Fixed-wing UAV Transient Longitudinal Aerodynamic Characteristic Testing Device and Method

Abstract

The present invention belongs to the field of unmanned aerial vehicle (UAV) aerodynamics, and particularly relates to a test device and method for transient longitudinal aerodynamic characteristics of a fixed-wing UAV. The device of the present invention uses an electric cylinder as an actuator, which can achieve dynamic adjustment of the pitch angle of the UAV by controlling the change in the elongation of the electric cylinder. The legs, chassis, front and rear vertical frames used in the device of the present invention can all be built with profiles, featuring simple structure, low cost, and convenient assembly.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned aerial vehicle aerodynamics, and particularly relates to a test device and method for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle. Background Technique

[0002] Fixed-wing unmanned aerial vehicles are widely used in military fields such as reconnaissance, navigation, and detection, and also have great practical value in civilian fields such as forest fire prevention, disaster relief, and meteorological monitoring. Therefore, the research on the aerodynamics of fixed-wing unmanned aerial vehicles has become a research hotspot in recent years. Generally, the aerodynamic force model of a fixed-wing unmanned aerial vehicle can be divided into a longitudinal model and a lateral model, and the longitudinal model can cover the main working conditions of the fixed-wing unmanned aerial vehicle flight. As a multi-input multi-output nonlinear system, a fixed-wing unmanned aerial vehicle has characteristics such as high order, strong coupling, and underactuation. How to establish a more accurate longitudinal aerodynamic force model has always been a research difficulty, and at the same time, it increasingly relies on a large amount of wind tunnel test data as the empirical guidance for model verification and model modification. At present, the tests on the longitudinal aerodynamic characteristics of fixed-wing unmanned aerial vehicles are all simple static tests, that is, the unmanned aerial vehicle 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 well fit the transient aerodynamic characteristics. Summary of the Invention

[0003] In view of this, the present invention proposes a test device and method for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle, which can realize the test of transient longitudinal aerodynamic characteristics.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A test device for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle includes leg I, leg II, an electric cylinder, a chassis, a front stand, a rear stand, a balance, and a connecting plate;

[0006] Among them, leg I is fixedly connected to the left front part of the chassis, leg II is fixedly connected to the right front part of the chassis, leg I and leg II are symmetrically distributed left and right, the electric cylinder is fixedly connected to the middle rear part of the chassis, the front stand is fixedly connected to the middle front cross beam of the chassis, the rear stand is fixedly connected to the middle rear cross beam of the chassis, the balance is fixed to the upper parts of the front stand and the rear stand, and the connecting plate is fixed to the upper part of the balance. The connecting plate is used to connect the balance and the unmanned aerial vehicle; the pitch angle of the unmanned aerial vehicle is changed by the extension and contraction actions of the electric cylinder. On this basis, the transient longitudinal aerodynamic characteristics test is realized by coordinating the change of the wind tunnel wind speed and the change of the unmanned aerial vehicle rudder surface angle.

[0007] The present invention also provides a test method for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle, which is realized by using the device of the present invention, and includes:

[0008] Step 1: Place the fixed-wing UAV transient longitudinal aerodynamic characteristic 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;

[0009] Step 2: Design the test conditions, including determining the wind tunnel air supply velocity, the change curve of the fixed-wing UAV aileron control surface angle the change curve of the fixed-wing UAV tail control surface angle and the change curve of the pitch angle of the test device;

[0010] Step 3: Conduct the test according to the designed test conditions. The upper computer reads the forces Fx1, Fy1, Fz1 on the x, y, z axes and the moments Ml, Mm, Mn about the three axes in the balance coordinate system obtained by the balance; perform coordinate transformation to obtain the forces Fx, Fy, Fz on the x, y, z axes in the airflow coordinate system; obtain the lift, drag, and side force at each equal-time interval sampling moment within the selected time period, and the set of each sampling moment constitutes a force time series; the lift, drag, and pitch moment are expressed as functional relationships of the wind tunnel air supply velocity V, pitch angle , pitch angular velocity q, and the fixed-wing UAV tail control surface angle ; use the least square fitting method to fit each aerodynamic coefficient K.

