Chaff - Radar Countermeasures
Chaff and flares are defensive mechanisms employed from military aircrafi to avoid detection and/or attack by adversary air defense systems. Chaff consists of small fibers that reflect radar signals and, when dispensed in large quantities from aircraft, form a cloud that temporarily hides the aircraft from radar detection. The two major types of military chaff in use are aluminum foil and aluminum-coated glass fibers. The aluminum foil-type is no longer manufactured, although it may still be in use.
When ejected from an aircraft, chaff forms the electromagnetic equivalent of a visual smoke screen that temporarily hides the aircraft from radar. Chaff also serves to decoy radar allowing aircraft to maneuver or egress from the area. It consists of small, extremely tie fibers of aluminum or aluminum-coated glass that disperse widely in the air when ejected from the aircraft and effectively reflect radar signals in various bands, in order to create a very large image of reflected signals ("return") on the radar screen. In the air, the initial burst from a chaff bundle forms a sphere that shows up on radar screens as an electronic cloud. The aircraft is obscured by the cloud, which confuses enemy radar. Since chaff can obstruct radar, its use is coordinated with the Federal Aviation Administration (FAA).
There are two types of chaff, aluminum foil and aluminum-coated glass fibers. The foil type is no longer manufactured, although it remains in the inventory and is used primarily by B-52 bombers. Both types are cut into dipoles ranging in length from 0.3 to over 2.0 inches. They are made as small and light as possible so they will remain in the air long enough to confuse enemy radar. The aluminum foil dipoles are 0.45 mils (0.00045 inches) thick and 6 to 8 mils wide. The glass fiber dipoles are generally 1 mil (25.4 microns) in diameter, including the aluminum coating which is 0.12 f 0.06 mils thick. A new superfine glass fiber chaff is being manufactured that is 0.7 mil (17.8 microns) in diameter.
Both chaff types have a slip coating to prevent end welding of fibers when cut and to minimize clumping when ejected. The coating is a 1 percent solution of Neofat 18 (90 percent stearic acid and 10 percent pahnitic acid) with naphtha as the solute. The naphtha is driven off during the curing process. The foil chaff has each cut wrapped in a thin paper sleeve. At one time, the foil chaff contained in cardboard boxes was manufactured with a lead-based stripe coating designed to offset the center of gravity of each dipole to increase flutter. The specification for that chaff is no longer in effect, and lead has not been used since the early 1980s.
Chaff is intended to act as decoy for radar and/or increase ground clutter at the same time. However, modern pulse-doppler radar can recognize such decoys, especially in the lookdown/shootdown mode. This is particularly true because simple decoys, in contrast to true targets, do not exhibit a corresponding doppler shift in the radar band.
The methods used to disperse chaff have evolved over the years, from simply tossing it out of airplane windows to launching it with spring-loaded or pneumatic machines. Currently, the services use pyrotechnic charges, rockets, mortars, air flows, or motors to disperse chaff. Chaff is ejected either mechanically or pyrotechnically. Mechanical ejection uses small foillaminated cardboard boxes (2.8 by 4.8 by 0.8 inches) that are tom open during ejection. Debris from the cardboard boxes consists of the opened box, two high impact polystyrene plastic support pieces (2.75 by 4.75 by 0.06 inches), and paper wrapping for each dipole cut. Cardboard specifications have been changed from virgin kraft paper to recycled kraft paper because it biodegrades more quickly. The sealing adhesive for these boxes is an aqueous type polyvinyl acetate.
Pyrotechnic ejection uses hot gases generated by an explosive impulse cartridge. The gases push a small plastic piston down a chaff-filled tube 8 inches long with a 1 inch square cross-section. This ejects a small plastic end cap, followed by the chaff fibers. The tube remains in the aircraft. Debris that is ejected consists of two 1 inch square pieces of plastic l/8 inch thick (the piston and the end cap) and a felt spacer.
Chaff cartridges must demonstrate ejection of 98 percent of the chaff in undamaged condition, with a reliability of 95 percent at a 95 percent confidence level. They must be able to withstand any combination of environmental conditions that might be encountered during storage, shipment, and operation.
