Device and method for testing transient longitudinal aerodynamic characteristics of fixed-wing unmanned aerial vehicle

Abstract

The invention belongs to the field of unmanned aerial vehicle aerodynamics, and particularly relates to a device and a method for testing transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle. According to the scheme, the electric cylinder is used as an actuator, and the pitching angle of the unmanned aerial vehicle can be dynamically adjusted by controlling the elongation change of the electric cylinder. The supporting legs, the bottom frame, the front vertical frame and the rear vertical frame which are used by the device can be built by adopting profiles, and the device is simple in structure, low in cost and convenient to assemble.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned aerial vehicle (UAV) aerodynamics, and in particular to a device and method for testing transient longitudinal aerodynamic characteristics of a fixed-wing UAV. Background Art

[0002] Fixed-wing UAVs are widely used in military fields such as reconnaissance, navigation, and detection. They also have great practical value in civilian fields such as forest fire prevention, disaster relief, and meteorological monitoring. Therefore, the aerodynamic research of fixed-wing UAVs has become a research hotspot in recent years. Generally, the aerodynamic model of fixed-wing UAVs can be divided into longitudinal model and lateral model, among which the longitudinal model can cover the main working conditions of fixed-wing UAV flight. As a nonlinear system with multiple inputs and multiple outputs, fixed-wing UAVs have the characteristics of high order, strong coupling, and under-actuation. How to establish a more accurate longitudinal aerodynamic model has always been a research difficulty. At the same time, it is increasingly inseparable from a large amount of wind tunnel test data as an empirical guide for model verification and model modification. At present, the longitudinal aerodynamic characteristics test of fixed-wing UAVs is a simple static test, that is, the UAV is fixedly connected to the wind tunnel turntable, the pitch angle cannot be adjusted, and there is no information related to the pitch angular velocity. The test data and the aerodynamic equation cannot fit the transient aerodynamic characteristics well. Summary of the invention

[0003] In view of this, the present invention proposes a fixed-wing UAV transient longitudinal aerodynamic characteristics testing device and method, which can realize the testing of transient longitudinal aerodynamic characteristics.

[0004] To achieve the above object, the technical solution of the present invention is: A fixed-wing UAV transient longitudinal aerodynamic characteristics testing device comprises a leg I, a leg II, an electric cylinder, a base frame, a front frame, a rear frame, a balance and a connecting plate; Among them, leg I is fixedly connected to the left front part of the base frame, leg II is fixedly connected to the right front part of the base frame, legs I and II are symmetrically distributed on the left and right, the electric cylinder is fixedly connected to the rear middle part of the base frame, the front frame is fixedly connected to the front cross beam in the middle part of the base frame, the rear frame is fixedly connected to the rear cross beam in the middle part of the base frame, the balance is fixed to the upper part of the front frame and the rear frame, the connecting plate is fixed to the upper part of the balance, and the connecting plate is used to connect the balance and the UAV; the pitch angle change of the UAV is realized by the extension and contraction action of the electric cylinder, and on this basis, the transient longitudinal aerodynamic characteristics test is realized in conjunction with the wind speed change in the wind tunnel and the angle change of the UAV rudder surface.

[0005] The present invention also provides a method for testing transient longitudinal aerodynamic characteristics of a fixed-wing UAV, which is implemented using the device of the present invention, and includes: Step 1: Place the fixed-wing UAV transient longitudinal aerodynamic characteristics test device on the wind tunnel rotating platform, and make the wind tunnel air supply direction parallel to the x direction of the test device; Step 2: Design the test conditions, including determining the wind tunnel wind speed and the aileron rudder angle of the fixed-wing UAV Change curve, fixed-wing drone tail rudder angle Change curve and pitch angle change curve of the test device; Step 3: Conduct the test according to the designed test conditions. The host computer reads the x, y, z three-axis forces Fx1, Fy1, Fz1 and the moments Ml, Mm, Mn around the three axes in the balance coordinate system obtained by the balance; perform coordinate conversion to obtain the x, y, z three-axis forces Fx, Fy, Fz in the airflow coordinate system; obtain the lift, drag and lateral force at the sampling moments of equal time intervals within the time period, and the collection of each sampling moment constitutes a force time series; lift, drag and pitch moment are expressed as wind tunnel air supply wind speed V, pitch angle , pitch angular velocity q and the tail rudder angle of the fixed-wing UAV The functional relationship of the aerodynamic coefficients K is fitted using the least squares fitting method.

