Method for automatic level adjustment and attitude measurement of three-degree-of-freedom support system of low-speed wind tunnel

Abstract

This invention provides a method for automatically leveling and attitude measurement of a three-degree-of-freedom support system in a low-speed wind tunnel. The method includes: installing a dual-axis accelerometer on the support system's strut, such that its first sensitive axis is parallel to the pitch axis of the aircraft model and its second sensitive axis is parallel to the roll axis of the model; controlling the roll motor and angle-of-attack motor of the support system so that the output values ​​of both the first and second sensitive axes are zero, thus achieving automatic leveling of the model; during wind tunnel testing, comparing the roll angle measured by a first encoder (detecting the roll angle) and the angle of attack measured by a second encoder (detecting the angle of attack), using a first threshold and a second threshold, selecting the roll angle detected by the first sensitive axis or the measurement value of the first encoder as the actual roll angle of the model, and selecting the angle of attack detected by the second sensitive axis or the measurement value of the second encoder as the actual angle of attack of the model, thereby improving the measurement accuracy of the aircraft model's attitude angle during wind tunnel dynamic testing.

Description

Technical Field

[0001] This invention belongs to the field of aerospace aerodynamics wind tunnel testing technology, specifically relating to a method for automatically adjusting the level and measuring the attitude of a three-degree-of-freedom support system in a low-speed wind tunnel. Background Technology

[0002] Before conducting wind tunnel tests, the wind tunnel support system usually needs to level the supported test model to ensure it is in a horizontal position. Currently, this is mostly done manually using a level. However, low-speed wind tunnels often have relatively small diameters, such as a test section diameter of 1.2m and a test section length of 1.2m, allowing the angle mechanism to occupy a square area of ​​1.2m x 1.2m. Due to the small area, manually leveling such wind tunnel systems is very difficult and inefficient.

[0003] In addition, existing low-speed wind tunnel three-degree-of-freedom support systems measure the model's angles by encoders when adjusting the model's attitude during wind tunnel testing. However, for angle-of-attack mechanisms, the encoder measures the rotation angle of the motor shaft, which is connected to the load end through numerous mechanisms such as reducers and bevels. Similarly, for roll mechanisms, the motor shaft is also connected to the load end through a reducer. Therefore, the measured roll angle and angle of attack cannot accurately reflect the model's true attitude and include transmission chain errors. In particular, when the load is performing reciprocating commutation motion, transmission chain errors will have a significant impact on the test results. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies in low-speed wind tunnel three-degree-of-freedom support systems, such as the difficulty in leveling the test model manually and the inaccuracy in reflecting the true attitude angles of the model when using encoders to measure attitude angles. This invention provides a method for automatically leveling and measuring the attitude of a low-speed wind tunnel three-degree-of-freedom support system. This method uses a dual-axis accelerometer to automatically level the aircraft model, which is easy to operate. Furthermore, by combining accelerometers and encoders to measure the model's attitude angles, the accuracy of the model's attitude angle measurement is improved.

[0005] To achieve the above objectives, the technical solution provided by this invention is:

[0006] A method for automatically adjusting the level and measuring the attitude of a three-degree-of-freedom support system in a low-speed wind tunnel, characterized by the following steps:

[0007] Step 1: Install a dual-axis accelerometer on the support rod of the support system, such that the first sensitive axis of the dual-axis accelerometer is parallel to the pitch axis of the aircraft model supported by the support system, and the second sensitive axis is parallel to the roll axis of the aircraft model.

[0008] Step 2: Control the roll motor of the support system to make the output value of the first sensitive axis zero, and control the angle of attack motor of the support system to make the output value of the second sensitive axis zero, thereby achieving the leveling of the aircraft model;

[0009] Step 3: During the wind tunnel test, after the support system moves the aircraft model, the actual roll angle and actual angle of attack of the aircraft model are determined based on the measurements from the dual-axis accelerometer, the first encoder for detecting the roll angle, and the second encoder for detecting the angle of attack. This includes the following sub-steps:

[0010] Step 3.1: Obtain the roll angle detected by the first sensitive axis and the roll angle detected by the first encoder, and obtain the angle of attack detected by the second sensitive axis and the angle of attack detected by the second encoder;

[0011] Step 3.2, determine the actual roll angle and actual angle of attack of the aircraft model, including the following sub-steps:

[0012] Step 3.2.1: When the roll angle detected by the first encoder is greater than the first threshold, the roll angle detected by the first encoder is taken as the actual roll angle of the aircraft model; when the angle of attack detected by the second encoder is greater than the first threshold, the angle of attack detected by the second encoder is taken as the actual angle of attack of the aircraft model.

