Fixed-wing unmanned aerial vehicle winglet optimization design method

Abstract

The invention relates to the technical field of fixed-wing unmanned aerial vehicles, in particular to a fixed-wing unmanned aerial vehicle winglet optimization design method which comprises the following steps: step 1, modeling through cata to obtain winglets of various different winglet geometric parameter analysis and research configurations, and selecting three parameters of height, camber angle and tip-root ratio; step 2, performing pneumatic data analysis on the optimal configuration solution through a CFD numerical method based on ansys software; step 3, obtaining an optimal configuration solution of the winglet through a design response surface method; and step 4, printing an actual optimal solution winglet model through a 3d printing technology, installing the model on an aircraft, carrying out actual endurance test flight, and analyzing a result. According to the method, the winglet of the fixed-wing unmanned aerial vehicle can be optimized well.

Description

Technical Field

[0001] The present invention relates to the technical field of fixed-wing unmanned aerial vehicles, and in particular to a method for optimizing the design of a winglet of a fixed-wing unmanned aerial vehicle. Background Art

[0002] In the design of fixed-wing UAVs, the application of wingtip devices is to optimize flight performance. Specifically, the main function of the winglets installed at the wingtips is to effectively reduce the impact of wingtip vortices. Wingtip vortices are rotating air flows caused by the pressure difference at the wingtips during flight. This phenomenon will increase induced drag and thus affect the flight efficiency of the aircraft. It is also equivalent to increasing the effective aspect ratio of the wing, increasing the effective lift area, and the increase in wingtip bending moment will not be too large. However, the addition of winglets will also increase the complexity of aerodynamic and structural coupling, increase certain friction and other resistances, and when the induced drag accounts for a small proportion of the total drag, the lift-to-drag ratio may decrease. In addition, incorrect design or excessive weight added to the wingtips may aggravate wing vibration and affect wing strength, especially when the aspect ratio of the UAV is relatively large.

[0003] For small drones, the design of winglets cannot be considered because the R&D cycle is generally short. Many drone manufacturers have added winglets and claimed that the lift-to-drag ratio of the drone has been significantly improved, but this does not mean that the winglet solution is good. It may only be because the benefit is brought by the disguised increase in the aspect ratio of the wing, or it may just be aesthetically pleasing without actual lift-increasing effect. If the aircraft layout is special and the heading stability needs to be increased, then adding winglets can not only improve the heading stability but also increase the cruise lift-to-drag ratio, which is a better choice.

[0004] The four major sources of resistance for an aircraft are the shock wave drag under high-speed flight, the friction resistance generated by the wing and the air, the induced drag at the wing tip and the interference resistance caused by various other factors.

[0005] Winglets are a device specifically used for fixed-wing aircraft. Their main purpose is to increase the lift of the aircraft and reduce drag during flight. The ingenious design of this device is that a small auxiliary wing with a specific angle is installed at the end of the aircraft wing. This design effectively reduces the impact of vortices generated by the wing tip and significantly reduces the induced drag caused by vortices. The initial flight test and subsequent extensive flight tests and data analysis showed that the overall drag of the aircraft equipped with winglets decreased by 7.2%, and the lift-to-drag ratio increased by 8%. This improvement is equivalent to reducing fuel consumption by about 9% and increasing the aircraft's range by about 640 kilometers. This discovery highlights the great potential and practicality of this technology, proving that it deserves further research and experimental exploration.

[0006] Generally speaking, winglets improve flight efficiency by dispersing and consuming wingtip vortices and optimize the lift-to-drag ratio of the aircraft. Although this technology slightly increases the effective aspect ratio of the wing, it does not significantly increase the structural stress or cause an additional increase in structural weight.

[0007] Therefore, for low-speed fixed-wing UAVs, the aerodynamic advantages of lift-to-drag ratio improvement and endurance increase brought by using winglets far outweigh any adverse effects that may be caused by weight increase. However, the optimization effect of the current fixed-wing UAV winglets is still not ideal enough. Summary of the Invention

[0008] The content of the present invention is to provide an optimized design method for winglets of a fixed-wing UAV, which can overcome certain or some defects of the prior art.

[0009] According to an optimized design method for winglets of a fixed-wing UAV of the present invention, it includes the following steps: Step 1: Model winglets with various geometric parameter analysis and research configurations of winglets through catia, and select three parameters: height, sweep angle, and tip-to-root ratio; Step 2: Conduct aerodynamic data analysis on the optimal configuration solution through the CFD numerical method based on the ansys software; Step 3: Obtain the optimal configuration solution of the winglets through the design response surface method; Step 4: Print out the actual optimal solution winglet model through 3D printing technology, install it on the aircraft, conduct actual endurance test flights, and analyze the results.

