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The Mach number (M or Ma), often only Mach, (/ m ɑː k /; German:) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. [ 1 ] [ 2 ] It is named after the Austrian physicist and philosopher Ernst Mach .
The subsonic speed range is that range of speeds within which, all of the airflow over an aircraft is less than Mach 1. The critical Mach number (Mcrit) is lowest free stream Mach number at which airflow over any part of the aircraft first reaches Mach 1. So the subsonic speed range includes all speeds that are less than Mcrit.
Supersonic speed is the speed of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level , this speed is approximately 343.2 m/s (1,126 ft/s; 768 mph; 667.1 kn; 1,236 km/h).
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates ... Objects moving at speeds greater than the speed of sound (Mach 1) ...
Ernst Waldfried Josef Wenzel Mach (/ m ɑː x / MAHKH; German: [ɛʁnst ˈmax]; 18 February 1838 – 19 February 1916) was an Austrian [2] physicist and philosopher, who contributed to the physics of shock waves. The ratio of the speed of a flow or object to that of sound is named the Mach number in his honour.
Mach number is defined as = where is true airspeed is the local speed of sound. Both the Mach number and the speed of sound can be computed using measurements of impact pressure, static pressure and outside air temperature.
A Machmeter is an aircraft pitot-static system flight instrument that shows the ratio of the true airspeed to the speed of sound, a dimensionless quantity called Mach number. This is shown on a Machmeter as a decimal fraction. An aircraft flying at the speed of sound is flying at a Mach number of one, expressed as Mach 1.
In aerodynamics, the critical Mach number (Mcr or M*) of an aircraft is the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it. [1] At the lower critical Mach number, airflow around the entire aircraft is subsonic.