A Comparative Study of a Multi-Gas Generator Fan to a Turbofan Engine on a Vertical Takeoff and Landing Personal Air Vehicle

This paper attempts to assess the benefits of a unique distributed propulsion concept, known as the Multi-Gas Generator Fan (MGGF) system, over conventional turbofan engines on civilian vertical takeoff and landing (VTOL) applications. The MGGF-based system has shown the potential to address the fundamental technical challenge in designing a VTOL aircraft: the significant mismatch between the power requirements at lift-off/hover and cruise. Vehicle-level performance and sizing studies were implemented using the Grumman Design 698 tilt-nacelle V/STOL aircraft as a notional personal air vehicle (PAV), subjected to hypothetical single engine failure (SEF) emergency landing requirements and PAV mission requirements. An integrated analysis environment, which consists of design and simulation tools for SEF emergency landing; MGGF cycle analysis and sizing; and aircraft sizing and synthesis, was developed to perform studies on vehicle sizing, MGGF optimization, mission requirement tradeoffs, and sensitivity analyses of SEF emergency landing conditions. It was found that the MGGF system has distinctive advantages over the conventional turbofan engine when a stringent SEF emergency landing requirement was enforced. The unconventional system also showed superior specific fuel consumption (SFC) trends during hover and low speed cruise (less than 250 knots) conditions. Nevertheless, the turbofan tilt-nacelle PAV showed its competitiveness over its MGGF counterpart in high speed cruise (higher than 300 knots) conditions.