Evaluation of the effects of a hybrid electric propulsion system on range in a high altitude long endurance unmanned aerial vehicle

Various studies are being carried out to reduce the negative environmental impact resulting from the widespread use of fossil fuels in aircraft, to reduce dependence on fossil fuels in this field, and to prevent future supply problems. The main goal is to use fully electric aircraft in the long term, but this is not yet possible with current technology. Hybrid propulsion systems are considered as a transition step. In this study, using the range equation previously published in the literature for aircrafts using hybrid electric propulsion systems, range calculations were made for a HALE class UAV with different engine types and different altitudes. The study shows that the energy density of the batteries used in hybrid electric propulsion systems, engine efficiency and cruise altitude have a significant impact on the range of hybrid electric UAVs. Additionally, this study presents a case study that reveals the connection between battery energy density, the efficiency of the subsystems that make up the propulsion system, the degree of hybridization, and the range of the UAV. It has been determined that when current battery technology is used, the degree of hybridization and range are inversely proportional. Unlike the studies seen in the literature, the effects of altitude factor on the range of a UAV with a hybrid electric propulsion system were also examined in this study.