[0011] Among them, the coordinate transformation formula is as follows: , , .

[0012] Among them, the functional relationship is:

[0013]

[0014]

[0015] Among them, is the dynamic pressure, is the total surface area of the aircraft wing, is the mean aerodynamic chord 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 conditions.

[0016] Among them, a transient correction function is introduced to describe the aerodynamic behavior during dynamic flight and is used for transient longitudinal aerodynamic characteristic testing.

[0017] Among them, the transient pitch angle adjustment process is:

[0018] Step 1: Adjust the electric cylinder so that the chassis is in a horizontal posture. Set the length of the electric cylinder at this time to zero. Measure the upper limit bmax and lower limit bmin of the elongation of the electric cylinder at zero, and measure the distances a between the first leg, the second leg and the electric cylinder in the x direction.

[0019] Step 2: Obtain the conversion formula between the elongation b of the electric cylinder and the pitch angle α through geometric relationships. When the electric cylinder elongates at the starting position, the pitch angle is positive; when the electric cylinder contracts at the starting position, the pitch angle is negative. The conversion formula is as follows: , , calculate the maximum pitch angle according to the upper limit bmax and the lower limit bmin , the 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, obtain the expected electric cylinder elongation b change curve through the formula .

[0020] Step 3: The host computer sends control instructions to the electric cylinder controller through serial communication. A pitch angle is generated under the change of the elongation of the electric cylinder, and the actual value of the electric cylinder elongation is read . Through the formula , obtain the actual value of the UAV pitch angle . Take the pitch angles at an equal time interval sampling period to form a pitch angle time series, and perform differential derivation on the pitch angle time series to obtain the time series of the pitch angular velocity q.

[0021] Among them, the derivation formula is as follows: , where is the pitch angular velocity at the i-th moment, is the pitch angle at the i -th moment, is the pitch angle at the (i - 1)-th moment, is the time interval between adjacent sampling points, and n is the total number of sampling points.

[0022] Beneficial effects

[0023] 1. The device of the present invention uses the electric cylinder as an actuator, which can realize the dynamic adjustment of the UAV pitch angle by controlling the change of the electric cylinder elongation, and can overcome the deficiency that the longitudinal aerodynamic characteristic test device of the fixed-wing UAV can only perform static tests.

[0024] 2. In the device of the present invention, the used chassis, front and rear vertical frames can all be built with profiles, with simple structure, low cost, convenient assembly, and using the electric cylinder as an actuator, the control method is simple and the control precision is high.

[0025] 3. The device of the present invention realizes multi-degree-of-freedom simulation, can accurately simulate complex motions such as pitch and roll of a fixed-wing unmanned aerial vehicle (UAV) under different flight conditions, and provides a more realistic test environment than traditional single-condition tests. This helps to more comprehensively understand the aerodynamic characteristics of the UAV in various flight states; and by precisely controlling the telescopic motion of the electric cylinder, fine adjustment of the UAV's attitude can be achieved, ensuring high-precision attitude control during the test. This high precision is crucial for studying the aerodynamic performance of the UAV under subtle attitude adjustments.

[0026] 4. The test device of the present invention supports free switching between steady-state and transient conditions, as well as independent or combined adjustment of the pitch angle and roll angle, greatly enhancing the flexibility of experimental design. Researchers can easily set and adjust experimental conditions according to different research purposes. By introducing a transient correction function, the dynamic characteristics of the UAV during the transition from transient to steady state can be captured more accurately, which is very crucial for evaluating the dynamic performance of the UAV, such as response speed, stability, and maneuverability.

[0027] 5. Based on the data obtained from this device, the present invention can deeply analyze the aerodynamic characteristics of the UAV under different flight conditions, and then optimize the design parameters and flight control strategies of the UAV to improve the overall performance of the UAV. Compared with actual flight tests, using this test device can complete a large number of preliminary tests under laboratory conditions, effectively reducing the number of flight tests, and reducing the R & D cost and risk.

