Analysis and simulation of the longitudinal control of an unmanned aerial vehicle

Analyses the performance of a longitudinal controller for the ARMOR UAV (unmanned aerial vehicle) RC (robust control) model, submitted to gust disturbances. The final aim of the analysis is a practical solution to be implemented in the ARMOR UAV microprocessor. We explore the difficulties that may arise from competitive specifications derived from the actual aircraft characteristics. In order to control the longitudinal model of the ARMOR UAV, a robust controller was designed in agreement with the traditional requirements of good tracking of speed and altitude, but taking into account the characteristics of the real actuators. Essentially, the engine installed turns out to be a poor actuator, both in terms of time constant and in allowable thrust, and its operation easily reaches the limitations. In terms of gust response, the comparison of open and closed loop, in terms of frequency analysis, demonstrates that the altitude control is achieved, but no further improvement is obtained. The time simulations are in perfect agreement with the previous results and don´t exhibit any influence due to the nonlinear characteristics. Finally, the changes of physical parameters are perfectly transparent to the controller, except for the phugoid zone where the gust sensitivity behaves like in open loop. The properties of the robust controller design have thus been verified, but the quality of the actuators, and particularly the engine, appear to be of great importance for a good gust disturbance control