Originally Posted by Mad (Flt) Scientist
If you want a non-maths way of thinking about it, the properties change because in subsonic flow the flow can 'see' changes in the downstream conditions and adjust accordingly. Once sonic the flow is essentially travelling 'blind' and can only react to the local and previous conditions, but not the ones in front. (It's not exactly a rigourous explanation, but it might help ?)
It does help a lot =) I'm not that good at supersonic aerodynamics and I have to say that I'm having a hard time understanding some books where the author depends on the reader having such knowledge...
Can you reccomend any good reading? the ATPL course books from oxford doesn't say much about it... mostly only concentrates on flow over and under a wing... =(