Conceptual design of a high-endurance hybrid electric unmanned aerial vehicle

Small electric unmanned aerial vehicles (UAVs) have the advantages of low visual, heat and acoustic signatures, but have only limited flight endurance. For electric motor/battery powered UAV designs, to increase the flight endurance means an increase in the weight of the onboard battery, which in turn adds to the overall weight of the UAV and hence more power is used, especially during the ascent and possibly loiter stages of the mission. A marked increase in an aircraft's endurance can be achieved with the inclusion of an internal combustion engine in the design, but this will result in high noise levels and possibly, an unwanted heat signature. The objective of this preliminary work is to show the feasibility of combining the two power sources, an internal combustion engine and electric motor to obtain a hybrid-electric UAV which will provide high flight endurance capability together with low visual/heat/acoustic signatures.