Nonlinear aerodynamic coefficient derivation method for flying wing unmanned aerial vehicle

Abstract

This invention discloses a nonlinear aerodynamic coefficient biasing method for a flying-wing UAV, comprising the following steps: 1) obtaining wind tunnel test data of the UAV through force measurement wind tunnel testing; 2) performing correlation correction on the wind tunnel test data to obtain the basic aerodynamic data of the UAV; 3) determining the biasing parameters of the UAV aerodynamic data and performing biasing calculations on the UAV aerodynamic data. This invention considers various influencing factors that cause deviations in the aerodynamic coefficients, achieving biasing of different values ​​of the six-component aerodynamic coefficients, which can adaptively meet the biasing requirements of the UAV under different deviation states; the determined aerodynamic coefficients can fully assess the stability of the UAV flight control system, the robustness of the control law, and the limit states of key parameters of the control law, preventing the flight control system design from being overly conservative or overly aggressive, thus reducing the difficulty of flight control system design.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) control technology, specifically to a method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV. Background Technology

[0002] UAV aerodynamic data is typically obtained by correlating and correcting wind tunnel test data, and it forms the basis for the control law design in the UAV flight control system. Due to potential malfunctions during manufacturing, assembly, and flight, aerodynamic data deviations during actual flight can occur, affecting the flight control system's control of the UAV. In severe cases, this can lead to control overshoot and compromise flight safety. Therefore, it is necessary to adjust the aerodynamic data. Based on the adjusted aerodynamic data, the stability of the flight control system, the robustness of the control law, and the limiting states of key control law parameters are verified and evaluated through semi-physical simulation experiments of the flight control system.

[0003] Aerodynamic coefficient biasing refers to determining the limit deviation value of the aerodynamic coefficient based on wind tunnel test data after correlation correction, considering factors that cause deviations. The aerodynamic coefficient biasing method has not yet appeared in publicly available literature. However, Chinese patent CN103576554B, "Component and Hierarchical Design Method for Aerodynamic Error Model of Aircraft Based on Control Requirements," mentions that for hypersonic gliders, the traditional aerodynamic error model is in the form of "constant term + proportional term," which can be considered a type of aerodynamic coefficient biasing method. Taking the deviation of the normal force coefficient as an example, it is generally |ΔC N |≤(0.05+15%·|C N The flying wing configuration of UAVs results in significant nonlinearity in their aerodynamic coefficients as the angle of attack changes. Using a "constant term + proportional term" method to bias the aerodynamic coefficients has certain limitations. This method applies the same bias to all aerodynamic coefficient components, resulting in equal upper and lower limit deviations. This can lead to either overly conservative or overly aggressive biases, failing to adequately assess the stability of the UAV's flight control system, the robustness of the control rate, and the extreme states of key control rate parameters. Summary of the Invention

[0004] The purpose of this invention is to provide a method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV, which reduces the difficulty of flight control system design by preventing it from being too conservative or too aggressive.

[0005] This invention is achieved through the following technical solution: a method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV, comprising the following steps:

[0006] (1) Obtain wind tunnel test data of UAVs through force measurement wind tunnel tests;

[0007] (2) Correlation correction was performed on the wind tunnel test data to obtain the basic aerodynamic data of the UAV;

[0008] (3) Determine the deflection parameters of the UAV aerodynamic data and perform deflection calculations on the UAV aerodynamic data.

[0009] To better implement the method of the present invention, further, in step (1), the wind tunnel test data of the UAV obtained by force measurement wind tunnel test includes the six-component aerodynamic coefficients of the UAV under different Mach numbers Ma, different angles of attack α, and different sideslip angles β.

[0010] To better implement the method of the present invention, the six-component aerodynamic coefficients of the UAV are further defined as lift coefficient CL, drag coefficient CD, pitch moment coefficient Cm, side force coefficient Cc, yaw moment coefficient Cn, and roll moment coefficient Cl.

[0011] To better implement the method of the present invention, further, in step (2), different flight altitudes H are added as variables to correct the correlation of wind tunnel test data, so as to obtain the basic aerodynamic data of the UAV.

