Control allocation framework for a tilt-rotor vertical take-off and landing transition aircraft configuration

In this paper, a control allocation framework for incremental nonlinear dynamic inversion (INDI) baseline controller is proposed. Incremental controllers command pseudo control increments, leading to a control allocation problem with path dependency. Path dependency is a phenomenon of incremental controllers for redundant systems, implying possible control input positions that are not only dependent on the commanded pseudo controls but also historical trajectory of the inputs. It can lead to internal input conflicts thus waste of control power and reduction of stability margin. The proposed controller framework applies a new control allocation algorithm based on pseudo inverse, and then solves the path dependency problem with a null space transition scheme. A correction algorithm that accounts for elementary modification of effectiveness matrix is also included. The framework is implemented with an INDI baseline controller for a vertical-take-off-landing (VTOL) transition vehicle, for which flight test results are presented.