[0010] Preferably, in Step 1, simulate the curvature and shape of the Cessna wing to establish a three-dimensional model of the winglet; according to the software and wing data, perform airfoil settings for the wing, use the generative surface for the winglet, add guide lines and enclose the entity with multiple sections. During the modeling process, simplify the model by removing the struts, servos, and pull rods of the control surfaces of the wing. The UAV airframe layout used has a wingspan of 120 cm, a semi-wingspan of 60 cm, and a wingtip chord length of 19 cm; Establish winglet configuration models with different configurations, including winglet configuration models with different heights, sweep angles, and tip-to-root ratios.

[0011] Preferably, in Step 2, the CFD numerical method adheres to the basic conservation laws in fluid mechanics, including the law of mass conservation, the law of momentum conservation, and the law of energy conservation, etc.; use the ansys software to perform numerical calculations, and the software performs simulation calculations based on the three-dimensional integral form of the Reynolds-averaged N-S equation: ; Where: is a conserved quantity; V is the volume of the control volume; S is the surface area of the control volume; f is the sum of the inviscid flux and the viscous flux through the surface S, and n is the unit normal vector of the outer normal of the control surface S; Any flow must satisfy the law of conservation of mass: within a unit of time, the increase or decrease in the mass of a fluid element is equal to the net mass of the fluid flowing in and out of the fluid element during the same time; the expression is: ; In the expression, represents density, t represents time, represents the velocity vector, represents the horizontal and vertical gradient operators; The law of conservation of momentum can be expressed as: the rate of change of the momentum of a fluid element with respect to time is equal to the resultant external force on the fluid element, and the expression is: ; In the expression, p represents pressure, τ represents the viscous stress acting on the fluid element due to molecular viscosity, represents the viscous stress component, F represents the body force on the fluid element; represents the velocity components in the x, y, and z directions, represents the velocity vector; The law of conservation of energy is expressed as: the rate of increase in the energy in a fluid element is equal to the sum of the net heat flux flowing into the fluid element and the work done by the body force on the fluid element; the expression is: ; In the expression, c p represents specific heat capacity, T represents temperature, k represents the heat transfer coefficient of the fluid, S T represents viscous dissipation.

[0012] Preferably, in step 2, specifically: 3.1) Select the left wing as the object of numerical simulation analysis, and use CATIA software to construct a complete three-dimensional solid model of the UAV including the wing and winglet; 3.2) The model is then imported into ANSYS Workbench, and fluent is imported for further analysis; 3.3) To ensure the accuracy of numerical simulation, create a large outer flow field region shell with dimensions of 20 m × 20 m × 15 m; in space, construct a three-dimensional solid model of the UAV's outer flow field, and set and name the model's inlet, outlet, flow field wall surfaces, flow field symmetry planes, and wings; perform structured grid division on the outer flow field; 3.4) Conduct initialization, and then perform data simulation calculations on the generated grid for the outer flow field; select the SST k-ω model, set the simulated inlet velocity to 15 m / s, and keep the outlet pressure at standard atmospheric pressure and set other boundary conditions, and select the pressure far field as the air flow inlet condition; 3.5) Select the wing material density, conduct numerical simulations on 17 different winglet configurations of single factors and different configurations required to obtain the optimal configuration, view the lift-drag coefficient reports to define and obtain a series of numerical simulation results of the lift-drag ratio of the outer flow field, and then convert the results into the lift-drag ratio to provide reference data for the subsequent design optimization of the UAV.

[0013] Preferably, in step 3, import the reasonable value ranges of height, camber angle, and tip-to-root ratio into the design software. The design software gives 17 sets of data. Import the data into catia to establish a model, then import it into ansys to solve the lift-drag ratio, import it into the printer to obtain the weight, bring these data back to the design software, and obtain the regression equation of the winglet and the response surfaces of different factors on the lift-drag ratio and weight through the response surface method, and thus obtain the data of the optimal configuration winglet.

[0014] Preferably, in step 4, specifically: 4.1) Output the catia model in stp format and import it into the software; 4.2) Use Bambu Studio software for 3D printing software slicing processing; 4.3) Print out the winglet model through a 3D printer; 4.4) Install the winglet on the aircraft; 4.5) Conduct actual endurance test flights, flight experiments, and collection of flight data; 4.6) Data analysis.

