Frequency measurement method suitable for star-shaped flexible hub helicopter blade

Abstract

The invention provides a frequency measurement method suitable for a star-shaped flexible hub helicopter blade, which comprises the following steps: moving a lifting hook 3 above a blade tip of a blade to be measured, supporting a lifting belt 2 at the lower part of a blade tip airfoil and tying the lifting hook, so that the lifting hook hangs the blade tip of the blade, and measuring and adjusting the length of the lifting belt. The swing inherent frequency of the hanging system is less than 1 / 5 of the first-order bending frequency of the paddle; the swing inherent frequency # imgabs0 # g of the hanging system is the gravitational acceleration, and L is the length of the hanging belt; a plurality of knocking points are arranged from the root of the blade to the tip of the blade in a matrix mode, each knocking point is knocked once in each measurement, and the inherent frequency of the blade is obtained through measurement of a three-axis vibration sensor. According to the invention, the constraint mode of the blade root can be accurately simulated, the action of the centrifugal force when the blade works is simulated by hanging the spring rope, and the inherent frequency of the blade in a non-rotating state can be more accurately and truly measured. A test result and a calculation result are shown in a table 1.

Description

Technical Field

[0001] The invention relates to the field of aerospace testing and experiment, and relates to a frequency measurement and installation method for a star-shaped flexible hub helicopter blade, which is used to improve the accuracy and reliability of measurement when performing a blade inherent characteristic test. Background Art

[0002] The rotor is the main vibration source of the helicopter. The alternating blade load generated by the alternating aerodynamic load not only affects the fatigue life of the blade, but also the hub vibration load synthesized at the center of the hub is the main cause of helicopter vibration. Through the reasonable configuration of the blade frequency and the adjustment of the blade vibration mode, the natural frequency of the blade is reasonably configured, so that the natural frequency of the blade within the normal working speed, maximum rotation speed and ground speed range has a certain difference with the aerodynamic excitation frequency force, so as to avoid resonance or excessive vibration with the aerodynamic excitation force, and at the same time control the rotor blade dynamic stress level generated by the rotor alternating load to meet the fatigue life requirements of the rotor. Therefore, accurately obtaining the natural frequency of the blade is the basis for the reasonable configuration of the blade frequency and is also a prerequisite for the optimization design of the blade dynamics. Verifying the analysis results through the blade natural frequency test is a common technical means used by engineers.

[0003] At present, there are three main installation methods for measuring the natural frequency of blades in a non-rotating state: the root clamping method, the vertical suspension method, and the horizontal suspension method. The stiffness of the workpiece clamped by the root clamping method affects the measured frequency of the blade. The vertical suspension method has high requirements for the installation space of the blade, and brings great difficulties to the installation and test measurement of the blade. Although the installation space of the horizontal suspension method is not large, its constraint method cannot simulate the actual installation state of the blade, and the analysis model needs to be further revised. The present invention not only eliminates the influence of the root clamping workpiece on the measured blade frequency caused by the root clamping method, but also simulates the installation state of the blade in a non-rotating state, and its measurement results are true and reliable. Summary of the invention

[0004] The purpose of the present invention is to propose a method for measuring the blade natural frequency of a star-shaped flexible hub helicopter, truly simulate the blade constraint form, solve the problem that traditional test methods cannot truly simulate the blade root constraint state, and ensure that the measurement result of the blade natural frequency in the non-rotating state is true and reliable.

[0005] The technical solution of the present invention is:

[0006] A frequency measurement method applicable to a star-shaped flexible hub helicopter blade is provided, the method comprising the following steps:

[0007] Step 1: Install the rotor blade 1 on the hub 4 through the blade pin, and the hub is installed on the main rotor shaft, and brake the rotor to ensure that the rotor cannot rotate;

[0008] Step 2, move the hook 3 to the tip of the blade to be tested, support the lower part of the blade tip wing surface with the sling 2 and tie it to the hook, so that the hook hangs the tip of the blade, measure and adjust the length of the sling, and ensure that the swing natural frequency of the hanging system is less than 1 / 5 of the first-order bending frequency of the blade; the swing natural frequency of the hanging system g is the acceleration due to gravity, L is the length of the sling;

[0009] Step 3: Use the hook to adjust the height of the propeller tip so that the propeller blade is level with the hub plane. Use the rangefinder to measure the distance h1 from the center of gravity of the propeller blade to the ground, the distance h2 from the tip of the propeller blade to the ground, the distance R1 from the hub center to the center of gravity of the propeller blade, and the distance R2 from the hub center to the tip of the propeller. Use the formula and The angles θ1 and θ2 are calculated respectively. When the angles θ1 and θ2 are both 4.5°, the requirement that the blade is level with the hub plane is met. If not, continue to operate the hook to adjust the height of the blade tip, and change the distances h1 and h2 until they are met.