[0012] To better implement the method of the present invention, the pull parameter of the lift coefficient CL is further defined as follows: The formula for calculating its deviation is as follows:

[0013]

[0014]

[0015] Among them, CL + CL is the maximum value of the lift coefficient. - CL0 represents the minimum lift coefficient, and CL0 is the lift coefficient corresponding to an angle of attack α = 0°.

[0016] To better implement the method of the present invention, the pull parameter of the drag coefficient CD is further defined as follows: The formula for calculating its deviation is as follows:

[0017]

[0018]

[0019] Among them, CD + CD is the maximum value of the drag coefficient. - CD0 represents the minimum drag coefficient, and CD0 is the drag coefficient corresponding to an angle of attack α = 0°.

[0020] To better implement the method of the present invention, the yaw parameter of the pitching moment coefficient Cm is further defined as follows: The formula for calculating its deviation is as follows:

[0021]

[0022]

[0023] Among them, Cm + Cm is the maximum value of the pitching moment coefficient. - This represents the minimum value of the pitching moment coefficient.

[0024] To better implement the method of the present invention, the tension parameter of the lateral force coefficient Cc is further defined as follows: ΔCc + , ΔCc - The formula for calculating its deviation is as follows:

[0025]

[0026]

[0027] Among them, Cc + Cc is the maximum value of the lateral force coefficient. - The minimum value of the lateral force coefficient, ΔCc β This represents the increment of the lateral force coefficient caused by the sideslip angle β.

[0028] To better implement the method of the present invention, the yaw moment coefficient Cn is further defined as follows: ΔCn + , ΔCn - The formula for calculating its deviation is as follows:

[0029]

[0030]

[0031] Among them, Cn + Cn is the maximum value of the yaw moment coefficient. - ΔCn is the minimum value of the yaw moment coefficient. β This represents the increment of the yaw moment coefficient caused by the sideslip angle β.

[0032] To better implement the method of the present invention, the pull parameter of the rolling moment coefficient C1 is further defined as follows: ΔCl + , ΔCl - The formula for calculating its deviation is as follows:

[0033]

[0034]

[0035] Among them, Cl + Cl is the maximum value of the rolling moment coefficient. - ΔCl is the minimum value of the rolling moment coefficient. β This represents the increment of the rolling moment coefficient caused by the sideslip angle β.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] (1) This invention considers various factors that cause deviations in aerodynamic coefficients. The lift coefficient is deflected by adding a nonlinear incremental proportional term to a zero angle-of-attack lift proportional term. The drag coefficient is deflected by adding a zero angle-of-attack drag proportional term. The pitch moment coefficient is deflected by adding a zero lift moment constant term to a longitudinal static stability margin constant term. The side force coefficient, yaw moment coefficient, and roll moment coefficient are deflected by adding a constant term to a proportional term. This invention achieves deflection of different values ​​of the six-component aerodynamic coefficients and can adaptably meet the deflection requirements of UAVs under different deviation conditions.

[0038] (2) The aerodynamic coefficient determined by the method described in this invention can fully assess the stability of the UAV flight control system, the robustness of the control law, and the limit state of the key parameters of the control law, so that the design of the flight control system is not too conservative or too aggressive, thus reducing the difficulty of designing the flight control system. Attached Figure Description

[0039] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0040] Figure 1 This is a flowchart of the method described in this invention;

[0041] Figure 2 This is a comparison diagram of the lift coefficient deflection curve determined in this invention and the basic lift coefficient curve;

[0042] Figure 3 This is a comparison chart of the lift coefficient deflection curve determined by the linear deflection method in this invention and the basic lift coefficient curve. Detailed Implementation

[0043] To make the objectives, process conditions, and advantages of the present invention clearer, the present invention will be further described in detail with reference to the following embodiments. However, the embodiments of the present invention are not limited thereto. Various substitutions and modifications can be made based on common technical knowledge and conventional means in the art without departing from the above-described technical concept of the present invention, and all such substitutions and modifications should be included within the scope of the present invention. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] Example 1:

[0045] This embodiment provides a method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV, with the specific process as follows: Figure 1 As shown, it includes the following steps:

[0046] (1) Wind tunnel test data of UAV were obtained through force measurement wind tunnel test. The obtained data includes the six-component aerodynamic coefficients of UAV under different Mach numbers Ma, different angles of attack α, and different sideslip angles β.

