Energy Efficiency in Unmanned Aircraft Systems: A Review

This paper presents a review of the state of the art of energy efficiency in unmanned aircraft systems. Key characteristics include the dominance of battery-powered small and micro-unmanned aircraft, micro-turbine powered micro unmanned aircraft and gas turbine-powered large unmanned aircraft. Key development trends include the improvement of fuel cell technologies for usability in unmanned aircraft systems and improved composite structures for lighter weight unmanned aircraft. Key current issues such as the specific energy density and power of all the available propulsion types are highlighted. The paper concludes with a discussion of expected future trends in the efficiency of unmanned aircraft propulsion during coming years.