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Dynamics of flutter is an important consideration in the design of aircraft structures. Flutter is an unstable selfexcitation of the structure due to an undesirable coupling of structural elasticity and aerodynamics. Flutter is very difficult to predict and its occurrence can lead to catastrophic structural failure. The dynamics of flutter are affected by several factors including nonlinearities in structural stiffness, damping, and free-play in control surfaces. The free-play nonlinearity in control surfaces mechanisms is similar to the backlash in gears. Such nonlinearity introduces persistent limit cycle oscillations (LCO's) and significantly affects the onset of flutter. The impact of free-play on the flutter speed and frequency is not fully understood and is an active area of research. Historically, very conservative estimates have been used for the allowable freeplay. The current military specification limit for free-play is based on the wind tunnel tests performed in 1950's at the Wright Air Development Center (WADC). The key contribution of this paper lies in gaining deeper understanding of free-play dynamics to enable more accurate modeling of free-play and predict its impact on flutter speed and frequency. The proposed modeling methodology is validated via close agreement of the simulation with WADC test data. Energy-based novel approach is presented for life cycle assessment and to predict flutter instability.

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