Estimation of aeroelastic models in structural limit-cycle oscillations from test data

An optimal estimation algorithm to identify aeroelastic models in structural limit-cycle oscillations (LCO) is developed. This algorithm is based on an optimal estimation theory with a continuous cost function to minimize the difference between the estimates and data. The optimality equations are reformulated in the frequency domain through Beecham-Titchener's averaging technique. The resulting equations are then solved by a finite difference method. A wing rock model of an 80-deg delta wing is used to verify the method. The method is then applied to the left engine nacelle of a jet transport airplane in structural LCO. Estimated system models include terms representing nonlinear stiffness and damping. On the basis of these estimated aeroelastic models, the necessary additional damping for LCO suppression can be computed. It is also shown that increasing the system stiffness alone may not eliminate the structural LCO.