## 1 Introduction
As weight is a great concern in aviation, the power-to-weight ratio is of utmost importance, and currently it is 7 kWh/kg. The other disadvantages are associated with the costs of the SOFCs and complex fabrication. As it operates at high temperatures, material degradation has been a drawback in implementing this technology on a large scale. The applicability of the SOFC/GT hybrid system in aircraft finds validation through numerous proof-of-concept studies documented in recent publications. These studies provide a foundation for building successive or iterative research. Notably, NASA's pioneering SOFC/GT auxiliary power unit (APU) system [15] marked an early attempt to explore its aerospace application. [PERSON] et al. [16] conducted a comparative analysis between an aircraft SOFC/GT APU and a PEMFC/GT APU under similar flight conditions. Their research revealed that the SOFC demonstrated superior efficiency throughout the flight cycle. Notably, it was more fuel-efficient, exhibited higher potential for water recovery, and required a 20% smaller fuel cell stack size to yield 400 kW of electric power. Although these studies have provided support for the implementation of hybrid systems in aircraft, it is essential to acknowledge that these studies were restricted to APUs. These APUs are typically integrated within the aircraft fuselage and utilize cabin air instead of atmospheric air. This distinction in operating environments presents a limitation in comprehending the system's applicability in aircraft propulsive power systems. Both the APU GT and SOFC are responsible for generating electrical power for the aircraft's cabin and components, but they do not contribute to thrust generation. Therefore, to enhance our understanding of this system within aircraft applications, it is imperative to evaluate its performance in primary propulsion. Recent studies have started exploring SOFC/GT applications in primary propulsion systems analyzing thermodynamic performance, system component integration, fuel selection, and different configurations. When applied in primary propulsion systems, the SOFC is mainly responsible for generating electric power, while the GT is responsible for propulsive power. [PERSON] et al. [17] analyzed a commercial turbofan SOFC system's thermodynamic performance, emphasizing performance variation under different fuels. [PERSON] et al. [18] designed an aircraft SOFC/GT based on natural gas, evaluating its performance under long and short-haul flights. [PERSON] et al. [19] performed design iterations on a 50 kW system for UAVs using liquid hydrogen, focusing on pressure ratio, oxygen utilization, and current density effects. [PERSON] et al. [20] conducted comparative studies on turbojet engines, emphasizing the advantages of the inter-stage turbine burner (ITB)-SOFC configuration, and developed a turbine-less engine integrated with SOFC for UAVs [21]. Most publications based on this hybrid system have mostly been computational analysis through modeling and simulations. However, [PERSON] et al. [22] recently created an experimental rig of an SOFC/GT liquid hydrogen-fueled electric propulsion system. It is a combined cycle with 1500 W planar type SOFC and two-spool 10 kW GT. It is an essential proof of concept, and the performance results obtained are essential to validate the adoption of such a system for aircraft propulsion. [PERSON] et al. [23] also analyzed an SOFC/GT system that demonstrated higher fuel-to-electricity conversion efficiency than traditional gas turbine engines fitted with generators. However, challenges exist when the hybrid system's mass and volume significantly impact aircraft aerodynamics. [PERSON] [5] addressed volume issues, suggesting geometry modifications to minimize aerodynamic drag within the hybrid system. [PERSON] and [PERSON] [24] provided a detailed power density comparison, and [PERSON] et al. [25] explored turbine-less hybrid electric propulsion, evaluating system performance in variable configurations. In a comprehensive analysis conducted by [PERSON] et al.