[0006] Wherein, the coordinate transformation formula is as follows: , , .

[0007] Wherein, the functional relationship is:

[0008]

[0009] in, is the dynamic pressure, is the total surface area of ​​the aircraft wing, is the average aerodynamic chord length of the aircraft, is the drag aerodynamic coefficient under longitudinal conditions, is the lift aerodynamic coefficient under longitudinal conditions, is the pitching moment aerodynamic coefficient under longitudinal conditions.

[0010] Among them, a transient correction function is introduced to describe the aerodynamic behavior in dynamic flight and is used for transient longitudinal aerodynamic characteristics testing.

[0011] Among them, the transient pitch angle adjustment process is: Step 1: Adjust the electric cylinder until the base is horizontal, set the length of the electric cylinder to zero, measure the upper limit bmax and lower limit bmin of the elongation of the electric cylinder at zero, and measure the distance a between the outriggers I and II and the electric cylinder in the x direction; Step 2: The conversion formula between the electric cylinder extension b and the pitch angle α is obtained through geometric relationship. When the electric cylinder is extended at the starting position, the pitch angle is positive. When the electric cylinder is retracted at the starting position, the pitch angle is negative. The conversion formula is as follows: , , calculate the maximum pitch angle based on the upper limit bmax and the lower limit bmin , minimum pitch angle After designing the expected pitch angle change curve of the UAV under the constraints of the maximum pitch angle and the minimum pitch angle, the formula Obtain the expected electric cylinder extension b variation curve; Step 3: The host computer sends control instructions to the electric cylinder controller through serial communication, generates a pitch angle when the extension of the electric cylinder changes, and reads the actual extension value of the electric cylinder. , through the formula , get the actual value of the drone's pitch angle , take the pitch angle of the sampling period with equal time interval A pitch angle time series is constructed, and the pitch angle time series is differentially derived to obtain a time series of pitch angular velocity q.

[0012] The derivation formula is as follows: ,in is the pitch angular velocity at the ith moment, It is i The pitch angle at a moment, is the pitch angle at the i-1th moment, is the time interval between adjacent sampling points, and n is the total number of sampling points.

[0013] Beneficial Effects 1. The device of the present invention uses an electric cylinder as an actuator, which can realize dynamic adjustment of the pitch angle of the UAV by controlling the elongation change of the electric cylinder, and can overcome the deficiency that the longitudinal aerodynamic characteristics test device of the fixed-wing UAV can only perform static testing.

[0014] 2. In the device of the present invention, the base frame and the front and rear frames can be constructed with profiles, which have a simple structure, low cost, and convenient assembly. In addition, an electric cylinder is used as an actuator, which has a simple control method and high control accuracy.

[0015] 3. The device of the present invention realizes multi-degree-of-freedom simulation, and can accurately simulate the pitch, roll and other complex movements of fixed-wing UAVs under different flight conditions, providing a more realistic test environment than the traditional single-condition test. This helps to more fully understand the aerodynamic characteristics of UAVs under various flight conditions; and by precisely controlling the extension and retraction of the electric cylinder, the attitude of the UAV can be fine-tuned, ensuring high-precision attitude control during the test. This high precision is crucial for studying the aerodynamic performance of UAVs under subtle attitude adjustments.

[0016] 4. The test device of the present invention supports the free switching between steady-state and transient conditions, as well as the independent or joint adjustment of pitch angle and roll angle, which greatly enhances the flexibility of experimental design. Researchers can easily set and adjust experimental conditions according to different research purposes. By introducing the transient correction function, the dynamic characteristics of the UAV during the transition from transient to steady state can be more accurately captured, which is critical for evaluating the dynamic performance of the UAV, such as response speed, stability and maneuverability.

