Flare (countermeasure) - AbsoluteAstronomy.com

A flare is an aerial infrared countermeasure to counter an infrared homing

Infrared homing

Infrared homing refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track and follow it. Missiles which use infrared seeking are often referred to as "heat-seekers", since infrared is just below the...

("heat seeking") surface-to-air missile

Surface-to-air missile

A surface-to-air missile or ground-to-air missile is a missile designed to be launched from the ground to destroy aircraft or other missiles...

or air-to-air missile

Air-to-air missile

An air-to-air missile is a missile fired from an aircraft for the purpose of destroying another aircraft. AAMs are typically powered by one or more rocket motors, usually solid fuelled but sometimes liquid fuelled...

. Flares are commonly composed of a pyrotechnic composition

Pyrotechnic composition

A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

based on magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

or another hot-burning metal, with burning temperature equal to or hotter than engine exhaust. The aim is to make the infrared-guided missile seek out the heat signature from the flare rather than the aircraft's engines.

Tactics

In contrast to radar-guided missiles

Missile guidance

Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missile's target accuracy is a critical factor for its effectiveness...

, IR-guided missiles are very difficult to find as they approach aircraft. They do not emit detectable radar, and they are generally fired from a rear visual-aspect, directly toward the engines. In most cases, pilots have to rely on their wingmen to spot the missile's smoke trail and alert them. Since IR-guided missiles are inherently far shorter-legged in distance and altitude range than their radar-guided counterparts, good situational awareness of altitude and potential threats continues to be an effective defense. More advanced electro-optical

Electro-optics

Electro-optics is a branch of technology involving components, devices and systems which operate by modification of the optical properties of a material by an electric field...

systems can detect missile launches automatically from the distinct thermal emissions of a missile's rocket motor.

Once the presence of a "live" IR missile is indicated, flares are released by the aircraft in an attempt to decoy

Decoy

A decoy is usually a person, device or event meant as a distraction, to conceal what an individual or a group might be looking for. Decoys have been used for centuries most notably in game hunting, but also in wartime and in the committing or resolving of crimes.-Duck decoy:The term duck decoy may...

the missile; some systems are automatic, while others require manual jettisoning of the flares.

The aircraft would then pull away at a sharp angle from the flare (and the terminal trajectory of the missile) and reduce engine power in attempt to cool the thermal signature. Optimally, the missile's seeker head is then confused by this change in temperature and flurry of new signatures, and therefore follows the flare(s) rather than the aircraft.

Usage

Apart from military use, some civilian aircraft are also equipped with countermeasure flares, against terrorism

Terrorism

Terrorism is the systematic use of terror, especially as a means of coercion. In the international community, however, terrorism has no universally agreed, legally binding, criminal law definition...

: the Israel

Israel

The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

i airline El-Al, having been the target of the failed 2002 airliner attack, in which shoulder-launched

Shoulder-launched missile weapon

A shoulder-fired missile, shoulder-launched missile or man-portable missile is a projectile fired at a target, small enough to be carried by a single person, and fired while held on one's shoulder...

surface-to-air missiles were fired at an airliner

Airliner

An airliner is a large fixed-wing aircraft for transporting passengers and cargo. Such aircraft are operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an aircraft intended for carrying multiple passengers in commercial...

while taking off, began equipping its fleet with radar-based, automated flare release countermeasures from June 2004. This caused concerns in some European countries, which proceeded to ban such aircraft from landing at their airports.

Ignition

Most flares, like the MJU-27A/B flares, must be kept in an airtight storage compartment before deployment. These flares, known as pyrophoric flares, are made of special materials that ignite when they come in contact with the air. This is a safety and convenience factor, since attempting to ignite a flare inside the fuselage and then deploying it is risky. However pyrotechnic flares (such as the MJU-32) also exist, and offer their own safety benefit; requiring an external ignition method, an accidental leak or puncture in the storage compartment would not result in a catastrophic fire on board the aircraft as with a pyrophoric flare.

Deployment

Flares are most commonly gravity-fed from a dispenser inside the aircraft's fuselage. These dispensers can be programmed by the pilot or ground crew to dispense flares in short intervals, one at a time, long intervals, or in clusters. Most currently-used flares are of the pyrophoric variety, and thus the dispensers do not have to ignite and deploy the flare at the same time. With pyrotechnic flares, a lanyard automatically pulls off a friction cap covering the exposed end of the flare as it falls from the dispenser. A friction surface inside the cap rubs against the exposed end of the flare (similar to a match-head and striking surface) and ignites the flare.

Decoying

Flares burn at thousands of degrees, which is much hotter than the exhaust of a jet engine. IR missiles seek out the hotter flame, believing it to be an aircraft in afterburner

AfterBurner

The AfterBurner is a lighting solution for the Game Boy Advance system that was created by Triton-Labs.Originally, portablemonopoly.net was a website created to petition Nintendo to put some kind of light in their Game Boy Advance system...

or the beginning of the engine's exhaust source.

