallel double-plate strain gauges 6 are attached to the N1 section (0 section is the top of the inner shaft 4) at four positions along the rotation direction of the upper rotor: 0°, 90°, 180°, and 270°. The parallel double-plate strain gauges 6 at 0° and 180° form a longitudinal bending moment bridge BU1P, and the parallel double-plate strain gauges 6 at 90° and 270° form a transverse bending moment bridge BU1N. Similarly, parallel double-plate strain gauges 6 are attached to the same four positions on the N2 section. The parallel double-plate strain gauges 6 at 0° and 180° form a longitudinal bending moment bridge BU2P, and the parallel double-plate strain gauges 6 at 90° and 270° form a transverse bending moment bridge BU1N. Parallel double-strain gauges 6 form a transverse bending moment full bridge BU2N; "V-type" double-strain gauges 7 are attached to the same four positions on the N3 section, forming a torque full bridge BUTQ1 with "V-type" double-strain gauges 7 at 0° and 180°, and forming a torque full bridge BUTQ2 with "V-type" double-strain gauges 7 at 90° and 270°; "T-type" double-strain gauges 8 are attached to the four positions on the N3 section at 45°, 135°, 225° and 315°, forming a tension full bridge BUT1 with "T-type" double-strain gauges 8 at 45° and 225°, and forming a tension full bridge BUT2 with "T-type" double-strain gauges 8 at 135° and 315°.

[0022] like Figure 1 As shown, the outer shaft 5 of the (lower rotor) has its center line at the missing tooth of the top spline as 0°. Parallel double-plate strain gauges 6 are attached to the N4 sections (0 section is the top of the outer shaft 5) at four positions along the rotation direction of the lower rotor: 0°, 90°, 180° and 270°. The parallel double-plate strain gauges 6 at 0° and 180° form a longitudinal bending moment full bridge BL1P, and the parallel double-plate strain gauges 6 at 90° and 270° form a transverse bending moment full bridge BL1N. Similarly, parallel double-plate strain gauges 6 are attached to the same four positions on the N5 section. The longitudinal bending moment full bridge BL2P is composed of parallel double-plate strain gauges 6 at 0° and 180°, and the transverse bending moment full bridge BL2N is composed of parallel double-plate strain gauges 6 at 90° and 270°. "V-type" double-plate strain gauges 7 are attached to the same four positions on the N6 section. The torque full bridge BLTQ1 is composed of "V-type" double-plate strain gauges 7 at 0° and 180°, and the torque full bridge BLTQ2 is composed of "V-type" double-plate strain gauges 7 at 90° and 270°. "T-type" double-plate strain gauges 8 are attached to the four positions on the N6 section at 45°, 135°, 225° and 315°. The tension full bridge BLT1 is composed of "T-type" double-plate strain gauges 8 at 45° and 225°, and the tension full bridge BLT2 is composed of "T-type" double-plate strain gauges 8 at 135° and 315°.

[0023] The typical resistance value of the dual-plate strain gauges 6, 7, and 8 is 350Ω. The strain gauge temperature self-compensating material is alloy steel, the sensitivity coefficient dispersion is ≤±1%, and the fatigue life is ≥ .

[0024] The photoelectric pulse sensor 3 has a measurement range of no less than 2 meters and a response time of no more than 300 microseconds. The photoelectric pulse sensor 3 is arranged at a 160° azimuth position on the top of the fuselage, with the sensor installed vertically upwards. Select any lower rotor blade and rotate it to the 160° azimuth position, which is directly above the photoelectric pulse sensor 3. The laser emitted by the photoelectric pulse sensor 3 hits the lower surface of the lower rotor blade. A 10 cm (length) × 2 cm (width) reflective paper is pasted along the span of the lower surface of the rotor blade with the laser reflection point as the center.

[0025] A method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter, wherein the method is applied in the aforementioned hardware environment.

[0026] After the outer shaft 5 (lower rotor) is fitted with patches, it is fixed on the calibration bench. The point of application of the loading torque is set at the center of the lower rotor hub using a calibration fixture. Axial tension Fy, torque My, longitudinal bending moment Mx, and lateral bending moment Mz are calibrated. The principal axis coordinate system and the load loading direction are as follows: Figure 2 As shown, the loading direction includes both positive and negative directions (tension direction is positive). The rated load for each direction is divided into m (m≥5) levels (excluding zero point), i.e., 0, , … 100%, to obtain the tension full-axle assembly of the (lower rotor) outer shaft 5. (BL1T+BL2T), Torque Axle Combination (BLTQ1 + BLTQ2), longitudinal bending moment full bridge combination (BL1P+BL2P) and the full bridge combination with lateral bending moment The strain response of (BL1N+BL2N) under various loading conditions is obtained by solving the linear equation system (Equation 1) based on the 4×(m+1) set of load and strain responses to obtain the external shaft strain-load transformation coefficient matrix. :

