Flares - Infrared Countermeasures
Chaff and flares are defensive mechanisms employed from military aircrafi to avoid detection and/or attack by adversary air defense systems. Flares are high-temperature heat sources ejected from aircraft that mislead heat-sensitive or heat-seeking targeting systems and decoy them away corn the aircraft. Self-protection flares are magnesium pellets that, when ignited, burn for a short period of time (less than 10 seconds) at 2,000 degrees Fahrenheit. The burn temperature is hotter than the exhaust of an aircraft and therefore attracts and decoys heat-seeking weapons targeted on the aircraft. Flares ejected from the target with an object of decoying a hostile missile have been extensively utilized for IR countermeasures because even a two-pound unit can provide up to 10-seconds protection against IR-seeking missiles.
Typically, flares are wrapped with an aluminum-filament-reinforced tape and inserted into an aluminum (0.03 inches thick) case that is closed with a felt spacer and a small plastic end cap. The top of the case has a pyrotechnic impulse cartridge that is activated electrically to produce hot gases that push a piston, the flare material, and the end cap out of the aircraft into the airstream.
There are two types of flares, pyrotechnic and pyrophoric.The pyrotechnic flares produce highly visible white light and smoke. When ejected they ignite and produce a large amount of infrared energy for 5 to 10 seconds to distract and confuse the missile's seeker. They can start fires if they land on the ground before they have burned out. The pyrophoric flares are much less visible since they are small pieces of foil that oxidize (rust) very quickly, producing heat, and then cool in the atmosphere as they fall to the ground as rusted metal debris.
Aircraft, especially military aircraft, often carry pyrotechnic decoy flares as countermeasures for luring incoming anti-aircraft missiles away from the aircraft. A particular type of anti-aircraft missile known as a heat-seeking missile is designed to seek infrared ("IR") radiation emissions of the aircraft. As a countermeasure to the anti-aircraft missiles, the decoy flares produce heat output designed to attract the anti-aircraft missiles. The decoy flares typically are ejected from the aircraft and remotely or automatically ignited in flight. More sophisticated flares contain a propulsion system for propelling the flare over a flight path similar to, but divergent in direction from, the path of the aircraft. The propulsion system is designed to confuse anti-aircraft missiles that can discriminate between a free-falling flare and a propulsion-powered object, e.g., the aircraft. If the decoy flares function correctly, the anti-aircraft missile will lock into and follow the decoy flare, and cease pursuit of the aircraft, allowing the aircraft to proceed unharmed by the missile.
Since the introduction of compositions based on the magnesium-fluorocarbon in 1959, infrared (IR) decoy flares have utilized this energy source. Flares which are currently in use are made from a solid pyrotechnic composition of magnesium, polytetrafluoroethylene (PTFE) and VITON.RTM. brand fluoroelastomer copolymers or similar synthetic rubber binders. These are commonly called MTV flares and are ejected from an aircraft and simultaneously ignited by the action of a pyrotechnic squib. The burning MTV emits IR radiation that is essentially a spectral continuum attenuated by atmospheric absorption. It is intended that the falling flare will cause a missile seeker head to turn away from the target aircraft. The MTV flares are quite effective against older type missiles that seek heat in a single IR band.
Many attempts have been made in the past two decades to increase the intensity of IR decoys and to modify the spectral distribution of the radiation they emit. These attempts have not met with significant success. The reports on these attempts make it evident that the work has been based on schemes to modify or increase the mass flow rate, the energy of the chemical reaction or the emitting species. While a large increase in radiance can be achieved either by a modest temperature increase or by a proportional increase in the radiating area, another largely ignored method for increasing the intensity depends on increasing the efficiency with which the flare flame is utilized as a source of radiant energy. One way in which this can be done is by insuring that the optical thickness of the flame is optimum. Another largely neglected concept is that intensity may be increased by increasing the area of the pyrotechnic flame.
The goal of the latest development in infrared seeker heads is to make the seeker heads "intelligent" and thus to make them immune to conventional infrared fake targets, i.e., to design them in such a manner that they respond to the object signature, in particular the aircraft signature. A method to eliminate false targets consists of a frequency analysis by means of the seeker head, which can distinguish between the radiation characteristics of the infrared radiators (for example aircraft engines) of the target that exhibit a comparatively low temperature and the radiation characteristics of a hot fake target cloud. Thus, in summary the known infrared fake target clouds are not in a position to defend an object against missiles equipped with intelligent seeker heads.