As the more modern infrared seekers tend to have spectral sensitivity tailored to more closely match the emissions of airplanes and reject other sources (the so-called CCM, or counter-countermeasure

Electronic counter-countermeasures

Electronic counter-countermeasures is a part of electronic warfare which includes a variety of practices which attempt to reduce or eliminate the effect of electronic countermeasures on electronic sensors aboard vehicles, ships and aircraft and weapons such as missiles. ECCM is also known as...

s), the modernized decoy flares have their emission spectrum optimized to also match the radiation of the airplane (mainly its engines and engine exhaust). In addition to spectral discrimination, the CCMs can include trajectory discrimination and detection of size of the radiation source.

The newest generation of the FIM-92 Stinger

FIM-92 Stinger

The FIM-92 Stinger is a personal portable infrared homing surface-to-air missile , which can be adapted to fire from ground vehicles and helicopters , developed in the United States and entered into service in 1981. Used by the militaries of the U.S...

uses a dual IR and UV

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

seeker head, which allows for a redundant tracking solution, effectively negating the impact of modern decoy flares (according to the U.S. Department of Defense

United States Department of Defense

The United States Department of Defense is the U.S...

). While research and development in flare technology has produced an IR signature on the same wavelength as hot engine exhaust, modern flares still produce a notably (and immutably) different UV signature than an aircraft engine burning kerosene jet-fuel.

Materials used

For the infrared generating charge, two approaches are possible: pyrotechnic and pyrophoric.

As stored, chemical-energy-source IR-decoy flares contain pyrotechnic compositions, liquid or solid pyrophoric substances, and/or liquid or solid highly flammable substances.

Upon ignition of the decoy flare, a strongly exothermal reaction is started, releasing infrared energy and visible smoke and flame, emission being dependent on the chemical nature of the payload used.

There is a wide variety of calibres and shapes available for aerial decoy flares. Due to volume storage restrictions on board platforms, many aircraft of American origin use square decoy flare cartridges. Nevertheless, cylindrical cartridges are also available on board American aircraft, such as MJU 23/B on the B-1 Lancer

B-1 Lancer

The Rockwell B-1 LancerThe name "Lancer" is only applied to the B-1B version, after the program was revived. is a four-engine variable-sweep wing strategic bomber used by the United States Air Force...

or MJU-8A/B on the F/A-18 Hornet

F/A-18 Hornet

The McDonnell Douglas F/A-18 Hornet is a supersonic, all-weather carrier-capable multirole fighter jet, designed to dogfight and attack ground targets . Designed by McDonnell Douglas and Northrop, the F/A-18 was derived from the latter's YF-17 in the 1970s for use by the United States Navy and...

; however, these are used mainly on board French aircraft and those of Russian origin, e.g. PPI-26 IW on the MiG 29.

i

Square calibres and typical decoy flares:

1x1x8 Inch . e.g. M-206, MJU-61, (Magnesium/Teflon/Viton
Magnesium/Teflon/Viton
Magnesium/Teflon/Viton is a pyrolant. Teflon and Viton are trademarks of DuPont for polytetrafluoroethylene, n, and vinylidenfluoride-hexafluoroisopropene-copolymer, nn.-History:...

(MTV) based) M-211, M-212 (spectral flares)
2x1x8 Inch . e.g. MJU-7A/B (MTV based), MJU-59/B (spectral flare)
2x2,5x8 Inch e.g. MJU-10/B (MTV based)

Cylindrical calibres and typical decoy flares:

2,5 Inch e.g. MJU-23/B (MTV based)
1,5 Inch e.e. MJU 8 A/B (MTV based)
1 Inch e.g. PPI 26 IW

Pyrotechnic flares

Pyrotechnic flares use a slow-burning fuel-oxidizer mixture that generates intense heat. Thermite

Thermite

Thermite is a pyrotechnic composition of a metal powder and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction...

-like mixtures, e.g. Magnesium/Teflon/Viton

Magnesium/Teflon/Viton

Magnesium/Teflon/Viton is a pyrolant. Teflon and Viton are trademarks of DuPont for polytetrafluoroethylene, n, and vinylidenfluoride-hexafluoroisopropene-copolymer, nn.-History:...

(MTV), are common. Other combinations include ammonium perchlorate

Ammonium perchlorate

Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...

/anthracene

Anthracene

Anthracene is a solid polycyclic aromatic hydrocarbon consisting of three fused benzene rings. It is a component of coal-tar. Anthracene is used in the production of the red dye alizarin and other dyes...

/magnesium, or can be based on red phosphorus.

To adjust the emission characteristics to match closer the spectrum of jet engines, charges on the base of double base propellants. These compositions can avoid the metal content and achieve cleaner burning without the prominent smoke trail.

Blackbody Payloads

Certain pyrotechnic compositions, for example MTV, give a great flame emission upon combustion and yield a temperature-dependent signature and can be understood as gray bodies of high emissivity

Emissivity

The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...