[0017] 5. Based on the data obtained by the device, the present invention can deeply analyze the aerodynamic characteristics of the UAV under different flight conditions, thereby optimizing the design parameters and flight control strategy of the UAV and improving the overall performance of the UAV. Compared with actual flight tests, the test device can complete a large number of preliminary tests under laboratory conditions, effectively reducing the number of flight tests and reducing R&D costs and risks.

[0018] 6. The fixed-wing UAV transient longitudinal aerodynamic characteristics test device of the present invention provides a test method, which has simple steps and can more accurately obtain the relationship between the lift, drag, pitch moment of the UAV and the wind tunnel air supply wind speed, the fixed-wing UAV rudder angle, and the pitch angle and pitch angular velocity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an axonometric diagram of the transient longitudinal aerodynamic characteristics test device for fixed-wing UAV according to the present invention; Figure 2 This is a left view of the transient longitudinal aerodynamic characteristics testing device for fixed-wing UAV of the present invention; Figure 3 This is a front view of the fixed-wing UAV transient longitudinal aerodynamic characteristics testing device of the present invention; Figure 4 This is a schematic diagram of the instantaneous pitch angle adjustment of the fixed-wing UAV of the present invention; Figure 5 It is a schematic diagram of the three-axis force conversion between the balance coordinate system and the airflow coordinate system of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0021] The present invention provides a fixed-wing UAV transient longitudinal aerodynamic characteristics testing device, comprising a leg Ⅰ1-1, a leg Ⅱ1-2, an electric cylinder 2, a base frame 3, a front frame 4-1, a rear frame 4-2, a balance 5 and a connecting plate 6.

[0022] Among them, leg Ⅰ1-1 is fixedly connected to the left front part of the base frame 3, leg Ⅱ1-2 is fixedly connected to the right front part of the base frame 3, legs Ⅰ1-1 and legs Ⅱ1-2 are symmetrically distributed on the left and right, the electric cylinder 2 is fixedly connected to the rear middle part of the base frame 3, the front frame 4-1 is fixedly connected to the front cross beam in the middle part of the base frame 3, the rear frame 4-2 is fixedly connected to the rear cross beam in the middle part of the base frame 3, the balance 5 is fixed to the upper part of the front frame 4-1 and the rear frame 4-2, the connecting plate 6 is fixed to the upper part of the balance 5, and the connecting plate 6 is used to connect the balance 5 and the drone.

[0023] The device for testing transient longitudinal aerodynamic characteristics of fixed-wing UAV of the present invention realizes the pitch angle change of the UAV through the extension and contraction action of the electric cylinder 2, thereby realizing the pitch angle adjustment of the fixed-wing UAV. On this basis, transient longitudinal aerodynamic characteristics testing can be realized by coordinating the wind tunnel wind speed change and the UAV rudder surface angle change.

[0024] The present invention also provides a method for testing transient longitudinal aerodynamic characteristics of a fixed-wing UAV, and the test is implemented using the device of the present invention, comprising the following steps: Step 1: Place the fixed-wing UAV transient longitudinal aerodynamic characteristics test device on the wind tunnel rotating platform, and align it with the test device through the wind tunnel test platform laser alignment device, so that the wind tunnel air supply direction is parallel to the x direction of the test device.

[0025] Step 2: Design the test conditions, including determining the wind tunnel wind speed and the aileron rudder angle of the fixed-wing UAV Change curve, fixed-wing drone tail rudder angle Change curve and pitch angle change curve of the test device.

[0026] Step 3: Test according to the designed test conditions, the host computer reads the x, y, z three-axis forces Fx1, Fy1, Fz1 and the moments Ml, Mm, Mn around the three axes in the balance coordinate system obtained by the balance 5. Since the balance 5 is fixedly connected to the chassis 3 and changes with the pitch angle during the test, conversion is required to obtain the x, y, z three-axis forces Fx, Fy, Fz in the airflow coordinate system. The conversion formula is as follows: , , Thus, the lift, drag, and lateral force at the sampling moments of equal time intervals within the period can be obtained, and the collection of each sampling moment constitutes a force time series. The lift, drag, and pitching moment can all be expressed as the wind tunnel air supply speed V, the pitch angle , pitch angular velocity q, fixed-wing drone tail rudder angle Functional relationship:

[0027]

[0028] in, is the dynamic pressure, is the total surface area of ​​the aircraft wing, is the average aerodynamic chord length of the aircraft, is the drag aerodynamic coefficient under longitudinal conditions, is the lift aerodynamic coefficient under longitudinal conditions, is the pitch moment aerodynamic coefficient under longitudinal working conditions. All variables in the above formula are known under the longitudinal aerodynamic characteristics test, and the aerodynamic coefficients K can be fitted using the least squares fitting method. The above formula can be used for steady-state longitudinal aerodynamic characteristics testing.

