# Why are aircrafts more stable traveling faster than sound than at the speed of sound?

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Why are aircrafts more stable traveling faster than sound than at the speed of sound?

In: Physics

If you go faster than speed of sound, you are cutting through the air like a knife.

If you go slower than the speed of sound, air flows around the plane smoothly.

If you go just at the speed of sound, you can neither cut like a clean knife nor flow around the plane. You are on the edge of chaos. Physics is confused. It’s like trying to slowly cut through the air like a knife, but having the knife get stuck.

Imagine a wave in the ocean. It’s smooth behind the wave and in front of the wave. But it’s not smooth _on_ the wave.

A plane compresses the air in front of it. As it approaches Mach 1 it creates a shockwave right at the nose and it sits there. If you go faster the shockwave moves towards the rear of the plane.

This shockwave is what creates a sonic boom.

Air waves act a lot like water waves.

When on a boat, moving forward constantly creates waves. If the boat moves as fast (or just a little slower) as the waves it is creating, they will build up in front of it. Eventually the built up waves will effectively be an uphill swim for the boat, slowing it down and destabilizing the boat’s speed. It is much easier to just go a little faster, and now the build up of waves happens behind the boat.

Aircraft is almost the same, but in 3 dimensions and higher speed.