(

~0.95). Such payloads are called blackbody payloads. Other payloads, like iron/potassium perchlorate pellets, only yield a low flame emission but also show temperature-dependent signature. Nevertheless, the lower combustion temperature as compared to MTV results in a lower amount of energy released in the short-wavelength IR range. Other blackbody payloads include ammonium perchlorate/anthracene/magnesium and hydroxyl-terminated polybutadiene (HTPB) binder.

Spectrally balanced payloads

Now other payloads provide large amounts of hot carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

upon combustion and thus provide a temperature-independent selective emission in the wavelength range between 3 and 5 µm. Typical pyrotechnic payloads of this type resemble whistling compositions

Whistle mix

Whistle mix is a general term to refer to any pyrotechnic composition that emits a whistling sound when pressed into a tube and ignited. It is used as a rocket propellant, particularly in small bottle rockets...

and are often made up from potassium perchlorate

Potassium perchlorate

Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...

and hydrogen lean organic fuels.
Other spectrally balanced payloads are made up similarly as double base propellants and contain nitrocellulose

Nitrocellulose

Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...

(NC), and other esters of nitric acid or nitro compound

Nitro compound

Nitro compounds are organic compounds that contain one or more nitro functional groups . They are often highly explosive, especially when the compound contains more than one nitro group and is impure. The nitro group is one of the most common explosophores used globally...

s as oxidizers such as e.g. hexanitroethane

Hexanitroethane

Hexanitroethane is an organic compound with chemical formula C2N6O12 or 3C-C3. It is a solid matter with a melting point of 135 °C....

and nitro compounds and nitramines as high energy fuels. The main advantage of the latter payloads is their low visibility due to the absence of metals such as sodium and potassium that may be either easily thermally excited and give prominent emissions or give condensed reaction products (such as carbonate

Carbonate

In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

s and chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

s), which would cause a distinct smoke trail.

Pyrophoric flares

Pyrophoric flares work on the principle of ejecting a special pyrophoric material out of an airtight cartridge, usually using a gas generator

Gas generator

A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many...

, e.g. a small pyrotechnic charge or pressurized gas. The material then self-ignites in contact with air. The materials can be solid, e.g. iron platelets coated with ultrafine

Ultrafine particles

Ultrafine particles are nanoscale, less than 100 nanometres. Regulations do not exist for this size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 size classes and are believed to have several more aggressive health implications than those classes...

aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, or liquid, often organometallic compounds; e.g. alkyl aluminium compounds, e.g. triethylaluminium

Triethylaluminium

Triethylaluminium is an organoaluminium compound. This volatile, colorless liquid is highly pyrophoric, igniting immediately upon exposure to air. It is normally stored in stainless steel containers either as a pure liquid or as a solution in hydrocarbon solvents such as hexane, heptane, or ...

. Pyrophoric flares may have reduced effectivity at high altitudes, due to lower air temperature and lower availability of oxygen; however oxygen can be coejected with the pyrophoric fuel.

The advantage of alkyl aluminium and similar compounds is the high content of carbon and hydrogen, resulting in bright emission lines similar to spectral signature of burning jet fuel. Controlled content of solid combustion products, generating continuous black body radiation, allows further matching of emission characteristics to the net infrared emissions of fuel exhaust and hot engine components.

The flames of pyrophoric fuels can also reach the size of several metres, in comparison with about less than one metre flame of MTV flares. The trajectory can be also influenced by tailoring the aerodynamic properties of the ejected containers.

To be merged:

As with the pyrotechnic payloads these will also give either graybody radiation or selective emissions.
In contrast to pyrotechnic payloads, pyrophoric substances use the oxygen from the environment for oxidation. Hence specific energy density of pyrophorics is always higher as compared to any pyrotechnic; however, pyrophorics suffer from low oxygen partial pressure at greater heights.
A typical liquid pyrophoric fuel is triethylaluminium

Triethylaluminium

. Upon combustion of triethylaluminium, a selective IR spectrum is obtained, which is mainly determined from carbon dioxide and water vapour. Any transient or permanent combustion product of aluminium are not IR-active in this region of the electromagnetic spectrum.

Solid pyrophoric payloads are based on iron platelets coated with a porous aluminium layer. Based on the very high specific surface area of aluminium those platelets instantaneously oxidize upon contact with air. In contrast to triethylaluminium combustion, those platelets yield a temperature-dependent signature.

Highly flammable payloads

These payloads contain red phosphorus as an energetic filler. The red phosphorus is mixed with organic binders to give brushable pastes that can be coated on thin polyimide

Polyimide

Polyimide is a polymer of imide monomers. The structure of imide is as shown. Polyimides have been in mass production since 1955...

platelets. The combustion of those platelets yields a temperature-dependent signature. Endergonic additives such as highly dispersed silica or alkali halides may further lower the combustion temperature.