[0015] The present invention combines numerical simulation and comparative research on different configuration winglets, designs a new type of efficient UAV winglet in combination with the influence characteristics of various factors, conducts model wind tunnel tests on the new winglet, ansys analysis, conducts data calculations, and systematically studies the actual flight optimization effect, specifically as follows: (1) Select the basic configuration of the winglet of a fixed-wing UAV, verify the airfoil through a 3D model, and refer to the airfoil of the UAV wing to construct a combined model of the 3D basic wing and the winglet.

[0016] (2) Use caita to establish multiple models, and establish the winglet with the optimal structure and other winglets with ordinary configurations.

[0017] (3) Through the FLUENT software, conduct simulation analysis on winglets with different configurations under the cruise state, obtain and statistically analyze the results. The data analysis shows that: the winglet has a significant effect on increasing lift and performs well in terms of lift-drag characteristics. It shows the characteristics of low resistance, has a drag reduction effect, and is suitable for cruise flight. Description of the Drawings

[0018] Figure 1 It is a flowchart of an optimization design method for the winglet of a fixed-wing UAV in the embodiment; Figure 2 It is a comparison diagram of winglets with different tip-to-root ratios in the embodiment; Figure 3 It is a comparison diagram of winglets at different heights in the embodiment; Figure 4 It is a comparison diagram of winglets with different dihedral angles in the embodiment; Figure 5 It is a data diagram of the relationship between the lift-drag ratio and the tip-to-root ratio of the winglet in the embodiment; Figure 6 It is a data diagram of the relationship between the dihedral angle and the lift-drag ratio of the winglet in the embodiment; Figure 7 It is a data diagram of the relationship between the height and the lift-drag ratio of the winglet in the embodiment. Detailed Implementation Manner

[0019] To further understand the content of the present invention, the present invention will be described in detail in combination with the drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention and not for limiting it.

[0020] Embodiment As Figure 1 shown, this embodiment provides an optimization design method for the winglet of a fixed-wing UAV, which includes the following steps: Step 1: Use catia to model winglets with various geometric parameter analysis and research configurations of winglets, and select three parameters: height, dihedral angle, and tip-to-root ratio; Step 2: Conduct aerodynamic data analysis on the optimal configuration solution through the CFD numerical method based on the ansys software; Step 3: Obtain the optimal configuration solution of the winglet through the design response surface method; Step 4: Print out the actual optimal winglet model through 3D printing technology, install it on the aircraft, conduct actual endurance test flights, and analyze the results.

[0021] In Step 1, the arc and shape of the Cessna wing were simulated to establish a 3D model of the winglet; according to the software and wing data, the airfoil of the wing was set. The winglet used generative surfaces, added guide lines, and closed the solid with multi-sections. During the modeling process, the struts, servos, and pull rod structures of the rudder surface of the wing were simplified. The layout of the unmanned aerial vehicle (UAV) carrier was adopted, with a wingspan of 120 cm, a semi-wingspan of 60 cm, and a wingtip chord length of 19 cm.

[0022] Establish winglet configuration models with different configurations, including winglet configuration models with different heights, angles of inclination, and tip-to-root ratios. Figure 2 、 Figure 3 and Figure 4 are the comparison diagrams of winglets with different configurations.

[0023] Influence of the tip-to-root ratio of the winglet In the design of the winglet, the tip-to-root ratio is a key parameter, which is the ratio of the wingtip chord length to the wing root chord length of the winglet. By adjusting the tip-to-root ratio, that is, changing the wingtip length of the winglet, the change of the tip-to-root ratio can be realized, and its value range is from 0.2 to 0.5. When other parameters remain unchanged, the change of the tip-to-root ratio will affect the surface area of the winglet and have an impact on the lift-to-drag ratio of the UAV. In this regard, in this embodiment, by analyzing the schematic diagrams of winglets with different tip-to-root ratios, the lift and drag coefficients of the UAV with winglets with different tip-to-root ratios are calculated, and the results are as Figure 5 shown.

