Researches On Helicopter Radar Stealth Technology Based On High-accuracy Prediction Methods

Comprehensive stealth design is the future development trend of the design of armed helicopters,and radar stealth performance has become an important indicator in helicopter stealth design.Considering the complicated configuration and electromagnetic scattering characteristics,a numerical method based on computational electromagnetics method(CEM)is established to analyze radar scattering characteristics(RCS).On these bases,the radar target scattering characteristics of rotor,fuselage and whole helicopter are numerically investigated.Then,the influences of the radar absorbing materials(RAM)on the RCS characteristics of rotor,fuselage and whole helicopter are investigated.The major contents are as follows:In Chapter one,the research and development in the field of stealth aircraft,the experimental techniques and theoretical methods of radar stealth characteristics,and the stealth technology of helicopter are introduced briefly.Then,the importance of stealth design platform considering stealth performances of helicopter is pointed out.In addition,the methods used in the present research are briefly brought forward.In Chapter two,the helicopter geometric model and the electromagnetic computational grids are generated.In order to accurately reflect the complicated configuration of the helicopter,the geometric model including rotor,fuselage and whole helicopter can be generated.The appropriate electromagnetic computation grids of the helicopter are generated according to the accuracy and efficiency requirements of the CEM method.In Chapter three,Maxwell's equations are taken as the governing equations of Finite Volume Time Domain(FVTD)method,and they are solved by spatial discretization with Steger-Warming flux-vector splitting algorithm and five-stage WENO discretization.On the other hand,on the basis of the conventional Finite-Difference Time-Domain(FDTD)method,the Non-uniform grids technique based on the equivalent medium parameters is developed.The high precision of the numerical methods for predicting RCS characteristics are verified by comparisons of the metal sphere and the conductor sphere coated with absorbing material.In Chapter four,in order to accurately reflect the minutiae of the electromagnetic scattering field of the rotor,the effects of rotor rotation,rotor hub and fairing on the RCS characteristic of the rotor is analyzed based on the high precision CEM method.Furthermore,the design scheme of the structure absorbing material and the rotor coated with absorbing material are compared with the metal rotor and analyzed.On these bases,the influence of RAM on the helicopter rotor is summarized.In Chapter five,based on the scattering characteristics of attitude angle response of the isolated fuselage,the RCS change regulation of the fuselage with different structural parameters and the expanding trend of the strong scattering zones are analyzed in the different incidence angles,and then the scattering mechanism of the component has been revealed.Then,by comparing the RCS response characteristics and the strong scattering zones of coated fuselage and metal fuselage in all azimuth,as a result,the stealth design methods of fuselage which can reduce its RCS characteristics have been explored.In Chapter six,based on the scattering characteristics of attitude angle response of the whole helicopter,the RCS change regulation of the whole helicopter with the weapons and the expanding trend of the strong scattering zones are analyzed,and afterwards the scattering mechanism of the component has been revealed.Then,by analyzing the RCS response characteristics of the helicopter coated with RAM in the typical angle domain,the experience and scheme applied to the stealth design of the armed helicopter are summarized.