The current research is focused around the development of a variable cycle micro-turbofan engine an existing micro-turbojet with less than 1kN thrust. The project involves the conversion of a single spool micro turbojet via integration of a fan, a continuously variable transmission (CVT) and a variable bypass nozzle.
As the micro gas turbine market suffers from restrained design costs, in order to shorten the design process to a minimum, the aspiration is to entail as few changes as possible to the core design. The solution, analyzed in the scope of this work, significantly improves maximum thrust, reduces fuel consumption by maintaining the core independently running at its optimum, and enables a wider operational range, all the meanwhile preserving a simple single-spool configuration. Moreover, the introduction of a variable fan coupling would allow real-time optimization for several operational modes. Small gear ratio would yield a lower fan bypass ratio, and therefore performance resembling a turbojet suitable for high speed flight, whereas large gear ratio would alter the engine cycle towards a modern turbofan, which provides improved fuel consumption during loitering and take-off. Thus, a small UAV equipped with this high-performance and cost-effective variable-gear-speed turbofan, would be able to operate efficiently in both “fly-fast” and “loiter” modes.
In addition, the acquired thrust increase translates into greater take-off weight, while independently varying bypass area and fan speed enables transonic flight and general reduction in fuel consumption. The combination of these effects yields an increase in range and loiter time. The aircraft architecture equipped with this adaptive engine can enable realization of unique missions that were prior unattainable or required different UAV propulsion systems. These unique characteristics are explored in a set of realistic scenarios.