[0010] Step 4: Keep the propeller hub inertia weight and the limiter support separated, and ensure that the distance between the measured inertia weight and the limiter support is greater than 3 mm, so as to truly simulate the root constraint state of the blade in the working environment;

[0011] Step 5: Arrange multiple tapping points in a matrix from the root of the blade to the tip of the blade. Perform a tap at each tapping point for each measurement, and measure the blade's natural frequency using a three-axis vibration sensor.

[0012] Furthermore, the three-axis vibration sensors are respectively installed at the blade root, the blade airfoil section and the blade tip during each measurement.

[0013] Furthermore, a plurality of triaxial vibration sensors are respectively installed at the blade root, the blade airfoil section and the blade tip.

[0014] Furthermore, the blade natural frequency obtained from each striking measurement is averaged.

[0015] Furthermore, the hub inertia weight is kept separated from the limiter support by using a strap to bind the hub root and tighten it.

[0016] Furthermore, from the root of the blade to the tip of the blade, on the equivalent plane of the airfoil, with the span direction as the horizontal direction and the vertical direction perpendicular to the span direction as the vertical direction, longitudinal and transverse matrix points are drawn, with at least two rows in the horizontal direction and at least ten columns in the vertical direction. Furthermore, the longitudinal and transverse matrix points are 24.

[0017] Furthermore, the three-axis vibration sensor is installed by gluing.

[0018] The advantages of the present invention are that the present invention can accurately simulate the constraint mode of the blade root, and at the same time, by suspending the blade with a spring rope to simulate the centrifugal force when the blade is working, the natural frequency of the blade in a non-rotating state can be measured more accurately and truly. The test results and the calculation results are shown in Table 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram for implementing the method of the present invention;

[0020] Figure 2 This is a schematic diagram of the hammering point;

[0021] Among them: 1-blade, 2-sling, 3-hook, 4-hub, 5-helicopter. DETAILED DESCRIPTION

[0022] The disclosed examples will be more fully described with reference to the accompanying drawings, in which some (but not all) of the disclosed examples are shown. In fact, many different examples may be described and these examples should not be construed as limited to the examples set forth herein. Instead, these examples are described so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art.

[0023] A frequency measurement method applicable to a star-shaped flexible hub helicopter blade is provided, the method comprising the following steps:

[0024] Step 1: Install the rotor blades on the hub through the blade pins. The hub is installed on the main rotor shaft. Brake the rotor to ensure that the rotor cannot rotate.

[0025] Step 2: Move the hook to the tip of the blade to be tested, and use a sling to support the lower part of the blade tip wing surface and tie it to the hook so that the hook hangs on the tip of the blade. Measure and adjust the length of the sling to ensure that the swing natural frequency of the hanging system is less than 1 / 5 of the first-order bending frequency of the blade; the swing natural frequency of the hanging system g is the acceleration due to gravity, L is the length of the sling;

[0026] Step 3: Use the hook to adjust the height of the propeller tip so that the propeller blade is level with the hub plane. Use the rangefinder to measure the distance h1 from the center of gravity of the propeller blade to the ground, the distance h2 from the tip of the propeller blade to the ground, the distance R1 from the hub center to the center of gravity of the propeller blade, and the distance R2 from the hub center to the tip of the propeller. Use the formula and The angles θ1 and θ2 are calculated respectively. When the angles θ1 and θ2 are both 4.5°, the requirement that the blade is level with the hub plane is met. If not, continue to operate the hook to adjust the height of the blade tip, and change the distances h1 and h2 until they are met.

[0027] Step 4: Keep the propeller hub inertia weight and the limiter support separated, and ensure that the distance between the measured inertia weight and the limiter support is greater than 3 mm, so as to truly simulate the root constraint state of the blade in the working environment;

[0028] Step 5: Arrange multiple tapping points in a matrix from the root of the blade to the tip of the blade. Perform a tap at each tapping point for each measurement, and measure the blade's natural frequency using a three-axis vibration sensor.

