Tail rotor test bench and inherent frequency measurement verification method thereof

Abstract

The invention provides a tail rotor test bench and an inherent frequency measurement verification method thereof. The method comprises the following steps: step 1, adjusting an axial distance between an upper rack and an upper transmission shaft on the upper rack; 2, the coaxiality self-positioning function of an upper transmission shaft and a speed reducer output shaft is achieved in the rack inherent frequency adjusting process; 3, the inherent frequency is adjusted; and 4, measuring the inherent frequency by adopting a pulse hammering method. The problem that due to the fact that different blades are installed on the tail rotor table, the inherent frequency is different, and the tail rotor table is affected is solved.

Description

Technical Field

[0001] The present application belongs to the technical field of helicopter tail rotor ground bench testing, and specifically relates to a tail rotor test bench and a natural frequency measurement and verification method thereof. Background Art

[0002] The helicopter tail rotor is an important part of a single-rotor helicopter. It is installed at the tail of the helicopter. When the helicopter is flying, the reaction torque of the rotor rotation will cause the helicopter to rotate in the opposite direction of the rotor rotation. The pulling force generated by the tail rotor can offset this rotation and achieve heading stability. Changing the pulling force of the tail rotor can control the heading. Before the tail rotor is installed on the helicopter, it needs to be fully tested and evaluated on the ground test bench to provide a reliable test basis and safety guarantee for the installation of the tail rotor.

[0003] The tail rotor test bench is mainly used to provide the necessary ground test conditions for conducting tests and assessments on aerodynamic performance, functionality, rotational dynamic characteristics, stability, noise and durability of tail rotors of different types. It is one of the key ground equipment in the development process of helicopter tail rotors.

[0004] The tail rotor test bench is mainly composed of a power traction system, a transmission system, a control system, a data acquisition system, a force measuring balance, a hydraulic control system, a lubrication system, a test system and a test bench. The test bench is universal. When different types of tail rotors are installed on the test bench, different tail rotor installation transition connectors can be designed according to the interface size of the test bench and the tail rotor to meet the needs of different types of tail rotors, thereby realizing the testing of different types of tail rotors on the tail rotor test bench.

[0005] When testing the tail rotor test bench, the natural frequency of the test bench must avoid the operating frequency range of the test tail rotor to ensure that dynamic instability and damage to the test bench will not occur due to the tail rotor operating frequency overlapping or being close to the natural frequency of the test bench. Summary of the invention

[0006] Purpose of the invention: Since the operating speeds of tail rotors of different models are generally different, the natural frequency of the test bench must avoid the operating frequency range of the test tail rotor during the test to ensure that dynamic instability does not occur. Therefore, the tail rotor test bench must have the ability to adjust the natural frequency.

[0007] In a first aspect, the present application provides a method for measuring and verifying the natural frequency of a tail rotor test bench, the method comprising:

[0008] Step 1, adjusting the axial spacing between the upper stand and the upper transmission shaft thereon;

[0009] Step 2: Realization of the coaxiality self-positioning function between the upper transmission shaft and the output shaft of the reducer during the natural frequency adjustment of the test bench;

[0010] Step 3: Adjust the natural frequency;

[0011] Step 4: Use the pulse hammer method to measure the natural frequency.

[0012] Preferably, the step 1 comprises:

[0013] The upper frame, upper transmission, lower transmission, balance, rotation and translation conversion mechanism and test connection parts are integrated into one module, which ensures that the frame and transmission system are disengaged as a whole at the disengagement position;

[0014] The upper frame is designed with four jacking points evenly distributed around the circumference;

[0015] The output shaft of the reducer is connected to the lower end of the upper transmission shaft by a spline coupling;

[0016] The lower end surface of the upper frame and the upper end surface of the bottom frame are connected circumferentially by bolts. When lifting, the jack is placed on the upper surface of the bottom frame. By lifting the upper frame, the upper frame and the upper transmission shaft are driven to translate synchronously along the axial direction.

[0017] Preferably, the step 2 comprises:

[0018] Consider designing a cylindrical guide mechanism with a positioning function on the upper end surface of the bottom frame and the lower end surface of the upper frame so that the coaxiality requirement of the test bench transmission shaft installation is not changed during the adjustment of the natural frequency of the test bench.

[0019] Preferably, the step 2 further comprises:

[0020] The cylindrical guide boss has an adjustment range of not less than 50 mm.

