Coaxial helicopter hub load identification method

Abstract

The invention belongs to coaxial helicopters, and relates to a coaxial helicopter propeller hub load identification method. The method comprises the following steps: in a test flight test, respectively pasting two groups of strain gauges on an inner rotor shaft and an outer rotor shaft for measuring section bending moment loads of the inner rotor shaft and the outer rotor shaft; the torque and tension of the upper and lower rotor shafts are directly obtained through the test load; the rotor shaft section bending moment load measured by two groups of strain gauges of an inner rotor shaft is actually measured through test flight, and the load at the center of an upper rotor hub is calculated; by means of the obtained load at the center of the upper rotor hub, the supporting force of two pairs of bearings of the inner rotor shaft is obtained according to the moment balance principle; calculating the load proportions shared by the two bearings; the rotor shaft section bending moment load measured by two sets of strain gauges of the outer rotor shaft and the obtained bearing force are actually measured through test flight, and the load at the center of a lower rotor hub is obtained; torque and tension of the upper and lower rotor shafts and loads at the centers of the upper and lower rotor hubs are used as six-force elements of the upper and lower rotor hubs.

Description

Technical Field

[0001] The invention belongs to a coaxial helicopter and relates to a coaxial helicopter hub load identification method. Background Art

[0002] Conventional helicopters have a single rotor with a tail rotor. The six forces at the hub can be directly calculated through measured load data. The force transmission path is single, and there is no coupling relationship between the loads of multiple rotors. However, since coaxial helicopters have two rotors, the load relationship between the two rotors is more complicated and there is currently no solution. Summary of the invention

[0003] Purpose of the invention: The present invention obtains the force transmission relationship between the bearings of each rotor through further calibration and solution, and then obtains the six force factors of the hub of the upper and lower rotors.

[0004] Technical solution:

[0005] A method for identifying hub loads of a coaxial helicopter is provided. The coaxial helicopter comprises two rotor systems, wherein an upper rotor is driven by an inner rotor shaft and a lower rotor is driven by an outer rotor shaft. The method comprises:

[0006] During the flight test, two sets of strain gauges will be attached to the inner and outer rotor shafts respectively to measure the section bending moment load of the inner and outer rotor shafts;

[0007] Directly obtain the torque and tension of the upper and lower rotor shafts through the test load;

[0008] The rotor shaft section bending moment load was measured by two sets of strain gauges on the inner rotor shaft during flight test, and the load at the center of the upper rotor hub was calculated;

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

[0010] Calculate the load ratio shared by the two bearings;

[0011] The load at the center of the lower rotor hub is obtained by using the rotor shaft section bending moment load measured by two sets of strain gauges on the outer rotor shaft during the test flight and the obtained bearing force;

[0012] The torque and tension of the upper rotor shaft and the load at the center of the upper rotor hub are taken as the six force elements of the upper rotor hub; the torque and tension of the lower rotor shaft and the load at the center of the lower rotor hub are taken as the six force elements of the lower rotor hub.

[0013] Further, the rotor plane is taken as the xoy plane, and the z-axis is perpendicular to the xoy plane and vertically upward;

[0014] The section bending moment loads of the inner and outer rotor shafts include six forces Fx1, Fy1, Fz1, Mx1, My1, and Mz1 at the center of the upper rotor hub, and six forces Fx2, Fy2, Fz2, Mx2, My2, and Mz2 at the center of the lower rotor hub.

[0015] Furthermore, the torque and tension of the upper and lower rotor shafts are directly obtained by testing the load, including:

[0016] Since there is no coupling relationship between the torque and tension loads of the upper and lower rotor shafts, Mz1 at the center of the upper rotor hub is used as the measured torque load of the inner rotor shaft, and Mz2 at the center of the lower rotor hub is used as the measured torque load of the outer rotor shaft; Fz1 at the center of the upper rotor hub is used as the measured tension load of the inner rotor shaft, and Fz2 at the center of the lower rotor hub is used as the measured tension load of the outer rotor shaft.