[0027]

[0028] Furthermore, similar to step 1, static loading calibration is performed on the inner shaft 4 (upper rotor). The point of application of the loading torque is fixed at the center of the upper rotor hub using a calibration fixture. The loading direction, magnitude, and number of loading stages of the calibration load are exactly the same as in the previous step. Similarly, a linear equation system is solved based on 4×(m+1) sets of calibration loads and strain responses to obtain the inner shaft strain-load transformation coefficient matrix. ;

[0029] Furthermore, the inner shaft 4 (upper rotor) and the outer shaft 5 (lower rotor) are combined, as follows: Figure 3 As shown, align the notches on the top flanges of the inner and outer shafts. The direction from the center of the top end face to the centerline of the notch is the X-axis. The loading position, load, and direction are the same as in step 2. Perform static loading on the inner shaft 4 (upper rotor) to obtain the strain coupling response of the outer shaft 5 (lower rotor). Multiply by the external axis strain-load transformation coefficient matrix The coupled load response of the (lower rotor) outer shaft 5 can then be obtained. Then divide by the rated load respectively. The inner-outer-axis coupling response coefficients can then be obtained. ;

[0030] Furthermore, the average response values ​​of all strain bridges of the (upper rotor) inner shaft 4 and the (lower rotor) outer shaft 5 at low speeds (below 30 rpm) for no less than 10 revolutions are recorded as the initial dynamic readings. Then, in all subsequent rotational states, the combined response values ​​of the strain bridges of the (upper rotor) inner shaft 4 and the (lower rotor) outer shaft 5, after deducting the initial dynamic readings, are obtained. and ; Furthermore, the inner shaft 4 (upper rotor) and the outer shaft 5 (lower rotor) are mounted on a coaxial helicopter. The rotor blades are rotated in a static state to trigger the photoelectric pulse sensor 3, and the initial azimuth angle of the top flange notch of the inner shaft 4 (upper rotor) and the outer shaft 5 (lower rotor) is measured. and ;,like Figure 4 As shown.

[0031] Furthermore, the rotor telemetry acquisition unit 1 and the lower rotor telemetry acquisition unit 2 are set to the same sampling rate S for fixed-frequency acquisition. When the rotor speed is stable at N (rpm), it can be assumed that the phase of the sampling points between two consecutive rising edges of the pulse acquired by the photoelectric pulse sensor 3 is uniformly distributed. The phase information of each sampling point in one revolution is obtained by calculating the sampling points between the two rising edges of the pulse. The specific method is as follows: based on the rising edge of the continuous pulse signal acquired by the photoelectric pulse sensor 3, the strain full-bridge combination value of the (upper rotor) inner shaft 4 and the (lower rotor) outer shaft 5 is truncated to an integer cycle. The first sampling point after exceeding the first rising edge threshold is the initial azimuth angle of the top flange notch of the (upper rotor) inner shaft 4 and the (lower rotor) outer shaft 5. and Since the inner shaft 4 of the upper rotor rotates in the positive direction, the phase of the full-bridge strain values ​​of the inner shaft 4 of the upper rotor increases point by point. The outer shaft 5 of the (lower rotor) rotates in the opposite direction, therefore the phase of the full-bridge strain values ​​of the outer shaft 5 of the (lower rotor) decreases point by point. By analogy, the azimuth angles corresponding to the nth strain full-bridge numerical points of the (upper rotor) inner axis 4 and the (lower rotor) outer axis 5 in one sampling circle can be obtained. and

[0032]

[0033]

[0034] Furthermore, since the loads in all directions on the (lower rotor) outer shaft 5 will not cause a coupled response to the strain full-bridge combination on the (upper rotor) inner shaft 4, the load on the (upper rotor) inner shaft 4 is calculated first. The strain full-bridge combination value of the nth sampling point of the (upper rotor) inner shaft 4 in one revolution is used. Multiply by the inner axis strain-load transformation coefficient matrix The longitudinal and transverse axial bending moment loads under the rotational coordinates of the propeller hub can then be obtained. Based on the azimuth angle of the inner shaft 4 of the (upper rotor) By transforming the rotating coordinate system to the body coordinate system, the longitudinal and transverse bending moment loads of the (upper rotor) inner shaft 4 in the body coordinate system can be obtained. Then multiply the axial bending moment load of the inner shaft 4 (upper rotor) by the inner shaft-outer shaft coupling response coefficient. Longitudinal and transverse axis bending moment coupled response coefficient elements Thus, the coupled longitudinal and transverse axial bending moment loads of the inner shaft 4 (upper rotor) to the outer shaft 5 (lower rotor) in the airframe coordinate system can be obtained. ;

