Disclaimer:
▪︎This content is Not an official document and does not represent the views of Airbus or any other aviation authority.
▪︎The information provided may be incorrect or misinterpreted and should not be relied upon for decision-making.
▪︎Always refer to official documents and consult with a qualified aviation professional before making any decisions based on the information provided in this blog post.
▪︎The information provided in this blog post is based on personal study and review.
1. Definition of Mach Number.
“Mach number” is the ratio of the true airspeed of the aircraft to the speed of sound in the same atmospheric conditions.
The speed of sound varies with factors such as temperature, which means that the Mach number of an object can change as it moves through regions with different temperatures.
2 . Coffin Corner
If the aircraft climbed high enough at this constant MMO with decreasing (Knots IAS) KIAS, KCAS, and KTAS, it would begin to approach its stall speed. At some point, the stall speed of the aircraft in Mach number could equal the M MO of the aircraft, and the pilot could neither slow down (without stalling) nor speed up (without exceeding the max operating speed of the aircraft). This has been dubbed the “coffin corner.”
Aside from all the complicated physics formulas, as the aircraft climbs higher, the margin between stall speed and Mmo is reduced, creating the so-called 'coffin corner.' Does this depend on the temperature?
As the aircraft climbs higher, the atmospheric temperature gets colder, which in turn reduces the coffin corner.
However, this ratio appears to remain the same at the same altitude.
In the aircraft, We can observe the relationship between IAS and Mmo is as below picture as shown from FCOM limitation.
For example, at fl311. we can see the maximum IAS which matches at Vmo is about 305kt like the table shows.
The atmospheric temperature typically decreases, and this decrease in temperature does indeed contribute to the reduction of the margin between stall speed and maximum operating Mach number (Mmo), commonly known as the "coffin corner."
The phenomenon occurs because both stall speed and Mmo are affected by changes in air density, which decreases as altitude increases. As air density decreases, indicated airspeed (IAS) decreases, leading to a lower stall speed. Additionally, the speed of sound also decreases with decreasing temperature, which affects the Mmo of the aircraft.
3. how to gret true airspeed using E6b computer.
We can get TAS using E6B, simply put maxh number index of E6B to the current temperature. (SAT) and then we can just read the TAS at the scale outside while finding the current mach number on the inner scale,
for example when the temperature is -30 degrees, and the mach number is 80, the TAS is 494kt.
Disclaimer:
▪︎This content is Not an official document and does not represent the views of Airbus or any other aviation authority.
▪︎The information provided may be incorrect or misinterpreted and should not be relied upon for decision-making.
▪︎Always refer to official documents and consult with a qualified aviation professional before making any decisions based on the information provided in this blog post.
▪︎The information provided in this blog post is based on personal study and review.