A Test Method for Large Strain Flight Tests of Flexible Components of a Helicopter

Abstract

The present invention discloses a method for testing large strain during the flight test of helicopter flexible components. A damping pad with a specific material and thickness is pasted at the strain measurement position of the flexible component. A strain gauge M1 is pasted on the damping pad, and a strain gauge M2 is directly pasted near the strain measurement position. Through ground bench tests and flight tests, the strain signals at the two locations are compared and tested to select a suitable damping pad material and thickness, and the damping coefficient of the damping pad is obtained. During the helicopter flight test, the true strain value of the flexible component can be obtained through the strain gauge signal and the damping coefficient on the damping pad. By using the testing method proposed by the present invention, the problem of short service life of strain gauges during the flight test of helicopter flexible components is effectively solved, and the service life of strain gauges is significantly improved; it provides true load testing of flexible components for flight tests.

Description

Technical Field

[0001] The present invention belongs to the technical field of helicopter flight test measurement, and particularly relates to a method for flight test measurement of large strains of helicopter flexible components. Background Art

[0002] Helicopter flexible components mainly refer to the main rotor flexible beam and the tail rotor flexible beam. The flexible beam plays a role in connecting the blade and the hub. Through the deformation of the flexible beam, blade pitch change is generated, and the strain of the flexible beam is a key parameter for the life determination of the flexible beam and the safety of helicopter flight tests. During the helicopter flight test, due to the blade aerodynamic load and blade pitch change, the flexible beam undergoes a large amount of deformation and can generate high-cycle strains above ±5000 με. The measurement range of conventional strain gauges can reach 108 cycles of life at ±1200 με. In a working environment of large strains, the number of cycles of the strain gauge will be significantly reduced. During the flight test, the life of the strain gauge on the flexible component is only dozens of minutes to one or two hours, and it is necessary to repeatedly disassemble and assemble the rotor system to repair the strain gauge on the flexible beam, which seriously affects the implementation of the helicopter flight test mission. Summary of the Invention

[0003] Object of the Invention: The present invention proposes a method for flight test measurement of large strains of helicopter flexible components to effectively improve the service life of the strain gauge on the flexible beam of the rotor system.

[0004] Technical Solution: A method for flight test measurement of large strains of helicopter flexible components, a damping pad with a specific material and thickness is pasted at the strain measurement position of the flexible component, a first strain gauge is pasted on the damping pad, and a second strain gauge is directly pasted near the strain measurement position; through ground bench tests and flight tests, the strain signals at the two places are compared and tested to determine the appropriate damping pad material and thickness, and the damping coefficient of the damping pad is obtained. During the helicopter flight test, the true strain value of the flexible component can be obtained through the strain gauge signal output on the damping pad and the damping coefficient.

[0005] The method for flight test measurement of large strains of helicopter flexible components according to the present invention includes the following steps:

[0006] Step 1: Paste a damping pad with a specific material and thickness at the strain measurement position of the flexible component, paste a first strain gauge (M1) on the damping pad, the elastic modulus of the damping pad is not greater than 1 / 50 of the elastic modulus of the flexible component, and the thickness is not greater than 1 / 3 of the thickness of the flexible component itself;

[0007] Step 2: Directly paste a second strain gauge (M2) near the strain measurement position of the flexible component for comparative testing;

[0008] Step 3: Use the ground test bench to perform dynamic loading according to the main working frequency points of the flexible component. The loading load is about 60% of the actual working load. Measure the strain outputs ε1 and ε2 of strain gauges M1 and M2 respectively, and obtain the damping coefficient K1 = ε2 / ε1;

[0009] Step 4: The estimated maximum deformation of the measured position of the flexible component is ξ (με). Calculate the value of ξ / K1. If 300με ≤ ξ / K1 ≤ 1200με, proceed to the next step. If ξ / K1 > 1200με or ξ / K1 < 300με, re-enter Step 1 to adjust the material and thickness of the damping pad;

[0010] Step 5: Install the flexible component on the helicopter. The helicopter conducts ground start-up and flight inspection. Measure the strain outputs ε3 and ε4 of strain gauges M1 and M2 respectively, and obtain the actual damping coefficient K2 = ε4 / ε3 during the flight test. Calculate the value of ξ / K2. If 300με ≤ ξ / K2 ≤ 1200με, proceed to the next step. If ξ / K2 > 1200με or ξ / K2 < 300με, re-enter Step 1 to adjust the material and thickness of the damping pad;

[0011] Step 6: The helicopter conducts a flight test. Measure the strain output of strain gauge M1 as ε5, and the actual strain of the flexible component can be obtained as K2 * ε5.

