A coaxial helicopter hub load identification method

Abstract

The present application belongs to coaxial helicopter, and relates to a coaxial helicopter hub load identification method. The method comprises the following steps: in the flight test, two groups of strain gauges are pasted on the inner and outer rotor shafts respectively to measure the cross-section bending moment load of the inner and outer rotor shafts; the torque and tension of the upper and lower rotor shafts are directly obtained through the test load; the load at the center of the upper rotor hub is calculated according to the rotor shaft cross-section bending moment load measured by the two groups of strain gauges on the inner rotor shaft through the flight test; the support force of the two bearings of the inner rotor shaft is obtained according to the torque and tension of the upper and lower rotor shafts and the load at the center of the upper rotor hub; the load proportion shared by the two bearings is calculated; the load at the center of the lower rotor hub is obtained according to the rotor shaft cross-section bending moment load measured by the two groups of strain gauges on the outer rotor shaft through the flight test and the obtained bearing force; and the torque and tension of the upper and lower rotor shafts and the load at the center of the upper and lower rotor hubs are taken as the six force elements of the upper and lower rotor hubs.

Description

TECHNICAL FIELD

[0001] The application belongs to coaxial helicopter, and relates to a coaxial helicopter hub load identification method. BACKGROUND

[0002] The conventional configuration helicopter is a single-rotor tail rotor configuration, which can directly calculate the hub six force elements through the measured load data, the transmission path is single, and there is no coupling relationship between the loads of multiple rotors. The coaxial helicopter has two rotors, and the load relationship between the two rotors is relatively complex, and there is no solution method at present. SUMMARY

[0003] The application aims to obtain the transmission relationship between each rotor and each bearing through further calibration and solution, and then obtain the hub six force elements of the upper and lower rotors.

[0004] TECHNICAL SCHEME

[0005] The application provides a coaxial helicopter hub load identification method, and the coaxial helicopter includes two sets of rotor systems, the upper rotor is driven by an inner rotor shaft, and the lower rotor is driven by an outer rotor shaft, and the method comprises the following steps:

[0006] In the flight test, two groups of strain gauges are pasted on the inner and outer rotor shafts respectively, and are used for measuring the section bending moment load of the inner and outer rotor shafts;

[0007] The torque and tension of the upper and lower rotor shafts are directly obtained through the test load; the torque of the upper and lower rotor shafts refers to the torque around the z-axis, and the tension of the upper and lower rotor shafts refers to the tension along the z-axis; wherein the coordinate system takes the rotor plane as the xoy plane, and the z-axis is perpendicular to the xoy plane and vertically upward;

[0008] The load at the hub center of the upper rotor is calculated through the rotor shaft section bending moment load measured by the two groups of strain gauges of the inner rotor shaft in the flight test; the load at the hub center of the upper rotor includes the bending moment M up-x and force F up-x in the x direction, and the bending moment M up-y and force F up-y in the y direction;

[0009] The support force of the two bearings of the inner rotor shaft is obtained according to the moment balance principle by using the obtained load at the hub center of the upper rotor;

[0010] The load proportion shared by the two bearings of the outer rotor shaft is calculated;

[0011] The rotor shaft sectional bending moment load measured by the two groups of strain gauges on the rotor shaft and the bearing force obtained are used to obtain the load at the center of the lower rotor hub; the load at the center of the lower rotor hub includes the bending moment and force in the x direction M down-x and the bending moment F down-x and force in the y direction M down-y and the bending moment F down-y .

[0012] Further, the torque and tension of the upper and lower rotor shafts are directly obtained by testing the load, including:

[0013] Since the torque and tension load of the upper and lower rotor shafts do not have a coupling relationship, the measured torque load of the inner rotor shaft is taken as the torque of the upper rotor hub center around the z axis, and the measured torque load of the outer rotor shaft is taken as the torque of the lower rotor hub center around the z axis; the measured tension load of the inner rotor shaft is taken as the tension of the upper rotor hub center along the z axis, and the measured tension load of the outer rotor shaft is taken as the tension of the lower rotor hub center along the z axis. Further, M up-x 、 F up-x 、 M up-y and F up-y The calculation formula is:

[0014] ;

[0015] ;

[0016] ;

[0017] ;