[0021] Preferably, the step 3 comprises:

[0022] The natural frequency of the test bench is changed by adding elastic gaskets of different thicknesses at the connection bolts between the upper end surface of the bottom bench and the lower end surface of the upper bench;

[0023] When adjusting the natural frequency of the test bench, first loosen the nuts on the connecting bolts between the upper and lower frames. Under the lifting action of the jack, the upper frame and the upper transmission shaft move upward along the positioning guide cylindrical boss as a whole, so that the upper and lower frames can move quickly along the axial direction, freeing up space for installing elastic gaskets, so that the work of adding elastic gaskets can be quickly implemented;

[0024] Then, the natural frequency of the tail rotor platform is adjusted by adding elastic gaskets at the 12 bolts connecting the upper and lower frames. If the natural frequency does not meet the requirements after measurement, the thickness of the elastic gasket is adjusted until the natural frequency meets the test requirements.

[0025] Preferably, the step 3 further comprises:

[0026] The stand and the transmission system are automatically positioned under the guidance of the positioning guide cylindrical boss to achieve in-situ reassembly.

[0027] Preferably, step 4 comprises:

[0028] The natural frequency is measured by pulse hammer method. During measurement, vibration sensors are arranged on the hammer, and vibration sensor measuring points are arranged on the test bench at the same time to establish a test model. The test adopts pulse hammer method to obtain the frequency response function of each measuring point, and the natural frequency and vibration mode of the high-power tail rotor test bench are obtained through data analysis and processing. During measurement, the test bench is in the working state, and the balance locking screw is in two states: loosened and locked. When the hammer is excited, it is excited along the heading and lateral directions respectively.

[0029] In the second aspect, the present application also provides a tail rotor test bench, which includes a motor, a reducer, a lower transmission, a torque balance, an upper transmission, a test bench, a lift balance, an actuator, a rotation-translation conversion mechanism, a test connector and a connection to the tail rotor.

[0030] This application has the following technical effects:

[0031] This application solves the problem of the different natural frequencies of the tail rotor platform caused by the installation of different blades on the tail rotor platform, which affects the tail rotor platform. After the frequency modulation measures are taken on the tail rotor platform and the elastic gasket is added to the reserved position of the test bench, the natural frequency of the tail rotor platform is significantly reduced when the balance locking screw is loosened and locked, meeting the requirements of this type of test. In the test after frequency modulation, the test bench operated normally, and the reliability and safety of each system were good. Through the frequency modulation measures, the natural frequency of the tail rotor platform is effectively adjusted to meet the natural frequency requirements of tail rotor tests of different types of blades, ensuring the smooth progress of the tail rotor test and laying a solid foundation for the subsequent tail rotor installation test flight. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the tail rotor station structure and the vibration sensor placement and striking positions;

[0033] Figure 2 Spline connection diagram of the transmission system (partial enlargement A);

[0034] Figure 3 Elastic gasket structure dimension drawing;

[0035] Figure 4 Schematic diagram of the padding part (section view BB);

[0036] Figure 5 Schematic diagram of the location of the jack joint;

[0037] Figure 6Schematic diagram of the pulse hammer test principle. DETAILED DESCRIPTION

[0038] See also Figure 1-Figure 6 This invention mainly proposes a design method for adjusting the natural frequency of the test bench conveniently and quickly. In the past, the same type of tail rotor test bench did not include the requirements for adjusting the natural frequency of the test bench in the design stage. When the natural frequency of the test bench needed to be adjusted later, the method of adding counterweights at the appropriate position of the test bench or adding elastic elements at the bottom of the test bench was temporarily adopted.

[0039] However, these methods have a limited range for adjusting the natural frequency of the test bench, and the workload is large, and even require synchronous adjustment of the coaxiality of the power transmission system. However, this invention takes into account the test bench's natural frequency adjustment capability when designing the test bench. When adjusting the frequency, it is only necessary to add elastic gaskets to the natural frequency adjustment part of the test bench that has been designed to adjust the natural frequency of the test bench, without adjusting the power transmission system of the test bench. This method is simple, efficient, safe and reliable, and the test bench has a large natural frequency adjustment range, which can meet the test of various types of tail rotors.

