The development of electric Vertical Take-Off and Landing (eVTOL) aircraft is increasingly linked to the low-altitude economy, with tiltrotor configurations gaining industry favor. Precisely defining the conversion corridor is key to ensuring the safe completion of transition flights for such configurations. Traditional conversion corridors are determined by solving for speed ranges of steady-level flight at different rotor tilt angles (static conversion corridor). However, this method inadequately reflects the dynamic process where configuration and speed change synchronously between helicopter and airplane modes, posing safety risks. To address this issue, boundary conditions for both low-speed and high-speed segments of the conversion corridor are formulated based on a nonlinear flight dynamics model of a tiltrotor aircraft. The effects of different accelerations and climb/descent rates on the dynamic conversion corridor are systematically analyzed and compared with the static conversion corridor. Results show that as acceleration increases, the maximum flight speed corresponding to various rotor tilt angles decreases linearly, while the reduction in minimum flight speed slows as the rotor tilt angle decreases. In specific flight states involving accelerated climbing, the dynamic conversion corridor area is reduced by about 52% compared to the static conversion corridor. Flight simulation results of different transition paths further indicate that relying solely on static conversion corridor designs may introduce flight safety hazards such as power exceedance and wing stall. Consequently, this paper proposes using the overlapping region of dynamic and static conversion corridors as the safety boundary for path design, thereby, improving the safety of transition flights.

The maximum cruise speed and maximum level flight speed are among the most important performance indexes for coaxial rigid rotor high-speed helicopters, whose special configuration and operating mechanism lead to serious rotor hub loading problems. The trim strategy design parameters such as high-speed flight pitch attitude, horizontal tail installation angle, differential lateral cyclic pitch, and rotor speed, induce significant cross-coupling effects on the required power, rotor hub loads, controllability, and stability. In this paper, the optimal design method of the trim strategy for high-speed flight is conducted under the handling qualities requirements. The aim is to provide a methodology for achieving the optimal trim strategy that achieves the best trade-off between flight performance and rotor hub loads. Firstly, based on the nonlinear flight dynamics model of the coaxial rigid rotor high-speed helicopter, the impact of design parameters of different trim strategies on the trim characteristics, stability, and controllability was analyzed. Subsequently, the trim strategy design problem was described as a mathematical optimization problem. Lastly, to improve optimization computational efficiency and reduce the risk of optimization failure, the trim strategy optimization design was conducted based on the Kriging surrogate model. The optimization results indicate that, at the maximum cruise speed and maximum flight speed, the required power is reduced by 5.7% and 6.9% under the optimal power trim strategy compared to the baseline strategy; the rotor hub moment load is reduced by 55.6% and 55.2% under the optimal rotor hub moment trim strategy; the required power is reduced by 1.8% and 3.1%, and the hub moment load is reduced by 49.4% and 46.2%, under the integrated optimal strategies for both power and hub moment. These results validate the effectiveness of the proposed optimization design method for trim strategy.