Tilt-wing electric vertical take-off and landing (eVTOL) aircraft face distinctive safety challenges during transition due to configuration variations, highly nonlinear aerodynamics and coupled effects of distributed electric propulsion. These characteristics impose substantial design efforts when conventional envelope protection methods are applied. This paper proposes a transition-corridor-based protected control framework which is compatible with both nonlinear model-based control and conventional feedback control. First, a transition corridor prediction method incorporating electric propulsion constraints is presented, yielding pitch angle and pitch angular acceleration limits as limit commands. Second, a corridor-based protected control strategy is established and integrated into incremental nonlinear dynamic inversion (INDI) and proportional-integral-derivative (PID) controllers. Furthermore, a comparative study is conducted across different protection strategies and controllers to assess the proposed protected control method in safety-critical transition flight. Simulation results demonstrate that the proposed method provides effective protection while exploiting available maneuvering margins. Moreover, incorporating electric propulsion constraints improves the physical consistency of corridor prediction and envelope protection. Overall, this study provides a practical corridor-based protection framework that integrates transition corridor constraints into closed-loop flight control, enabling safer transition for tilt-wing eVTOL aircraft.