Over the last few years, fuel cell technology has significantly advanced and has become a mode of clean power generation for many engineering applications. Currently the dominant application for fuel cell technology is with stationary power generation. Very little has been published for applications on mobile platforms, such as unmanned aerial vehicles. With unmanned aerial vehicles being used more frequently for national defense and reconnaissance, there is a need for a more efficiency, longer endurance power system that can support the increased electrical loads onboard. It has already been proven by others that fuel cell gas turbine hybrid systems can achieve higher system efficiencies at maximum power. The integration of a solid oxide fuel cell combustor with a gas turbine engine has the potential to significantly increase system efficiency at off-design conditions and have a higher energy density compared to traditional heat based systems. This results in abilities to support larger onboard electrical loads and longer mission durations. The majority of unmanned air vehicle mission time is spent during loiter, at part load operation. Increasing part load efficiency significantly increases mission duration and decreases operational costs. These hybrid systems can potentially have lower power degradation at higher altitudes compared to traditional heat based propulsion systems. The purpose of this research was to analyze the performance of a solid oxide fuel cell combustor hybrid gas turbine power system at design and off-design operating conditions at various altitudes. A system level MATLAB/Simulink model has been created to analyze the performance of such a system. The hybrid propulsion system was modeled as an anode-supported solid oxide fuel cell integrated with a commercially-available gas turbine engine used for remote control aircraft. The design point operation of the system was for maximum power at sea-level. A steady-state part load performance analysis was conducted for various loads ranging from 10 = L = 100 percent design load at varying altitudes ranging from 0 = Y = 20,000 feet. This analysis was conducted for four different fuel types: humidified hydrogen, propane, methane, and JP-8 jet fuel. The analysis showed that maximum system efficiency was achieved at loads of 40 = L = 60 percent design load at each altitude and fuel type. The system utilizing methane fuel, internally-steam reformed within the fuel cell, proved to have the highest system efficiency of 46.8 percent (LHV) at a part load of L = 60 percent and an altitude of Y = 20,000 feet.