Chaff and Flares
Chaff
and flares are defensive counter measures used on aircraft
to confuse radar and heat seeking missiles. Chaff is used
as a decoy for radar seeking missiles and is made of glass
silicate fibers with an aluminum coating. The fibers are approximately
60% glass fiber and 40% aluminum by weight. The typical Air
Force RR-188 chaff bundle contains about 150 g of chaff or
about 5 million fibers. The fibers are 25 microns in diameter
and typically 1 to 2 cm in length. In 1997, the Air Force
used about 1.8 million bundles worldwide.
The amount
of chaff released worldwide by all of the services is approximately
500 tons per year. Chaff falls to the earth at a settling
velocity of approximately 30 cm per second. Atmospheric residence
times range from 10 minutes for the majority of chaff released
at 100 m to approximately 10 hours for chaff released at 10,000
feet. Chaff fibers experience little breakup before reaching
the ground.
After
the chaff is ejected from the aircraft and into the aircraft
slipstream, the chaff packages burst open and the fibers scatter
to form a radar-reflective cloud called a chaff corridor.
Each chaff package is designed to simulate an aircraft. Several
aircraft can create a chaff curtain, consisting of thousands
of false targets, which confuse the radar guidance package
on a missile so they are unable to locate the real targets
within the chaff cloud.
Virtually
all chaff fibers are 10-100 times larger than PM10 and PM2.5,
the air particulates of concern for public health. The primary
fiber size is usually too large to be inhaled by livestock,
but if they are inhaled they do not penetrate far into the
respiratory system and can be easily cleared out. The possible
nutritional effects due to chaff ingestion and the risk is
minimal to nil for both humans and livestock, considering
the chemical composition of chaff (essentially identical to
soil) and low chaff loading on the environment. Chaff decomposing
in water has no adverse impacts on water chemistry or aquatic
life.
Flares
are of two types: decoy flares that protect aircraft from
infrared missiles, and ground illumination flares. Decoy flares
are typically made of magnesium that burns white-hot and are
designed to defeat a missile's infrared (IR) tracking capability.
The intense heat of the pyrotechnic candle consumes the flare
housing. Common aerial flares are: ALA-17/B, M-206, MJU-2,
MJU-7 A/B, MJU-10/B, MJU-23/B, and RR-119.
Ground
illumination flares, are designed to descend by parachute
and provide up to 30 minutes of illumination of ground targets
or activities. Typical flares are the LUU-1, LLU-5, and LLU-2B.
A typical LLU-2B sectional is shown below.
The ground
illumination flare enhances a pilot's ability to see targets
while using Night Vision Goggles (NVGs). Flares burn at uneven
rates and fluctuate in brightness and are not used as frequently
as in the past as the intense light interferes with the newer
NVGs more sensitive sensors.
The composition
and materials of flares used by the military are similar to
standard flares used for aerial, highway and marine purposes.
(Skyline).
While unburned decoy flares falling from high altitude could
be dangerous, flares are designed to burn up during the descent
(even the aluminum casing is burned).
Chaff
and flares are deployed on most Air Force aircraft from a
common MJU-11 Chaff/Flare magazine that is integrated with
the warning receiver (a device that alerts the aircraft a
missile has locked onto the aircraft). The magazine has a
capacity of 30 RR-188 or 30 M-206 flares.
A very
thorough independent description of military systems, equipment,
and capabilities is published by the American
Federation of Scientists.
Typical
chaff and flare deployments and patterns are shown in the
following pictures.
|
