Fighter aircraft encounter aeroelastic Limit Cycle Oscillations (LCO) when carrying certain combinations of under-wing stores, leading to structural fatigue, pilot discomfort and flight envelope restrictions. The roles of various aerodynamic and structural factors in this store-induced LCO are not sufficiently understood, and their numerical exploration via time marching is computationally expensive. This work examines the effects of nonlinear stiffness and damping in the wing-store attachments of two systems, namely a generic wing and the F-16 aircraft, using the computationally efficient Harmonic Balance method. While the generic wing is modeled directly, a dynamic decoupling/coupling method is applied to the F-16 model to accommodate the nonlinearity. Results for cubic restoring force, freeplay and Coulomb friction are discussed, and useful relationships are established between the type of nonlinearity and the nature of the LCO response.
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