Aeroelastic analysis for the flexible control surface of a flight vehicle with concentrated structural nonlinearities has been performed. The purpose of this study is to suggest an efficient numerical analysis method in the time domain and to examine the nonlinear aeroelastic response of the flexible nonlinear model. In this study, two and three dimensional elastic model of a control surface with a root freeplay nonlinearity in pitch are considered. Finite element structural model is used for the structural analysis and doublet lattice unsteady aerodynamic model is used for the calculation of aerodynamic loads. In approximating frequency domain aerodynamic forces, Roger and Abel's least square rational function approximating method is used with optimizing algorithm. To transform the frequency domain aerodynamic forces to the time domain forces, the method of Brace and Eversman is used. To reduce the problem size and the computation time, the fictitious mass modal approach is used, which can afford the possible local change of structural property. Both frequency and time domain nonlinear aeroelastic analysis are performed. The fictitious mass modal approach is shown to be an efficient method for the aeroelastic analysis involving the concentrated structural nonlinearities. The effects of the torsional spring stiffness and initial amplitude ratio on the aeroelastic characteristics are examined. The aeroelastic response are sensitive to the pitch torsional spring stiffness and initial conditions. Limit cycle oscillation, periodic motion and chaotic motion are observed at the velocities below the divergent flutter boundary. The presence of the freeplay nonlinearity generally makes the divergent flutter speeds larger than those of the linear case.