[0024] Further analyze the relationship between the lift-to-drag ratio of the UAV and the tip-to-root ratio of the winglet. In the entire value range of the tip-to-root ratio, the lift-to-drag ratio shows a peak-like change. Especially when the tip-to-root ratio is less than 0.4, the lift-to-drag ratio of the UAV increases with the increase of the tip-to-root ratio and reaches the peak when the tip-to-root ratio reaches 0.4, and then gradually decreases with the continuous increase of the tip-to-root ratio. This discovery provides an important reference basis for the design of winglets and helps to optimize the overall aerodynamic performance of the UAV.

[0025] By observing the variation trend graph of the lift-to-drag ratio, we can find that the lift-to-drag ratio first increases and then decreases. In the process of optimizing the lift-to-drag ratio, the selection of the tip-to-root ratio should be crucial. A suitable tip-to-root ratio, such as about 0.4, can effectively balance the structural complexity and aerodynamic performance. When the tip-to-root ratio is too small, i.e., less than 0.4, it will lead to an overly small chord length at the wing tip of the winglet, which not only increases the structural requirements of the winglet, making the manufacturing of the curved surface more complex, but also reduces the chord length at the wing root, which is not conducive to blocking the airflow under the wing tip from flowing around the wing tip to the upper surface, thus greatly reducing the upward spoiler effect. Further research shows that when the tip-to-root ratio exceeds 0.4, although the area of the winglet increases, its effect on increasing the lift coefficient is not obvious, but instead it will significantly increase the drag coefficient, structural weight, and frictional drag.

[0026] The increase in the tip-to-root ratio will also cause an increase in the wing root moment, especially when the angle of sweep increases, the increase in the wing root moment will be further aggravated. This increased wing root moment will bring a series of adverse effects. For example, it is necessary to strengthen the wing root and add structures such as carbon fiber reinforcement rods, which not only increases the weight of the whole aircraft, but also goes against the lightweight design requirements of the UAV. Therefore, when designing the winglet, the selection of the tip-to-root ratio uses the ansys software to simulate the structure of the semi-span plus the winglet, and the lift-to-drag ratio data of the UAV is obtained. This data shows that as the tip-to-root ratio of the winglet increases, the lift coefficient of the UAV shows a gradually increasing trend and reaches the highest point when the tip-to-root ratio is about 0.4. Subsequently, the lift coefficient slowly decreases as the tip-to-root ratio further increases. Regarding the drag coefficient, its variation trend can be divided into two stages: when the tip-to-root ratio is less than 0.4, the drag coefficient increases with the increase of the tip-to-root ratio; while when the tip-to-root ratio is between 0.4 and 0.55, the drag coefficient decreases with the increase of the tip-to-root ratio.

[0027] Effect of the winglet angle of sweep The angle of sweep of the winglet refers to the angle between the chord plane of the winglet and the vertical plane of the main wing of the aircraft. This angle plays a crucial role in effectively reducing the induced drag and reducing the airflow interference at the junction of the wing tip and the root of the winglet. Therefore, to achieve this effect, the winglet must be tilted outward from the wing by a certain angle. However, the increase in the angle of sweep may cause an increase in the rolling moment, thus affecting the rudder effectiveness of the aircraft aileron and increasing the moment at the wing root of the wing, which requires strengthening the structural strength of the wing and may increase the structural weight. In addition, the increase in the angle of sweep may also lead to a slowdown in the rate of increase in the lift-to-drag ratio. Therefore, it is particularly important to select a suitable range of the angle of sweep. The test results are as Figure 6 shown.

[0028] As Figure 6The test data shows that when the tilt angle increases from 15° to 25°, the lift-to-drag ratio of the drone increases by approximately 6%. Generally, the tilt angle of the winglet is recommended to be between 15° and 25°. Without changing other geometric parameters of the winglet, simply by changing the tilt of the winglet at the wing tip, the aerodynamic effect of the drone can be significantly affected. In addition, as the dihedral angle of the winglet increases, the increase in the lift-to-drag ratio coefficient of the drone will gradually decrease, while the drag coefficient decreases with the increase in the angle, but the decreasing speed will also gradually slow down. Especially after the dihedral angle of the winglet reaches 20 degrees, the increasing trend of the lift-to-drag ratio coefficient of the drone significantly slows down, indicating that beyond this angle, the improvement effect of the lift-to-drag ratio is no longer obvious. Therefore, the dihedral angle of the winglet around 20 degrees may be an ideal value, which can not only effectively improve the lift-to-drag ratio but also improve the flow situation at the wing root, thereby optimizing the overall aerodynamic performance.

