maKh

Makh is the transliteration of the Cyrillic мах, used in Russian and other languages that employ Cyrillic script to denote the Mach number in aviation and aerodynamics. The term is not a separate unit; it represents the same dimensionless quantity as Mach, the ratio of an object's speed to the local speed of sound.

Defined as M = v/a, where v is the true speed of the object relative to the surrounding medium and a is the local speed of sound. The speed of sound in air depends on temperature, so Mach number changes with altitude and atmospheric conditions. As a result, speeds described as Mach numbers are comparative and not fixed in meters per second.

Historically, the Mach number is named after Ernst Mach, a 19th-century Austrian physicist. In practice, many Russian-language texts write мах and refer to Mach numbers in the same way English texts use Mach. In transliteration, makh is often used to render the Cyrillic spelling.

Flight regimes are often described by Mach ranges: subsonic (below about Mach 0.8–0.9, depending on context), transonic (near Mach 1), supersonic (above Mach 1), and hypersonic (typically above Mach 5).

Typical examples: at sea level and standard conditions, the speed of sound is about 343 meters per second, so Mach 1 is roughly 343 m/s, Mach 2 about 686 m/s.

See also Mach number, Ernst Mach, speed of sound.