Boeing Ditches Chevrons on 777X Engines Due to Aerodynamic Advancements

The Boeing 777X was initially designed to feature sawtooth chevrons on its massive GE9X engines, but those were quietly replaced by smooth nacelles and clean exhaust nozzles before the aircraft's final configuration was rolled out.

This design change wasn't a compromise on noise compliance or environmental standards, but rather a demonstration of how rapidly propulsion aerodynamics advanced over a single decade. Chevrons were used to reduce jet mixing noise by 5-6 decibels, but they came with an inherent aerodynamic tax that engineers sought to eliminate.

The GE9X engine's ultra-high bypass ratio and lower exhaust velocity made external chevrons redundant, allowing Boeing to shift its focus to reducing intake noise at the front of the engine. The company redesigned the fan geometry, reducing blade count and suppressing turbulence and cabin buzzsaw noise.