What do Mach number and the transonic region mean?
Mach number compares a speed with the local speed of sound. Mach 1 means travelling as fast as sound under those conditions. It is not a fixed speed in metres per second. In air, the speed of sound changes particularly with temperature.
Mach number compares a speed with the local speed of sound. Mach 1 means travelling as fast as sound under those conditions. It is not a fixed speed in metres per second. In air, the speed of sound changes particularly with temperature.
Below the speed of sound, motion is called subsonic; above it, supersonic. The transition region is called transonic. Different flow conditions can occur around a body in this region, with significant changes in airflow and drag.
This does not mean every bullet suddenly becomes unstable at the same distance. Shape, motion and environmental conditions interact. A claim that a product is suitable for supersonic use does not by itself prove a particular level of precision. Tests therefore need to state what was actually measured and the velocity range to which the claim applies. A general technical term does not replace testing a specific product.