Aircraft are undeniably loud!

Here is something of interest, aircraft are now 100 times quieter than there counterparts from 40years ago.

The noise we here from an aeroplane is mostly produced by the engines, this happens because there is a difference in air speed between air being exhausted out of the rear, compared to the air passing around the engine. However aeroplane designers use a design that allows cool air to be bypassed through the engine, and this allows it to be exhausted at the same speed as the combusted air. This causes an attenuation in noise (the hot air is enveloped). Applying a larger fan can also be considered which allows more cool air to be bypassed, increasing attenuation.  Some noise is also produce by the body of the aircraft, for example, sharp changes in airflow lead to unnecessary noise.

So, aircraft engineers are constantly working on the survival of our ears. But what are they doing? Research in the way the air is expelled, research and application shows us that shaping exhaust gas leads to attenuation. Also looking at the wings of birds has lead to improvements of wing design, as the feather design that birds use, has a reduced noise compared to scale models of aircraft.

References:

http://www.sciences360.com/index.php/why-are-airplanes-so-loud-17217/