How to Muffle a Plane
Noise engineers from Airbus and Boeing gave a breakdown of all the factors in a plane's design that contribute to its noise.
The new high-bypass engines are dominated by fan noise, which tends to be higher-pitched tones, as opposed to lower-pitched exhaust noise. By sending more of the air coming into the engine around the burner, that is, having more of it "bypass" the burning process, more air passes out the back of the engine at a lower velocity, which makes it quieter.
On takeoffs, planes can
be made quieter if wings are designed to give more lift at lower speeds.
Changing how the fans inside the jet engine are shaped could reduce
noise, though there are challenges in creating a design that does not
compromise the engine's efficiency. On approach, as much as half the
noise can be caused by flaps and landing gear, making them promising
targets for further research. A presentation can be found here.