[0028] 6. The test device for transient longitudinal aerodynamic characteristics of the fixed-wing UAV of the present invention provides a test method. This test method has simple steps and can relatively accurately obtain the relationships between the lift, drag, pitch moment of the UAV and the wind tunnel air supply velocity, the control surface angle of the fixed-wing UAV, as well as the pitch angle and pitch angular velocity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is an axonometric view of the test device for transient longitudinal aerodynamic characteristics of the fixed-wing UAV of the present invention;

[0030] Figure 2 is a left view of the test device for transient longitudinal aerodynamic characteristics of the fixed-wing UAV of the present invention;

[0031] Figure 3 is a front view of the test device for transient longitudinal aerodynamic characteristics of the fixed-wing UAV of the present invention;

[0032] Figure 4 is a schematic diagram of the transient pitch angle adjustment of the fixed-wing UAV of the present invention;

[0033] Figure 5 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 OF THE INVENTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings and by way of examples.

[0035] The present invention provides a test device for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle, which includes a leg Ⅰ 1-1, a leg Ⅱ 1-2, an electric cylinder 2, a chassis 3, a front upright frame 4-1, a rear upright frame 4-2, a balance 5, and a connecting plate 6.

[0036] Among them, the leg Ⅰ 1-1 is fixedly connected to the left front part of the chassis 3, the leg Ⅱ 1-2 is fixedly connected to the right front part of the chassis 3, the leg Ⅰ 1-1 and the leg Ⅱ 1-2 are symmetrically distributed left and right, the electric cylinder 2 is fixedly connected to the middle rear part of the chassis 3, the front upright frame 4-1 is fixedly connected to the middle front cross beam of the chassis 3, the rear upright frame 4-2 is fixedly connected to the middle rear cross beam of the chassis 3, the balance 5 is fixed to the upper parts of the front upright frame 4-1 and the rear upright frame 4-2, and the connecting plate 6 is fixed to the upper part of the balance 5. The connecting plate 6 is used to connect the balance 5 and the unmanned aerial vehicle.

[0037] The test device for transient longitudinal aerodynamic characteristics of the fixed-wing unmanned aerial vehicle of the present invention realizes the change of the pitch angle of the unmanned aerial vehicle through the extension and contraction actions of the electric cylinder 2, and realizes the adjustment of the pitch angle of the fixed-wing unmanned aerial vehicle. On this basis, with the change of the wind tunnel airspeed and the change of the control surface angle of the unmanned aerial vehicle, the transient longitudinal aerodynamic characteristics test can be realized.

[0038] The present invention also provides a test method for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle, which uses the device of the present invention to realize the test, and includes the following steps:

[0039] Step 1: Place the test device for transient longitudinal aerodynamic characteristics of the fixed-wing unmanned aerial vehicle on the wind tunnel rotating platform, and align it with the test device through the laser alignment device of the wind tunnel test platform, so that the wind tunnel air supply direction is parallel to the x direction of the test device.

[0040] Step 2: Design the test conditions, including determining the wind tunnel air supply speed, the change curve of the aileron control surface angle of the fixed-wing unmanned aerial vehicle, the change curve of the tail control surface angle of the fixed-wing unmanned aerial vehicle, and the change curve of the pitch angle of the test device. the change curve of the tail control surface angle of the fixed-wing unmanned aerial vehicle and the change curve of the pitch angle of the test device.

[0041] Step 3: Conduct the test according to the designed test conditions. The upper computer reads the forces Fx1, Fy1, Fz1 on the x, y, and z axes and the torques Ml, Mm, Mn about the three axes in the balance coordinate system obtained through the balance 5. Since the balance 5 is fixedly connected to the chassis 3 and changes with the pitch angle during the test, in order to obtain the forces Fx, Fy, Fz on the x, y, and z axes in the airflow coordinate system, conversion is required. The conversion formulas are as follows: , , . Thus, the lift, drag, and side force at each sampling moment with equal time intervals within the selected time period can be obtained, and the set of each sampling moment constitutes a force time series. The lift, drag, and pitch moment can all be expressed as functions of the wind tunnel air supply velocity V, pitch angle , pitch angular velocity q, and the angle of the fixed-wing UAV tail rudder surface :

[0042]

[0043] Among them, is the dynamic pressure, is the total surface area of the aircraft wing, is the mean 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 conditions. All variables in the above formula are known under longitudinal aerodynamic characteristic tests, and each aerodynamic coefficient K can be fitted using the least squares fitting method. The above formula can be used for steady-state longitudinal aerodynamic characteristic tests.

