Design and Performance Evaluation of Hybrid Electric Propulsion Systems for UAVs

This paper aims to conduct a design domain analysis and development of workflow for analyzing the performance of existing unmanned aerial vehicles (UAVs) when considering the transition from internal combustion engines (ICEs) to electrified or hybrid propulsion systems. For a precise analysis and performance evaluation, we first evaluate the performance of the baseline UAV’s range and endurance. Then, we calculate the same metrics when hybrid or electric batteries are adopted on the same baseline model. As a result, the performance deficiency guides us in establishing design criteria to match or compensate for the deficiency. The MQ-1C Gray Eagle UAV, used by the US Army, was selected as the baseline aircraft, featuring a diesel-based engine and a propeller located at the rear of the vehicle. It has a range of 2,500 nautical miles and about 25 hours of flight time. The first adopted new propulsion system is electric power battery packs. As a thruster, the same propeller of MQ-1C Gray Eagle is considered. Due to their significantly lower energy density compared to diesel engines, battery-driven propulsion systems achieve approximately 1/10 of the baseline in both flight distance and endurance. Although the performance of alternative power systems surpasses that of the current model, their significance lies in their extremely low thermal signatures and high stealth capabilities. The detailed analysis includes mass breakdown, energy density, endurance, and range estimations based on the Breguet range equation. Results demonstrate that batteries offer zero carbon emissions but incur a trade-off in flight endurance and range, which may be justified for strategic missions requiring sustainable fuel alternatives or low thermal and noise signature. This also implies that the need for design criteria to match performance can suggest new configurations for future tactical and more mission-oriented vehicle designs. This paper begins with the performance analysis and validation of the baseline aircraft, comparing it to the nominal performance data sheet provided by the manufacturer and operator. Once the validation processes of the performance are guaranteed, another performance analysis is calculated when electric power systems are adopted, following the same procedures.