Nonlinear analysis of store-induced limit cycle oscillations

Abstract

Flight tests of modern high-performance fighter aircraft reveal that when these aircraft are carrying certain configurations of underwing stores, the aircraft will encounter a limit cycle oscillation at speeds much lower than those predicted by conventional linear aeroelastic analysis. Although nonlinearity is widely believed to contribute to this phenomenon, known as store-induced limit cycle oscillation, no theory has been forwarded to completely explain the mechanisms responsible. This work examines a two degree-of-freedom aeroelastic system which possesses kinematic nonlinearities and a strong nonlinearity in pitch stiffness. Nonlinear analysis techniques are used to gain insight into the characteristics of the behavior of the system. Numerical simulation is used to verify and validate the nonlinear analysis techniques. It is found that when system damping is low, the system clearly exhibits nonlinear interaction between modes, but this interaction effectively disappears when the system damping is high. It is also shown that certain forcing conditions applied to the damped system may appear negligible under certain circumstances, but these same forcing conditions produce a relatively large amplitude limit cycle oscillation under other circumstances.