| Vertical taking off and landing(VTOL)Unmanned Aerial Vehicle(UAV)makes up the shortcomings of multi-rotor aircraft and fixed-wing aircraft,which can meet the increasingly complex requirements of agricultural low-altitude remote sensing missions.This study mainly designed and analyzed the dynamics of agricultural tailsitter VTOL UAV.Structural optimization of the aerodynamic was carried out with horizontal flight mode and VTOL mode of the vehicle.Aerodynamic characteristics and attitude transformation equation of the tailsitter at high angle of attack were studied,which can provide the attitude control theory for tailsitter UAV and a theoretical basis for the design and optimization of the agricultural remote sensing VTOL UAV.The main research contents and conclusions of the thesis are as follows:(1)Tailsitter UAV layout selection and overall parameter design.The parameters of the existing remote sensing UAVs were analyzed to determine the design specifications of the tailsitter UAV.The results of the design indicators as well as the aerodynamic layout and power system layout indicated that the dual-power front-pull layout of the flying wing is the optimal layout of the study.Based on the estimate of wing load,power-to-weight ratio and the power system efficiency to determine the take-off weight was 3kg,and the wing area was 0.5m~2.Combined with the screening results of the airfoil pole curve,the airfoil of the tailsitter was Sipkill 1.7/10.(2)Optimization of structural parameters of the wing and winglet.The main parameters of the tail-sitter,wingspan,wing root,wing slightly,sweep angle,winglet slightly longer,winglet height,winglet sweep angle,winglet thickness,and winglet length were investigated to optimize structural parameters.The lift-drag ratio and deformation were analyzed under the combination of 9 structural parameters by fluid-solid coupling.The simulation results showed that the lift-drag ratio was a linear and positive correlation with the wing length,winglet height,and winglet thickness,and nonlinear negative relationship with the sweep angle.The lift-to-drag ratio decreased and then increased with the sweep angle at 10?30°,the lift-to-drag ratio decreased with the sweep angle at 30?60°;The deformation was a negative linear correlation with wing root and wing slightly,linear positive relationship with wingspan,and nonlinear positive correlation with the sweep angle.According to the stability analysis results of the winglet,the deformation of the winglet was a nonlinear negative correlation with winglet length,and positive linear relationship with winglet slightly;the buckling load was linear negative correlation with winglet slightly,and positive linear correlation with winglet length.The optimal structural parameters of the tailsitter UAV were determined by multi-objective genetic algorithm and stability analysis results:wing root 500mm,wing slightly 300mm,wingspan 1200mm,sweep angle 28°,winglet slightly 280mm,winglet sweep angle 56°,winglet height 30mm,winglet thickness 6mm,and winglet length 200mm.(3)Optimization of the installation position of the tailsitter UAV motors.Eleven sample points were designed based on the single variable principle for the horizontal distance of the motor.The CFD numerical simulation method was used to compare the lift-drag ratio and the flow field distribution in the horizontal flight state,and the torque,deformation,and flow in the vertical hover state.According to the simulation results in the horizontal flight state,with the horizontal distance increased,the turbulence between the two propellers gradually weakened.The interference between the propellers disappeared,when d?224mm;as the horizontal distance of the motor increased,the lift-to-drag ratio first reduced and then keep constant,and the lift-to-drag ratio got maximum at d=206mm.From the simulation results in the vertical hover state,the turbulence effect of the leading edge of the wing gradually reduced with the increase of the horizontal distance.When d>212mm,the flow field distribution of the wing surface was uniform;with the increase of the horizontal distance,the amount deformation of the seat gradually decreased,and the minimum value of the deformation amount obtained at d=224 mm.Considering the lift-to-drag ratio,propeller spoiler and motor seat deformation,the optimal installation parameters of the motor were 224mm horizontal distance and 14mm motor seat height.(4)Transition dynamics model of tailsitter UAV.The relationship between the motor pull,lift,drag,velocity,and attack angle of the UAV in different attitude was studied.At the same attack angle,with the increase of velocity,lift coefficient remained unchanged,and lift increased in a quadratic function;with the increase of attack angle,lift increased first and then decreased and the maximum lift was achieved at the attack angle around 15°.As the angle of attack decreased,the drag coefficient decreased in a cubic function,and the drag increased first and then decreased.When the attack angle decreases from 90°to 0°,the pull of the motor increased first and then decreased.The motor pulls increased sharply at the attack angle about80°and rapidly reduced at the attack angle about 10°.(5)The endurance model of tailsitter UAV.CFD was used to simulate the aerodynamic and mass coefficients under 130 different combinations of structural parameters.The specific factors were extracted by variance analysis and geometric analysis,and the specific factors constructed the response surface model of endurance time.According to the results of extracting specific factors,the specific factors of aerodynamic coefficients in variance analysis were wingspan,sweep angle,wing thickness,and winglet length.The aerodynamic coefficients were linear positive correlation with wingspan,quadratic negative correlation with sweep angle,and linear negative correlation with wing thickness and winglet length.The specific factors of mass coefficients with geometric analysis were wing root,wing slightly,and wingspan.The mass coefficient was linear positive correlation with the three factors.A quadratic regression model of aerodynamic coefficients was established by fusing four specific factors,wingspan,sweep angle,winglet thickness,and winglet length.Finally,a relationship model of endurance time was established by combining the three-dimensional regression model of the mass coefficient.The accuracy of the model is 0.97.According to the results of wind tunnel test and flight test,the error between wind tunnel test data and simulation calculation data is less than 14%,the CFD numerical simulation method is reliable,the relative error between test duration and model prediction time is less than 15%,and the duration model is reliable.(6)The application of agricultural tailsitter UAV remote sensing system.Assembly and debugging of the tailsitter UAV were carried out,and the flight altitude,pitch attitude stability,and the endurance performance were tested during vertical hover,transition,and horizontal flight model.From the stability test results,the height fluctuation reached 10 m,and the pitch angle fluctuation reached 10°in transition mode.The height fluctuation was less than 2 m,and the pitch attitude fluctuation less than 2°during vertical hover and horizontal flight model.The tailsitter UAV was in a controllable range during the whole flight process.According to the endurance test results,the endurance time reached 30 minutes.The vertical taking off and landing phase cost 20%of the total power consumption,and the power consumption increased with the increase of climbing height.The tailsitter UAV could collect farmland remote sensing information with an optical camera.The ground resolution of the image was 2cm with no distortion.The tailsitter UAV can meet the requirements of agricultural information monitoring. |
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