[0047] (2) Correlation correction is performed on the wind tunnel test data to obtain the basic aerodynamic data of the UAV. The main method is to add different flight altitudes H as variables to the wind tunnel test data for correlation correction. Among them, the aerodynamic coefficient C is a function of H, Ma, α, β, which can be expressed as C=f(H,Ma,α,β). The six components of the UAV aerodynamic data include the lift coefficient CL, the drag coefficient CD, the pitch moment coefficient Cm, the side force coefficient Cc, the yaw moment coefficient Cn, and the roll moment coefficient Cl.

[0048] (3) Determine the deflection parameters of the UAV's aerodynamic data and perform deflection calculations on the UAV's aerodynamic data, wherein the deflection parameter of the lift coefficient CL is: The formula for calculating its deviation is as follows:

[0049]

[0050]

[0051] Among them, CL + CL is the maximum value of the lift coefficient. - CL0 is the minimum lift coefficient, where CL0 is the lift coefficient at an angle of attack α = 0°.

[0052] The pull parameter of the drag coefficient CD is: The formula for calculating its deviation is as follows:

[0053]

[0054]

[0055] Among them, CD+ CD is the maximum value of the drag coefficient. - CD0 is the drag coefficient at its minimum value, where CD0 is the drag coefficient at an angle of attack α = 0°.

[0056] The pitching moment coefficient Cm has the following pull parameter: The formula for calculating its deviation is as follows:

[0057]

[0058]

[0059] Among them, Cm + Cm is the maximum value of the pitching moment coefficient. - This represents the minimum value of the pitching moment coefficient.

[0060] The pull parameter of the lateral force coefficient Cc is: ΔCc + , ΔCc - The formula for calculating its deviation is as follows:

[0061]

[0062]

[0063] Among them, Cc + Cc is the maximum value of the lateral force coefficient. - The minimum value of the lateral force coefficient, ΔCc β This represents the increment of the lateral force coefficient caused by the sideslip angle β;

[0064] The yaw moment coefficient Cn has the following pull parameter: ΔCn + , ΔCn - The formula for calculating its deviation is as follows:

[0065]

[0066]

[0067] Among them, Cn + Cn is the maximum value of the yaw moment coefficient. - ΔCn is the minimum value of the yaw moment coefficient. β This represents the increment of the yaw moment coefficient caused by the sideslip angle β.

[0068] The pull parameter of the rolling moment coefficient Cl is ΔCl + , ΔCl -The formula for calculating its deviation is as follows:

[0069]

[0070]

[0071] Among them, Cl + Cl is the maximum value of the rolling moment coefficient. - ΔCl is the minimum value of the rolling moment coefficient. β This represents the increment of the rolling moment coefficient caused by the sideslip angle β.

[0072] Example 2:

[0073] This embodiment takes the formula for calculating the lift coefficient CL as an example, and gives the calculation principle of the formula as follows:

[0074] The relationship between the lift coefficient and the angle of attack α within the linear range can be expressed as:

[0075] CL = CL0 + CL α ·α

[0076] Among them CL α The slope of the lift line, i.e., the derivative of the lift coefficient CL with respect to the angle of attack α, is given.

[0077] The lift coefficient can be expressed as follows:

[0078]

[0079]

[0080] Since the linear range of the lift coefficient variation curve of flying wing UAV with angle of attack is small, the above formula is no longer applicable to data outside the linear range. Therefore, the relationship between lift coefficient and angle of attack is expressed as a nonlinear form of CL=CL0+ΔCL, where ΔCL=CL-CL0 represents the change in lift coefficient caused by angle of attack. The formula is obtained by proportionally adjusting the nonlinear form of lift coefficient.