[0044] Specifically, in the embodiment of the present invention, the transient pitch angle adjustment is achieved through the following method:

[0045] Step 1: Adjust the electric cylinder 2 to a horizontal posture with the base frame 3, set the length of the electric cylinder 2 at this time as the starting position, i.e., the zero position, measure the upper limit bmax and lower limit bmin of the elongation of the electric cylinder 2 at the zero position, and measure the distances a of the leg Ⅰ1-1, leg Ⅱ1-2, and the electric cylinder 2 in the x direction (taking the horizontal forward as the x direction, the vertical upward as the z direction, and the y direction conforming to the right-hand coordinate rule).

[0046] Step 2: Obtain the conversion formula between the elongation b of the electric cylinder 2 and the pitch angle α through geometric relations. When the electric cylinder 2 elongates at the starting position, the pitch angle is positive, and when the electric cylinder 2 contracts at the starting position, the pitch angle is negative. The conversion formula is as follows: , , since the stroke of the electric cylinder 2 is limited, calculate the maximum pitch angle , the minimum pitch angle . After designing the desired pitch angle change curve of the UAV under the constraints of the maximum pitch angle and the minimum pitch angle, the desired elongation b change curve of the electric cylinder 2 can be obtained through the formula .

[0047] Step 3: The upper computer sends a control command to the electric cylinder 2 controller through serial communication, generates a pitch angle under the change of the elongation of the electric cylinder 2, reads the actual value of the elongation of the electric cylinder 2, and through the formula , the actual value of the pitch angle of the UAV is obtained , take the pitch angle at an equal time interval sampling period to form a pitch angle time series. Differentiating the pitch angle time series can obtain the time series of the pitch angular velocity q. The differentiation formula is as follows: , where is the pitch angular velocity at the i-th moment, is the pitch angle at the i-th moment, is the pitch angle at the (i - 1)-th 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.

[0048] Further, the aerodynamic characteristic test method of this embodiment realizes a more accurate description of the aerodynamic behavior during dynamic flight by introducing a transient correction function. For example, in the transient longitudinal condition, the aerodynamic response under a pitch angle step. The correction formula is used for transient longitudinal aerodynamic characteristic test, as follows:

[0049]

[0050]

[0051]

[0052]

[0053]

[0054] where V is the wind tunnel air supply velocity, t is time, and c is the characteristic chord length of the UAV. Compared with the steady-state aerodynamic characteristic test, the transient aerodynamic characteristics not only need to fit each aerodynamic coefficient K, but also need to fit the parameter , which is used to reflect the time evolution characteristics of the force response, that is, the dynamic process from transient to steady state.

[0055] Through the above steps, the transient longitudinal aerodynamic characteristic test of the fixed-wing UAV can be realized, which is used for the aerodynamic research of the fixed-wing UAV. Each aerodynamic coefficient K is obtained through the transient longitudinal aerodynamic characteristic test. Combining the aircraft's own parameters and flight environment parameters, the transient force information during flight can be obtained.

