This paper presents a designated-time adaptive output feedback control scheme for quadrotors affected by sampling constraints. First, based on the principle of invariant manifolds, an efficient filter-based unknown system dynamics estimator is developed for overall uncertainty estimation. The unknown system dynamics estimator （USDE） design introduces a variable-threshold event-triggered state observer to replace the actual velocity measurements, maintaining estimation accuracy at low computational cost. Secondly, considering the strict response speed requirements of the quadrotor, an appointed-time funnel control （ATFC） scheme is designed to ensure that displacement errors converge within the predetermined time and to constrain error boundaries, thereby enhancing the system′s transient and steady-state performance. Finally, the stability of the closed-loop system is proven through Lyapunov analysis theory, and simulation results validate the effectiveness and superiority of the proposed method.