Distributed electric propulsion tilt-rotor unmanned aerial vehicles (TRUAVs) with a lift-increasing flap in the propulsion wake have better aerodynamic efficiency than traditional tilt-rotor unmanned aerial vehicles and better takeoff/landing capacity than fixed-wing aircraft. However, for this configuration, establishing the propulsion–aerodynamic coupling model between the flap and the duct is difficult. This paper presents a flight dynamics model with propulsion–aerodynamic coupling components and analyzes dynamic characteristics during the transition period for TRUAVs with a distributed-propulsion/flap configuration. The development of the flight dynamics model considers the descriptions of the duct model, the lift-increasing flap model, and the propeller model. The model of the lift-increasing flap in both the duct exhaust jet and the freestream is the key component of the vehicle dynamics equations and is validated with experimental data and computational fluid dynamics results. Based on the dynamics model, the transition corridor of the tilt-rotor aircraft with multiple asynchronous tilting components and a geometrical constraint is calculated and analyzed. Additionally, the longitudinal dynamics stability of the aircraft in different flight speeds and configurations is assessed based on the numerical differentiation method. The results showed that the vehicle flight speed has more influence on longitudinal short-period stability than the angle of attack (AOA) of the flap. Also, the longitudinal long-period stability is affected by both the vehicle flight speed and the AOA of the flap. Finally, a mathematical derivation is developed to analyze the aircraft’s unstable state. The presented analysis results show that the stability of the long period is affected by the velocity derivative of the fuselage’s lift.

The integration of propulsion and wing in distributed propulsion–wing UAVs (DPW UAVs) introduces significant propulsion-aerodynamic coupling, complicating dynamic modeling and flight control. This complexity is heightened by using induced wing surfaces for vertical takeoff and landing, requiring controllers to adapt to configuration changes and disturbances during transition flight. This paper develops a propulsion-aerodynamic coupling model for a medium-sized DPW UAV with induced wings (DPW-IW), enabling real-time aerodynamic performance calculations. Furthermore, a unified flight-control framework is proposed to avoid controller scheduling and switching during flight mode transitions. The proposed control framework employs the time-scale separation principle, divided into an outer loop and an inner loop. The outer loop uses a fuzzy controller to adjust allocation parameters, while the inner loop applies incremental nonlinear dynamic inversion (INDI) and control allocation (INCA) methods, providing robustness to nonlinear changes during flight transitions. Finally, simulations under various conditions demonstrate the controller’s effectiveness in ensuring smooth and robust transitions.

For vertical takeoff 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 strategies. 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.

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.