[0018] wherein, L 11 is the distance from the center of the first group of strain gauges on the inner rotor shaft to the center of the upper hub, L 12 is the distance from the center of the second group of strain gauges on the inner rotor shaft to the center of the upper hub; the first group of strain gauges is located above the second group of strain gauges; M 11-x and M 11-y are the x-axis component and y-axis component of the rotor shaft sectional bending moment load measured by the first group of strain gauges on the inner rotor shaft; M 12-x and M 12-yMx and My are the x and y components of the rotor shaft section bending moment load measured by the second group of strain gauges on the inner rotor shaft;

[0019] Further, M down-x , F down-x , M down-y , F down-y The calculation formula is:

[0020] ;

[0021] ;

[0022] ;

[0023] ;

[0024] Wherein, L 21 is the distance from the center of the first group of strain gauges to the center of the lower hub on the outer rotor shaft, L 22 is the distance from the center of the second group of strain gauges to the center of the lower hub on the outer rotor shaft; the first group of strain gauges is located above the second group of strain gauges; M 21-x and M 21-y are the x and y components of the rotor shaft section bending moment load measured by the first group of strain gauges on the outer rotor shaft; M 22-x and M 22-y are the x and y components of the rotor shaft section bending moment load measured by the second group of strain gauges on the outer rotor shaft; F 21-x and F 21-y are the x and y components of the rotor shaft section force measured by the first group of strain gauges on the outer rotor shaft; F 22-x and F 22-y are the x and y components of the rotor shaft section force measured by the second group of strain gauges on the outer rotor shaft; F up-in-x and F up-in-y are the x and y components of the support force of the support bearing on the inner rotor shaft; F down-in-x and F down-in-y are the x and y components of the support force of the lower support bearing on the inner rotor shaft; ax and a y are the x-axis component and y-axis component of the load sharing ratio coefficient of the upper support bearing of the outer rotor shaft; b x and b y are the x-axis component and y-axis component of the load sharing ratio coefficient of the lower support bearing of the outer rotor shaft; is the distance between the center of the upper rotor upper bearing and the center of the upper strain gauge of the outer rotor shaft; is the distance between the center of the upper rotor upper bearing and the center of the lower strain gauge of the outer rotor shaft; is the distance between the center of the lower hub and the center of the upper bearing of the lower rotor; is the distance between the center of the lower hub and the center of the lower bearing of the lower rotor.

[0025] Further, the outer rotor shaft is disassembled separately, and the positions of the two pairs of support bearings are marked. Two groups of strain gauges are pasted at the positions of the support bearings, and the distances between the strain gauges and the center of the hub are S1 and S2;

[0026] The outer rotor shaft is installed, and a force is applied at the center of the hub along the radial direction of the rotor shaft F basic , and the bending moment load is measured at the positions of the two pairs of support bearings;

[0027] According to the bending moment load, the support forces of the two pairs of support bearings of the outer rotor shaft are calculated, and the load sharing ratio is obtained.

[0028] Further, the calculation formula of the support force is:

[0029] ;

[0030] ;

[0031] ;

[0032] ;

[0033] wherein, F basic includes the x-axis component F basic-x and the y-axis component F basic-y ; M 1x , M 1y , M 2x , M 2y are the x-axis component and y-axis component of the bending moment load measured at the positions of the two pairs of support bearings;F 1x 、 F 1y 、 F 2x 、 F 2y are the x-axis component and y-axis component of the support force at the position of the two sets of support bearings.

[0034] Further, the calculation formula of the load sharing ratio coefficient of the two sets of support bearings is:

[0035] ;

[0036] ;

[0037] ;

[0038] ;

[0039] a x and b x 、 a y and b y are the x-axis component and y-axis component of the load sharing ratio coefficient of the two sets of support bearings.

[0040] Advantages:

[0041] The hub load identification of the coaxial helicopter cannot be obtained by the conventional method, and the method can obtain the six force element time domain digital signals of the hubs of the upper and lower rotors by using the measured rotor shaft bending moment, torque and tension load in the flight test, and further calculate the hub vibration load and structure response by using the data. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a structural simplified schematic diagram.

[0043] Figure 2 is a calibration schematic diagram of the outer rotor shaft. DETAILED DESCRIPTION

[0044] The coaxial helicopter includes two sets of rotor systems, and generally, the upper rotor is driven by the inner rotor shaft, and the lower rotor is driven by the outer rotor shaft. The upper rotor shaft is generally fixed by two groups of bearings, and the outer rotor shaft is generally also fixed by two groups of bearings, and the main structural form is as shown in Figure 1 .