[0029] Figure 6 The graph showing the change in the lift-to-drag ratio of the drone with the installation angle of the winglet as shown further confirms this point. It can be observed from the graph that as the dihedral angle of the winglet increases, the growth rate of the lift coefficient gradually slows down, while the growth rate of the drag coefficient becomes faster and faster. This phenomenon indicates that although a too large dihedral angle can still increase the lift, its influence on the drag also increases, thus inhibiting the overall improvement effect of the lift-to-drag ratio. Therefore, for this drone, controlling the dihedral angle of the winglet around 20 degrees can not only achieve the purpose of increasing the lift-to-drag ratio but also effectively control the growth of the drag, which is a relatively reasonable design choice.

[0030] Influence of Winglet Height As the height of the winglet increases, the endplate effect in preventing the flow around it gradually enhances, which helps to improve the overall lift-to-drag ratio. However, this increase in height will also lead to an increase in the frictional resistance between the airflow at the wing tip of the wing and the wing. It should be noted that the relationship between the winglet height and its endplate effect is not a simple linear relationship. By keeping other parameters unchanged and only changing the height of the winglet, data tests can be carried out through an actual model in ANSYS. As Figure 7 The results show that between a height of 8 degrees and 10 degrees, the lift-to-drag ratio shows an upward trend and reaches a maximum value at a height of approximately 10 degrees. When the height continues to increase to 12 degrees, the lift-to-drag ratio begins to decline. Thus, in the design of the drone, maintaining the height of the winglet at approximately 55% of the wing tip chord length is the optimal choice. Beyond this ratio, the blocking effect of the winglet endplate on the airflow weakens, resulting in a gradual attenuation of the drag reduction effect and an increase in the overall weight and air resistance.

[0031] On the other hand, the continuous increase in the height of the winglet will also lead to an increase in the weight of the wing structure. This weight gain will increase the bending moment borne by the wing root, thus requiring the strengthening of the wing's structural strength. If the increased height is too high, it may cause problems with the normal lift coefficient of the winglet under non-designed high-lift conditions, possibly leading to severe separation of the wing's airflow boundary layer. This separation will reduce the lift-enhancing effect generated by the winglet. Therefore, during design, the height of the winglet should be controlled, generally not exceeding 60% of the chord length of the wingtip of the horizontal straight wing.

[0032] Although increasing the height of the winglet is theoretically similar to increasing the wingspan of the UAV, which can generate greater lift, an excessively high winglet height will lead to a reduced increase in the lift-to-drag ratio, while increasing the weight of the wingtip structure. This weight gain will also cause larger wing root bending moment problems and may lead to a reduction in the spoiler effect of the winglet, and the overall structural weight will also increase accordingly. In summary, although winglets play an important role in improving flight performance, their design and installation need to consider the above factors to ensure the optimization of aircraft performance and the reliability of the structure. These considerations not only relate to the rationality of the design but also directly affect the flight safety and economy of the UAV.

[0033] In step 2, the CFD numerical method adheres to the basic conservation laws in fluid mechanics, including the laws of mass conservation, momentum conservation, and energy conservation, etc.; the basic equations of fluid motion are the mathematical expressions of these conservation laws, providing a solid theoretical basis for the study of fluid mechanics. In this embodiment, the ansys software is used to perform numerical calculations. The software performs simulation calculations based on the Reynolds-averaged N-S equations in three-dimensional integral form: ; In the formula: is the conserved quantity; V is the control volume; S is the control surface area; f is the sum of the inviscid flux and viscous flux passing through the surface S, and n is the unit outer normal vector of the control surface S; Any flow must satisfy the law of mass conservation: within a unit time, the mass increment and decrement of the fluid microelement are equal to the net mass of the fluid flowing in and out of the fluid microelement during the same time; the expression is: ; In the expression, represents density, t represents time, represents the velocity vector, represents the horizontal and vertical gradient operators; The law of momentum conservation can be expressed as: the rate of change of the momentum of the fluid microelement with respect to time is equal to the resultant external force on the fluid microelement, and the expression is: ; In the expression, p represents the pressure, τ represents the viscous stress acting on the fluid element due to molecular viscosity, represents the viscous stress component, F represents the body force on the fluid element; represents the velocity components in the x, y, and z directions, represents the velocity vector; The law of conservation of energy is expressed as: the rate of increase of energy in a fluid element is equal to the sum of the net heat flux flowing into the fluid element and the work done by the body force on the fluid element; the expression is: ; In the expression, c p represents the specific heat capacity, T represents the temperature, k represents the heat transfer coefficient of the fluid, S T represents the viscous dissipation.