[0081] The process of deriving the drag coefficient CD, pitch moment coefficient Cm, lateral force coefficient Cc, yaw moment coefficient Cn, and roll moment coefficient Cl from the formula is similar to the process of deriving the lift coefficient CL from the formula, and will not be repeated here.

[0082] Example 3:

[0083] This embodiment provides a specific implementation process, as follows:

[0084] The aerodynamic coefficient C is a function of H, Ma, α, and β, and can be expressed as C = f(H, Ma, α, β). The aerodynamic coefficients include the lift coefficient CL, the drag coefficient CD, the pitch moment coefficient Cm, the side force coefficient Cc, the yaw moment coefficient Cn, and the roll moment coefficient Cl.

[0085] Obtain the lift coefficient CL pull amount Considering the deviation in lift coefficient caused by manufacturing and assembly factors, take The lift coefficient is calculated using formula (1):

[0086] CL + =(CL-CL0)×(1+10%)+CL0×(1+20%)

[0087] CL - = (CL-CL0)×(1-10%)+CL0×(1-50%) Equation (1)

[0088] Among them CL + CL is the maximum value of the lift coefficient. - CL0 is the minimum lift coefficient, where CL0 is the lift coefficient at an angle of attack α = 0°.

[0089] Obtain the drag coefficient CD pull amount Considering factors such as manufacturing, assembly, and engine thrust characteristics, we take... The drag coefficient is adjusted according to formula (2):

[0090] CD + =CD + CD0 × 20%

[0091] CD - =CD-CD0×5% Formula (2)

[0092] CD + CD is the maximum value of the drag coefficient. - CD0 is the drag coefficient at its minimum value, where CD0 is the drag coefficient at an angle of attack α = 0°.

[0093] Obtain the pitch moment coefficient Cm and the eccentricity. Considering factors such as manufacturing, assembly, and the deviation of the engine thrust line from the center of gravity, we take... The pitch moment coefficient is calculated according to formula (3):

[0094] Cm + =Cm+0.02×(CL·cosα+CD·sinα)+0.0079

[0095] Cm -=Cm-0.02×(CL·cosα+CD·sinα)-0.0079 Formula (3)

[0096] Where Cm + Cm is the maximum value of the pitching moment coefficient. - This represents the minimum value of the pitching moment coefficient;

[0097] Obtain the lateral force coefficient Cc and the amount of eccentricity. ΔCc + , ΔCc - Considering factors such as manufacturing, assembly, and the asymmetry of the thrust lines of the twin engines, we take... ΔCc + =ΔCc-=0.01 Lateral force coefficient is applied, calculated according to formula (4):

[0098] Cc + =ΔCc β ·(1+10%)+0.01

[0099] Cc - =ΔCc β • (1-10%)+0.01 Equation (4)

[0100] Where Cc + Cc is the maximum value of the lateral force coefficient. - The minimum value of the lateral force coefficient, ΔCc β This represents the increment of the lateral force coefficient caused by the sideslip angle β;

[0101] Obtain the yaw moment coefficient Cn and the amount of yaw pull. ΔCn + , ΔCn - Considering factors such as manufacturing, assembly, asymmetric thrust lines of the twin engines, single engine failure, and center of gravity deviation, we take... ΔCn + =ΔCn - =0.0032 to apply the yaw moment coefficient, calculated according to formula (5):

[0102] Cn + =ΔCn β ·(1+10%)+0.0032

[0103] Cn - =ΔCn β ·(1-10%)+0.0032 Equation (5)

[0104] Where Cn + Cn is the maximum value of the yaw moment coefficient. - ΔCn is the minimum value of the yaw moment coefficient.β This represents the increment of the yaw moment coefficient caused by the sideslip angle β.

