Impact of Failure on the Tilt-Wing eVTOL Backward Transition

Abstract

The backward transition from cruise to hover flight is the crucial flight maneuver for tilt-wing aircraft, as it allows for a safe vertical landing. Unfortunately, this flight phase is especially challenging due to low thrust settings and thereby reduced slipstream effects, which push the wing states toward or beyond flow separation. This raises the question of how failure conditions further impact these already severe conditions, and if the remaining flight performance suffices to perform the backward transition. This study therefore assesses the tilt-wing's fault tolerance against single and combined component failures. The reference scenario of a longitudinal level backward transition is investigated with optimal-control-based trajectory optimization on a 6DoF aircraft model. The results indicate fault tolerance of the tilt-wing aircraft for most failure cases. The majority of failure cases leading to unfeasible transition trajectories suffer from unbalanced hover or cruise conditions. Only for the failure case of control surface runaways on the same side of canard and main wing, the transition maneuver itself is the limiting factor due to increased thrust settings and thus longer transition times.