# Integration and Flight Test of a 7 kW Turboelectric Vertical Take-Off and Landing Unmanned Aircraft
## 2 Background  
[PERSON] et al. [12] has conducted work on the analytical design of a small-scale turboelectric generator for unmanned aircraft applications. However, there remains a distinct lack of physically constructed turboelectric systems, and thus, a lack knowledge related to the integration of those systems into an aircraft. Recent work by researchers at Oklahoma State University (OSU) focused on creating an analytical model and then validating that model for converting existing sub-scale turbopro engines into turboelectric systems [13; 14]. Then, a turboelectric system was integrated into a fixed wing unmanned aircraft system (UAS) platform [15]. Subsequent work was done to refine and measure the performance of three different turboelectric systems for unmanned aircraft [16]. The reader is directed to the previous work for details regarding the control scheme and experimental validation of the active throttle control system used to govern the turbogenerator inside the test vehicle utilized in the current study [17].  
The aircraft that is the focus of this paper is shown in Figure 1. A 7 kW turboelectric system was integrated into a new UAS, with heavier takeoff weight than the previous one, with a 3.6 m wingspan that is also VTOL capable. The aircraft serves as a small-scaledemonstrator representative of a UAM system, which also has distributed lift rotors for VTOL takeoff. It utilizes a turboelectric system as the main powerplant and is augmented by batteries. The primary objective of this paper is to highlight design choices and identify challenges associated with integrating the turboelectric system into the aircraft. Furthermore, the secondary objective of this paper is to evaluate flight performance as an initial step toward assessing the design of UAM systems.  
The aircraft in this study is a VTOL version of the Mugin 3600. This aircraft has a maximum takeoff weight of 391 N (88 lbf) and includes four electrically driven lift rotors. The aircraft is powered by a turboelectric system based on a Kingtech K-60 TP turboprop and includes batteries in a series hybrid configuration [18]. The K-60 TP generates electrical power by driving a brushless DC motor mechanically coupled to the output shaft from the power turbine reduction gearbox. This motor acts as a generator and creates three-phase alternating current (AC) electricity. The three-phase AC flows through a passive diode rectifier for conversion to direct current (DC) like that of a battery.  
Though the aircraft is a small-scale demonstrator representative of UAM concepts, it also has potential direct application to UAS platforms. The turbine engine offers potentially quieter operation than a reciprocating engine, as well as potentially reduced vibrations and the ability to maintain power at higher altitudes. These advantages make small turbine engines an attractive option for further research. The VTOL UAS mission profile in this study, shown in Figure 2, is representative of a VTOL UAM system. The aircraft takes off vertically utilizing batteries and the turboelectric system before transitioning to forward flight. After transitioning to traditional fixed-wing flight, the aircraft utilizes only power from the turboelectric system and can use excess power produced to recharge the batteries. At the end of the mission, it lands vertically, once again utilizing power from the batteries, as needed. In this study, the aircraft flew at an altitude of 60 m above ground level (AGL), with a ground level of about 300 m at OSU, and a cruise speed of about 16 m/s.  
Figure 1: Test vehicle a modified Mugin 3600 VTOL unmanned aircraft.  
Figure 2: Idealized VTOL turboelectric mission profile.