[0040] This design method can take the test bench natural frequency adjustment scheme into consideration during the test bench design phase, and can reserve the natural frequency adjustment interface at a reasonable position according to the test bench structure. When the natural frequency of the test bench needs to be adjusted, it is only necessary to add elastic gaskets at the reserved position to adjust the natural frequency of the test bench, and no other modifications to the test bench are required during adjustment. This design method mainly considers the following aspects:

[0041] a) Method for quickly adjusting the axial spacing of the upper frame and the upper transmission shaft thereon:

[0042] 1) The upper frame, upper transmission, lower transmission, balance, rotation and translation conversion mechanism and test connector are integrated into one module, ensuring that the frame and transmission system can be disengaged as a whole at the disengagement position, such as Figure 1 As shown;

[0043] 2) The design of the upper frame takes into account the circumferential distribution of 4 jacking points, such as Figure 5 As shown;

[0044] 3) The output shaft of the reducer is connected to the lower end of the upper transmission shaft by a spline coupling, such as Figure 2 As shown;

[0045] 4) The lower end surface of the upper frame and the upper end surface of the bottom frame are connected by bolts in the circumferential direction, such as Figure 4 As shown, during lifting, the jack is placed on the upper surface of the bottom frame, and by lifting the upper frame, the upper frame and the upper transmission shaft are driven to translate synchronously along the axial direction.

[0046] b) Method for realizing the self-positioning function of the coaxiality between the upper transmission shaft and the output shaft of the reducer during the natural frequency adjustment of the test bench:

[0047] Consider designing a cylindrical guide mechanism with a positioning function on the upper end surface of the bottom frame and the lower end surface of the upper frame, so that the coaxiality requirement of the test bench drive shaft installation is not changed during the adjustment of the natural frequency of the test bench, and the cylindrical guide boss has an adjustment range of not less than 50mm.

[0048] c) Implementation method of natural frequency adjustment:

[0049] The natural frequency of the test bench is mainly changed by adding elastic gaskets of different thicknesses at the connection bolts between the upper end face of the bottom bench and the lower end face of the upper bench. When adjusting the natural frequency of the test bench, first loosen the nuts on the connection bolts between the upper bench and the bottom bench. Under the lifting action of the jack, the upper bench and the upper transmission shaft move upward along the positioning guide cylindrical boss as a whole, so that the upper bench and the bottom bench can move quickly along the axial direction, freeing up space for installing elastic gaskets, so that the work of adding elastic gaskets can be quickly implemented. See Figure XX for the specific location of adding gaskets.

[0050] Then, the natural frequency of the tail rotor platform is adjusted by adding elastic gaskets at the 12 bolts connecting the upper and lower test stands. If the natural frequency does not meet the requirements after measurement, the thickness of the elastic gasket is adjusted until the natural frequency meets the test requirements. Figure 2 The in-situ reassembly is achieved by automatic positioning under the guidance of a positioning guide cylindrical boss.

[0051] d) Natural frequency measurement method (mainly pulse hammer method): The natural frequency is measured by pulse hammer method. During the measurement, a vibration sensor is arranged on the hammer, such as the attached Figure 1 The vibration sensor measuring points are arranged on the test bench at the same time, and the test model is established. The test adopts the pulse hammer method to obtain the frequency response function of each measuring point. The natural frequency and vibration mode of the high-power tail rotor test bench are obtained through data analysis and processing. The principle of the pulse hammer method test is shown in Figure 6 During measurement, the test bench is in the working state, the balance locking screw is in the loosened and locked states, and the hammer is excited along the heading and lateral directions respectively.

[0052] 1) Selection of hammer signal points

[0053] The hammer signal point is generally selected at a position that can maximize the excitation of the vibration sensor response. Through calculation analysis and experience, the excitation position is usually selected at the hub of the test bench and the corresponding position with high stiffness.

[0054] 2) Selection of the number and location of vibration sensors on the platform

[0055] The vibration sensors are arranged on the test bench from top to bottom, at positions with high rigidity and which can represent the overall situation of the test bench. The sensors should be staggered as much as possible and should not be too close.

[0056] The number of sensors arranged is related to the vibration shape of the platform to be obtained. The higher the order of the vibration shape, the more sensors are needed. Generally, to avoid the first-order passing frequency of the tail rotor, it is necessary to measure the 2nd-3rd order vibration shape, and the number of arranged sensors is about 5-8. Combined with the actual situation of the tail rotor test bench, there are 6 positions arranged, and the specific arrangement is shown in Table 1.

[0057] Table 1

[0058]

[0059] 3) Determination of test status

[0060] Because the test bench is equipped with a force balance, which has two states: loose and locked. Generally, the vibration measurement of the helicopter is divided into two states: heading and lateral. Combined with the vibration shape to be measured, taking the third order as an example, a total of 12 states need to be measured.