[0029] Specifically, in the embodiment of the present invention, the transient pitch angle adjustment is achieved by: Step 1: Adjust the electric cylinder 2 until the base frame 3 is in a horizontal position, set the length of the electric cylinder 2 at this time to the starting position, i.e., zero position, measure the upper limit bmax and lower limit bmin of the elongation of the electric cylinder 2 at zero position, and measure the distance a between the legs Ⅰ1-1, Ⅱ1-2 and the electric cylinder 2 in the x direction (the horizontal forward direction is the x direction, the vertical upward direction is the z direction, and the y direction conforms to the right-hand coordinate rule).

[0030] Step 2: The conversion formula between the extension b of the electric cylinder 2 and the pitch angle α is obtained through geometric relationship. When the electric cylinder 2 is extended at the starting position, the pitch angle is positive. When the electric cylinder 2 is retracted at the starting position, the pitch angle is negative. The conversion formula is as follows: , Since the stroke of electric cylinder 2 is limited, the maximum pitch angle is calculated based on the upper limit bmax and the lower limit bmin , minimum pitch angle After designing the expected pitch angle change curve of the UAV under the constraints of the maximum pitch angle and the minimum pitch angle, the formula The desired elongation b curve of the electric cylinder 2 is obtained.

[0031] Step 3: The host computer sends a control command to the controller of electric cylinder 2 through serial communication, generates a pitch angle under the change of the extension of electric cylinder 2, and reads the actual extension value of electric cylinder 2 , through the formula , get the actual value of the drone's pitch angle , take the pitch angle of the sampling period with equal time interval The pitch angle time series is formed. The time series of the pitch angle velocity q can be obtained by differentially derivation of the pitch angle time series. The derivation formula is as follows: ,in is the pitch angular velocity at the ith moment, is the pitch angle at the ith moment, is the pitch angle at the i-1th moment, is the time interval between adjacent sampling points, and n is the total number of sampling points. The pitch angle and pitch angular velocity are used for subsequent data analysis.

[0032] Furthermore, the aerodynamic characteristics test method of this embodiment can more accurately describe the aerodynamic behavior in dynamic flight by introducing a transient correction function. For example, in transient longitudinal conditions, the aerodynamic response under a pitch angle step. The correction formula is used for transient longitudinal aerodynamic characteristics testing, as shown below:

[0033]

[0034]

[0035]

[0036]

[0037] Where V is the wind speed of the wind tunnel, t is the time, and c is the characteristic chord length of the UAV. Compared with the steady-state aerodynamic characteristics test, the transient aerodynamic characteristics not only need to fit the aerodynamic coefficients K, but also need to fit the parameters , which is used to reflect the time evolution characteristics of the force response, that is, the dynamic process of transition from transient to steady state.

[0038] Through the above steps, the transient longitudinal aerodynamic characteristics test of fixed-wing UAV can be realized, which is used for the aerodynamic research of fixed-wing UAV. The aerodynamic coefficients K are obtained through the transient longitudinal aerodynamic characteristics test. Combining the aircraft's own parameters with the flight environment parameters, the transient force information during the flight can be obtained.

