<p>This paper introduces a novel approach for designing sliding surfaces within the Sliding Mode Control framework using the regional eigenvalue assignment method. In the proposed approach, the pointwise eigenvalues of a reduced-order model are placed within a predefined circular region, representing the instantaneous linearization of the nonlinear system. Two update algorithms are developed to adaptively adjust the disk region parameters–its center and radius–at each sampling time, improving transient response and robustness. The effectiveness of the proposed method is validated both numerically and experimentally on a three-degree-of-freedom helicopter setup. Comparative results with the State-Dependent Riccati Equation-based Sliding Mode Control and fixed-disk regional eigenvalue assignment-based Sliding Mode Control demonstrate that the proposed update algorithms offer superior trajectory tracking performance and transient response.</p>