Critical Mach number 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. At the lower critical Mach number, airflow around the entire aircraft is subsonic. At the upper critical Mach number, airflow around the entire aircraft is supersonic. 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
GNU Mach GNU Mach GNU Mach is an implementation of the Mach microkernel. It is the default microkernel in the GNU Hurd. GNU Mach runs on IA-32 machines. GNU Mach is maintained by developers on the GNU project. It is distributed under the terms of the GNU General Public License (GPL). Early versions of the Hurd were developed on top of CMU's Mach 3.0. In 1994, CMU stopped working on Mach, and the GNU Project switched to the University of Utah's Mach 4. The kernel known as "GNU Mach" was derived from Mach 4 once Utah stopped development. The first ChangeLog entry