Theoretical And Compatational Flutter Study For Folding Wing Configuration

Recently years, many countries show great interesting in morphing aircraft.Folding wing, as one of these choices, has been profoundly concerned, too.It also brings great influence to the traditional vehicle design. As an expanding of traditional fixed wing, it not only has to face the problems of the traditional vehicle, but has technical innovation under the background of folding wing and conquers new problems and difficulties which conclude special changes because of the great shape change during flight. The varied folding angle and hinge stiffness have a major influence on the vehicle's aerodynamic characteristics, structure characteristics and flutter characteristics.In this arcticle we firstly build a half modal of the folding wing and do modal analysis,then we compute the unsteady aerodynamics of the folding wing by doublet lattice formulation,get the state-space representation of the folding wing using minimum state approximation method and work out the flutter speed,lastly we do modal analysis using MSC/Nastran. The main work of the paper are given as follows:(1)The physical modal of the folding wing was builded,do finite element analysis on it and compute the modal modes of vibration.The first several modes are reserved and the trend of influence of the inner and outer hinger stiffness on the structural characteristics is got by changing the hinger stiffness and folding angle.(2)The establishment process of the unsteady doublet lattice method is recounted in detail.Besides this, a matlab program which proved reliability in one circumstances of flate surface is written.Subsequently the program is used on the folding wing in this article and aerodynamics influence coefficients crucial to flutter analysis under various reduced frequencies are concluded.Then the generalized aerodynamics matrix is computed with the nomal velocity distribution of the control point using the vibration mode data and the infinite plane spline as the connection between aerodynamic and structural grids.(3)Nastran is used to do flutter analysis for the folding wing.We repeat steps of dynamic analysis and get the flutter characteristic under the circumstance of different folding angle and hinge stiffness. Work out the critical speed of every configuration and study effect of interrelation of nature modes on flutter.(4)The basic concepts of the aeroelastic state-space method are introduced. The generalized aerodynamics matrix is extended to Laplace domain with minimum state approximation and approximation of partial aerodymics is given.Based on this, corresponding state-space equation is concluded. Root locus diagram is drawn up to show the unsteady modal branch.The real parts of engenvalues varied with air speed are drawn up to judge the flutter point of unsteady branch futher.Lastly these results are compared with Nastran results.