Advanced Trajectory Design for the Tunnel-in-the-Sky Display: The Use Of Clothoids

Abstract

The tunnel-in-the-sky display is generally believed to allow pilots to manually conduct complex curved approaches with a suitable level of workload. Several flight tests using the tunnel display, however, revealed considerable difficulties in flying these curved approaches. One of the main problems was considered to be the current nonsmooth interception of circular tunnel sections from straight tunnel sections (and vice versa) which highly contributed to pilot workload. In order to achieve a smooth interception of curved trajectories, a so-called clothoid transition path is advocated that can be inserted between the straight and circular sections of the trajectory. A clothoid function yields a curvature that changes from zero (yielding a straight trajectory) to the desired curvature (yielding a circular trajectory) in a certain amount of space traveled. Pilot-in-the-loop experiments show that the use of clothoid transients eases the flying of complex (tight) curved approaches, through a better match of the trajectory with the aircraft response, which results in an elongation of the total maneuvre time and improved interceptory timing of the pilot. This causes the clothoid augmented tunnels to have better path-following performance, lower control activity and higher comfort levels due to less aggressive steering. This paper discusses the clothoid trajectory design and summarizes the results of an experimental evaluation in a fixed-base flight simulator.