[0061] The first type: the balance is loosened, the heading, the first order;

[0062] The second type: the balance is loosened, the heading, the second order;

[0063] The third type: the balance is loosened, the heading, and the third order;

[0064] The fourth type: the balance is loose, sideways, and one step;

[0065] The fifth type: the balance is loose, sideways, and second order;

[0066] Type 6: loose balance, sideways, three steps;

[0067] The seventh type: balance lock, heading, first order;

[0068] Type 8: Balance lock, heading, second order;

[0069] Ninth type: balance lock, heading, three levels;

[0070] Type 10: Balance locked, sideways, first order;

[0071] Type 11: Balance lock, sideways, second order;

[0072] Type 12: Balance locked, sideways, three stages.

[0073] It should be noted that:

[0074] 1. When the natural frequency of the test bench needs to be adjusted, it is necessary to add an elastic gasket to the reserved position and adjust the tightening torque of the clamping bolt at the spring gasket to achieve the purpose of adjusting the natural frequency of the test bench. No other modifications to the test bench are required during adjustment, and the adjustment method is simple and quick.

[0075] 2. This method takes the natural frequency adjustment scheme of the test bench into consideration when designing the test bench. The bottom frame and the upper frame adopt a cylindrical boss structure with a positioning guide along the axial direction, and a spline coupling is used between the upper reducer output shaft and the upper transmission shaft, so that the upper frame and the upper transmission shaft can be moved upward conveniently and quickly as a whole.

[0076] 3. The test bench and the transmission system can achieve self-positioning when they are restored and installed. The test bench meets the circumferential position requirements before installation, and the transmission system meets the coaxiality requirements. This eliminates the need to adjust the position of the test bench and the coaxiality of the transmission system when the test bench and the transmission system are restored and installed after the natural frequency adjustment is completed.

[0077] 4. The test bench natural frequency does not change the original test bench positioning requirements and the transmission shaft coaxiality requirements during the entire adjustment process, and can achieve self-positioning. This eliminates the need for the adjustment of the test bench natural frequency that may cause the test bench positioning and transmission shaft coaxiality adjustment.

[0078] 5. The selection of hammer signal point location, sensor quantity and location should be reasonable and accurate.

[0079] 6. The test state is determined completely, which can achieve the purpose of adjusting the natural frequency of the test bench.

[0080] The scheme of the present invention is reasonable and feasible, and solves the problem that the different natural frequencies of the tail rotor platform caused by installing different blades have an impact on the tail rotor platform. After the frequency modulation measures are taken on the tail rotor platform and an elastic gasket is added to the reserved position of the test bench, the natural frequency of the tail rotor platform is significantly reduced when the balance locking screw is loosened and locked, thereby meeting the requirements of this model test.

[0081] In the test after frequency modulation, the test bench operated normally, and the reliability and safety of each system were good. Through frequency modulation measures, the natural frequency of the tail rotor bench was effectively adjusted to meet the natural frequency requirements of different types of blade tail rotor tests, ensuring the smooth progress of the tail rotor test and laying a solid foundation for the subsequent tail rotor installation test flight.

[0082] In other embodiments of this application, see Figure 1 to Figure 6 The present invention further describes the present application in detail. The present invention designs a method for quickly adjusting the natural frequency of the tail rotor test bench, which is mainly designed synchronously with the structural form of the tail rotor bench in the early stage of the tail rotor bench design. Figure 1It mainly includes a motor 1, a reducer 2, a lower transmission 3, a torque balance 4, an upper transmission 5, a test stand 6, a lift balance 7, an actuator 8, a rotation-translation conversion mechanism 9, a test connector 10 and a connecting tail rotor 11.

[0083] The adjustment method of the present invention requires Figure 1 The padding position shown, increase Figure 3 The elastic gasket shown in the figure has the following specific padding positions: Figure 4 12 bolts as shown.

[0084] During the design, the entire transmission system and test bench adopt a modular design. The transmission system is divided into an upper transmission assembly 5 and a lower transmission assembly 3, and the test bench is divided into an upper test bench and a lower test bench. The weight of the upper transmission assembly 5 and the force of the tail rotor on the upper transmission are transmitted to the upper test bench. This part of the force and the weight of the lower transmission assembly are transmitted to the lower test bench, and then transmitted to the motor mounting seat through the lower test bench, and finally transmitted to the ground. The design of the transmission and the test bench ensures that the test bench and the transmission system can be disengaged as a whole at the disengagement position. The upper transmission and the lower transmission, as well as the lower transmission and the motor are connected by splines, and the splines only transmit torque. In specific implementation, the upper part of the jack is connected to the jack joint 15 fixed to the lower test bench. The jack joint is as follows: Figure 5 As shown, the jack joint is designed in a ball and socket form, which is convenient for positioning and will not slip during use, while ensuring the circumferential position requirements of the entire jacking part.

