Flight control law design criteria for the transition phase for a tiltwing aircraft using multi-objective parameter synthesis

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Aircraft in tiltwing configuration combine the advantages of helicopters, such as hovering and vertical take-off and landing capabilities (VTOL), with the advantages of conventional fixed-wing aircraft, in particular long endurance and economic flight at higher velocities. During the transition phase between hovering and aerodynamic horizontal forward flight the aerodynamic forces and moments, the direct forces due to propulsion system and propulsion-induced aerodynamic forces and moments have to be properly balanced. Tilting the wing from vertical to horizontal position (and vice versa) poses a significant change in configuration. In combination with the given large velocity range this influences the control device efficiency significantly. At the same time, the tilting of the wing provides an additional control parameter. During flight control law design for an unmanned tiltwing aircraft with focus on the transition phase multi-objective parameter analysis and synthesis provides a powerful means to identify interdependencies and sensitivities. Key aspects of the longitudinal motion during the transition phase are investigated in this study using the multi-objective parameter synthesis tool MOPS, developed by the DLR Institute of System Dynamics and Control. Aim of this paper is to analyze quality criteria with respect to design and evaluation of control laws during transition phase. To achieve these parameters forward velocity and pitch attitude controller are optimized with respect to control and disturbance responses. At the same time the overall robustness against selected uncertain model parameters, such as actuator dynamics is considered explicitly. Different quality criteria characterizing these motions are developed and discussed in detail.