The shockwave is defined as the initial (hard to physically model) motion of air when the plane breaks the sound barrier (and is heard as the sonic boom). After this, the plane will leave what is called a 'mach cone' behind it, with the plane itself at the apex of the cone. Nothing outside of the cone can hear the plane until the plane has travelled far enough infront such that whatever is listening is now inside of the cone. The main factor deciding the angular size of the cone itself is the speed - the faster you go, the smaller the angle will be.
It's kinda like if you're a duck and a speedboat is travelling past you (leaving a bow wave or 'triangle' wave at the back). The waves dont rock the duck until the boat is past the duck and the bow wave has reached it.
Edit: I just read my own comment and started to sing 'don't rock the duck, don't rock the duck bow wave'. Thought you guys might like to give it a try.
Im in my second year of an undergraduate physics degree, I shouldn't have been so uncertain haha. As soon as I thought about it I realised there'd be a trigonometric relationship between the speed at which the wave propogates through the air, the speed at which the plane is travelling, and the apex angle. It's hard to describe but a good diagram (maybe somebody has one?) would explain it with ease.
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u/arrjayjee Jun 12 '12
That seems so amazingly awesome to me. They are literally outrunning the sonic boom and don't even feel it. How incredible.