Emergency Landing of a Hybrid Electric Tiltrotor After Engine Failure

Due to the increase in short-range air mobility, tiltrotors are expected to get a market share in civil operations. Concomitantly, the need to reduce pollutants and noise emissions requires adopting innovative propulsion, but full-electric tiltrotors are not a feasible solution yet. A series-hybrid retrofit of the XV-15 is thus proposed. An emergency landing procedure is suggested for the critical case of engine failure when batteries are fully discharged. Aircraft rotors act as wind turbines, extracting power during the glide, and recharging the batteries for electrically powered conversion and landing. The propulsive retrofit of the XV-15 shows that current battery technology is not mature to make it a viable solution, and a complete vehicle redesign would be required, exploiting other side-effects of hybrid propulsion on aerodynamic performance. However, the improvement in the performance of the accumulators in the next decade can significantly modify this scenario. The proposed emergency landing procedure consists of a constant-speed descent after and before a constant altitude deceleration. The analysis shows that the optimal descent speed is between 55 and 60 m/s. The limited variation of rotor collective pitch and glide path angle should make performing the emergency sequence relatively easy for the pilot.