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] Furthermore, similar to the previous step, the strain full-bridge combination value of the nth sampling point of the (lower rotor) outer shaft 5 in the 1-circle sampling points is used. Multiply by the external axis strain-load transformation coefficient matrix This allows us to obtain the longitudinal and transverse axial bending moment loads in the rotor hub rotation coordinate system. Based on the azimuth angle of the (lower rotor) outer shaft 5 By transforming the rotating coordinate system to the body coordinate system, the longitudinal and transverse bending moment loads of the (lower rotor) outer shaft 5 in the body coordinate system can be obtained. Then, the coupled longitudinal and transverse bending moment loads of the (upper rotor) inner shaft 4 on the (lower rotor) outer shaft 5 in the body coordinate system can be subtracted. The longitudinal and transverse bending moment loads of the single external shaft in the body coordinate system can then be obtained. ;

[0041]

[0042]

[0043]

[0044] like Figure 5 The diagram shown is a schematic of the decoupling calculation results of pitch moment and roll moment.

[0045] This method solves the system of linear equations relating tension, torque, longitudinal axial bending moment, and transverse axial bending moment to obtain the external shaft strain-load transformation coefficient matrix. and the inner axis strain-load transformation coefficient matrix The linear fit is higher, which significantly improves the measurement accuracy of longitudinal and transverse bending moment loads. This method considers the coupling response of the inner shaft longitudinal and transverse bending moment loads to the outer shaft longitudinal and transverse bending moment loads, further improving the measurement accuracy of the outer shaft longitudinal and transverse bending moment loads.

Claims

1. A method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter, characterized in that, The method includes: S1. After the inner and outer shafts are fitted with patches, they are fixed on the calibration bench. The point of application of the applied torque is set at the center of the lower rotor hub using the calibration fixture. The axial tension Fy, torque My, longitudinal bending moment Mx, and lateral bending moment Mz are calibrated to obtain the strain-load transformation coefficient matrix of the inner and outer shafts. , ; S2, combine the inner shaft and the outer shaft, align the notches on the top flanges of the inner and outer shafts, and apply static loading to the inner shaft in the direction X, from the center of the top end face to the centerline of the notch, to obtain the strain coupling response of the outer shaft, and thus obtain the inner shaft-outer shaft coupling response coefficient. ; S3, converts the strain load measured in the inner and outer axis rotating coordinate system to the body coordinate system; S4. In the body coordinate system, calculate the axial bending moment load of the inner shaft and the coupled axial bending moment load of the inner shaft to the outer shaft. S5. In the body coordinate system, calculate the axial bending moment load of the outer shaft and eliminate the coupled axial bending moment load of the inner shaft to the outer shaft to obtain the true axial bending moment load of the outer shaft.

2. The method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter according to claim 1, characterized in that, The coaxial twin-rotor helicopter has an upper rotor telemetry data acquisition unit and a lower rotor telemetry data acquisition unit installed on its upper and lower rotor blades, respectively; and strain gauges are attached to the upper and lower rotor shafts, respectively; the upper rotor telemetry data acquisition unit and the lower rotor telemetry data acquisition unit are two sets of blade strain load acquisition units that are synchronously acquired, and are used to acquire the strain signals of the upper rotor blade with attached strain gauges and the lower rotor blade with attached strain gauges, respectively; the photoelectric pulse sensor is arranged at a preset position on the top of the fuselage, and the photoelectric pulse sensor is installed vertically upward; the upper and lower rotor shafts are respectively referred to as the inner and outer shafts.

3. The method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter according to claim 1, wherein S1 specifically comprises: After the outer shaft is patched, it is fixed on the calibration stand, and the point of application of the applied torque is set at the center of the lower rotor hub by the calibration fixture. The axial tensile force Fy, torque My, longitudinal bending moment Mx, and lateral bending moment Mz were calibrated. The loading directions included both positive and negative directions, and the calibration load amounts in each direction were divided into m levels, where m≥5. The tension of the outer shaft was then obtained for the full-bridge combination. Torque axle combination Longitudinal bending moment full bridge combination and lateral bending moment full bridge combination Based on the 4×(m+1) group of load and strain responses under various loading conditions, the external shaft strain-load transformation coefficient matrix is ​​obtained. ; The inner shaft was statically calibrated by applying a load, and the point of application of the loading torque was fixed at the center of the rotor hub using a calibration fixture. The loading direction, magnitude, and number of load stages were exactly the same as those for the outer shaft. Based on 4×(m+1) sets of calibration loads and strain responses, the strain-load transformation coefficient matrix of the inner shaft was obtained. .

