Feasibility Assessments of a Hybrid Turboelectric Medium Altitude Long Endurance Unmanned Aerial Vehicle

Electrified propulsion systems can provide potential environmental and performance benefits for future aircraft. The choice of the right propulsion architecture and the power management strategy depends on a number of factors, the airframe, electrification objectives and metrics of interest being the most critical ones. Therefore, the generic advantages and disadvantages of various electrified propulsion architectures must be quantified to assess feasibility and any possible benefits. Moreover, the objectives and the metrics of interest can be different for military applications than commercial ones. This research investigates the feasibility of turboelectric and hybrid turboelectric propulsion architectures integrated within a medium altitude long endurance surveillance unmanned aerial vehicle. The electrified propulsion system is desired to provide the same endurance and takeoff and landing field length characteristics of the baseline aircraft. This paper presents the results of the first phase of this research where only the electrified propulsion system is sized while the airframe is kept fixed. Physics-based models and a generic mission analysis methodology are used to evaluate the performance of the major subsystems of the propulsion system and to provide a full flight mission history. A state of the art rechargeable battery is employed for the hybrid case. Various power management strategies where the battery is discharged and charged in different flight segments are explored for varying sizes of battery packs. Results indicate that, while none of the architectures can offset the added weight and the efficiency factors of the electrical components as expected, the hybrid turboelectric propulsion architecture can provide fuel burn and performance benefits when sized for, and operated under, a specific set of power management strategies.