Magnesium/PTFE flares may either exhibit an entirely inappropriate adaptation of the aircraft's IR radiation and, moreover, radiate excessively in the UV band, or when they function as area flares on the basis of red phosphorus, they can not only be recognized as such because of the absence of independent motion, but because they do not emit their IR radiation until after they are beyond the sighting window of the IR searchhead which is locked onto the true target. In addition, flares will also be ineffective against imaging searchheads expected to be available in the future because such decoys, in contrast to true targets, exhibit no contours or edges in the low-frequency range.
Currently, the EW community has turned its attention to the very latest dual spectral IR seeking MANPAD of which there is significant proliferation, particularly in geographical areas of major concern. This generation of weapon uses a dual sensor system that can discriminate between the low energy IR output of an aircraft and the high energy IR output of a classic magnesium based countermeasure flare. Pyrotechnic flare's spectral signature are, in fact, very different from that of an aircraft because they emit principally in the first spectral band that would be analyzed by newer guided missiles IR seeker equipped with spectral CCM, whereas a jet aircraft's signature shows high intensities in the second and third bands. This spectral mismatched signature generally limits the usefulness of current pyrotechnic flares to the previous generation of IR guided missiles. This ability to compare target energy with flare energy has provided the weapon with a counter-countermeasure (CCM), which is extremely effective. Further, the quality and reliability in the manufacturing of this dual seeker is so variable that its CCM trigger level against flares is equally as variable. In other words, for each level of discrimination an aircraft would need a flare of matched performance.
Pyrophoric flares are readily made from foils that are continuously activated. Thin foils or screens of nickel or iron, or steel, or alloys of these materials with each other or with other metals, can be made highly pyrophoric. The pyrophoricity can thus be arranged to bring the temperature of the metal to 1800.degree. F. or even higher. Pyrophoricity is very effectively provided by a Raney type activation using pack diffusion to form on the surface of the metal. Such activated foils about 1 inch wide and wet with propylene oxide, can be continuously chopped into 1/2 inch lengths that are stacked in groups of about 500 per stack. Three or four of these stacks can be stuffed into a casing of a flare cartridge. When such a cartridge is fired the pyrophoric foils are blown out in a scattered mass, their blocking coating promptly evaporates, and they then undergo pyrophoric reaction as they flutter down. When so discharged from airplanes at high altitudes, the temperature dwell time is significantly longer than at sea level. For packing strips of activated metal in a container such as a flare cylinder, a protective packing atmosphere is preferably used. The strips can also be wet with a volatile protective liquid such as propylene oxide or ethyl ether and even n-butylamine.
Operational analysis, based on measured experimental flare performance, show that pyrophoric flares offer a strong potential to provide the required performance to decoy the newer generation of IR seeking missiles. The spectral signature of a pyrophoric liquid, such as alkyl aluminum compounds that burn spontaneously when sprayed into the air, more closely resemble a jet aircraft's spectral signature so that an IR seeking missile would not recognize that type of flare as a countermeasure. The basic functioning principles of any pyrophoric flare would have very little in common to the existing pyrotechnic flares except for the fact that they are both ejected from a launcher by an impulse cartridge. A pyrophoric flare would require a liquid in a perfectly sealed reservoir since pyrophoric liquids react and burn on exposure to air using the oxygen of the air as an oxidant. Some attempts were made to develop effective flares using pyrophoric liquids during the 1980's but were unsuccessful.
Once again the flare manufacturing community has risen to the challenge in providing the answer. The manufacture of dual spectral flare countermeasures is already here and in all of the usual formats, deployed by warfighters. These new flares are already being flown and successfully deployed by the coalition forces operating in Iraq. However, the development of these next generation spectral flares has been a hard fought battle. If it were not for the continued liaison between the flare manufacturing industry, government officials, and (ultimately) the warfighter, this successful result may not have been achieved.
The effective employment of chaff and flares in combat requires training and frequent use by aircrews to master the capabilities of these devices and to ensure safe and efficient handling by ground crews. Training is conducted through simulated battle conditions within Department of Defense (DOD) weapons ranges and electronic combat ranges and other airspace areas, such as MOAs, MTRs, that have been assessed and approved for chaff or flare use. Chaff and flares are also used in field exercises such as Red Flag at Nellis Air Force Range.
