Longitudinal modeling and control for the convertible unmanned aerial vehicle: Theory and experiments

The field of unmanned aerial vehicles (UAVs) has grown in the last years, showing its utility in broader applications. For instance, in surveillance, precision agriculture, pack delivery, among others. The UAVs characteristics demand more suitable configurations for increasing their flight time, maneuverability, stability, and reliability for attending a growing quantity of services. One of the UAV configurations that has gained popularity in the last years is the Convertible Unmanned Aerial Vehicle (CUAV). This paper aims to provide a control strategy to stabilize the CUAV in all the flight modes: hover, cruise, and transition mode, in which the CUAV changes between hover and cruise flight mode. For that, we propose longitudinal modeling that considers realistic aerodynamics and even disturbances. This model presents a precise balance between complexity and practicality for control implementations. The control algorithm design is based on the Lyapunov stability theory and uses saturation functions intending not to saturate the actuators. Besides, the control algorithm does not include any switching function, is easy-to-implement, and demands the usually available feedback in the vast majority of low-cost commercial autopilots. The control allocation problem for this control is also solved. A mathematical proof based on Lyapunov theory demonstrates that the proposed controller performs the closed-loop system globally exponentially stable. Simulation and real flight experiments conducted with the CUAV demonstrate the effectiveness of theoretical results. Moreover, we present several comparative studies with the state of the art that demonstrate the paper's contribution to the field of convertible aerial vehicles.