A New Nonlinear Guidance Logic for Trajectory Tracking

A new nonlinear guidance logic, that has demonstrated superior performance in guiding unmanned air vehicles (UAVs) on curved trajectories, is presented. The logic approximates a proportional-derivative controller when following a straight line path, but the logic also contains an element of anticipatory control enabling tight tracking when following curved paths. The method uses inertial speed in the computation of commanded lateral acceleration and adds adaptive capability to the change of vehicle speed due to external disturbances, such as wind. Flight tests using two small UAVs showed that each aircraft was controlled to within 1.6 meters RMS when following circular paths. The logic was ultimately used for air rendezvous of the two aircraft, bringing them in close proximity to within 12 meters of separation, with 1.4 meters RMS relative position errors. Nomenclature Vehicle velocity A line defined from vehicle position to a reference point on a desired trajectory Angle created from V to the line L1 (clockwise direction is positive) Acceleration command sideways i.e. perpendicular to vehicle velocity direction Cross-track error Radius of circle or circular segment Lyapunov function I.