Aerodynamicists disagree over the precise definition of hypersonic flow ; minimum Mach numbers for hypersonic flow range from 3 to 12.

The ratio of the flow speed to the speed of sound was named the Mach number after Ernst Mach, who was one of the first to investigate the properties of supersonic flow which included Schlieren photography techniques to visualize the changes in density.

Theodore von Kármán and Hugh Latimer Dryden introduced the term transonic to describe flow speeds around Mach 1 where drag increases rapidly.

Because of the increase in drag approaching Mach 1, aerodynamicists and aviators disagreed on whether supersonic flight was achievable.

Image showing shock waves from NASA's X-43A hypersonic research vehicle in flight at Mach 7, generated using a computational fluid dynamics algorithm. On September 30, 1935 an exclusive conference was held in Rome with the topic of high velocity flight and the possibility of breaking the sound barrier.

The Mach number is used to evaluate whether the incompressibility can be assumed or the flow must be solved as compressible.

In air, compressibility effects are usually ignored when the Mach number in the flow does not exceed 0. 3 ( about 335 feet ( 102m ) per second or 228 miles ( 366 km ) per hour at 60 ° F ).

In general, this is the case where the Mach number in part or all of the flow exceeds 0. 3.

The term Transonic refers to a range of velocities just below and above the local speed of sound ( generally taken as Mach 0. 8 – 1. 2 ).

It is defined as the range of speeds between the critical Mach number, when some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1. 2, when all of the airflow is supersonic.

Thus, when the fluid finally does strike the object, it is forced to change its properties -- temperature, density, pressure, and Mach number -- in an extremely violent and irreversible fashion called a shock wave.

In the 1970s, the term generally came to refer to speeds of Mach 5 ( 5 times the speed of sound ) and above.

A smokeless, solid-propellant, booster-sustainer rocket motor propels the missile at speeds over Mach 2.

The Phoenix has several guidance modes and achieves its longest range by using mid-course updates from the F-14A / B AWG-9 radar ( APG-71 radar in the F-14D ) as it climbs to cruise between and at close to Mach 5.

Similarly, the Soviet Union used the intermediate-range Tu-22M ' Backfire ' in the 1970s, but their Mach 3 bomber project came to naught.

The Mach 2 Tu-160 ' Blackjack ' was built only in tiny numbers, leaving the 1950s Tupolev Tu-16 and Tu-95 ' Bear ' heavy bombers to continue being used into the 21st century.

There would have to be a balance between the size of the warhead ( Orange Herald or Green Bamboo as developed by the Atomic Weapons Research Establishment ( AWRE ) and the need for it to be carried by any of the three V-bomber types in use, and that it should be able to reach Mach 3.

Once close to the target, the second chamber of the engine ( 6, 000 lb ) would accelerate the missile to Mach 3.

* Speed: Mach 2. 3

It was designed to fly below the enemy's radar at speeds above Mach 3 and carry a number of hydrogen bombs that it would drop on its path over enemy territory.

As a rough guide, compressible effects can be ignored at Mach numbers below approximately 0. 3.

* Mach 3, a video game developed and published by Loriciels

The project at Carnegie Mellon ran from 1985 to 1994, ending in apparent failure with Mach 3. 0, which was finally a true microkernel.

The resulting Mach 3 was released in 1990, and generated intense interest.

Mach received a major boost in visibility when the Open Software Foundation ( OSF ) announced they would be hosting future versions of OSF / 1 on Mach 2. 5, and were investigating Mach 3 as well.

Mach 3 led to a number of efforts to port other operating systems parts for the microkernel, including IBM's Workplace OS and several efforts by Apple Computer to build a cross-platform version of the Mac OS.

Benchmarks on 1997 hardware showed that Mach 3. 0-based UNIX single-server implementations were about 50 % slower than native UNIX.

When Mach 3 attempted to move most of the operating system into user-space, the overhead became higher still: benchmarks between Mach and Ultrix on a MIPS R3000 showed a performance hit as great as 67 % on some workloads.

Mach 3 attempted to address this problem by providing a simple pager, relying on user-space pagers for better specialization.

IPC overhead is a major issue for Mach 3 systems.

The only remaining widespread uses of the Mach kernel are Apple's Mac OS X and its sibling iOS, which run atop a heavily modified Mach 3 kernel.

This occurs because of the presence of a " transonic regime " around M = 1 where approximations of the Navier-Stokes equations used for subsonic design actually no longer apply, the simplest of many reasons being that the flow locally begins to exceed M = 1 even when the freestream Mach number is below this value.

At a certain point along the airfoil, a shock is generated, which increases the pressure coefficient to the critical value C < sub > p-crit </ sub >, where the local flow velocity will be Mach 1.

Here is a critique due to Mach arguing that only relative motion is established:

The fastest speed flown during an air show is 700 mph ( just under Mach 1 ) and the slowest speed is 120 mph.

For flow of gases, to determine whether to use compressible or incompressible fluid dynamics, the Mach number of the flow is to be evaluated.

* is the lift coefficient at the desired angle of attack, Mach number, and Reynolds number

The BrahMos cruise missile which is a joint venture between India and Russia, is the fastest cruise missile in the world with a top speed of Mach 2. 8-3.

By 2000, most large-scale ( Mach-like ) efforts had ended, although OpenStep used an adapted Mach kernel called XNU, which is now used in the OS known as Darwin, which is the open source part of Mac OS X .. As of 2012, the Mach-based GNU Hurd is also functional and its inclusion in testing versions of Arch Linux and Debian in progress.

* GNU Mach, the microkernel upon which GNU Hurd is based

In fluid mechanics, Mach number ( or ) ( generally, sometimes or ) is a dimensionless quantity representing the speed of an object moving through air or other fluid divided by the local speed of sound.

: is the Mach number,