Design Of Large And Medium-sized Bionic Flapping Wing Aerial Vehicle And Research On Its Flight Performance

Among the various flapping creatures(birds,bats,insects,etc.),large and medium-sized birds with a wingspan of more than 1 meter generally have the characteristics of high flight efficiency,long flight endurance and long flight distance,making the research of bionics of large and medium-sized birds has become a new research hotspot in recent years.However,due to the limited understanding of unsteady aerodynamics and the design of time-varying nonlinear control systems,especially the influence of unsteady aerodynamic characteristics and different structural parameters on flight performance is not clear,the flight performance of the many designed large and medium scaled flapping wing aerial vehicles(FWAV)falls far behind their natural counterparts presently.In order to explore the factors that will affect flapping flight performance,and to develop FWAV prototype systems that can achieve efficient and stable flight,bionic design and its influence on flight performance is carried out in this paper,and typical FWAV prototypes of highperformance are developed.According to the biological and structural characteristics and flight modes of large and medium-sized birds,a flapping-wing flying robot system scheme is proposed,which consists of a symmetrical flapping mechanism driven by a single motor and a tail adjustment mechanism driven by two servo-motors.Prototypes with different wingspans and different wing planforms have successfully achieved outdoor flight,which verifies the effectiveness of the system scheme.In the proposed scheme,the wings are confined to can only flap ups and downs,which enabled us to ignore the complex aerodynamics of real bird wings when folding and twisting.When explaining the flight principles of the prototype,we proposed the method of cycleaveraging to ignore the ever-changing vectors of the aerodynamic force and aerodynamic moments at different stroke positions.On the basis of that,roll stability is achieved by using equivalent anhedral and pitch stability is obtained by using equivalent conventional aerodynamic layout referring to fixed wing airplanes.Thus,the various FWAV prototypes designed in this paper can not only fly but can also stably fly.Aiming at the needs of different tests on the aerodynamic characteristics and comprehensive performance of large and medium-sized bionic flapping-wing flying robots at different stages of research and development,this paper proposes and designs four test schemes from different test angles and taking into account factors such as test frequency and test cost.The corresponding experimental systems are no inflow flapping experiment,wind tunnel experiment,rotational flight experiment and outdoor flight experiment.The no inflow flapping experiment and wind tunnel experiment can respectively be used to test wing performance and tail performance in conditions of no inflow and steady inflow.These two experimental schemes will measure both aerodynamic forces and torques at the same time,the test results are richer and more comprehensive compare to other researchers’ findings.The rotational flight experiment is an easy way that can test the aerodynamic forces of wings when flapping in a rotational test stand.This experimental system is efficient,of low cost and more accurate in matching the inflow velocity and flapping parameters.Thus,it has higher test precision and the results are more reliable.Outdoor flight experiment is the most direct way to investigate the comprehensive flight performance of the FWAV prototypes.It relies on the designed onboard flight control system to collect fight data of kinematics and power consumption characteristics when flying,which will be used to evaluate the flight performance.The four experimental systems complement each other and play different roles in different stages of the design process of FWAV prototypes from conceptual design to finalization.In order to find out the influence of wing structure parameters on the aerodynamic characteristics of flapping flight,36 kinds of wings with different parameters and structural characteristics(mainly from aspects like planform,aspect ratio,airfoil,thickness,stiffness layout,and wing materials,etc.)and 28 sets of control experiments were carried out.The aerodynamic forces,torques and flapping efficiencies of wings in different experimental control groups were investigated by the first three experimental schemes proposed aforementioned,i.e.,no inflow flapping experiment,wind tunnel experiment and rotational flight experiment.The results showed that the relative inflow is beneficial to the generation of aerodynamic forces and the decrement of pitch moment,the stiffness layout of the wing is the most influential factor on the lift-thrust ratio,the distribution of mass and moment of inertia of the wing are the most influential factors on the power consumption and flight efficiency,and the camber and thickness of the airfoil also affect the performance of the flapping flight to a certain extent.Furtherly,inspired by the different forms of tails of different birds in nature,a total of 6 forms and 30 tails with different structures and sizes were designed and fabricated in this paper.After that,experiments with no inflow and with coming flow of constant velocity in wind tunnel were conducted to study the detailed aerodynamic characteristics of different tails.By comparison,the results show that the proposed arc-shaped tail wings have the maximum pitch and roll moment coupling characteristics,while the proposed web-liked tail-wings have the maximum maneuverability.In the last chapter of this paper,combined with the research content and conclusions in the preceding chapters,several FWAV prototype schemes based on different design objectives are given: The HIT-Phoenix with relatively outstanding wind resistance,the bionic Eagle with a large climb rate,the patchwork FWAV prototype with a web-liked tail turns in a rather small radius,and the single-segment straight winged FWAV prototype with a rather long flight endurance.The successful flight of these prototypes fully proved the rationality and validated the feasibility of the proposed design methods and experimental schemes in the previous chapters of this paper,and the correctness of the research conclusions on wings and tail wings for FWAV.