Chaff and flares are used by fighter and bomber units over a wide range of altitudes and flight maneuvers or tactics. Deployment of chaff and flares does not interfere with the flight characteristics of the dispensing aircraft. Fighters can drop chaff or flares at any approved altitudes during any flight maneuvers (turns, climbs, descents), airspeed, and G-loading. Although less maneuverable than fighters, bombers can drop chaff or flares at any approved altitudes while in a turn, climb, or descent. Specific descriptions of how chaff or flares are actually employed in training for a combat situation are not releasable.
Fighter aircraft flight profiles are more diverse in vertical movement than bomber profiles, due to their low altitude air-to-ground and higher altitude air-to-air roles. Fighter-type aircraft may ingress to a low level target at 200 to 300 feet AGL and 480 to 600 knots to establish their climb angle, climb to 4,000 to 4,500 feet AGL, release the weapon, execute a hard turn while descending to 200 to 300 feet AGL, with multiple hard turns to exit the target area. If target defenses contain infkred capability, flares will be dispensed in place of chaff. High altitude ingress to a target area may require a "combat descent" to the target or to a lower approach altitude. Depending on the defensive capabilities of the target area, chaff and/or flares may be used in the descent. Aircraft dependent, the descent may be accomplished at 30 to 60 degrees or near vertical angle at airspeeds ranging f%om 500 to 600 knots to supersonic speeds. Some B-52 aricrews drop chaff on virtually all training missions except local sorties in the traffic pattern. This includes their low- and high-altitude flights on which they drop from 500 AGL to 40,000 feet MSL.
Military self-protection flares vary in composition, with the primary flare body comprised of a molded mixture of magnesium and polytetrafluoroethylene (Teflon). Attached to the primary flare body are additional compounds to aid in proper flare ignition. These include the first fire mixture, the intermediate fire mixture, and the dip coat. These compounds are more sensitive than the main magnesium and Teflon flare body and help to ensure proper ignition. The entire flare is protected in a primarily aluminum casing.
In order to be effective, the self-protection flare is designed to be ejected from the aircraft and be consumed (bum out) prior to reaching the ground. If the flare performs as designed, it will be completely consumed while still in the air, leaving only reaction gases released to the air and solid by-products to reach the ground.
Toxicity is not a concern with flares, since the primary material in flares, magnesium, is not highly toxic, and it is highly unlikely that humans or animals would ingest flare material. The main issue with flares is their potential to start fires that can spread and have significant adverse impacts on the environment. Fires can cause a wide variety of significant secondary effects on personnel safety, soil, water resources, biological resources, land use, visual resources, and cultural resources. Another issue is the potential for dud flares and falling debris to pose safety risks. Although the probability of injury from falling debris was found to be extremely remote, there may be a risk associated with untrained people finding dud flares dropped over land that is not controlled by the Department of Defense.
The hazard associated with flare-induced fires depends on a number of factors, including the probability of a burning flare or flare material reaching the ground (or a flare igniting after reaching the ground), the probability of the burning flare/material igniting vegetation on the ground, and the probability of a fire spreading and causing significant damage. The frequency of burning flares or associated materials landing on the ground is not information collected in mishap databases, and calculating a probability would involve too many unknown variables to be accurate. However, methodologies exist for predicting the risk that a fire will start and spread. Using a combination of computer modeling and input databases, with information on meteorological conditions and the flammability of various types of vegetation, the relative risk of wildfires can be predicted. This analysis can only be conducted on a site-specific basis because conditions vary so widely from location to location. A flare fire risk assessment methodology is presented in this report. Impulse cartridges and initiators used with some flares contain chromium and, in some cases, lead, which are hazardous air pollutants under the Clean Air Act. A screening health risk assessment concluded that they do not present a significant health risk.
Laboratory analyses of flare pellets and flare ash indicate that these materials have little potential for affecting soil or water resources, except possibly in small, confined freshwater habitats that support threatened or endangered species. Potential impacts on biological resources are primarily related to fire.
Flare debris is similar to chaff debris, and litter may be a concern in certain pristine areas. However, field studies indicated that debris does not tend to accumulate in noticeable quantities. The principal issues concerning potential effects on cultural resources are related to fire and associated suppression activities. No specific studies were conducted on whether Native Americans perceive that flare use affects traditional resources. As with other resources, traditional resources can be adversely affected by ff are-caused fires.