[0017] Furthermore, the load at the center of the upper rotor hub includes the bending moment M in the x direction. up-x Heli F up-x , and the bending moment M in the y direction up-y Heli F up-y , the calculation formula is:

[0018]

[0019] Among them, 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 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 hub; the first set of strain gauges is located above the second set of strain gauges; M 11-x and M 11-y are the x-axis component and y-axis component of the rotor shaft section bending moment load measured by the first set of strain gauges on the inner rotor shaft; M 12-x and M 12-y are the x-axis component and y-axis component of the rotor shaft section bending moment load measured by the second set of strain gauges on the inner rotor shaft;

[0020] Furthermore, the load at the center of the lower rotor hub includes the bending moment M in the x direction. down-x Heli F down-x , bending moment M in the y direction down-y Heli F down-y ;

[0021]

[0022]

[0023] Among them, 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 upper hub, L 22is the distance from the center of the second set of strain gauges on the outer rotor shaft to the center of the upper hub; the first set of strain gauges is located above the second set of strain gauges; M 21-x and M 21-y are the x-axis component and y-axis component 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 are the x-axis component and y-axis component 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 are 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 are 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 F is the x-axis component and y-axis component of the support force of the inner rotor shaft support bearing; down-in-x and F down-in-y are the x-axis component and y-axis component of the support force of the inner rotor shaft support bearing; a x and a y are the x-axis and y-axis components of the load proportionality coefficient of the support bearing on the inner rotor shaft; b x and b y are the x-axis component and y-axis component of the partial load proportional coefficient of the lower support bearing of the inner rotor shaft; ΔL3 is the distance between the center of the upper bearing of the upper rotor and the center of the strain gauge on the upper side of the outer rotor shaft; ΔL4 is the distance between the center of the upper bearing of the upper rotor and the center of the strain gauge on the lower side of the outer rotor shaft; ΔL5 is the distance from the center of the lower hub to the center of the upper bearing of the lower rotor; ΔL6 is the distance from the center of the upper hub to the center of the lower bearing of the upper rotor.

[0024] Furthermore, the outer rotor shaft is disassembled separately, and the positions of the two supporting bearings are marked. Two sets of strain gauges are pasted at the positions of the supporting bearings, and the distances between the strain gauges and the center of the hub are S1 and S2;

[0025] Restore the outer rotor shaft installation and apply force F at the center of the hub along the radial direction of the rotor shaft. basic , the moment load measured at the two supporting bearing positions;

[0026] According to the moment load, the supporting force of the two supporting bearings of the inner rotor shaft is calculated, and then the load ratio shared by them is obtained.

[0027] Furthermore, the calculation formula of the supporting force is:

[0028]

[0029]

[0030] Among them, F basic Including 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 and y-axis components of the moment load measured at the two supporting bearings; F 1x 、F 1y 、F 2x 、F 2y are the x-axis and y-axis components of the support force at the two support bearing positions.

[0031] Furthermore, the calculation formula for the load distribution ratio coefficient of the two supporting bearings is:

[0032]

[0033] a x and b x 、a y and b y It is the load proportional coefficient of the two pairs of support bearings in the x-axis component and the y-axis component.

[0034] Beneficial effects:

[0035] The hub load identification of a coaxial helicopter cannot be obtained through conventional methods. This method can be used to utilize the rotor shaft bending moment, torque, and tensile load measured during the test flight to obtain the six-force element time-domain digital signals of the hubs of the upper and lower rotors. This data can then be used to further calculate the hub vibration load and structural response. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A simplified schematic diagram of the structure.

[0037] Figure 2 This is a schematic diagram of the outer rotor shaft calibration. DETAILED DESCRIPTION

[0038] A coaxial helicopter consists of two rotor systems. Generally speaking, 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 sets of bearings, and the outer rotor shaft is generally also fixed by two sets of bearings. Its main structural forms are as follows: Figure 1 shown.

[0039] During the flight test, two sets of strain gauges are attached to the inner and outer rotor shafts respectively to measure the section bending moment load. The section load can be used to solve the six force elements at the center of the upper and lower rotor hubs, that is, F at the center of the upper rotor hub. x1 、F y1 、F z1 、M x1、M y1 、M z1 , F at the center of the lower rotor hub x2 、F y2 、F z2 、M x2 、M y2 、M z2 However, since the lower rotor, i.e. the outer rotor shaft, is an over-static structure, an additional calibration is required to decouple the force transmission relationship of multiple bearings. The specific implementation steps are as follows:

[0040] In the first step, since there is no coupling relationship between the torque and tension loads of the upper and lower rotor shafts, they can be directly obtained through test loads. Therefore, Mz1 at the center of the upper rotor hub is the measured torque load of the inner rotor shaft, and Mz2 at the center of the lower rotor hub is the measured torque load of the outer rotor shaft; Fz1 at the center of the upper rotor hub is the measured tension load of the inner rotor shaft, and Fz2 at the center of the lower rotor hub is the measured tension load of the outer rotor shaft.

