Boeing Ditches Noise-Cutting Chevrons on New Aircraft

The Quieter Engines on Boeing's Aircraft Come With a Penalty

NASA developed the chevrons, which are jagged-edged nozzle engines designed to reduce noise levels for communities. In 2001, NASA started flight testing these experimental engines with a modified Learjet 25.

The technology was built on accumulated knowledge from the military sector and was found to have a negligible 0.25% reduction of thrust. However, it significantly reduced engine noise by helping mix hot air from the engine core and cooler air blowing through the engine fan.

Boeing adopted this technology for its Boeing 787 Dreamliner and used some of the same innovations in updating the Boeing 747 (747-8), Boeing 737 (MAX), and Boeing 777 (777X). However, with the new Boeing 777X, Boeing has moved away from using chevrons.

The reason behind this shift is unclear, but it's possible that the new extra-high bypass engines are quiet enough to meet current and future noise regulations, and the GE9X engines will have a better fuel burn without them. Additionally, there have been improvements in fan blade aerodynamics, allowing composite fans to have lower tip speeds.