[0105] Obtain the rolling moment coefficient Cl and the amount of pull. ΔCl + , ΔCl - Considering factors such as manufacturing, assembly, engine mounting angle deviation, and center of gravity position deviation, we take... ΔCl + =ΔCl - =0.0053 is used to apply the rolling moment coefficient, which is calculated according to formula (6):

[0106] Cl + =ΔCl β ·(1+10%)+0.0053

[0107] Cl - =ΔCl β • (1-10%)+0.0053 Equation (6)

[0108] Cl + Cl is the maximum value of the rolling moment coefficient. - ΔCl is the minimum value of the rolling moment coefficient. β This represents the increment of the rolling moment coefficient caused by the sideslip angle β.

[0109] Additionally, a comparison chart is provided between the lift coefficient skew curve determined by the method of the present invention and the basic lift coefficient curve, as well as a comparison chart between the lift coefficient skew curve determined by the linear skew method and the basic lift coefficient curve. Figure 2 , Figure 3 As shown, by Figure 2 , Figure 3 The comparison shows that the trend of the lift coefficient deflection curve determined by the present invention has good consistency with the trend of the lift coefficient basic curve, and the matching is good. The lift coefficient deflection curve determined by the linear deflection method fails to reflect the nonlinear characteristics of the lift coefficient basic curve, and there is an error in which the minimum lift coefficient is greater than the basic lift coefficient at the corresponding angle of attack.

[0110] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV, characterized in that, Includes the following steps: (1) Obtain wind tunnel test data of UAV through force measurement wind tunnel test; the wind tunnel test data of UAV obtained through force measurement wind tunnel test includes the six-component aerodynamic coefficients of UAV under different Mach numbers Ma, different angles of attack α, and different sideslip angles β; the six-component aerodynamic coefficients of UAV are specifically the lift coefficient CL, drag coefficient CD, pitch moment coefficient Cm, side force coefficient Cc, yaw moment coefficient Cn, and roll moment coefficient Cl; (2) Correlation correction was performed on the wind tunnel test data to obtain the basic aerodynamic data of the UAV; different flight altitudes H were added as variables to perform correlation correction on the wind tunnel test data to obtain the basic aerodynamic data of the UAV. (3) Determine the deflection parameters of the UAV aerodynamic data and perform deflection calculations on the UAV aerodynamic data.

2. The nonlinear aerodynamic coefficient adjustment method for a flying-wing UAV according to claim 1, characterized in that, The pull parameter of the lift coefficient CL is , , , The formula for calculating its deviation is as follows: in, This is the maximum value of the lift coefficient. This is the minimum value of the lift coefficient. This is the lift coefficient corresponding to an angle of attack α = 0°.

3. A method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV according to claim 1 or 2, characterized in that, The pull parameter of the drag coefficient CD is: , The formula for calculating its deviation is as follows: in, This is the maximum value of the drag coefficient. This is the minimum value of the drag coefficient. This is the drag coefficient corresponding to an angle of attack α = 0°.

4. A method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV according to claim 1 or 2, characterized in that, The pitching moment coefficient Cm has the following pull parameter: , , , The formula for calculating its deviation is as follows: in, This represents the maximum value of the pitch moment coefficient. This represents the minimum value of the pitching moment coefficient.

5. A method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV according to claim 1 or 2, characterized in that, The pull parameter of the lateral force coefficient Cc is: , , , The formula for calculating its deviation is as follows: in, This represents the maximum value of the lateral force coefficient. This represents the minimum value of the lateral force coefficient. This represents the increment of the lateral force coefficient caused by the sideslip angle β.

6. A method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV according to claim 1 or 2, characterized in that, The yaw moment coefficient Cn has the following pull parameter: , , , The formula for calculating its deviation is as follows: in, This represents the maximum value of the yaw moment coefficient. This represents the minimum value of the yaw moment coefficient. This represents the increment of the yaw moment coefficient caused by the sideslip angle β.

7. A method for adjusting the nonlinear aerodynamic coefficient of a flying-wing UAV according to claim 1 or 2, characterized in that, The pull parameter of the rolling moment coefficient Cl is , , , The formula for calculating its deviation is as follows: in, This represents the maximum value of the rolling moment coefficient. This is the minimum value of the rolling moment coefficient. This represents the increment of the rolling moment coefficient caused by the sideslip angle β.

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