[0041] The second step is to divide the rotor plane into the xoy plane. The methods for solving the forces and moments in the x-axis and y-axis directions are the same. The following methods are applicable to both the x-axis and the y-axis. The rotor shaft section bending moment load M measured by two sets of strain gauges on the inner rotor shaft during flight test is 11-x 、M 12-x , the M at the center of the upper rotor hub is calculated by the following formula up-x 、F up-x ;

[0042] M 11-x =M up-x +F up-x ·L 11

[0043] M 12-x =M up-x +F up-x ·L 12

[0044]

[0045] The third step is to use the M at the center of the upper rotor hub. up-x 、F up-x , the support force F of the two bearings of the inner rotor shaft is obtained by the following balance formula: up-in-x and F down-in-x ;

[0046] F up-in-x +F down-in-x +F up-x =0

[0047] M up-x +F up-xΔL1+F up-in-x ΔL2=0

[0048]

[0049] The fourth step is Figure 2 As shown, the outer rotor shaft is disassembled separately, the positions of the two supporting bearings are marked, and two sets of strain gauges are pasted at the bearing positions. The distance between the strain gauges and the center of the hub is S1 and S2. Restore the installation of the outer rotor shaft. For the x-axis direction, apply a force F along the radial direction of the rotor shaft at the center of the hub. basic , the moment load M measured at two bearing positions 1x 、M 2x , using the formula

[0050] F basic =F 1x +F 2x

[0051] F basic (S1+S2)=F 1x ·S2+M 1x +M 2x

[0052] Calculate the bearing support force F at two locations 1x 、F 2x ,

[0053]

[0054] Then the load ratio they share can be calculated, that is, ax and bx are the load sharing ratio coefficients of the two bearings.

[0055]

[0056] Using the above method and formula relationship, we can find a in the y-axis direction. y 、b y Load proportionality factor.

[0057] Step 5: Use the outer rotor shaft to measure the bending moment load M 21-x 、M 22-x , and the bearing force obtained, the M at the center of the lower rotor hub is obtained by the following formula: down-x 、F down-x ;

[0058] M 21-x =M down-x +F down-x ·L 21 +F up-in-x ·ΔL3+F down-x ·a x ΔL5

[0059] M 22-x =M down-x +F down-x ·L 22 +F up-in-x ·ΔL4+F down-x b x ΔL6

[0060]

[0061] Step 6: Repeat steps 2 to 5, use the x-axis direction to get the result, and calculate the y-axis direction M up-y 、F up-y 、M down-y 、F down-y ;

[0062] The seventh step is to obtain the final six force factors of the upper and lower rotor hubs by taking the square root of the sum of the x-axis and y-axis loads.

Claims

1. A method for identifying the hub load of a coaxial helicopter, characterized in that: The coaxial helicopter includes two rotor systems, the upper rotor is driven by the inner rotor shaft, and the lower rotor is driven by the outer rotor shaft. The method includes: During the flight test, two sets of strain gauges will be attached to the inner and outer rotor shafts respectively to measure the section bending moment load of the inner and outer rotor shafts; Directly obtain the torque and tension of the upper and lower rotor shafts through test loads; The rotor shaft section bending moment load was measured by two sets of strain gauges on the inner rotor shaft during flight test, and the load at the center of the upper rotor hub was calculated; Using the load at the center of the upper rotor hub, according to the moment balance principle, the support force of the two bearings of the inner rotor shaft is obtained; Calculate the load ratio shared by the two bearings; The load at the center of the lower rotor hub is obtained by using the rotor shaft section bending moment load measured by two sets of strain gauges on the outer rotor shaft during the test flight and the obtained bearing force; The torque and tension of the upper rotor shaft and the load at the center of the upper rotor hub are taken as the six force elements of the upper rotor hub; the torque and tension of the lower rotor shaft and the load at the center of the lower rotor hub are taken as the six force elements of the lower rotor hub.