[0045] In the flight test, two groups of strain gauges are pasted on the inner and outer rotor shafts respectively to measure the sectional bending moment load, which can be used to calculate the six force elements at the center of the upper and lower rotor hubs, i.e. F x1 、 F y1 、 F z1 、M x1 、 M y1 、 M z1 , the force elements at the center of the lower rotor hub F x2 、 F y2 、 F z2 、 M x2 、 M y2 、 M z2 . However, since the lower rotor, i.e. the outer rotor shaft, is statically indeterminate, an additional calibration is needed to decouple the force transmission relationship of the multiple bearings. The specific implementation steps are as follows:

[0046] Firstly, since the torque and tension load of the upper and lower rotor shafts do not have a coupling relationship, they can be directly obtained by testing the load. Therefore, the measured torque load of the inner rotor shaft is taken as the torque around the z-axis at the center of the upper rotor hub, and the measured torque load of the outer rotor shaft is taken as the torque around the z-axis at the center of the lower rotor hub; the measured tension load of the inner rotor shaft is taken as the tension along the z-axis at the center of the upper rotor hub, and the measured tension load of the outer rotor shaft is taken as the tension along the z-axis at the center of the lower rotor hub.

[0047] Secondly, the rotor plane is divided into the xoy plane, and the method for solving the force and moment in the x-axis and y-axis directions is the same, which is applicable to both x and y axes. The sectional bending moment load of the rotor shaft measured by the two groups of strain gauges on the inner rotor shaft in the flight test 、 is calculated by the following formula to obtain the force elements at the center of the upper rotor hub 、 .

[0048]

[0049]

[0050]

[0051]

[0052] Third step, using the upper rotor hub center of the above-mentioned 、 , through the following balance equation, the support force of the inner rotor shaft two pairs of bearings and ;

[0053]

[0054]

[0055]

[0056]

[0057] Fourth step, as shown in Figure 2 , the outer rotor shaft is disassembled alone, and the positions of the two pairs of support bearings are marked. Two groups of strain gauges are pasted at the bearing positions, and the distance between the strain gauges and the hub center is S1 and S2. The outer rotor shaft is restored to its original position. For the x-axis direction, a force is applied at the hub center in the radial direction of the rotor shaft. Through the bending moment loads M 1x and M 2x measured at the two bearing positions, the support forces F 1x and F 2x of the two bearings are calculated using the formula

[0058]

[0059]

[0060]

[0061] ;

[0062] ;

[0063] Further, the load proportion shared by the two bearings can be calculated, that is, a x , b x is the load proportion coefficient of the two bearings.

[0064] ;

[0065] ;

[0066] Using the above method and formula relationship, the load proportion coefficient of the y-axis direction a y , b y can be calculated.

[0067] ​Fifth step, using the measured bending moment load of the outer rotor shaft , , and the obtained bearing force, the six force elements at the center of the lower rotor hub are obtained by the following formula , ;

[0068]

[0069]

[0070]

[0071]

[0072] Sixth step, repeat the second to fifth steps, using the results obtained in the x-axis direction to calculate the y-axis direction , , , ;

[0073] Seventh step, square sum the x-axis and y-axis loads, and then take the square root to obtain the final six force elements of the upper and lower rotor hubs.

Claims

1. A coaxial helicopter hub load identification method, characterized by, The coaxial helicopter comprises two sets of rotor systems, the upper rotor is driven by the inner rotor shaft, and the lower rotor is driven by the outer rotor shaft, and the method comprises: In the flight test, two groups of strain gauges are pasted on the inner and outer rotor shafts respectively for measuring the sectional bending moment load of the inner and outer rotor shafts; The torque and tension of the upper and lower rotor shafts are directly obtained through the test load; the torque of the upper and lower rotor shafts refers to the torque around the z-axis, and the tension of the upper and lower rotor shafts refers to the tension along the z-axis; wherein the coordinate system takes the rotor plane as the xoy plane, and the z-axis is perpendicular to the xoy plane and vertically upward; The rotor shaft sectional bending moment load measured by the two groups of strain gauges of the inner rotor shaft is calculated to obtain the load at the center of the upper rotor hub M up-x and force F up-x in the x direction M up-y and force F up-y in the y direction The support forces of the two pairs of bearings of the inner rotor shaft are obtained according to the moment balance principle by using the obtained load at the hub center of the upper rotor; The load proportion of the two pairs of bearings of the outer rotor shaft is calculated; The rotor shaft cross-sectional bending moment load measured by two groups of strain gauges on the rotor shaft and the bearing force obtained are used to obtain the load at the center of the lower rotor hub, which includes the bending moment and force in the x direction M down-x and force F down-x in the y direction M down-y and force F down-y .