[0013] Step 3.2.2: When the roll angle detected by the first encoder is less than the second threshold, the roll angle detected by the first sensitive axis is taken as the actual roll angle of the aircraft model; when the angle of attack detected by the second encoder is less than the second threshold, the angle of attack detected by the second sensitive axis is taken as the actual angle of attack of the aircraft model.

[0014] Step 3.2.3: When the roll angle detected by the first encoder is between the second threshold and the first threshold, determine whether the roll angular velocity detected by the first encoder is less than zero. If it is less, the roll angle detected by the first sensitive axis is taken as the actual roll angle of the aircraft model. If it is not less, the roll angle detected by the first encoder is taken as the actual roll angle of the aircraft model. When the angle of attack detected by the second encoder is between the second threshold and the first threshold, determine whether the pitch angular velocity detected by the second encoder is less than zero. If it is less, the angle of attack detected by the second sensitive axis is taken as the actual angle of attack of the aircraft model. If it is not less, the angle of attack detected by the second encoder is taken as the actual angle of attack of the aircraft model.

[0015] Further, step 3.2 includes step 3.2.0 of determining the first threshold and the second threshold, which includes the following sub-steps:

[0016] Step 3.2.0.1: Select an angle as the judgment threshold value based on the linearity of the dual-axis accelerometer;

[0017] Step 3.2.0.2: Use the judgment limit value plus the first extended value as the first threshold, and use the judgment limit value minus the second extended value as the second threshold.

[0018] Furthermore, in step 3.2.0.2, the first extended value and the second extended value are set to the same value.

[0019] Furthermore, in step 3.2.0.2, both the first extended value and the second extended value are set to 0.1.

[0020] Further, in step 3.2.0: the judgment threshold value is set to 5°; the first threshold value is set to 5.1°, and the second threshold value is set to 4.9°.

[0021] Furthermore, step 1 includes the following sub-steps:

[0022] Step 1.1: Machin a plane on the support rod, which is parallel to the plane formed by the roll axis and pitch axis of the aircraft model;

[0023] Step 1.2: Mount the bottom surface of the biaxial accelerometer onto the plane.

[0024] The advantages of this invention are:

[0025] The present invention provides a method for automatically leveling and measuring attitude of a three-degree-of-freedom support system in a low-speed wind tunnel. This method utilizes a dual-axis accelerometer mounted on the test model's support rod to automatically level the aircraft model, saving manpower, simplifying operation, and increasing efficiency. Furthermore, based on the good linearity of the dual-axis accelerometer's detection range, a first threshold and a second threshold are selected. These two thresholds are compared with the roll angle measured by a first encoder (detecting the roll angle) and the angle of attack measured by a second encoder (detecting the angle of attack). The roll angle detected by the first sensitive axis of the dual-axis accelerometer or the measurement value of the first encoder is selected as the actual roll angle of the model, and the angle of attack detected by the second sensitive axis of the dual-axis accelerometer or the measurement value of the second encoder is selected as the actual angle of attack of the model. This improves the measurement accuracy of the aircraft model's attitude angle during wind tunnel dynamic testing. Attached Figure Description

[0026] The features and advantages of the invention will become more readily apparent from the following description with reference to the accompanying drawings, which are not drawn to scale and some features are enlarged or reduced to show details of specific parts.

[0027] Figure 1 This is a schematic diagram of the overall support system for a low-speed wind tunnel with three degrees of freedom.

[0028] Figure 2This is a schematic perspective view showing the mounting structure of the dual-axis accelerometer on the support system;

[0029] Figure 3 This is a flowchart of a method for automatically adjusting the level and measuring the attitude of a three-degree-of-freedom support system for a low-speed wind tunnel according to an exemplary embodiment of the present invention.

[0030] In the diagram: 1-base, 2-rolling motor, 3-rolling reducer, 4-rolling bracket, 5-support rod; 6-angle of attack motor, 7-angle of attack reducer, 8-roller, 9-slide rail rack seat; 10-traveling mechanism, 11-curved blade, 12-arc rack, 13-arc slide rail; 14-side sliding angle motor, 15-side sliding angle reducer; 100-aircraft model; 200-dual-axis accelerometer. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and exemplary embodiments thereof. It should be noted that the following detailed description of the present invention is for illustrative purposes only and is not intended to limit the scope of the invention.