2. The method according to claim 1, characterized in that The rotor plane is the xoy plane, and the z-axis is perpendicular to the xoy plane and points vertically upward; The section bending moment loads of the inner and outer rotor shafts include six forces Fx1, Fy1, Fz1, Mx1, My1, and Mz1 at the center of the upper rotor hub, and six forces Fx2, Fy2, Fz2, Mx2, My2, and Mz2 at the center of the lower rotor hub.

3. The method according to claim 2, characterized in that The torque and tension of the upper and lower rotor shafts are directly obtained through the test load, including: Since there is no coupling relationship between the torque and tension loads of the upper and lower rotor shafts, Mz1 at the center of the upper rotor hub is used as the measured torque load of the inner rotor shaft, and Mz2 at the center of the lower rotor hub is used as the measured torque load of the outer rotor shaft; Fz1 at the center of the upper rotor hub is used as the measured tension load of the inner rotor shaft, and Fz2 at the center of the lower rotor hub is used as the measured tension load of the outer rotor shaft.

4. The method according to claim 3, characterized in that The load at the center of the upper rotor hub includes the bending moment M in the x direction. up-x Heli F up-x , and the bending moment M in the y direction up-y Heli F up-y , the calculation formula is: Among them, 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 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 hub; the first set of strain gauges is located above the second set of strain gauges; M 11-x and M 11-y are the x-axis component and y-axis component of the rotor shaft section bending moment load measured by the first set of strain gauges on the inner rotor shaft; M 12-x and M 12-y are the x-axis component and y-axis component of the rotor shaft section bending moment load measured by the second set of strain gauges on the inner rotor shaft.

5. The method according to claim 4, characterized in that The load at the center of the lower rotor hub includes the bending moment M in the x direction. down-x Heli F down-x , bending moment M in the y direction down-y Heli F down-y ; Among them, 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 upper 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 upper hub; the first set of strain gauges is located above the second set of strain gauges; M 21-x and M 21-y are the x-axis component and y-axis component 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 are the x-axis component and y-axis component 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 are 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 are 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 F is the x-axis component and y-axis component of the support force of the inner rotor shaft support bearing; down-in-x and F down-in-y are the x-axis component and y-axis component of the support force of the inner rotor shaft support bearing; a x and a y are the x-axis and y-axis components of the load proportionality coefficient of the support bearing on the inner rotor shaft; b x and b y are the x-axis component and y-axis component of the partial load proportional coefficient of the lower support bearing of the inner rotor shaft; ΔL3 is the distance between the center of the upper bearing of the upper rotor and the center of the strain gauge on the upper side of the outer rotor shaft; ΔL4 is the distance between the center of the upper bearing of the upper rotor and the center of the strain gauge on the lower side of the outer rotor shaft; ΔL5 is the distance from the center of the lower hub to the center of the upper bearing of the lower rotor; ΔL6 is the distance from the center of the upper hub to the center of the lower bearing of the upper rotor.

6. The method according to claim 5, characterized in that Disassemble the outer rotor shaft separately, mark the positions of the two supporting bearings, and paste two sets of strain gauges at each supporting bearing position. The distance between the strain gauges and the center of the hub is S1 and S2; Restore the outer rotor shaft installation and apply force F at the center of the hub along the radial direction of the rotor shaft. basic , the moment load measured at the two supporting bearing positions; According to the moment load, the supporting force of the two supporting bearings of the inner rotor shaft is calculated, and then the load ratio shared by them is obtained.

7. The method according to claim 6, characterized in that The formula for calculating the supporting force is: Among them, F basic Including 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 and y-axis components of the moment load measured at the two supporting bearings; F 1x 、F 1y 、F 2x 、F 2y are the x-axis and y-axis components of the support force at the two support bearing positions.

8. The method according to claim 7, characterized in that The calculation formula for the load distribution ratio coefficient of the two pairs of support bearings is: a x and b x 、a y and b y It is the load proportional coefficient of the two pairs of support bearings in the x-axis component and the y-axis component.

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