Next Generation of Transport Engines

This article discusses the features of very high bypass ratio turbofans and open rotor engines. Each of these engine options has its pros and cons to consider. The very large bypass ratio turbofan engine maintains that the proven capability of containment of blade failures is inherently quieter due to ability to incorporate acoustic treatment in the fan duct and is not subject to high fan tip losses associated with direct exposure to higher cruise level flight speeds. The duct does not come for free, however, and installed weight becomes a primary concern as the increased bypass ratio drives up the engine diameter. Additionally, the fan is subject to higher local airfoil incidence when the fan nozzle un-chokes at low flight speed. The open rotor engine can achieve potentially greater improvements in propulsive efficiency than a turbofan but lacks the containment and noise reduction benefits of a duct. The rotor is also exposed to flight speed, driving up tip losses at today's accepted cruise flight speeds.