<p>Electric Short Takeoff and Landing (eSTOL) aircraft leveraging distributed electric propulsion and blown-lift technology offer a promising solution to advanced air mobility. Systematic research on their equilibrium performance boundaries remains limited, although such analysis is critical for flight performance assessment and control system design. Furthermore, establishing the equilibrium flight envelope for such over-actuated configurations poses significant computational challenges. This paper proposes an efficient optimization-based methodology for estimating the equilibrium flight envelope. By reformulating the conventionally constrained trim problem into a nonlinear least-squares problem using a soft penalty approach, rapid and reliable trim evaluations are achieved. Applying this method, we comprehensively analyze the effects of auxiliary propulsion and flap deflection on the flight envelope. The results demonstrate that the blown-lift effect dramatically reduces the minimum steady speed and extends the achievable climb rate range at low speeds. Finally, these model-based predictions are successfully validated with real-world flight-test data, confirming the eSTOL configuration’s good low-speed capabilities.</p>