[0056] In summary, the above are only the preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A test method for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle is realized by using a test device for transient longitudinal aerodynamic characteristics of a fixed-wing unmanned aerial vehicle, and is characterized in that, The device includes leg I, leg II, an electric cylinder, a chassis, a front upright, a rear upright, a balance, and a connecting plate; Among them, leg I is fixedly connected to the left front part of the chassis, leg II is fixedly connected to the right front part of the chassis, leg I and leg II are symmetrically distributed left and right, the electric cylinder is fixedly connected to the middle rear part of the chassis, the front upright is fixedly connected to the front cross beam in the middle of the chassis, the rear upright is fixedly connected to the rear cross beam in the middle of the chassis, the balance is fixed to the upper parts of the front upright and the rear upright, and the connecting plate is fixed to the upper part of the balance. The connecting plate is used to connect the balance and the unmanned aerial vehicle; the pitch angle change of the unmanned aerial vehicle is realized through the extension and contraction actions of the electric cylinder. On this basis, the transient longitudinal aerodynamic characteristics test is realized in cooperation with the change of the wind tunnel wind speed and the change of the unmanned aerial vehicle rudder surface angle; The test steps include: Step 1: Place the fixed-wing unmanned aerial vehicle 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 air supply velocity, the variation curve of the aileron rudder surface angle δ of the fixed-wing UAV, the variation curve of the tail rudder surface angle δ of the fixed-wing UAV, and the variation curve of the pitch angle of the test device; a variation curve, the variation curve of the tail rudder surface angle δ of the fixed-wing UAV b variation curve, and the variation curve of the pitch angle of the test device; Step 3: Conduct tests according to the designed test conditions. The host computer reads the x, y, and z-axis forces F x1 , F y1 , F z1 in the balance coordinate system obtained through the balance, and the torques M l , M m , M n about the three axes; perform coordinate transformation to obtain the forces F x , F y , F z on the x, y, and z axes in the airflow coordinate system; obtain the lift, drag, and side force at each equal-time interval sampling moment within the selected time period, and the set of each sampling moment constitutes a force time series; the lift, drag, and pitching moment are expressed as functional relationships of the wind tunnel air supply velocity V, pitching angle α ′ , pitching angular velocity q, and the fixed-wing UAV tail rudder surface angle δ b ; use the least squares fitting method to fit out each aerodynamic coefficient K; Introduce a transient correction function to describe the aerodynamic behavior during dynamic flight, which is used for the transient longitudinal aerodynamic characteristics test; the correction function is as follows: Among them, is the dynamic pressure, S is the total surface area of the UAV wing, is the mean aerodynamic chord of the UAV; K x0 , K xα , K xq , is the drag aerodynamic coefficient under longitudinal conditions; K z0 , K zα , is the lift aerodynamic coefficient under longitudinal conditions; K m0 , K mα , K mq , is the aerodynamic coefficient of pitching moment under longitudinal conditions; V is the wind tunnel air supply wind speed, t is the time, and c is the characteristic chord length of the unmanned aerial vehicle.

2. The method according to claim 1, characterized in that The transient pitch angle adjustment process is as follows: Step 1: Adjust the electric cylinder to a horizontal attitude with the chassis, set the length of the electric cylinder at this time as the zero position, measure the upper limit bmax and the lower limit bmin of the elongation of the electric cylinder at the zero position, and measure the distances a of leg I, leg II, and the electric cylinder in the x direction; Step 2: Obtain the conversion formula between the elongation b of the electric cylinder and the pitch angle α through geometric relationships. When the electric cylinder elongates at the starting position, the pitch angle is positive, and when the electric cylinder contracts at the starting position, the pitch angle is negative. The conversion formula is as follows: b = a × tanα. According to the upper limit b max and the lower limit b min calculate the maximum pitch angle and the 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, obtain the expected electric cylinder elongation b change curve through the formula b = a × tanα; Step 3: The host computer sends control instructions to the cylinder controller through serial communication, generates a pitching angle under the change of the elongation of the cylinder, and reads the actual value b of the cylinder elongation. ′ , through the formula α ′ = arctan b ′ / a, obtain the actual value α of the pitching angle of the drone ′ , take the pitching angles α within a sampling period of an equal time interval ′ to form a pitching angle time series, and perform differential derivation on the pitching angle time series to obtain the time series of the pitching angular velocity q.

3. The method according to claim 2, wherein The derivative formula is as follows: where q i is the pitch angular velocity at the i-th moment, and α i ′ is the pitch angle at the i-th moment, and α i ′ -1 is the pitch angle at the (i - 1)-th moment, Δt is the time interval between adjacent sampling points, and n is the total number of sampling points.

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