What does the Mach number represent?

The Mach number represents the ratio of an aircraft's speed to the speed of sound at that same temperature and pressure. It is a dimensionless number used to express how fast an aircraft is traveling relative to the speed of sound. When an aircraft is flying at a speed less than the speed of sound, it is said to be subsonic (Mach numbers less than 1). At Mach number equal to 1, an aircraft is at the speed of sound, and speeds greater than this indicate that the aircraft is supersonic.

Understanding the concept of the Mach number is essential in aviation because it impacts various aerodynamic characteristics, including drag, lift, and stability. For example, at high speeds, compressibility effects become more significant, and pilots must understand Mach number for safe operation, especially in high-speed flight environments.

In contrast, the weight of an aircraft, its altitude, or engine efficiency are unrelated to the Mach number. These factors are crucial for different aspects of flight performance and aircraft operation but do not directly define or relate to the concept of Mach number.