[0029] The triaxial vibration sensors were installed at the blade root, blade airfoil section and blade tip during each measurement.

[0030] The blade natural frequencies measured at each strike are averaged.

[0031] The hub inertia weight is kept separated from the limiter support by using a strap to tie the hub root and tighten it.

[0032] From the root of the blade to the tip of the blade, on the equivalent plane of the airfoil, with the span direction as the horizontal direction and the vertical direction perpendicular to the span direction as the vertical direction, draw longitudinal and transverse matrix points, with at least two rows horizontally and at least ten columns vertically, and a total of 24 longitudinal and transverse matrix points.

[0033] The triaxial vibration sensor is installed by gluing.

[0034] Table 1 Comparison of test results and calculation results (HZ)

[0035]

[0036] It can be seen from Table 1 that the error between the measured results and the calculated results of this method is controlled within 3%, and its experimental accuracy meets the requirements of engineering applications.

[0037] The description of different advantageous arrangements has been presented for purposes of illustration and description, but the description is not intended to be exclusive or limited to examples of the disclosed form. Many modifications and variations will be apparent to those of ordinary skill in the art. Additionally, different advantageous examples may describe different advantages over other advantageous examples. The selected example or examples are chosen and described in order to best illustrate the principles of the examples, the practical application, and to enable those of ordinary skill in the art to understand the disclosure with various examples with various modifications suitable for the particular use contemplated.

Claims

1. A frequency measurement method for star-shaped flexible hub helicopter blades, characterized in that: The method comprises the following steps: Step 1: Install the rotor blades on the hub through the blade pins. The hub is installed on the main rotor shaft. Brake the rotor to ensure that the rotor cannot rotate. Step 2: Move the hook to the tip of the blade to be tested, and use a sling to support the lower part of the blade tip wing surface and tie it to the hook so that the hook hangs on the tip of the blade. Measure and adjust the length of the sling to ensure that the swing natural frequency of the hanging system is less than 1 / 5 of the first-order bending frequency of the blade; the swing natural frequency of the hanging system g is the acceleration due to gravity, L is the length of the sling; Step 3: Use the hook to adjust the height of the propeller tip so that the propeller blade is level with the hub plane. Use the rangefinder to measure the distance h1 from the center of gravity of the propeller blade to the ground, the distance h2 from the tip of the propeller blade to the ground, the distance R1 from the hub center to the center of gravity of the propeller blade, and the distance R2 from the hub center to the tip of the propeller. Use the formula and The angles θ1 and θ2 are calculated respectively. When the angles θ1 and θ2 are both 4.5°, the requirement that the blade is level with the hub plane is met. If not, continue to operate the hook to adjust the height of the blade tip, and change the distances h1 and h2 until they are met. Step 4: Keep the propeller hub inertia weight and the limiter support separated, and ensure that the distance between the measured inertia weight and the limiter support is greater than 3 mm, so as to truly simulate the root constraint state of the blade in the working environment; Step 5: Arrange multiple tapping points in a matrix from the root of the blade to the tip of the blade. Perform a tap at each tapping point for each measurement, and measure the blade's natural frequency using a three-axis vibration sensor.

2. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 1, characterized in that: The triaxial vibration sensors were installed at the blade root, blade airfoil section and blade tip during each measurement.

3. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 1, characterized in that: Multiple triaxial vibration sensors are installed at the blade root, blade airfoil section and blade tip respectively.

4. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 1, characterized in that: The blade natural frequencies measured at each strike are averaged.

5. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 1, characterized in that: The hub inertia weight is kept separated from the limiter support by using a strap to tie the hub root and tighten it.

6. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 1, characterized in that: From the root of the blade to the tip of the blade, on the equivalent plane of the airfoil, with the span direction as the horizontal direction and the vertical direction perpendicular to the span direction as the vertical direction, draw longitudinal and transverse matrix points, with at least two rows horizontally and at least ten columns vertically.

7. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 6, characterized in that: There are 24 matrix points in the vertical and horizontal directions.

8. The frequency measurement method applicable to the star-shaped flexible hub helicopter blade according to claim 1, characterized in that: The triaxial vibration sensor is installed by gluing.

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