Robuste, fehlertolerante Basisregelung schwebeflugfähiger Flugzeuge
- Robust, fault-tolerant control of aircraft with hovering capability
Binz, Fabian; Moormann, Dieter (Thesis advisor); Alles, Wolfgang (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
Aircraft with vertical take-off and landing (VTOL) capability differ fundamentally from conventional airplanes due to their large flight envelope. This flight envelope ranges from the thrust-borne hover flight to the lift-borne aerodynamic flight, leading to highly variable, nonlinear aerodynamics. Modeling these aerodynamics requires elaborate computer simulations (i. e. CFD 1 ), wind-tunnel campaigns or flight experiments. When transitioning from the thrust-borne to the lift-borne flight regime, over-actuation often occurs, since both, the actuators required for thrust-borne and the actuators required for lift-borne flight, have a significant effectivity. This leads to the question of actuator allocation, which deals with the distribution of available actuators according to the commanded forces and moments. Over-actuation is the result of redundancy regarding the available actuators. While this redundancy complicates the controller design, in principle it also allows for fault-tolerance against actuator failure and should thus be considered in the controller design. In total, the inherent complexity due to aerodynamics, over-actuation and fault-tolerance are often reflected in the control system, creating a challenging control problem. With the goal of minimizing the required effort to design a controller, this work presents a control concept based on the principle of Incremental Nonlinear Dynamic Inversion (INDI). While classical Nonlinear Dynamic Inversion (NDI) is based on a comprehensive aerodynamic model, this dependency is largely eliminated when using the incremental form of NDI, as it only depends on the control effectivity. To enable a flexible implementation on different types of aircraft, the control effectivity is based on simple semi-empirical models and geometrical properties of the aircraft. Results from theory and practice show that this approach is sufficient in terms of controller performance. On top of that, the controller concept presented here incorporates a systematic approach to over- and under-actuation and thus enables a tolerance against actuator failure. The control concept is implemented on a tilt-wing aircraft. To validate the concept, both, simulation studies and flight tests are performed. Presenting selected failure modes in flight tests, the tolerance against actuator failure and the robustness against model uncertainties is confirmed.