[0032] Reference Figure 1 The low-speed wind tunnel three-degree-of-freedom support system includes a base, a roll angle mechanism, an angle of attack mechanism, and a sideslip angle mechanism. The base 1 supports the roll angle mechanism, angle of attack mechanism, and sideslip angle mechanism. The roll angle mechanism connects to the aircraft model 100 to be tested in the wind tunnel and adjusts the roll angle of the aircraft model 100. The roll angle range is -90° to 90°, the angular velocity is not less than 3° / s, and the angle error is less than 3′. The angle of attack mechanism adjusts the angle of attack of the aircraft model 100. The angle of attack range is -20° to 40°, the angular velocity is not less than 3° / s, and the angle error is less than 3′. The sideslip angle mechanism adjusts the sideslip angle of the aircraft model 100. The sideslip angle range is -30° to 30°, the angular velocity is not less than 3° / s, and the angle error is less than 3′.

[0033] The roll angle mechanism includes a roll drive mechanism for providing roll driving force to the aircraft model 100, which includes a roll motor 2 and a roll reducer 3 coaxially connected. The roll angle mechanism also includes a roll bracket 4 and a generally columnar support rod 5 for supporting the aircraft model 100.

[0034] A roll drive mechanism is mounted to a roll bracket 4. A support rod 5 is rotatably connected to the roll bracket 4. The output shaft of the roll reducer 3 is connected to the support rod 5 to drive the support rod 5 to rotate around the roll axis, i.e., the x-axis, of the aircraft model 100, thereby adjusting the roll angle of the aircraft model 100. The roll angle mechanism also includes a first encoder for the roll motor 2 to measure the roll attitude angle of the motor load end, i.e., the wind tunnel test model, when adjusting the roll angle. The roll motor 2 can be a motor with a built-in encoder, i.e., the first encoder is integrated into the roll motor 2. It should be understood that the first encoder can also be mounted externally to the roll motor 2.

[0035] The angle-of-attack mechanism includes an angle-of-attack drive mechanism for providing pitch drive force to the aircraft model 100. The angle-of-attack drive mechanism includes an angle-of-attack motor 6 and an angle-of-attack reducer 7. The angle-of-attack mechanism also includes a roller 8, a slide rail rack seat 9, a travel mechanism 10, and a scimitar 11.

[0036] The output shaft of the angle-of-attack reducer 6 is connected to the roller 8 to drive the roller 8 to rotate. The circumferential teeth on the roller 8 mesh with the arc-shaped rack 12 on the slide rail rack seat 9. Arc-shaped slide rails 13 are symmetrically arranged on both sides of the slide rail rack seat 9. The traveling mechanism 10 is used to reciprocate along the slide rail rack seat 9 and includes a slider and an angle-of-attack bracket connected to each other. The angle-of-attack reducer 7 is mounted to the angle-of-attack bracket. The curved blade 11 is arc-shaped. The upper end of the curved blade 11 is fixed to the rolling bracket 4, and the lower end of the curved blade 11 is fixed to the angle-of-attack bracket so that it moves with the angle-of-attack bracket, thereby causing the aircraft model 100 to rotate around its pitch axis, i.e., the y-axis, to adjust the pitch angle of the aircraft model 100. The angle-of-attack mechanism also includes a second encoder for the angle-of-attack motor 6 for detecting the angle-of-attack attitude of the aircraft model 100 during pitch angle adjustment. When selecting the angle-of-attack motor 6, you can choose a motor with a built-in encoder, that is, the second encoder is integrated into the angle-of-attack motor 6. Of course, you can also install the second encoder outside the angle-of-attack motor 6.

[0037] The sideslip mechanism includes a sideslip drive mechanism for providing yaw drive force to the aircraft model 100. The sideslip drive mechanism includes a sideslip motor 14 and a sideslip reducer 15. The sideslip reducer 15 is mounted to the base 1 such that the output shaft of the sideslip reducer 15 coincides with the yaw axis, i.e., the z-axis, of the aircraft model 100. The sideslip drive mechanism drives the slide rail rack seat 9 and the entire angle of attack mechanism and roll mechanism to rotate around the yaw axis of the aircraft model 100, thereby causing the aircraft model 100 to rotate around its yaw axis.

