Research On Diagonal Shear Variable-sweep Wing Of Morphing Aircraft Based On Flexible Skin

With the rapid development of advanced aircraft technology,the traditional fixed-wing has been difficult to meet the needs of complex missions in different flight environments.The aircraft in different speed and airspace has different requirements for lift surface area,plane shape and airfoil shape.It is difficult for traditional fixed-wing to achieve the optimal performance.Therefore,it is necessary to propose a morphing wing that can change its shape and aerodynamic layout with the flight environment and conditions.In order to take into account the advantages of different aircraft,this dissertation studied the variable-sweep wing of morphing aircraft.The variable-sweep wing can solve the problem that the aerodynamic performance of high speed and low speed can not be balanced.Therefore,the variable-sweep wing has good aerodynamic performance in subsonic,transonic and supersonic state,and has the ability to perform a variety of tasks.Based on the integrated design of flexible skin and modular skeleton,this dissertation presents two shear variable-sweep wings based on parallelogram units for wide-speed aircraft.And the length-width ratio of the diagonal shear variable-sweep wing parallelogram units is optimized.The differences of morphing mechanism and aerodynamic characteristics under different variable-sweep modes are studied.The optimization of variable-sweep modes is completed.Based on the class-shape function transformation method,a parametric model of two-dimensional variable airfoil is established.The lift coefficient,drag coefficient and lift-drag ratio of airfoils in subsonic,transonic and supersonic state are analyzed,and the airfoils with different relative thicknesses are selected.Based on the comparison results of the variable-sweep form and the optimization results of the airfoil,the composition of the diagonal shear variable-sweep wing system is proposed,and its working principle is described.This dissertation proposes a pre-stretching skin structure composed of silicone rubber on the surface and carbon fiber on the bottom.Based on the tension position theory,the theoretical model of critical shear angle of pre-stretching skin structure considering the viscoelasticity of silicone rubber is established.Based on the principle of virtual work,the theoretical model of in-plane shear driving force of pre-stretching skin structure is established.Based on the theory of elastic thin plate,the theoretical model of out-of-plane stiffness of pre-stretching skin structure is established.The theoretical models of out-of-plane stiffness,in-plane shear driving force and critical shear angle of the pre-stretching skin structure are verified by simulation and experiment,and the geometric parameters of the above theoretical models are analyzed.The critical shear angle of the pre-stretching skin structure can be increased and the shear driving force can be reduced by increasing the pre-stretching amount.Reducing the length,width and thickness of the pre-stretching skin structure can reduce its shear driving force.Increasing the parameters of carbon fiber and reducing its spacing can effectively improve the out-of-plane stiffness of pre-stretching skin structure.This dissertation proposes a composite reinforced skin structure that can be used for shear variable-sweep wing based on flexible silicone rubber and anisotropic composite structure.Based on the shear deformation theory and laminated plate theory,considering the contact between fiber a nd matrix,internal shear load and thermal load,the out-of-plane stiffness mechanical model of composite reinforced skin structure is established.Based on the principle of virtual work,the mathematical model of shear driving force and critical shear angle of composite reinforced skin structure is established.The accuracy of the out-of-plane stiffness theoretical model,in-plane shear driving force theoretical model and critical shear angle theoretical model of composite reinforced skin structure is verified by experiments,and the geometric parameters of the above theoretical models are analyzed.The out-of-plane stiffness,critical shear angle and in-plane shear driving force of the composite reinforced skin structure can be effectively improved by increasing the diameter of carbon fiber and reducin g the spacing,while the geometric parameters of Kevlar fiber have no obvious effect.The length and width of the composite reinforced skin structure also effectively affect the out-of-plane stiffness,critical shear angle and in-plane shear of the composite reinforced skin.Compared with the pre-stretching flexible skin structure and composite reinforced skin structure,the composite reinforced skin structure is used as the skin of the diagonal shear variable-sweep wing.In this dissertation,the diagonal shear variable-sweep wing based on flexible rubber skin structure is designed.Based on the quasi-static mechanical analysis and the principle of virtual displacement,the driving force balance equation of the parallelogram unit considering the composite reinforced skin structure is constructed,and a method for optimizing the actuator position of th e parallelogram unit is proposed.Based on the principle of virtual work,the spring equivalent model of composite reinforced skin structure is established,and the influence of composite reinforced skin structure with different sweep angles and geometric parameters on skeleton stiffness and fundamental frequency is analyzed.The diagonal shear variable sweep wing prototype with composite reinforced skin structure was developed.The accuracy of the stiffness and fundamental frequency analysis of the variable-sweep wing was verified by experiments.The deformation ability experiment,smooth performance experiment,wind tunnel experiment and uniform loading experiment are carried out to verify the aerodynamic performance and reliability of the developed diagonal shear variable sweep wing,which provide theoretical and technical support for the application of diagonal shear variable sweep wing in cross-domain aircraft.