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Recent studies have considered the use of flared folding wingtips (FFWTs) to enable higher aspect ratios—reducing overall induced drag—while reducing gust loading and meeting airport operational requirements. The majority of these analyses have employed linear assumptions despite the presence of large wingtip deformations. In this paper the effect of geometric nonlinearities introduced by an FFWT on the static and dynamic aeroelastic response of a wing is assessed. A geometrically exact expression was formulated to describe the change in the local angle of attack in the chordwise direction across all fold angles. This expression highlighted that the aerodynamic stiffness of an FFWT and, therefore, quantities such as the linear flutter speed are a function of the fold angle and, hence, the attitude of the wing. This effect was verified using both a wind tunnel model of a flexible semispan wing and a numerical …