[0038] The support system is connected to a control system to adjust the attitude angles of the aircraft model. The control system includes a host industrial computer, an RS485 communication module, a motion controller, and servo motor drivers corresponding to the roll drive mechanism, angle-of-attack drive mechanism, and sideslip drive mechanism. The host industrial computer sends commands to the four-axis motion controller via the RS485 bus. The motion controller uses pulse and position control. After receiving the command, the motion controller sends a signal to the corresponding servo motor driver to drive at least one of the roll drive mechanism, angle-of-attack drive mechanism, and sideslip drive mechanism, thereby changing the attitude angles of the aircraft model 100.

[0039] Reference Figure 2 Based on the above description of the support system structure, the attitude of the strut 5 reflects the attitude of the aircraft model 100. Therefore, a dual-axis accelerometer 200 can be installed on the strut 5 to automatically level the aircraft model 100 and measure roll and pitch acceleration during wind tunnel testing. Since the accelerometer 200 is installed at the load end, the load's attitude angle can be directly calculated while effectively avoiding transmission chain errors, thereby improving the accuracy of attitude angle measurement.

[0040] The principle of accelerometer in measuring tilt angle is as follows:

[0041] When the accelerometer's sensing axis is perpendicular to the vertical, the output is zero. When the accelerometer's sensing axis is not perpendicular to the vertical, the accelerometer's output is G1. Therefore, the angle α between the accelerometer's sensing axis and the horizontal plane is:

[0042]

[0043] In the formula, G represents the acceleration due to gravity. Therefore, this formula can be used to calculate the angle between the side axis and the horizontal plane based on the output of the accelerometer.

[0044] By combining the above formula with the characteristics of the sine function, it can be seen that the accelerometer exhibits good measurement linearity within a certain range, such as -10° to 10°, and even better linearity at smaller angles. However, when the load attitude angle is large, the nonlinearity of calculating the angle using accelerometer parameters is significant, which can also cause errors. Therefore, the accelerometer can be used to measure attitude angles within a small range where linearity is relatively good. Furthermore, for larger attitude angles where the accelerometer's linearity is poor, an encoder can be used for measurement. Combining the accelerometer and encoder to measure the load attitude angle can improve the accuracy of angle measurement.

[0045] Reference Figure 3 The method for automatically adjusting the level and measuring the attitude of a low-speed wind tunnel three-degree-of-freedom support system, as an exemplary embodiment of the present invention, may include the following steps:

[0046] Step 1: Install a dual-axis accelerometer 200 on the support rod 5 of the support system, such that the first sensitive axis of the dual-axis accelerometer 200 is parallel to the pitch axis of the aircraft model 100 supported by the support system, and the second sensitive axis is parallel to the roll axis of the aircraft model 100. Thus, the roll angle φ1 of the aircraft model 100 can be calculated using the above formula through the output value of the first sensitive axis of the dual-axis accelerometer 200, and the angle of attack θ1 of the aircraft model 100 can be calculated using the above formula through the output value of the second sensitive axis of the dual-axis accelerometer 200.

[0047] Step 2: Control the roll motor of the support system to make the output value of the first sensitive axis zero, and control the angle of attack motor of the support system to make the output value of the second sensitive axis zero, thereby realizing the leveling of the aircraft model 100. When the roll angle and / or angle of attack of the aircraft model 100 are not zero, the corresponding motor can be controlled by the control system to rotate in the direction of reducing the output of the accelerometer until the output values ​​of the two sensitive axes of the accelerometer are both zero, so that automatic leveling can be achieved conveniently and quickly. Therefore, leveling does not require manual operation, saving manpower and improving efficiency.

[0048] Step 3: During the wind tunnel test, after the support system drives the aircraft model 100 to move, the actual roll angle and actual angle of attack of the aircraft model 100 are determined based on the measurement value of the dual-axis accelerometer 200, the measurement value φ2 of the first encoder used to detect the roll angle of the aircraft model, and the measurement value θ2 of the second encoder used to detect the angle of attack of the aircraft model.

[0049] In an optional embodiment of the present invention, step 1 includes the following sub-steps:

[0050] Step 1.1: Machin a plane on the support rod 5, which is parallel to the plane formed by the roll axis and pitch axis of the aircraft model 100;

[0051] Step 1.2: Install the bottom surface of the biaxial accelerometer 200 onto the plane of the support rod 5.

[0052] It should be understood that, in the direction of the roll axis of the aircraft model 100, the accelerometer 200 is installed between the aircraft model 100 and the roll support 4, and is installed as close as possible to the aircraft model 100; in the direction of the yaw axis of the aircraft model 100, the accelerometer 200 is set as close as possible to the plane containing the roll axis and pitch axis of the aircraft model 100, in order to reduce the attitude angle measurement error.

