Research On Flexible Micro Air Vehicle Based On Bionic Dragonfly And Its Testing System

With the continuous change of technology,unmanned aerial vehicles(UAVs)have developed rapidly in civil and military fields,and people’s requirements for UAVs tend to be miniaturized and flexible.Through the exploration and study of the common flying organisms in nature,it is found that the bionic flapping-wing flight mode has more advantages than the traditional fixed-wing and rotary-wing flight mode in low Reynolds number environment.Compared with birds,insects are smaller and their flying skills are more complex and superb,which is more instructive for the miniaturization design of flapping-wing aircraft.Dragonfly’s flight ability is particularly prominent among all kinds of flying insects,and it can achieve acceleration and deceleration,sharp turn,hover,reverse flight and other flight actions that are difficult for other flying creatures to achieve under high-speed flight.Therefore,this paper takes dragonfly as a bionic prototype to design and prepare a flapping-wing micro aircraft vehicle(FWMAV),and develops experimental equipment around the test of aerodynamic and noise performance of the aircraft.In this paper,a flexible bionic aircraft was proposed,and the structural design of multi-degree-of-freedom FWMAV and the preparation of flexible bionic flapping-wing were carried out.A low-noise test platform and a low-noise wind tunnel suitable for flapping-wing micro-aircraft are designed and developed,and the self-designed four-point force balance group is equipped to test the thrust and low noise of the FWMAV.The main research work is as follows:(1)Taking yellow dragonfly widely distributed in north China as the basic research object,the bionic wing was designed and studied.The macroscopical profile of dragonfly wings and the structure of wing veins were observed and measured by automatic microscope and cold field emission scanning electron microscope.Based on the scale-rate principle of flying organisms,the topological design and optimization of the overall shape of dragonfly wings were carried out to meet the requirements of key parameters such as wingspan,wing area and aspect ratio of FWMAV.The modal analysis of the three-dimensional space structure of the wings of biomimetic dragonfly was carried out,and the mechanism of aerodynamic force utilization of the flexible deformation of wings in the course of dragonfly flight was expounded.Through transient response analysis,it is found that under the action of sinusoidal external load with frequency of 25 Hz,the wings of dragonfly flapping as a whole,without local deformation.The stress amplitude at the tip of the wing is the smallest and the displacement amplitude is the largest,while the response at the base of the wing is the opposite.(2)A prototype of a multi-degree-of-freedom FWMAV was developed.This prototype has multiple degrees of freedom and can achieve flapping,sweeping,and twisting motions under a single power source,imitating the flapping wing motion mode of organisms in nature to a high extent,and realizing the "8" shape trajectory of the wingtip.The overall flexibility of the wing-wing structure,which has the most critical influence on aerodynamic efficiency and noise characteristics,was further improved.A new design and preparation method of inflatable flexible bionic wing was proposed.The flexible bionic wing was made of thermoplastic two-dimensional polymer materials by hot-pressing cladding,which can independently plan the distribution and scale of wing veins,and realize controllable adjustment of wing stiffness while ensuring light weight.(3)A low-noise aerodynamic performance test system for FWMAV was designed and built.The system mainly includes a low-noise rotating test platform,a low-noise wind tunnel test platform and a four-point force balance set suitable for FWMAV.The velvet flexible cloth imitating the feather characteristics of flying organisms was attached to the rigid inner wall of the test wind tunnel,and the noise reduction characteristics of the velvet flexible cloth in macro and micro scales were compared and studied.Based on the stress-strain principle of flexible hinge and strain gauge,the four-component force balance group can measure the lift,thrust,lateral force and overturning moment of FWMAV,and then effectively obtain the aerodynamic data under different motion parameters and environmental parameters.(4)The aerodynamic and noise performance of micro-ornithopter was tested and analyzed.Based on the dynamic blow test system,the aerodynamic characteristics exploration test and dynamic blow test of FWMAV under different states were carried out to study the characteristics changes of vertical lift and horizontal thrust of FWMAV under different parameter states(flutter surface inclination,flutter frequency and wind speed,etc.).The flutter noise of wings of different materials(carbon fiber resin composite and high density polyethylene aerated film)was compared and tested.The results showed that the lift force can be effectively improved by reducing the inclination angle of the flapping surface during low speed flapping or fixed-point hovering flight.At the same time,by comparing the conventional CFRP flapping wings,it was found that the new high-density polyethylene aerated film wings designed in this paper have a remarkable effect on reducing the noise perceptible to the human ear.The development of a new FWMAV inspired by dragonflies,as well as the testing equipment focused on the aerodynamic and noise performance of the aircraft,greatly enriches the structural design research of multi-degree-of-freedom flapping-wing prototypes.It provides new ideas and technical support for addressing the challenge of noise reduction in flapping-wing aircraft.Additionally,it offers valuable insights and guidance for the development of engineering applications and controllable FWMAV.