Aero-Terms are designed to be a daily reminder of the terms,
names, acronyms and explanations of the unique language that
populates the aviation world. Aerospace, sport aviation, fixed
wing, helo, you name it... it's all fair game.
Aero-Terms should serve as a quick but intriguing reminder of
the terms you may use every day, or an introduction to an aspects
of the Aero-World you may not yet be familiar with. ANN also
encourages readers to go beyond the FMI link, and further research
any intriguing terms.
Suggestions for future Aero-Terms are ALWAYS
welcome, as are additions or discussion of the
explanations given for each Aero-Term.
Unit of speed, named after the Austrian physicist Ernst Mach
(1838-1916), equal to the ratio of the speed of a moving object to
the speed of sound in the surrounding medium under ambient
conditions. The actual speed of sound varies depending on the
altitude above sea level because sound travels at slightly
different speeds at different temperatures, and the temperature
varies according to altitude. At sea level, the speed of sound,
known as Mach 1.0, is about 761 miles per hour (1,225 km/h). At
20,000 ft (6,096 m), the speed of sound is 660 mph (1,062 km/h). If
an aircraft is traveling at half the speed of sound, it is said to
be traveling at Mach 0.5. A speed of Mach 2.0 is twice the speed of
sound. Because the speed of sound varies, a particular speed at sea
level expressed as a Mach number would be faster than the same
speed at 30,000 ft (9,144 m), which would be faster than the same
speed at 40,000 ft (12,192 m). In other words, Mach 2 at sea level
is a greater number of miles per hour (or kilometers per hour) than
Mach 2 at 30,000 ft, which is a greater number of miles per hour
than Mach 2 at 40,000 ft.