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This paper proposes a quasipassivity-based robust nonlinear control law for the position control of a rotary flap aimed at stabilizing the free-to-roll motion of an aerial vehicle. An antagonist-type shape memory alloy microactuator (SMA) is used. The plant is modeled as a cascade decomposition comprising a 2nd-order, parametric-uncertain system excited by a bounded exogenous aerodynamic moment and a 1st-order heat conduction system characterized by a hysteretic output. The control objective is to warrant accurate and fast rotation of the flap at an angle determined by the outer-loop controller. The control law is obtained from subsystem decomposition that is suitable for quasipassivation by application of feedback and feedforward control. The cascade control structure is composed of 1) sliding mode control with boundary layer, which robustifies the flap positioning, and 2) PD control that compensates for the delay induced by the hysteretic characteristics of the SMA. The control scheme provides ultimate boundedness (UB) of tracking error trajectories and robustness to uncertain, bounded, stiffness constant and aerodynamic moment. Simulations validate the proposed approach.