Transition Strategies for Tilt-Wing Aircraft

Kurzfassung

Despite being the critical flight phase for tilt-wings, the transition maneuver is still not well understood with respect to aerodynamics and flight dynamics. Flight and handling qualities in this regime are primarily defined by the size and shape of the transition corridor, which describes physical limitations and other boundaries. Typically, the corridor is obtained based on static trim analysis, which results in a conservative estimate that neglects the dynamic maneuverability of the aircraft. As a first fundamental step for the determination of the full transition corridor, this paper presents a comprehensive dynamic analysis of the longitudinal tilt-wing transition, considering various operational strategies for the maneuver. The analysis is based on an optimal control approach where the dynamic control problem is transcribed into a nonlinear programming (NLP) problem. The developed framework successfully explores different regions of the transition corridor by adapting constraints and objective functions, and thereby lays the foundation for future determination of transition boundaries. The optimized trajectories show that the phenomena of transition folds found in static analyses are damped within dynamic investigations. Furthermore, the re-transition maneuver proves to be more challenging from a flight physics perspective because of high effective angles of attack, and requires upward motion to avoid flow separation.