Fires resulting from flare use have the potential to cause impacts on a variety of resources. The degree of impact from fires will depend on the extent and intensity of the fire, the sensitivity of resources to damage by fire, and the value of the affected resources. Fire is part of the natural ecosystem of most plant communities (except for the antarctic, hot deserts, and tropical wetlands), and is a major force in all arid, temperate, boreal, and austral zones. The more fire-prone an ecosystem, the greater the role of natural fire in shaping the ecosystem.
Very little has been done in the way of assessing the probability of ignition of a wildland fire by a single source (such as a flare). Since there can be such an abundance of ignition sources, the probability associated with a single source becomes irrelevant to fire management. The release altitude would have to be above 1,500 feet AGL to ensure complete burn-out of a 10 second flare. The actual burn times of flares are classified, and based on that information, the safe altitude is likely to be significantly lower. If a burning flare reaches the ground or the canopy of a tree or shrub, it may or may not start a fire.
A review of the fire history data in existing flare use areas is documented in Technical Report on Chaff and Flares, Technical Report No. 6, Flare Fire Risk Assessment (USAF 1995). Fires caused by training operations occur in both dry and temperate or humid environments and can occur during times of relatively low fire hazard conditions if ignition sources are present. The flare training areas examined covered a range of environments, both ecologically and in terms of management and regulations. In most areas, the percentage of fires caused by flares was unknown but usually considered to be low to nonexistent.
The Alliant Kilgore Flares Company develops and produces infrared countermeasure flares, and a wide spectrum of pyrotechnic devices for the U.S. and foreign governments. It also makes pyrotechnics for various commercial activities. Kilgore is the world's leading supplier of infrared countermeasure products. Production programs include the MJU-7A/B, M206, MJU-10/B, MJU-32/B and MJU-38/B U.S. countermeasures. In addition, Kilgore-designed flare products, such as the 55mm KC-004/A flares, are routinely provided for export. Kilgore is currently manufacturing an Israeli flare design under a Foreign Military Funding contract. Kilgore manufactured over six million infrared flares during the 1990s. Kilgore was the original designer of the MJU-10/B and first sequenced version of the MJU-7 and 1x1 inch flares. Kilgore has patented a variety of advanced countermeasure designs.
As a world leader in the countermeasures marketplace, Tracor is best known for its development and production of the AN/ALE-47 countermeasures dispenser system, the most advanced system capable of deploying chaff, flares, active radio frequency decoys, and other decoys from military aircraft. The ALE-47 has been installed in more than 15 aircraft types for the U.S. Air Force, U.S. Navy, and more than 15 international customers. With the win of three flare contracts in 1997, Tracor also maintained its position as one of the world's top developers and producers of expendable decoys. Under these contracts, Tracor has added new flares to its product line, which includes flares for Air Force F-15, A-10, C-17, C-5, and C-130 aircraft, as well as U.S. Army AH-64, CH-47, and UH-60 helicopters. These flares are deployed by the ALE-47 and other dispenser systems to protect aircraft from heat-seeking missiles. Also, Tracor continues to be the world's largest supplier of chaff expendables, which decoy radar-guided missiles.
The Esterline Technologies Advanced Materials segment develops and manufactures thermally engineered components and high-performance products used in a wide range of military applications, combustible ordnance components and electronic warfare countermeasure devices for military customers. On June 26, 2006, an explosion occurred at the Company's Wallop facility, which resulted in one fatality and several minor injuries. The incident destroyed an oven complex for the production of advanced flares and significantly damaged a portion of the facility. The facility was expected to be closed for more than two years due to the requirement of the Health Safety Executive (HSE) to review the cause of the accident, normal operations are continuing at unaffected portions of the facility. The HSE investigation would not be completed until the Coroner's Inquest was filed, possibly in 2008. The operation was insured under a property, casualty and business interruption insurance policy and in June 2007, the Company settled its insurance claim for £24.0 million, including payments already received. In fiscal 2007, insurance recoveries totaled $37.5 million, net of the write-off of the damaged facility. The Company recorded business interruption insurance recoveries of $4.9 million for losses incurred in fiscal 2006.
|Join the GlobalSecurity.org mailing list|