RCS Calculations On High-speed Helicopter And Effect Analyses Of Structural Parameters

Both high-speed and stealth performances are the trends of armed helicopter in future,and radar stealth performance has become an important indicator in high-speed helicopter design.Estimating the radar cross section(RCS)of high-speed helicopter accurately and efficiently is the key in its stealth design.Considering the complex structural configuration characteristics and the application of radar absorbing material(RAM)in stealth design,the high efficiency and high precision pre-estimating method of RCS characteristics based on high frequency approximation method and computational electromagnetics method(CEM)is established.And the inf luence of the structure parameters of the high-speed helicopter and the effect of the coating RAM on the RCS characteristics of coaxial rotor high-speed helicopter are investigated,some instructive results are obtained.The major contents are as follows:In Chapter 1,the domestic and overseas development status of high-speed helicopters is briefly introduced.Aiming at the complex radar scattering problem on high-speed helicopter,the present situation and technical difficulties in the research on radar target characteristics and RCS prediction are analyzed.The significance of the combination of high-frequency method and CEM method in estimating the RCS of high-speed helicopter,and the necessity in the research on the influence of structural parameters and RAM application on stealth performance are pointed out.In Chapter 2,the high frequency approximation method and the FDTD method for the electromagnetic scattering problem on conductor targets with surface medium coating in free-space are established respectively.On the one hand,based on the theory of physical diffraction,a high-frequency method combined with the physical optics method and the equivalent electromagnetic flow method is established.The scattering of the target surface is calculated by the physical optics which combined with the equivalent impedance boundary condition,and the edge diffraction is calculated by the equivalent electromagnetic flow method.On the other hand,on the basis of the conventional FDTD method,the conformal grids technique based on the equivalent medium parameters is developed,the specific calculation process is given and the effectiveness of the two methods is verified by numerical examples.The accuracy and efficiency of different methods which are evaluated according to the different electrical size at different frequencies are compared.In Chapter 3,in order to accurately reflect the configuration details of the high-speed helicopter,X-2 helicopter is used as the research object to establish the geometric model including each component and the whole machine.The grid are generated according to the accuracy and efficiency requirements of the high-frequency method and FDTD method,and the corresponding electromagnetic computing grids for the two methods are obtained respectively.On this basis,the obscured parts in high frequency grids are removed,edges are identif ied,and conformal grids in the FDTD grids are extracted respectively.In Chapter 4,analyses on radar target characteristics and parameter influences of coaxial rotor are carried out.In order to reveal the RCS characteristics of coaxial rotors,the influence of structure parameters and the effect of RAM application on the stealth performance,the distribution of RCS,surface induced current and scattering field of single rotor and double rotor RCS are calculated.Based on the present analysis method,the influences of the frequency,double rotor spacing and rotor hub on the RCS characteristics of the coaxial rotors is analyzed.By extracting the strong scattering part of the rotor,analyzing the limitations of coating RAM in practical application,the design scheme of full-coated and partial-coated RAM is compared and analyzed.Some meaningful conclusions of the application of coated radar absorbing material to improving coaxial rotor stealth performance are summarized.In Chapter 5,considering the structure characteristics of the coaxial rotor high-speed helicopter,taking the isolated fuselage as the benchmark,the RCS characteristics change rules of the fuselage with the installation of the horizontal/vertical tail and the tail propeller are investigated.Focusing on the radar scatter characteristics and strong scatter source distribution in three typical azimuth in horizontal plane.By comparing the RCS,the surface current and the scattering field distribution of different parts of the fuselage and the whole helicopter,some conclusions on radar stealth performance such as the effect of RAM application and the change of the structural parameters of coaxial rotor helicopter are summarized by using the method of partial coating RAM under different frequency and different directions of radar wave.