Modeling and Control of Hover Flight for a Distributed Electric Propulsion VTOL

For vertical take-off and landing (VTOL) control of distributed-propulsion fixed-wing UAVs exhibiting strong nonlinearity and aerodynamic/propulsive coupling, traditional linearization methods incur significant modeling errors in pitch-roll coupling and vortex interference scenarios due to neglected high-order nonlinearities, leading to inherent control law limitations. This study focuses on a non-tilting distributed-propulsion VTOL UAV featuring integrated airframe-propulsion design. Each of its four propulsion units contains six ducted rotors, arranged in tandem-wing configuration on both fuselage sides. A revised propulsion-aerodynamic coupling model was established and validated through bench tests and CFD data, enabling the design of an Incremental Nonlinear Dynamic Inversion (INDI) control architecture. The UAV dynamics model was constructed in Matlab/Simulink incorporating this revised model. An INDI-based attitude control law was developed with cascade controllers (angular rate inner-loop/attitude outer-loop) for VTOL mode, integrated with propulsion-system and control-surface allocation strategy. Digital simulations validated the controller's effectiveness and robustness. Finally, tethered flight tests with physical prototypes confirmed the method's applicability for high-precision control of strongly nonlinear distributed-propulsion UAVs.