[0085] Lift the part above the lower frame with a jack. Figure 2 The position of the lower transmission assembly 3 and the spline 12 and the reducer output shaft 13 at the reducer 2 are disengaged, realizing the quick disengagement function of the transmission system. After the padding is completed, the jack is adjusted to make the entire upper part of the lower frame fall through the positioning flange 14, at which time the spline 12 and the reducer output shaft 13 are engaged. Positioning flanges are designed on the reducer frame and the lower frame respectively. The positioning flanges meet certain tolerance requirements so that the reducer frame and the lower frame are closely matched to ensure the coaxiality requirements of the spline 12 and the reducer output shaft 13 when restoring the installation. After the restoration installation, there is no need to readjust the coaxiality of the transmission system.

Claims

1. A method for measuring and verifying the natural frequency of a tail rotor test bench, characterized in that: The method comprises: Step 1, adjusting the axial spacing between the upper stand and the upper transmission shaft thereon; Step 2: Realization of the coaxiality self-positioning function between the upper transmission shaft and the output shaft of the reducer during the natural frequency adjustment of the test bench; Step 3: Adjust the natural frequency; Step 4: Use the pulse hammer method to measure the natural frequency.

2. The method according to claim 1, characterized in that The step 1 comprises: The upper frame, upper transmission, lower transmission, balance, rotation and translation conversion mechanism and test connection parts are integrated into one module, which ensures that the frame and transmission system are disengaged as a whole at the disengagement position; The upper frame is designed with four jacking points evenly distributed around the circumference; The output shaft of the reducer is connected to the lower end of the upper transmission shaft by a spline coupling; The lower end surface of the upper frame and the upper end surface of the bottom frame are connected circumferentially by bolts. When lifting, the jack is placed on the upper surface of the bottom frame. By lifting the upper frame, the upper frame and the upper transmission shaft are driven to translate synchronously along the axial direction.

3. The method according to claim 2, characterized in that The step 2 comprises: Consider designing a cylindrical guide mechanism with a positioning function on the upper end surface of the bottom frame and the lower end surface of the upper frame so that the coaxiality requirement of the test bench transmission shaft installation is not changed during the adjustment of the natural frequency of the test bench.

4. The method according to claim 3, characterized in that The step 2 also includes: The cylindrical guide boss has an adjustment range of not less than 50 mm.

5. The method according to claim 4, characterized in that The step 3 comprises: The natural frequency of the test bench is changed by adding elastic gaskets of different thicknesses at the connection bolts between the upper end surface of the bottom bench and the lower end surface of the upper bench; When adjusting the natural frequency of the test bench, first loosen the nuts on the connecting bolts between the upper and lower frames. Under the lifting action of the jack, the upper frame and the upper transmission shaft move upward along the positioning guide cylindrical boss as a whole, so that the upper and lower frames can move quickly along the axial direction, freeing up space for installing elastic gaskets, so that the work of adding elastic gaskets can be quickly implemented; Then, the natural frequency of the tail rotor platform is adjusted by adding elastic gaskets at the 12 bolts connecting the upper and lower frames. If the natural frequency does not meet the requirements after measurement, the thickness of the elastic gasket is adjusted until the natural frequency meets the test requirements.

6. The method according to claim 5, characterized in that The step 3 also includes: The stand and the transmission system are automatically positioned under the guidance of the positioning guide cylindrical boss to achieve in-situ reassembly.

7. The method according to claim 6, characterized in that The step 4 comprises: The natural frequency is measured by pulse hammer method. During measurement, vibration sensors are arranged on the hammer, and vibration sensor measuring points are arranged on the test bench at the same time to establish a test model. The test adopts pulse hammer method to obtain the frequency response function of each measuring point, and the natural frequency and vibration mode of the high-power tail rotor test bench are obtained through data analysis and processing. During measurement, the test bench is in the working state, and the balance locking screw is in two states: loosened and locked. When the hammer is excited, it is excited along the heading and lateral directions respectively.

8. A tail rotor test bench, characterized in that: The tail rotor test bench comprises a motor, a reducer, a lower transmission, a torque balance, an upper transmission, a test bench, a lift balance, an actuator, a rotation and translation conversion mechanism, a test connector and a connection tail rotor.

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