Date of Award


Document Type


Degree Name

Master of Science in Aeronautical Engineering


Department of Aeronautics and Astronautics

First Advisor

Frederick G. Harmon, PhD


Currently fielded electric-powered small unmanned aircraft systems (UAS) lack the endurance desired by warfighters, while their internal combustion engine (ICE) driven counterparts generate mission compromising acoustic and thermal signatures. Parallel hybrid-electric propulsion systems would meet the military’s needs by combining the advantages of hydrocarbon and electric power systems. Three distinct parallel hybrid-electric system designs, each with three unique battery discharging profiles, were analyzed and compared using a constrained static optimization formulation based upon traditional aircraft design equations. Each system combined an ICE sized for cruise speed with an electric motor sized for endurance speed. The nine hybrid variations were compared using a typical five hour intelligence, surveillance and reconnaissance mission profile for a UAS with a maximum gross takeoff weight of 13.6 kg (30.0 lbf). A detailed analysis determined that the most suitable design for the baseline mission used a clutch-start configuration and a charge sustaining battery discharging strategy. The hybrid design enabled a 1.225 kg (2.701 lbf) payload capacity while providing fuel savings of 30.5% compared to a similarly sized, conventional ICE powered aircraft.

AFIT Designator


DTIC Accession Number