[0034] In step 2, in order to estimate the flight performance of the fixed-wing UAV under different flight parameters, especially the lift and drag and their corresponding coefficients, this study used numerical simulation methods to conduct a detailed analysis of the external flow field of the UAV. This analysis helps to accurately predict the endurance time of the UAV and provides a scientific basis for the design and optimization of the UAV.

[0035] Specifically: 3.1) Since the design of this fixed-wing UAV adopts a left-right symmetric layout, which means that the flow field characteristics of the left wing can represent the right wing. Therefore, choosing the left wing as the object of numerical simulation analysis can effectively simplify the calculation process and ensure the accuracy of the results. After simplifying irrelevant components such as wing struts and servo pull rods, a complete three-dimensional solid model of the UAV including the wing and wingtip canards is constructed using CATIA software; 3.2) The model is then imported into ANSYS Workbench and imported into fluent for further analysis; 3.3) To ensure the accuracy of the numerical simulation, a large external flow field region shell with dimensions of 20 m × 20 m × 15 m is created; in the space, a three-dimensional solid model of the UAV's external flow field is constructed, and the inlet, outlet, flow field wall surfaces, flow field symmetry planes, and wings of the model are set and named; the external flow field is meshed with structured grids; 3.4) Initialize, and then perform data simulation calculations on the generated grid for the external flow field; select the SST k-ω model, set the simulated inlet velocity to 15 m / s, and keep the outlet pressure at standard atmospheric pressure and other boundary conditions. Select the pressure far field as the air inlet condition; 3.5) Select the appropriate wing material density. Through numerical simulation of 17 different winglet configurations of single factors and different configurations and those required to obtain the optimal configuration, view the lift-drag coefficient report definition to obtain a series of numerical simulation results of the lift-drag ratio of the external flow field, and then convert the results into the lift-drag ratio to provide reference data for the subsequent design optimization of the UAV.

[0036] Through detailed analysis of these data, the aerodynamic characteristics of the winglets of the UAV wing under different winglet configurations can be better understood. Statistics on height, sweep angle, and tip-to-root ratio are carried out to select the appropriate value range for subsequent establishment of the optimal deconstructed type. Then, solve the simulation data of the 17 groups of models required for the optimal solution, and then obtain the parameters of the optimal deconstructed type, optimize its design to achieve longer endurance and better flight performance.

[0037] In step 3, import the reasonable value ranges of height, sweep angle, and tip-to-root ratio into the design software. The design software gives 17 groups of data. Import the data into catia for model establishment, then import it into ansys for lift-drag ratio solution, and import it into the printer to obtain the weight. Bring these data back to the design software, and obtain the regression equation of the winglet and the response surface of different factors on the lift-drag ratio and weight through the response surface method, and thus obtain the data of the optimal configuration winglet.

[0038] The three factors are height, tip-to-root ratio, and sweep angle, and the conclusions are lift-drag ratio and weight. According to the previous calculation research and data display of the three factors, the factor intervals are shown in Table 1, and the data required to generate different models to be established are shown in Table 2. Establish three-dimensional models based on these data, and analyze the lift-drag ratio of these models through ansys respectively. After filling in the lift-drag ratio and weight, the software automatically analyzes and generates the optimal structure data, forming different response surfaces and calculation diagrams, and the data accuracy is relatively high. The data of the optimal winglet configuration is obtained.

[0039] Table 1 Experimental design table for response surface analysis of three factors: height, sweep angle, and tip-to-root ratio (response surface factor and level design) ; Table 2 Experimental design and results of lift-drag ratio and weight of optimized winglets ; The regression equation for the optimization of the UAV winglet is: Y lift-drag ratio = 8.05 + 0.087×A + 0.057×B + 0.043×C - 0.082×AB - 0.0075×AC - 0.047×BC - 0.16×A 2 - 0.097×B 2 - 0.087×C 2 Y weight = 33.08 - 0.59×A - 0.37×B - 0.51×C + 1.25×AB + 0.32×AC + 1.05×BC + 1.97×A 2 + 1.05×B 2 + 1.32×C 2 A, B, C, AB, AC, A 2 、B 2 and C 2 have a significant impact on the inspection indicators, while AC and BC have an insignificant impact on the inspection indicators.

