Aircraft speed: Difference between revisions

The '''Mach number''' is the ratio of an aircraft's TAS over the local speed of sound. A Mach number below 1 means that the plane moves subsonically, a Mach number above 1 indicates supersonic flight. The Mach number is interesting because a number of phenomena take place just around Mach 1, for example a sudden increase in drag induced by shockwave generation. However, since the speed of sound changes with the compressibility (and hence temperature) of air, the Mach number is dependent on altitude (as the air temperature drops at higher altitudes). This implies that Mach 2 at sea level corresponds to a faster TAS than Mach 2 at 30.000 ft. The precise relations between TAS, Mach number and altitude are rather complicated formulae and depend in essence on the local weather pattern determining the pressure and temperature gradients in the atmosphere.