Flutter Boundary Prediction of an Adaptrive Smart Wing during Process of Adaptation Using Steady-State Response Data

Abstract

This paper describes a flutter boundary prediction of a smart wing during the process of adaptation. As for a smart wing, aeroelastic safety might unexpectedly be endangered because of an increase in flexibility or a change in structural stiffness during on-going adaptation in a flight or wind-tunnel test. We perform a simulation analysis on estimation of aeroelastic characteristics and flutter boundary of a two-dimensional smart wing, using steady-state response data of the wing subjected to air turbulence while the smart wing flies at a fixed speed. The structural adaptation is represented by continuous change in its natural frequencies of the wing vibration modes. Numerical results show that the flutter boundary prediction based on the flutter margin of discrete-time systems which we proposed originally for fixed wings is much more effective than the damping coefficients of the aeroelastic modes. fatal destruction of airplane’s structure during its flight. Safety against flutter for a newly developed airplane is therefore guaranteed by carrying out a series of flight tests. In a conventional airplane the flight speed is the most visible variable to the instability. The higher the flight speed is, the more critical the stability becomes. This fact will be true for a morphing airplane with smart wings if it flies keeping the configuration fixed like conventional airplanes designed not to change purposely the shape of their wings except for flaps and ailerons. A morphing airplane is essentially more flexible than a conventional airplane. Particularly, during the process of structural morphing or adaptation of the smart wing, its main structure and supporting systems for morphing will become movable and less rigid, so that the structural morphing may lead to coalescence of the frequencies of aeroelastic modes. One may foresee possibilities that the airplane flying even at a constant speed encounters new aeroelastic instability caused by mechanisms different from the traditional sense. It is very important, therefore, to develop a flutter prediction method which is applicable to such newly emerging situations during the process of adaptation in flight and wind tunnel tests. Using digital techniques on flutter test data, a number of researchers 3-11 investigated prediction of flutter boundaries of conventional configuration-fixed wings. Among them, Matsuzaki and Ando 3 were the first who proposed an aeroelastic instability prediction based on the AR-MA process 12 together with Jury’s stability criteria 13 , and they applied their method to response data of wing models measured in supersonic wind tunnel tests on flutter 3 and divergence 5 . Extending the stability analysis based on Jury’s criteria, Torii and Matsuzaki 10 proposed a flutter margin for discrete-time systems (FMDS) with two-degrees of freedom, which was equivalent to Zimmerman’s Flutter Margin 14 for the continuous-time system. As for the FMDS, Bae, Kim, Lee, Matsuzaki and Inman 11 have