4. In the method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter according to claim 3, S2 specifically comprises: Combine the inner and outer shafts, aligning the notches on the top flanges of the inner and outer shafts. The direction from the center of the top end face to the centerline of the notch is defined as the X-axis. The loading position, load, and direction are the same as in the inner shaft calibration process. Perform static loading on the inner shaft to obtain the strain coupling response of the outer shaft. Multiply by the external axis strain-load transformation coefficient matrix The coupled load response of the outer shaft is obtained, and then divided by the rated load. Obtain the inner-axis-outer-axis coupling response coefficients .

5. In the method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter according to claim 4, S3 specifically comprises: Record the average response of the entire strain bridge of the inner and outer shafts at low speeds for no less than 10 revolutions as the initial dynamic reading, and obtain the combined response value of the entire strain bridge of the inner and outer shafts after deducting the initial dynamic reading in all subsequent rotational states. and ; The inner and outer shafts are mounted on a coaxial helicopter. The rotor blades are rotated in a static state to trigger the photoelectric pulse sensor, and the initial azimuth angles of the top flange notches of the inner and outer shafts are measured. and ; The rotor telemetry data acquisition unit and the lower rotor telemetry data acquisition unit are set to the same sampling rate S for fixed-frequency acquisition. When the rotor speed is stable at N, the photoelectric pulse sensor acquires the phase of the sampling point between two consecutive pulse rising edges, which is uniformly distributed. The phase angle of each sampling point in one revolution is obtained by calculating the sampling point between the two pulse rising edges. The specific method is as follows: based on the rising edge of the continuous pulse signal acquired by the photoelectric pulse sensor, the combined strain bridge values ​​of the inner shaft and the outer shaft are extracted in whole cycles. The first sampling point after exceeding the first rising edge threshold is the initial azimuth angle of the flange notch at the top of the inner shaft and the outer shaft. and Since the inner axis rotates in the positive direction, the phase of the full-bridge strain values ​​on the inner axis increases point by point. The outer shaft rotates in the opposite direction, therefore the phase of the full-bridge strain values ​​on the outer shaft decreases point by point. By analogy, the phase angle corresponding to the nth strain full-bridge numerical point of the inner axis and the outer axis in a series of sampling points is obtained. and 。 6. In the method for calculating the axial bending moment load of a coaxial twin-rotor helicopter according to claim 5, in S4, the axial bending moment load of the inner shaft is calculated in the body coordinate system, specifically as follows: Since the loads in all directions on the outer shaft will not cause a coupled response to the strain full-bridge combination on the inner shaft, the loads on the inner shaft are calculated first. The strain full-bridge combination value of the nth sampling point of the inner axis in a ring of sampling points. Multiply by the inner axis strain-load transformation coefficient matrix The longitudinal and transverse axial bending moment loads under the rotational coordinates of the propeller hub are obtained. ; Based on the azimuth angle of the inner axis By performing a transformation from the rotating coordinate system to the body coordinate system, the longitudinal and transverse bending moment loads of the inner shaft 4 in the body coordinate system are obtained. .

7. In the method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter according to claim 6, in S4, the coupled shaft bending moment load of the inner shaft to the outer shaft is calculated in the body coordinate system, specifically as follows: Multiply the axial bending moment load of the inner shaft by the inner shaft-outer shaft coupling response coefficient. Longitudinal and transverse axis bending moment coupled response coefficient elements The coupled longitudinal and transverse axial bending moment loads of the inner shaft to the outer shaft in the body coordinate system are obtained. .

8. The method for calculating the shaft bending moment load of a coaxial twin-rotor helicopter according to claim 7, S5, specifically comprises: The strain full-bridge combination value of the nth sampling point of the outer axis in a ring of sampling points. Multiply by the external axis strain-load transformation coefficient matrix The longitudinal and transverse axial bending moment loads in the rotational coordinates of the lower rotor hub are obtained. Based on the azimuth angle of the outer axis A transformation from the rotating coordinate system to the body coordinate system is performed to obtain the longitudinal and transverse bending moment loads of the outer shaft in the body coordinate system. Then, the coupled longitudinal and transverse bending moment loads of the inner shaft on the outer shaft in the body coordinate system are subtracted. Obtain the longitudinal and transverse bending moment loads of the outer shaft in the body coordinate system. .

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