Aircraft Performance Impact with a Turbofan Engine Using a Fan on Blade

Variable cycle engine (VCE) technology may offer solutions to the demanding and conflicting requirements of future fighter propulsion systems, combining high specific thrust at maximum engine power with low fuel consumption in subsonic cruise. The complexity and risk of VCE development programs have made companies reluctant to integrate VCEs. In this analytical study, the performance of a less complex architecture is studied, where an outer bypass stream is maintained by a single-stage fan on blade (FLADE). A FLADE is an outer fan that is mechanically connected to the fan of the main engine. The concept is evaluated for a typical fighter engine, a low-bypass-ratio mixed-flow turbofan engine with bypass ratios of 0.25 and 0.5. The analysis is focused on a subsonic cruise phase and an acceleration phase of a mission, as these phases reflect both subsonic part-power performance and maximum performance of the engine, but the analysis is also conducted for a wide range of engine power levels over the flight envelope. The relative improvements of the FLADE in specific range and endurance are 4% and 2% at the optimum cruise and loiter points, but greater improvements are available in other parts of the flight envelope.