Optimisation of proprotors for tilt-wing eVTOL aircraft

Abstract

Proprotors for tilt-wing advanced air mobility aircraft are often optimised without considering the transition from hover to cruise. This paper presents an optimisation method, which considers transition flight phases. Proprotors are optimised for a multi-rotor tilt-wing vehicle at nominal cruise, transition, and hover conditions. Results show that proprotors designed with transition flight conditions tend to have smaller chord distributions along the span than those designed without considering transition. The blade twist from root to tip of the transition proprotors is also more extreme, and a slight increase in pitch towards the tip section of the propeller is observed. The more significant overall twist avoids retreating blade stall during transition and transition power is the most sensitive to the pitch angle at the mid-radius to tip section of the blade. However, a proprotor that is designed taking transition into account requires a hover power that is 5.6% larger than a proprotor designed for cruise and hover only. Pareto-optimal proprotor designs from an optimisation case without transition cannot deliver enough thrust throughout all transition flight phases.