[0012] Furthermore, in Step 4, the specific adjustment method is as follows: If ξ / K1 > 1200με, select a damping pad material with a smaller elastic modulus or increase the thickness of the damping pad; if ξ / K1 < 300με, select a damping pad material with a larger elastic modulus or reduce the thickness of the damping pad;

[0013] Compared with the prior art, the positive effects of the present invention are: solving the problem of short service life of strain gauges in the flight test of helicopter flexible components, and providing real load testing for flexible components in flight tests; the specific manifestations are as follows:

[0014] 1. The service life of the strain gauge is significantly improved. Through implementation verification, the effective service life of the strain gauge can reach dozens of hours or more during actual flight;

[0015] 2. Compatible with the original acquisition equipment, without the need to change the backend acquisition equipment;

[0016] 3. It can measure larger strain signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be described by way of examples with reference to the accompanying drawings, wherein:

[0018] Figure 1 Schematic diagram of the bonding of strain gauges M1 and M2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0020] See the attached Figure 1 As shown, a damping pad with a specific material and thickness is pasted at the strain measurement position of the flexible component. A strain gauge is pasted on the damping pad, and another strain gauge is directly pasted near the strain measurement position. Through ground bench tests and flight tests, the strain signals at the two locations are compared and tested to determine the appropriate damping pad material and thickness, and the damping coefficient of the damping pad is obtained. During the helicopter flight test, the true strain value of the flexible component can be obtained through the strain gauge signal output and damping coefficient on the damping pad. The specific implementation process includes the following steps:

[0021] (1) Paste a damping pad with a specific material and thickness at the strain measurement position of the flexible component. A first strain gauge M1 is pasted on the damping pad. The elastic modulus of the damping pad is not greater than 1 / 50 of the elastic modulus of the flexible component, and the thickness is not greater than 1 / 3 of the thickness of the flexible component itself.

[0022] (2) Directly paste a second strain gauge M2 near the strain measurement position of the flexible component for comparative testing.

[0023] (3) Use a ground test bench to perform dynamic loading according to the main working frequency points of the flexible component. The loading load is about 60% of the actual working load. Measure the strain outputs ε1 and ε2 of the strain gauges M1 and M2 respectively, and obtain the damping coefficient K1 = ε2 / ε1.

[0024] (4) The estimated maximum deformation of the measured position of the flexible component is ξ (με). Calculate the value of ξ / K1. If 300με ≤ ξ / K1 ≤ 1200με, proceed to the next step. If ξ / K1 > 1200με or ξ / K1 <

[0025] 300με, re-enter step one and adjust the material and thickness of the damping pad. The specific adjustment method is as follows:

[0026] If ξ / K1 > 1200με, select a damping pad material with a smaller elastic modulus or increase the thickness of the damping pad. If ξ / K1 < 300με, select a damping pad material with a larger elastic modulus or reduce the thickness of the damping pad.

[0027] (5) Install the flexible component on the helicopter, start the engine on the ground and conduct pre-flight checks, measure the strain outputs ε3 and ε4 of strain gauges M1 and M2 respectively, and obtain the true damping coefficient K2 = ε4 / ε3 of the flight test, then calculate the value of ξ / K2; if 300 με ≤ ξ / K2 ≤ 1200 με, proceed to the next step, if ξ / K2 > 1200 με or ξ / K2

[0028] <300 με, re-enter Step 1 to adjust the material and thickness of the damping pad;

[0029] (6) Conduct a flight test on the helicopter, measure the strain output of strain gauge M1 as ε5, and the actual strain of the flexible component can be obtained as K2*ε5.