[0053] Step 3 includes the following sub-steps:

[0054] Step 3.1: Obtain the roll angle φ1 detected by the first sensitive axis and the roll angle φ2 detected by the first encoder, and obtain the angle of attack θ1 detected by the second sensitive axis and the angle of attack θ2 detected by the second encoder;

[0055] Step 3.2: Determine the actual roll angle and actual angle of attack of the aircraft model 100.

[0056] In step 3.2, it can be determined whether to use the attitude angle calculated from the output value of the accelerometer as the actual attitude angle or the detection value of the encoder as the actual attitude angle of the model, based on the measured angle range where the linearity of the accelerometer is good. In other words, it is necessary to select a threshold based on the measured angle range where the linearity of the accelerometer is good. For example, assuming that the linearity of the accelerometer is good in the attitude angle range of -8° to 8°, then 8° will be selected as the threshold for both roll angle measurement and angle of attack measurement. Furthermore, if only a specific angle is used as the judgment limit, the output angle will frequently jump between the accelerometer and the encoder when there is a disturbance at that position, resulting in unstable measurement results for that limit angle. Therefore, the selected threshold can be extended to a range, thus obtaining two thresholds, namely the first threshold λ1 as the upper limit and the second threshold λ2 as the upper limit. Taking 8° as an example, the first threshold can be selected as 8.1° and the second threshold can be selected as 7.9°. However, this is not intended to limit the present invention. Thus, the first threshold and the second threshold can be used as judgment limits to compare with the angle value measured by the encoder to determine whether the measurement value of the dual-axis accelerometer or the measurement value of the encoder is used as the actual attitude angle of the test model.

[0057] In other words, in an exemplary embodiment of the present invention, the first threshold λ1 and the second threshold λ2 can be determined by the following steps:

[0058] Based on the linearity of the dual-axis accelerometer 200, an angle is selected as the judgment threshold. This angle value is not subject to specific restrictions and can be selected according to the specific wind tunnel test requirements.

[0059] The first threshold λ1 is the selected judgment boundary value plus the first extended value, and the second threshold λ2 is the judgment boundary value minus the second extended value. The first extended value and the second extended value are decimals between 0 and 1, such as 0.1, 0.2, 0.3, etc.

[0060] In some embodiments, the first extension value and the second extension value may be the same value, specifically, both may be 0.1. For example, when the judgment threshold value is set to 5°, the first threshold λ1 may be 5.1° and the second threshold λ2 may be 4.9°.

[0061] According to the present invention, step 3.2 includes step 3.2.1: when the roll angle φ2 detected by the first encoder is greater than the first threshold λ1, the roll angle φ2 detected by the first encoder is taken as the actual roll angle of the aircraft model 100; when the angle of attack θ2 detected by the second encoder is greater than the first threshold λ1, the angle of attack θ2 detected by the second encoder is taken as the actual angle of attack of the aircraft model 100. Those skilled in the art will understand that the thresholds mentioned herein are vectors rather than scalars. For example, if the threshold is 5°, it means that the threshold can be +5° or -5°.

[0062] Step 3.2 also includes step 3.2.2: when the roll angle φ2 detected by the first encoder is less than the second threshold λ2, the roll angle φ1 detected by the first sensitive axis is taken as the actual roll angle of the aircraft model 100; when the angle of attack θ2 detected by the second encoder is less than the second threshold λ2, the angle of attack θ1 detected by the second sensitive axis is taken as the actual angle of attack of the aircraft model 100.

[0063] Step 3.2 further includes step 3.2.3: When the roll angle φ2 detected by the first encoder is between the second threshold λ2 and the first threshold λ1, it is determined whether the roll angular velocity detected by the first encoder is less than zero. If it is less than zero, the roll angle φ1 detected by the first sensitive axis is taken as the actual roll angle of the aircraft model 100. If it is not less than zero, the roll angle φ2 detected by the first encoder is taken as the actual roll angle of the aircraft model 100. When the angle of attack θ2 detected by the second encoder is between the second threshold λ2 and the first threshold λ1, it is determined whether the pitch angular velocity detected by the second encoder is less than zero. If it is less than zero, the angle of attack θ1 detected by the second sensitive axis is taken as the actual angle of attack of the aircraft model 100. If it is not less than zero, the angle of attack θ2 detected by the second encoder is taken as the actual angle of attack of the aircraft model 100.