[0040] The optimal optimized configuration parameters of the winglet are a height of 10.348 cm, an angle of sweep of 20.424°, and a tip-to-root ratio of 0.417. Under these conditions, the lift-drag ratio is 8.069 and the weight is 33.008 g. Under these conditions, a verification test is carried out. A 3D model of the winglet model is established in Catia and a numerical test is carried out using Ansys software. It is found that the lift-drag ratio is 8.053 and the weight is 31 g, which is close to the prediction result of the response surface model. The software also gives a confidence level of 0.931, proving that the model is accurate and reliable. The obtained optimal winglet configuration data has real practical value.

[0041] In step 4, specifically: 4.1) Output the model of Catia in stp format and import it into the software; 4.2) Use Bambu Studio software for 3D printing software slicing; 4.3) Print out the winglet model through a 3D printer; 4.4) Install the winglet on the aircraft; 4.5) Conduct actual endurance test flights, flight experiments, and collection of flight data; 4.6) Data analysis.

[0042] The effects of the changes in the three basic parameters of the winglet on the lift-drag characteristics are as follows: (a) Height: First, when the height of the winglet is set to approximately 60% of the wingtip chord length, i.e., h = 60%b, it is observed that the lift-to-drag ratio reaches its maximum value. Subsequently, when the height of the winglet continues to increase, the lift-to-drag ratio begins to gradually decrease. In addition, the induced drag shows a downward trend with the increase in the height of the winglet, especially after the height exceeds h = 60%b, and the downward trend becomes more obvious; (b) Dihedral angle: Regarding the dihedral angle of the winglet, we found that the lift-to-drag ratio increases with the increase in the dihedral angle, but the increasing amplitude begins to level off after the dihedral angle reaches approximately 20°. This is because although the increase in the dihedral angle will lead to an increase in lift, the induced drag increases at a faster rate, resulting in the lift-to-drag ratio increasing smoothly after the dihedral angle exceeds 20°; (c) Tip-to-root ratio: When the tip-to-root ratio varies within the range of 0.25 to 0.45, the lift-to-drag ratio slowly increases with the increase in the tip-to-root ratio and reaches its peak when the tip-to-root ratio is approximately 0.4. When the tip-to-root ratio exceeds 0.4, the lift-to-drag ratio begins to decrease with the continued increase in the tip-to-root ratio. At the same time, the induced drag decreases with the increase in the tip-to-root ratio when the tip-to-root ratio is less than 0.4 and reaches its minimum value when the tip-to-root ratio is 0.4; while when the tip-to-root ratio exceeds 0.4, the induced drag gradually increases with the increase in the tip-to-root ratio; (4) Based on the performance of different configuration wingtip devices, through the response surface method optimization of the design software, the software gave 17 data. These data were imported into catia for modeling, and then the modeling software was imported into ansys. Different lift-to-drag ratio data were calculated through ansys, and then the data were imported into the design software to obtain the optimal solution data of the most winglet. A new type of optimal winglet was obtained, and ansys and actual tests were carried out for verification, and it was obtained that it has the characteristic of the optimal lift-to-drag ratio.

[0043] (5) Based on the establishment of the optimal solution winglet model, the actual winglet model was printed through 3D printing technology and installed on the fixed-wing UAV carrier aircraft. Actual verification flights were carried out, and the optimized characteristics of this winglet were verified through the difference in flight endurance time.

[0044] The above schematically describes the present invention and its implementation manners. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the purpose of the present invention, creatively design structural manners and embodiments similar to this technical solution, they shall fall within the protection scope of the present invention.

Claims

1. An optimization design method for winglets of a fixed-wing unmanned aerial vehicle, characterized in that: It includes the following steps: Step 1: Model winglets with various geometric parameter analysis and research configurations of winglets through Catia, and select three parameters: height, sweep angle, and tip-to-root ratio; Step 2: Conduct aerodynamic data analysis on the optimal configuration solution through the CFD numerical method based on the ANSYS software; Step 3: Obtain the optimal configuration solution of the winglet through the Design response surface method; Step 4: Print the actual optimal solution winglet model through 3D printing technology, install it on the aircraft, conduct actual endurance test flights, and analyze the results.

2. The optimization design method of the winglet of the fixed-wing UAV according to claim 1, characterized in that: In Step 1, simulate the arc and shape of the Cessna wing to establish a three-dimensional model of the winglet; according to the software and wing data, perform airfoil settings for the wing. The winglet uses generative surfaces, adds guide lines, and closes the solid with multi-sections. During the modeling process, simplify the model by removing the struts, servos, and pull rods of the rudder surface of the wing. The unmanned aircraft carrier layout settings are adopted. The wingspan of the wing is 120 cm, the semi-wingspan is 60 cm, and the wingtip chord length is 19 cm; Establish winglet configuration models with different configurations, including winglet configuration models with different heights, sweep angles, and tip-to-root ratios.