[0030] In the actual implementation process, when adjusting the material and thickness of the damping pad, the material selection is determined according to the deviation value, and the thickness can be adjusted in a certain gradient; so as to shorten the test time. Of course, the measurement method proposed by the present invention can be loaded into the memory of a computer in the form of a computer program. The computer includes a processor and the memory. When the computer program is executed by the processor, the process of the measurement method is realized. In addition, the measurement method is loaded into a computer-readable storage medium in the form of a computer program. When the computer program is executed by the processor, the process of the method is realized. By using the test method proposed by the present invention, the problem of short service life of strain gauges in the flight test of helicopter flexible components is effectively solved, and the service life of strain gauges is significantly improved; it provides true load testing for flexible components in flight tests.

[0031] The above is only a specific embodiment of the present invention, and the present invention is described in detail. The unelaborated part is conventional technology. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. The protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A test method for large strain flight test of helicopter flexible components, characterized in that, The described test method pastes a damping pad with a specific material and thickness at the strain measurement position of the flexible component. A first strain gauge is pasted on the damping pad, and a second strain gauge is directly pasted near the strain measurement position. Through ground bench tests and flight tests, the strain signals at the two positions are compared and tested to determine the appropriate damping pad material and thickness, and the damping coefficient of the damping pad is obtained. During the helicopter flight test, the true strain value of the flexible component can be obtained through the strain gauge signal output and the damping coefficient on the damping pad. The described test method includes the following steps: Step S1: Paste a damping pad with a specific material and thickness at the strain measurement position of the flexible component, and paste a first strain gauge M1 on the damping pad. Step S2: Directly paste a second strain gauge M2 near the strain measurement position of the flexible component for comparative testing. Step S3: Use a ground test bench to perform dynamic loading according to the main working frequency points of the flexible component, and measure the strain outputs ε1 and ε2 of the first strain gauge M1 and the second strain gauge M2 respectively to obtain the damping coefficient K1 = ε2 / ε1. Step S4: The estimated maximum deformation of the measured position of the flexible component is ξ, and calculate the value of ξ / K1. If 300 με ≤ ξ / K1 ≤ 1200 με, go to Step S5; if ξ / K1 > 1200 με or ξ / K1 < 300 με, re-enter Step S1 to adjust the material and thickness of the damping pad. Step S5: Install the flexible component on the helicopter. The helicopter conducts ground start-up and inspection flights, and measures the strain outputs ε3 and ε4 of the strain gauges M1 and M2 respectively to obtain the true damping coefficient K2 = ε4 / ε3 during the flight test, and calculate the value of ξ / K2. If 300 με ≤ ξ / K2 ≤ 1200 με, go to Step S6; if ξ / K2 > 1200 με or ξ / K2 < 300 με, re-enter Step S1 to adjust the material and thickness of the damping pad. Step S6: The helicopter conducts a flight test, and measures the strain output of the strain gauge M1 as ε5, and the actual strain of the flexible component can be obtained as K2 * ε5.

2. The large-strain flight test method for helicopter flexible components according to claim 1, characterized in that, When pasting the damping pad with a specific material and thickness, the elastic modulus of the damping pad is not greater than 1 / 50 of the elastic modulus of the flexible component, and the thickness is not greater than 1 / 3 of the thickness of the flexible component itself.

3. The large-strain flight test method for helicopter flexible components according to claim 1, characterized in that The specific adjustment method in Step S4 is: if ξ / K1 > 1200 με, select a damping pad material with a smaller elastic modulus or increase the thickness of the damping pad.

4. The large-strain flight test method for helicopter flexible components according to claim 3, wherein, In Step S4, if ξ / K1 < 300 με, select a damping pad material with a larger elastic modulus or reduce the thickness of the damping pad.

5. A method for large strain flight test of a helicopter flexible component according to claim 3 or 4, characterized in that, When increasing or decreasing the thickness of the damping pad, a certain gradient adjustment is adopted.

6. The large-strain flight test method for helicopter flexible components according to claim 1, characterized in that In Step S3, the loading load is about 60% of the actual working load.

7. The large strain flight test method for helicopter flexible components according to claim 1, characterized in that The described test method is loaded in the memory of a computer in the form of a computer program. The computer includes a processor and the memory. When the computer program is executed by the processor, the process of the test method is realized.

8. The large strain flight test method for helicopter flexible components according to claim 1, characterized in that, The described test method is loaded in a computer-readable storage medium in the form of a computer program. When the computer program is executed by the processor, the process of the method is realized.

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