Minimum Fuel Circling Flight for Unmanned Aerial Vehicles in a Constant Wind

Abstract

This paper investigates characteristics of minimum-fuel trajectories for an Unmanned Aerial Vehicle (UAV) in high altitude, circling flight under a constant wind. Previous research has shown that periodic circling flight, consisting of a boost arc (maximum thrust) and a coast arc (minimum thrust), improves the fuel consumption when compared to steady-state circling. Since the periodic flight includes ascending flight at the boost arc and descending flight at the coast arc, it is naturally expected that the wind energy influences the trajectories. In this work, numerical simulations are used to investigate the effects of both wind speed and direction on a UAV flying around one loop enclosed in a cylindrical boundary area. The results show that the optimal wind direction manifests as a tail wind just at the coast arc. In addition, the results demonstrate that the optimal wind direction changes with the wind speed and, in some cases, the trajectory under high winds results in smaller fuel consumption than the zero wind case. Thus, the importance of these results is two fold. First, that the periodic flight reveals the existence of an optimal wind direction for the minimum fuel circling. Second, and probably more importantly, generating optimal trajectories without rejecting wind disturbances provides an autonomous capability of using wind to its advantage and therefore improving fuel consumption or perhaps other mission performance metrics.