[0039] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fixed-wing UAV transient longitudinal aerodynamic characteristics test device, characterized in that: It includes outrigger I, outrigger II, electric cylinder, base frame, front frame, rear frame, balance and connecting plate; Among them, leg I is fixedly connected to the left front part of the base frame, leg II is fixedly connected to the right front part of the base frame, legs I and II are symmetrically distributed on the left and right, the electric cylinder is fixedly connected to the rear middle part of the base frame, the front frame is fixedly connected to the front cross beam in the middle part of the base frame, the rear frame is fixedly connected to the rear cross beam in the middle part of the base frame, the balance is fixed to the upper part of the front frame and the rear frame, the connecting plate is fixed to the upper part of the balance, and the connecting plate is used to connect the balance and the UAV; the pitch angle change of the UAV is realized by the extension and contraction action of the electric cylinder, and on this basis, the transient longitudinal aerodynamic characteristics test is realized in conjunction with the wind speed change in the wind tunnel and the angle change of the UAV rudder surface.

2. A method for testing transient longitudinal aerodynamic characteristics of a fixed-wing UAV, implemented using the device according to claim 1, characterized in that: include: Step 1: Place the fixed-wing UAV transient longitudinal aerodynamic characteristics test device on the wind tunnel rotating platform, and make the wind tunnel air supply direction parallel to the x direction of the test device; Step 2: Design the test conditions, including determining the wind tunnel wind speed and the aileron rudder angle of the fixed-wing UAV Change curve, fixed-wing drone tail rudder angle Change curve and pitch angle change curve of the test device; Step 3: Test according to the designed test conditions. The host computer reads the x, y, z three-axis forces Fx1, Fy1, Fz1 and the moments Ml, Mm, Mn around the three axes in the balance coordinate system obtained by the balance; coordinate conversion is performed to obtain the x, y, z three-axis forces Fx, Fy, Fz in the airflow coordinate system; the lift, drag and lateral force at the sampling moments of equal time intervals in the taken time period are obtained, and the collection of each sampling moment constitutes a force time series; the lift, drag and pitch moment are expressed as the wind tunnel air supply wind speed V and the pitch angle , pitch angular velocity q and the tail rudder angle of the fixed-wing UAV The functional relationship of the aerodynamic coefficients K is fitted using the least squares fitting method.

3. The method according to claim 2, characterized in that The coordinate transformation formula is as follows: , , .

4. The method according to claim 2, characterized in that The functional relationship is: in, is the dynamic pressure, is the total surface area of ​​the aircraft wing, is the average aerodynamic chord length of the aircraft, is the drag aerodynamic coefficient under longitudinal conditions, is the lift aerodynamic coefficient under longitudinal conditions, is the pitching moment aerodynamic coefficient under longitudinal conditions.

5. The method according to any one of claims 2 to 4, characterized in that: A transient correction function is introduced to describe the aerodynamic behavior in dynamic flight and is used for transient longitudinal aerodynamic characteristics testing.

6. The method according to any one of claims 2 to 4, characterized in that: The transient pitch angle adjustment process is: Step 1: Adjust the electric cylinder until the base is horizontal, set the length of the electric cylinder to zero, measure the upper limit bmax and lower limit bmin of the elongation of the electric cylinder at zero, and measure the distance a between the outriggers I and II and the electric cylinder in the x direction; Step 2: The conversion formula between the electric cylinder extension b and the pitch angle α is obtained through geometric relationship. When the electric cylinder is extended at the starting position, the pitch angle is positive. When the electric cylinder is retracted at the starting position, the pitch angle is negative. The conversion formula is as follows: , , calculate the maximum pitch angle based on the upper limit bmax and the lower limit bmin , minimum pitch angle After designing the expected pitch angle change curve of the UAV under the constraints of the maximum pitch angle and the minimum pitch angle, the formula Obtain the expected electric cylinder extension b variation curve; Step 3: The host computer sends control instructions to the electric cylinder controller through serial communication, generates a pitch angle when the extension of the electric cylinder changes, and reads the actual extension value of the electric cylinder. , through the formula , get the actual value of the drone's pitch angle , take the pitch angle of the sampling period with equal time interval A pitch angle time series is constructed, and the pitch angle time series is differentially derived to obtain a time series of pitch angular velocity q.

7. The method according to claim 6, characterized in that The derivative formula is as follows: ,in is the pitch angular velocity at the ith moment, It is i The pitch angle at a moment, is the pitch angle at the i-1th moment, is the time interval between adjacent sampling points, and n is the total number of sampling points.

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