Flight control design and testing of a tiltwing VTOL aircraft

Thesis

Transition vertical take-off and landing (VTOL) aircraft configurations have risen in popularity as a result of the emerging “air taxi” market, i.e. the idea of point-to-point hybrid and electric aircraft transport solutions as a means to enable intra-city civilian air transport amidst rising global climate concerns. Such configurations benefit from the characteristics of both helicopters (high maneuverability and vertical flight) and conventional fixed-wing aircraft (efficient cruise) but remain a great challenge in the context of flight stability and control. This thesis explores the modeling, flight controller design, and testing of a unique tiltwing aircraft configuration: the Rolls-Royce eVTOL concept.

Minimum-energy transition trajectories are found that satisfy stall and dynamic constraints to gain an understanding of the aircraft’s achievable flight envelope. By studying the effects of center-of-gravity (CG) perturbations in combination with active flow control (AFC) concepts, the theoretical limits of performance are determined, where it is found that constant-altitude transition can be achieved in the forward direction (hover-to-cruise) but not the reverse (cruise-to-hover). Comparative solutions reveal that a redesign of the tail wing could expand the achievable flight envelope of the aircraft during backward transition. In either case, the use of AFC serves to maximize aircraft performance and increase robustness to CG variations.

Authors: Panish, L

• DOI: 10.5287/ora-veajkyqgd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: outer-loop velocity control; flight control design; air taxi; VTOL; optimal control theory; fault-tolerant control allocation; trajectory optimization; flight control; robust control; feedback control; feedback control systems; hover flight; fault tolerance; constant-altitude transition; Tiltwing; dynamical modeling; NDI; nonlinear control; inner-loop attitude control; LQR; hover flight testing; control allocation; minimum-energy trajectories; full-envelope flight controller design; Froude scaling; control theory; weighted pseudo-inverse; feedback linearization; eVTOL; nonlinear systems; scaled model; aircraft modeling; inner-loop; transition aircraft; flight testing; Urban Air Mobility; UAM; AFC; nonlinear dynamic inversion; feasible flight envelope; outer-loop; optimal control; full-envelope controller design; 6-DoF model; active flow control
• Subjects: Feedback control systems; Aircraft; Nonlinear control theory; Feedback control systems--Dynamics; Air taxis; Control theory; Feedback control systems--Mathematical models; Dynamics; Trajectory optimization; Flight testing; Flight control