2. The method of claim 1, wherein, The torque and tension of the upper and lower rotor shafts are directly obtained through the test load, including: Since the torque and tension loads of the upper and lower rotor shafts do not have a coupling relationship, the measured torque load of the inner rotor shaft is taken as the torque around the z-axis at the hub center of the upper rotor, the measured torque load of the outer rotor shaft is taken as the torque around the z-axis at the hub center of the lower rotor, the measured tension load of the inner rotor shaft is taken as the tension along the z-axis at the hub center of the upper rotor, and the measured tension load of the outer rotor shaft is taken as the tension along the z-axis at the hub center of the lower rotor.

3. The method of claim 2, wherein, M up-x , force F up-x , M up-y and F up-y The calculation formula is: ； ； ； ； wherein, L 11 is the distance from the center of the first set of strain gauges on the inner rotor shaft to the center of the upper mast hub, L 12 is the distance from the center of the second set of strain gauges on the inner rotor shaft to the center of the upper mast hub; the first set of strain gauges is located above the second set of strain gauges; M 11-x and M 11-y is the x-axis and y-axis components of the rotor shaft cross-sectional bending moment load measured by the first set of strain gauges on the inner rotor shaft; M 12-x and M 12-y is the x-axis and y-axis components of the rotor shaft cross-sectional bending moment load measured by the second set of strain gauges on the inner rotor shaft.

4. The method of claim 3, wherein, M down-x , F down-x , M down-y and F down-y The calculation formula is: ； ； ； ； wherein, L 21 is the distance from the center of the first set of strain gauges on the outer rotor shaft to the center of the lower hub, L 22 is the distance from the center of the second set of strain gauges on the outer rotor shaft to the center of the lower hub; the first set of strain gauges is located above the second set of strain gauges; M 21-x and M 21-y is the x-axis and y-axis components of the rotor shaft section bending moment load measured by the first set of strain gauges on the outer rotor shaft; M 22-x and M 22-y is the x-axis and y-axis components of the rotor shaft section bending moment load measured by the second set of strain gauges on the outer rotor shaft; F 21-x and F 21-y is the x-axis and y-axis components of the rotor shaft section force measured by the first set of strain gauges on the outer rotor shaft; F 22-x and F 22-y is the x-axis and y-axis components of the rotor shaft section force measured by the second set of strain gauges on the outer rotor shaft; F up-in-x and F up-in-y is the x-axis and y-axis components of the support force of the support bearing on the inner rotor shaft; F down-in-x and F down-in-y is the x-axis and y-axis components of the support force of the lower support bearing on the inner rotor shaft; a x and a y is the x-axis and y-axis components of the load sharing ratio coefficient of the support bearing on the outer rotor shaft; b x and b y is the x-axis and y-axis components of the load sharing ratio coefficient of the lower support bearing on the outer rotor shaft; is the distance from the center of the upper rotor upper side bearing to the center of the upper rotor upper side strain gauge on the outer rotor shaft; is the distance from the center of the upper rotor upper side bearing to the center of the upper rotor lower side strain gauge on the outer rotor shaft; is the distance from the center of the lower hub to the center of the lower rotor upper side bearing; is the distance from the center of the lower hub to the center of the lower rotor lower side bearing.

5. The method of claim 4, wherein, The outer rotor shaft is disassembled alone, the positions of the two pairs of support bearings are marked, two groups of strain gauges are pasted at the positions of the support bearings, and the distances between the strain gauges and the hub center are S1 and S2; Restoring the outer rotor shaft mounting, applying a force at the hub center radially along the rotor shaft F basic The bending moment load is measured at the positions of the two pairs of support bearings; According to the bending moment load, the support forces of the two pairs of support bearings of the outer rotor shaft are calculated, and the load proportion shared by the two pairs of support bearings is obtained.

6. The method of claim 5, wherein, The calculation formula of the support force is: ； ； ； ； wherein F basic comprises an x-axis component F basic-x and a y-axis component F basic-y ; M 1x , M 1y , M 2x , M 2y are the x-axis and y-axis components of the bending moment loads measured at the locations of the two pairs of support bearings; F 1x , F 1y , F 2x , F 2y are the x-axis and y-axis components of the support forces at the locations of the two pairs of support bearings.

7. The method of claim 6, wherein, The calculation formula of the load proportion shared by the two pairs of support bearings is: ； ； ； ； a x and b x , a y and b y are the load sharing ratio coefficients of the two pairs of support bearings in the x-axis component and the y-axis component, respectively.

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