3. The optimized design method of the winglet of a fixed-wing unmanned aerial vehicle according to claim 2, characterized in that: In Step 2, the CFD numerical method adheres to the basic conservation laws in fluid mechanics, including the law of conservation of mass, the law of conservation of momentum, and the law of conservation of energy; use the ANSYS software to perform numerical calculations. The software is based on the Reynolds-averaged N-S equations in three-dimensional integral form for simulation calculations: ； where: is the conserved quantity; V is the volume of the control volume; S is the surface area of the control volume; f is the sum of the inviscid flux and the viscous flux through the surface S, and n is the unit outer normal vector of the control volume surface S; Any flow must satisfy the law of conservation of mass: within a unit time, the mass increment or decrement of a fluid microelement is equal to the net mass of the fluid flowing into and out of the fluid microelement during the same time; the expression is: ； In the expression, represents density, t represents time, represents the velocity vector, represents the horizontal and vertical gradient operators; The law of conservation of momentum is expressed as: the rate of change of the momentum of a fluid microelement with respect to time is equal to the resultant external force acting on the fluid microelement. The expression is: ； In the expression, p represents the pressure, τ represents the viscous stress acting on the fluid element due to molecular viscosity, represents the viscous stress component, F represents the body force on the fluid element; represents the velocity components in the x, y, and z directions, represents the velocity vector; The law of conservation of energy is expressed as: the rate of increase of energy in a fluid microelement is equal to the sum of the net heat flux flowing into the fluid microelement and the work done by the body force on the fluid microelement; The expression is: ； In the expression, c p represents the specific heat capacity, T represents the temperature, k represents the heat transfer coefficient of the fluid, S T represents the viscous dissipation.

4. The optimized design method of the winglet of a fixed-wing UAV according to claim 3, characterized in that: In Step 2, specifically: 3.1) Select the left wing as the object of numerical simulation analysis, and use CATIA software to construct a complete three-dimensional solid model of the unmanned aircraft including the wing and winglet; 3.2) The model is then imported into ANSYS Workbench, and fluent is imported for further analysis; 3.3) To ensure the accuracy of the numerical simulation, create a large outer flow field region shell with dimensions of 20 m × 20 m × 15 m; in the space, construct a three-dimensional solid model of the outer flow field of the unmanned aircraft, and set and name the inlet, outlet, flow field wall surface, flow field symmetry plane, and wing of the model; perform structured grid division on the outer flow field; 3.4) Initialize, and then perform data simulation calculations on the generated grid for the outer flow field; select the SST k-ω model, set the simulated inlet velocity to 15 m / s, and keep the outlet pressure as the standard atmospheric pressure and other boundary condition settings. Select the pressure far field as the air flow inlet condition; 3.5) Select the density of the wing material. Through numerical simulation of 17 different winglet configurations with different single factors and the winglet configurations that need to be calculated to obtain the optimal configuration, view the lift-drag ratio numerical simulation results of a series of external flow fields obtained from the lift-drag coefficient report definition, and then convert the results into the lift-drag ratio to provide reference data for the design optimization of the UAV later.

5. The optimized design method of the winglet of a fixed-wing unmanned aerial vehicle according to claim 4, characterized in that: In step 3, import the reasonable value ranges of altitude, sweep angle, and tip-to-root ratio into the design software. The design software gives 17 groups of data. Import the data into catia for model establishment, then import it into ansys to solve the lift-drag ratio, and import it into the printer to obtain the weight. Bring these data back to the design software, and obtain the regression equation of the winglet and the response surface of different factors on the lift-drag ratio and weight through the response surface method, and thus obtain the data of the optimal configuration winglet.

6. The optimization design method of the winglet of a fixed-wing UAV according to claim 5, characterized in that: In step 4, specifically: 4.1) Output the model of catia in stp format and import it into the software; 4.2) Use Bambu Studio software for 3D printing software slicing processing; 4.3) Print out the winglet model through a 3D printer; 4.4) Install the winglet on the aircraft; 4.5) Conduct actual endurance test flights, flight experiments, and collection of flight data; 4.6) Data analysis.

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