Supersonic
Any speed over the
speed of sound, which is approximately 343
m/s, 1,087
ft/s, 761
mph or 1,235
km/h in air at sea level, is said to be
supersonic. Speeds greater than 5 times the speed of sound are sometimes referred to as
hypersonic.
Sounds are vibrations in an elastic medium. In gases sound travels longitudinally at different speeds, mostly depending on the
molecular mass and
temperature of the gas; whilst
pressure has a much smaller effect. Since air temperature and composition varies significantly with altitude,
mach numbers for aircraft are related to the speed of sound at sea level. In water at
room temperature supersonic can be considered as any speed greater than 1,440 m/s or 4,724 ft/s. In solids, sound waves can be longitudinal or transverse and have even higher velocities.
Supersonic fracture is crack motion faster than the speed of sound in a
brittle material. This phenomenon was first discovered by scientists from the Max Planck Institute for Metals Research in Stuttgart (
Markus J. Buehler and
Huajian Gao) and IBM Almaden Research Center in San Jose, California (
Farid F. Abraham).
Many modern
fighter aircraft are supersonic. The
Concorde and
Tupolev Tu-144 were
supersonic passenger aircraft. But, since Concorde's final retirement flight on
November 26 2003, there are no supersonic passenger aircraft left in service. Some large
bombers, such as the
Tupolev Tu-160 and
Rockwell/
Boeing B-1B are also supersonic-capable. The
BrahMos cruise missile is a supersonic missile.
Most modern
firearm munitions are supersonic, with rifle
projectiles often travelling at speeds approaching
Mach 3.
Most
spacecraft, most notably the
Space Shuttle are supersonic at least during portions of their reentry, even though most of their reentry flight time is considered
hypersonic.
See
Sound barrier.
Supersonic
aerodynamics are simpler than subsonic because the airsheets at different points along the plane often can't affect each other. Supersonic jets and rocket vehicles require several times greater thrust to push through the extra drag experienced within the
transonic region (around Mach 0.85-1.5).
Aerospace engineers can gently guide air around the
fuselage of the aircraft without producing new
shock waves but any change in cross sectional area further down the vehicle leads to shock waves along the body. Designers use the
Whitcomb area rule and minimize sudden changes in size.
It should be kept in mind, however, that the aerodynamic principles behind a supersonic aircraft are often more complex than described above due to the fact that such an aircraft must be efficient and stable at supersonic, transonic
and subsonic flight.
At high speeds
aerodynamic heating can occur, so an aircraft must be designed to operate and function under very high temperatures. For example, the
SR-71 Blackbird jet could fly continuously at Mach 3.1 while some parts were above 315°C (600°F).
image:Supersonic shockless engine.PNG|A cage around the engine reflects any shock waves.A spike behind the engine converts them into thrust.image:Supersonic shockless fuselage.PNG|To generate lift a supersonic aircraft has to produce at least two shock waves: One over-pressure downwards wave, and one under-pressure upwards wave. Withcomb's area rule states, we can reuse air displacement without generating additional shock waves. In this case the fuselage reuses some displacement of the wings.image:Supersonic_shocking_fuselage.png|Why real planes produce under-pressure shockwaves on the ground.image:supersonic_blunt_nose_inlet.png|Nasa has recently shown that a bow shock wave widens and flattens before it reaches the ground, while multiple shocks produce N-waves with a lot of energy in the audio range. As internal supersonic compression can unstart, designers want external compression. As these produce also external shocks, they have to be located at the nose.*
Aerodynamics#Supersonic aerodynamics*
De Laval nozzle*
Jet engine#Air intake design*
Jet engine#Nozzle*
Mach number*
Rocket engine nozzles*
Sonic boom*
Sound barrier*
The Right Stuff a movie about early *
Whitcomb area rule*
The Speed of Sound*
Sound*
Supersonic sound pressure levels*
Video of a supersonic blast.
