Performance Assessment of a Distributed Electric Propulsion System for a Medium Altitude Long Endurance Unmanned Aerial Vehicle

Abstract

Distributed propulsion systems are enabled by electrified aircraft and can provide aero-propulsive benefits. The magnitude and impact of these benefits rely on the location of propulsors on the vehicle, the amount of propulsive force generated by those propulsors, vehicle geometry, and the extent of hybridization of the propulsion system. With an increased number of degrees of freedom over conventionally electrified aircraft, the full extent of the impacts of this technology have not yet been explored, especially for military applications. This study builds on a previous one that implemented a series hybrid and turboeletric propulsion architecture on a turboprop UAV, by introducing a distributed electric propulsion system on the same vehicle. The previous study showed that with a hybrid architecture, the same performance, in terms of range and endurance, could not be achieved for a fixed gross take-off weight. This study investigates the impact of the distributed propulsion system with the goal of identifying the benefits over the previous vehicle and determining the level of technology required to break even with the conventional propulsion UAV. In incorporating the new propulsion system, the engine and main motor are resized, leading edge wing mounted propellers and motors are added to the configuration, and a new battery sizing strategy is implemented. Preliminary results show that, although this new system shows increased range and endurance over the series hybrid vehicle, it still falls short compared to the conventional vehicle with current levels of technology. Although improvements are needed to the electrical system technology to reduce the weight enough to break even with the conventional system, the new vehicle shows increased performance during climb, and has the capability to store energy during the mission. With the proper power management and battery utilization strategies, this system can provide reduction in fuel burn and improved performance during certain phases of the mission which could be beneficial for military applications.