Evaluation of Ultra-High Bypass Ratio Engines for an Over-Wing Aircraft Configuration

Abstract

Today, main hub airports are already at their capacity limit and hence, smaller airports get more interesting to provide point-to-point connections. Unfortunately, the use of regional airports induces an increased environmental footprint for the population living around it. In an attempt to solve the related problems, unconventional aircraft and engine designs are required. The research project Coordinated Research Centre 880 aims at examing the fundamentals of a single-aisle aircraft powered by two geared ultra-high bypass turbofan engines mounted over the wing. Low direct operating costs, noise shielding due to the over-wing configuration, and short runway lengths are the main advantages of such an aircraft. Highlighting the performance, economical and noise benefits of a geared ultra-high bypass engine is the key aim of this paper. This assessment includes a correspondingly adjusted aircraft. Open literature values are applied to design the two investigated bypass ratios; an engine with a bypass ratio of 5 respectively 17. Furthermore, a variable bypass nozzle area for the ultra-high bypass ratio engine is analyzed. Finally, the three engines are evaluated based on aircraft direct operating costs and an initial engine noise assessment. This study concludes that increasing the bypass ratio from 5 to 17 drops the direct operating costs by 5.6% and can reduce the sound at the source for a selected operating condition by up to 7dB. During the different flight phases the reduction in specific fuel consumption ranges between 18% to 40%. Applying a variable bypass nozzle leads to a further decrease by 0.6% for the direct operating costs. Opening the bypass nozzle during several flight phases stabilizes the fan shown by the surge margin increase. It is concluded that this unconventional aircraft configuration with ultra-high bypass ratio engines mounted over the wing has the potential to relieve main hub airports by also reducing the environmental impact.