Critical Mach number
In aerodynamics, the critical Mach number (Mcr or M*) of an aircraft is the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it.[1] At the lower critical Mach number, airflow around the entire aircraft is subsonic. Supersonic aircraft such as the Concorde and combat aircraft also have an upper critical Mach number at which the airflow around the entire aircraft is supersonic.[2]
Aircraft flight
For an aircraft in flight, the speed of the airflow around the aircraft differs considerably in places from the airspeed of the aircraft; this is due to the airflow having to speed up and slow down as it travels around the aircraft's structure. When the aircraft's airspeed reaches the critical Mach number, the speed of the airflow in some areas near the airframe reaches the speed of sound, even though the aircraft itself has an airspeed lower than Mach 1.0. This creates a weak
In aircraft not designed to fly at or above the critical Mach number, the shock waves that form in the airflow over the wing and tailplane are sufficient to
Although unknown at the time, compressibility was the cause of the phenomenon known as the
Early
The actual critical Mach number varies from wing to wing. In general, a thicker wing will have a lower critical Mach number, because a thicker wing deflects the airflow passing around it more than a thinner wing does, and thus accelerates the airflow to a faster speed. For instance, the fairly-thick wing on the
See also
- Drag divergence Mach number
References
- ISBN 0-273-01120-0
Notes
- ^ Clancy, L.J. Aerodynamics, Section 11.6
- ISBN 978-81-203-4839-4.
- ^ a b Clancy, L.J., Aerodynamics, Chapter 11