Waypoint based online trajectory generation and improved following control for the ACT/FHS

Abstract

New research activities on DLRs EC135 ACT/FHS research helicopter has led to new challenges for the automatic flight control software of this testbed. Noise abatement flights, innovative automatic approach trajectories and other topics all require the helicopter to follow a set of waypoints as precisely as possible. This paper presents a new algorithm which is capable of generating curvature-continuous trajectories. A modification of the natural cubic spline algorithm is presented, which allows to incrementally fit cubic splines with defined boundary conditions through subsets of the waypoint list. By joining several of these splines with matching boundary condition, a continuous trajectory is obtained. This approach allows to distribute the computational load of the cubic spline calculation over several execution cycles of the real-time system. Based on these results, a state feedback and a carrot chasing controller are developed and compared in terms of their ability to reduce and stabilize the distance between the trajectory and the helicopter. The approach is verified in DLRs Air Vehicle Simulator (AVES).