[0064] Through the above judgment process, the actual roll angle and angle of attack of the aircraft model 100 can be accurately measured, which can be achieved using a control system based on known mature technologies.

[0065] As described above, the method for automatically leveling and measuring attitude of a three-degree-of-freedom support system in a low-speed wind tunnel according to the present invention utilizes a dual-axis accelerometer mounted on the test model support rod to automatically level the aircraft model, saving manpower, simplifying operation, and increasing efficiency. Furthermore, based on the good linearity of the dual-axis accelerometer's detection range, a first threshold and a second threshold are set. These two thresholds are compared with the roll angle measured by the first encoder for detecting the roll angle of the model and the angle of attack measured by the second encoder for detecting the angle of attack of the model. The roll angle detected by the first sensitive axis of the dual-axis accelerometer or the measurement value of the first encoder is selected as the actual roll angle of the model, and the angle of attack detected by the second sensitive axis of the dual-axis accelerometer or the measurement value of the second encoder is selected as the actual angle of attack of the model, thereby improving the measurement accuracy of the aircraft model's attitude angle in wind tunnel dynamic tests.

[0066] The features mentioned and / or shown in the foregoing description of exemplary embodiments of the present invention may be combined in the same or similar manner with one or more other embodiments, combined with features in other embodiments, or substituted for corresponding features in other embodiments. These combined or substituted technical solutions should also be considered to be included within the scope of protection of the present invention.

Claims

1. A method for automatically adjusting the level and measuring the attitude of a three-degree-of-freedom support system in a low-speed wind tunnel, characterized in that... Includes the following steps: Step 1: Install a dual-axis accelerometer on the support rod of the support system, such that the first sensitive axis of the dual-axis accelerometer is parallel to the pitch axis of the aircraft model supported by the support system, and the second sensitive axis is parallel to the roll axis of the aircraft model. Step 2: Control the roll motor of the support system to make the output value of the first sensitive axis zero, and control the angle of attack motor of the support system to make the output value of the second sensitive axis zero, thereby realizing the leveling of the aircraft model; Step 3: During the wind tunnel test, after the support system moves the aircraft model, the actual roll angle and actual angle of attack of the aircraft model are determined based on the measurements from the dual-axis accelerometer, the first encoder for detecting the roll angle, and the second encoder for detecting the angle of attack. This includes the following sub-steps: Step 3.1: Obtain the roll angle detected by the first sensitive axis and the roll angle detected by the first encoder, and obtain the angle of attack detected by the second sensitive axis and the angle of attack detected by the second encoder; Step 3.2, determine the actual roll angle and actual angle of attack of the aircraft model, including the following sub-steps: Step 3.2.1: When the roll angle detected by the first encoder is greater than the first threshold, the roll angle detected by the first encoder is taken as the actual roll angle of the aircraft model; when the angle of attack detected by the second encoder is greater than the first threshold, the angle of attack detected by the second encoder is taken as the actual angle of attack of the aircraft model. Step 3.2.2: When the roll angle detected by the first encoder is less than the second threshold, the roll angle detected by the first sensitive axis is taken as the actual roll angle of the aircraft model; when the angle of attack detected by the second encoder is less than the second threshold, the angle of attack detected by the second sensitive axis is taken as the actual angle of attack of the aircraft model. Step 3.2.3: When the roll angle detected by the first encoder is between the second threshold and the first threshold, determine whether the roll angular velocity detected by the first encoder is less than zero. If it is less, the roll angle detected by the first sensitive axis is taken as the actual roll angle of the aircraft model. If it is not less, the roll angle detected by the first encoder is taken as the actual roll angle of the aircraft model. When the angle of attack detected by the second encoder is between the second threshold and the first threshold, determine whether the pitch angular velocity detected by the second encoder is less than zero. If it is less, the angle of attack detected by the second sensitive axis is taken as the actual angle of attack of the aircraft model. If it is not less, the angle of attack detected by the second encoder is taken as the actual angle of attack of the aircraft model. The first threshold is 5.1° and the second threshold is 4.9°.

2. The method for automatically adjusting the level and measuring the attitude of a three-degree-of-freedom support system for a low-speed wind tunnel according to claim 1, characterized in that, Step 1 includes the following sub-steps: Step 1.1: Machine a plane on the support rod, the plane being parallel to the plane formed by the roll axis and pitch axis of the aircraft model; Step 1.2: Mount the bottom surface of the biaxial accelerometer onto the plane.

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