Determining MACH Speed Value
We try to explain it as best we can and why we don't list them in our values.
Okay, let's try to explain what Mach is...
Mach values are quite variable and very situational. When an aircraft operates at high-speeds and high-altitudes, the outside air temperature tends to increase, requiring greater output from the engine - meaning more fuel consumption directly effecting the aircrafts operational range but at the same time resulting in an increase to speed. As the outside operating air temperature increases, so too does the speed of sound. As such, the speed of an aircraft essentially depends on the temperature of the air around the aircraft itself.
Mach can be attained at various altitudes but this is also reflected in the very different speeds needed to break the sound barrier at these altitudes.
The formula for determining Mach is as follows:
M = V o / Vs
This breaks down as "M" being the Mach Number, "Vo" representing the velocity of the object and divided by "Vs" representing the velocity of sound. Mach is always presented with the value after the unit as in "Mach 1".
According to the FAA Pilot's Encyclopedia of Aeronautical Knowledge, given a standard temperature condition of 15c, the speed of sound at sea level is 661 knots. But at 40,000 feet, where the temperature drops to -55c, the speed of sound value decreases to about 574 knots. This shows us the direct correlation between the variable value of Mach and outside operating temperatures where the temperature directly effects at what point the Mach speed value can actually be attained - thus breaking the speed of sound. The measurement of speed at high-altitude or high-speed flight is measured in this value of Mach. Mach values follows a series of ranges represented as these terms:
Subsonic covers any Mach number value below 0.75
Transonic covers any Mach number value between 0.75 and 1.20
Supersonic covers any Mach number value between 1.20 and 5.00
Hypersonic covers to any Mach number beyond 5.00
Mach speed is basically the ratio of true airspeed of a flying object against the speed of sound in like atmospheric conditions. The speed of sound is exactly Mach 1.0 so thusly an aircraft traveling at Mach 1.0 is traveling at the very edge of the speed of sound with anything more than that actually breaking the sound barrier.
In early jet designs, this barrier was a milestone to achieve with any regularity. Some aircraft could only exceed Mach 1.0 in a dive while other later models - built specifically for speed - were able to break this sound barrier at will but could still only operate within the limitations of their engines and airframe.
Mach Critical is a term used to describe the speed of airflow over an aircraft's wings. All things associated with the breaking of the sound barrier - such as the shock wave or the transferal of subsonic into transonic flight - occur at this critical value reaching Mach 1.0. The cruising speed of an aircraft is directly related to this Mach Critical number as it is often regarded as the value of pinnacle of efficiency in regards to an aircrafts design.
The MACH speed value is named after Austrian/Czechoslovakian physicist Ernst Mach (February 18th, 1838 - February 19th, 1916).