The following information isnt directly related to bullet shockwaves. However, I think that it might help folks understand the nature of shockwaves in general. I have highlighted some information related to ear damage. But, I suggest reading the entire article carefully if you want to learn a bit about shockwaves, their physics, and how they affect us.
NASA Facts
National Aeronautics and
Space Administration
Dryden Flight Research Center
P.O. Box 273
Edwards, California 93523
Voice 661-276-3449
FAX 661-276-3566
pao@dfrc.nasa.gov FS-2003-11-016 DFRC
Sonic Booms
Summary
A sonic boom is the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace
vehicle flies overhead faster than the speed of sound or supersonic.
Air reacts like a fluid to supersonic objects. As objects travel through the air, the air molecules are pushed aside
with great force and this forms a shock wave much like a boat creates a bow wave. The bigger and heavier the
aircraft, the more air it displaces.
The Cause
The shock wave forms a cone of pressurized air molecules which move outward and rearward in all directions
and extend to the ground. As the cone spreads across the landscape along the flight path, they create a continu-
ous sonic boom along the full width of the cone's base. The sharp release of pressure, after the buildup by the
shock wave, is heard as the sonic boom.
The change in air pressure associated with a sonic boom is only a few pounds per square foot -- about the same
pressure change experienced riding an elevator down two or three floors. It is the rate of change, the sudden
onset of the pressure change, that makes the sonic boom audible.
All aircraft generate two cones, at the nose and at the tail. They are usually of similar strength and the time
interval between the two as they reach the ground is primarily dependent on the size of the aircraft and its
altitude. Most people on the ground cannot distinguish between the two and they are usually heard as a single
sonic boom. Sonic booms created by vehicles the size and mass of the space shuttle are very distinguishable and
two distinct booms are easily heard.
General Factors Associated With Sonic Booms
There are several factors that can influence sonic booms -- weight, size, and shape of the aircraft or vehicle, plus
its altitude, attitude and flight path, and weather or atmospheric conditions.
A larger and heavier aircraft must displace more air and create more lift to sustain flight, compared with small,
light aircraft. Therefore, they will create sonic booms stronger and louder than those of smaller, lighter aircraft.
The larger and heavier the aircraft, the stronger the shock waves will be.
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Altitude determines the distance shock waves travel
before reaching the ground, and this has the most
significant effect on intensity. As the shock cone gets
wider, and it moves outward and downward, its
strength is reduced. Generally, the higher the aircraft,
the greater the distance the shock wave must travel,
reducing the intensity of the sonic boom. Of all the
factors influencing sonic booms, increasing altitude is
the most effective method of reducing sonic boom
intensity.
The width of the boom "carpet" beneath the aircraft is
about one mile for each 1000 feet of altitude. An
aircraft, for example, flying supersonic at 50,000 feet
can produce a sonic boom cone about 50 miles wide.
The sonic boom, however, will not be uniform. Maxi-
mum intensity is directly beneath the aircraft, and
decreases as the lateral distance from the flight path
increases until it ceases to exist because the shock
waves refract away from the ground. The lateral
spreading of the sonic boom depends only upon
altitude, speed and the atmosphere -- and is indepen-
dent of the vehicle's shape, size, and weight.
The ratio of aircraft length to maximum cross sec-
tional area also influences the intensity of the sonic
boom. The longer and more slender the aircraft, the
weaker the shock waves. The fatter and more blunt the
vehicle, the stronger the shock wave can be.
Increasing speeds above Mach 1.3 results in only
small changes in shock wave strength.
The direction of travel and strength of shock waves
are influenced by wind, speed, and direction, and by
air temperature and pressure. At speeds slightly
greater than Mach 1, their effect can be significant, but
their influence is small at speeds greater than Mach
1.3. Distortions in the shape of the sonic boom signa-
tures can also be influenced by local air turbulence
near the ground. This, too, will cause variations in the
overpressure levels.
Aircraft maneuvering can cause distortions in shock
wave patterns. Some maneuvers -- pushovers, accel-
eration and "S" turns -- can amplify the intensity of the
shock wave. Hills, valleys and other terrain features
can create multiple reflections of the shock waves and
affect intensity.
Overpressure
Sonic booms are measured in pounds per square foot
of overpressure. This is the amount of the increase
over the normal atmospheric pressure which surrounds
us (2,116 psf/14.7 psi).
At one pound overpressure, no damage to structures
would be expected.
Overpressures of 1 to 2 pounds are produced by
supersonic aircraft flying at normal operating alti-
tudes. Some public reaction could be expected be-
tween 1.5 and 2 pounds.
Rare minor damage may occur with 2 to 5 pounds
overpressure.
As overpressure increases, the likelihood of structural
damage and stronger public reaction also increases.
Tests, however, have shown that structures in good
condition have been undamaged by overpressures of
up to 11 pounds.
Sonic booms produced by aircraft flying supersonic at
altitudes of less than 100 feet, creating between 20 and
144 pounds overpressure, have been experienced by
humans without injury.
Damage to eardrums can be expected when overpres-
sures reach 720 pounds. Overpressures of 2160
pounds would have to be generated to produce lung
damage.Typical overpressure of aircraft types are:
SR-71: 0.9 pounds, speed of Mach 3, 80,000 feet
Concorde SST: 1.94 pounds, speed of Mach 2,
52,000 feet
F-104: 0.8 pounds, speed of Mach 1.93, 48,000 feet
Space Shuttle: 1.25 pounds, speed of Mach 1.5,
60,000 feet, landing approach
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