Motors feed chaff from rolls of about 40 pounds through cutters carried on some aircraft to produce either bursts or a continuous stream. The continuous stream technique, called saturation chaff, may be used by aircraft to cover a large area. By 2005 or 2006, the Army also planned to use saturation chaff to mask vehicle and troop movements. Using a cutter, 360 pounds of chaff from nine 40-pound rolls can be deployed in 10 minutes. Depending on the method and the number of aircraft, such releases could disperse billions of fibers. The B-52 can carry about 750 seven-ounce boxes of chaff; each box contains up to 11 million fibers that can be expelled continuously or in bursts.
Because of its effects on radar, inadvertent release of chaff is a safety concern. This event can occur due to release system electro-mechanical malfunctions, personnel error, or mechanical system degradation through wear and tear. During a period fi-om 1985 to 1986, a mechanical problem with the AN/ALE-40 chaff/flare dispensing system resulted in a high incidence of inadvertent releases. #WI3 The system was modified in 1987, correcting the problem.
The FAA has placed more stringent restrictions on DOD use of any type of chaff that operates within the bands used by air traffic control radar and navigational systems. In taking the more conservative approach to air traffic control and flight safety, FAA has limited or placed restrictions on the locations, altitudes, and/or time periods within which specific types of chaff can be employed.
The probability of debris from the chaff system hitting a person on the ground is difficult to quantify. Such an event would be dependent on many variables (e.g., location of use, population density beneath airspace, frequency of use, etc.). Ejected debris consists of the chaff itself, possibly a cardboard box which contains the chaff, flat plastic package stiffeners, a small plastic piston, and a small plastic end cap. Under normal circumstances, all of those elements weigh so little, or create so much drag in comparison to their weight, no injury would be anticipated even if a person were impacted. No incidences of injuries from falling chaff debris have ever been recorded. The only component of concern would be a full box of non-pyrotechnic chaff that failed to open during ejection. This would be a very rare occurrence, since the boxes are sliced open as they are ejected. For comparative purposes, the effect of being struck by such an object is equivalent to being struck by an eight-pound sledge hammer dropped from a height of approximately 10 inches.
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. Chaff will probably be released as the initial climb is established, just prior to weapon release, post weapon release, and as the hard turns are executed. 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.
The materials in chaff are generally nontoxic except in quantities significantly larger than those any human or animal could reasonably be exposed to from chaff use. Safety risks were found to be extremely low and isolated to specific circumstances that can be avoided or managed. The primary issue is the potential for interference with air traffic control radar, which is managed by requiring units to obtain a frequency clearance from the USAF Frequency Management Center and Headquarters Federal Aviation Administration (FAA) prior to using chaff that could interfere with air traffic control radar. Air quality issues included questions about the potential for chaff to break down into respirable particle sizes and the possibility that hazardous air pollutants may be generated from pyrotechnic impulse cartridges used with some chaff models. 'Ibe results of chaff particulate tests and a screening health risk assessment concluded that these are not significant concerns.
The potential for chaff to affect soil and water is remote. Levels of use and accumulation would have to be extremely high to generate any significant adverse effects. Laboratory tests of chaff, using a modified toxic characteristics leaching procedure, indicated little or no potential for adverse effects on soil. Adverse effects to sensitive aquatic organisms, although unlikely, may be possible in certain small, confined water bodies. These should be addressed on a case-by-case basis in areas proposed for chaff use that include highly sensitive aquatic habitats.
No adverse impacts on biological resources have been identified. Since chaff is generally nontoxic, toxicity-related impacts on wildlife are not anticipated. Based on their digestive processes, few animals are expected to suffer physical effects from chaff ingestion. Information was not available concerning the ability of surface or bottom feeding waterfowl and other aquatic species to process ingested chaff. Effects from inhalation are not considered a significant issue, since chaff particles would represent a small percentage of the particulates regularly inhaled by animals. Given the properties of chaff fibers, skin irritation is not expected to be a problem.
Impacts on land use and visual resources are directly related to the visibility and accumulation of chaff debris. A field study of the visibility of chaff and incidental debris in different environmental contexts concluded that significant aesthetic effects are unlikely. A survey of high-use areas did not indicate that chaff or chaff debris accumulates to create visual impacts. Use of chaff over or immediately adjacent to highly sensitive areas such as Wilderness Areas, Wild and Scenic Rivers, National Parks and Monuments, and other pristine natural areas may be incompatible with the land use management objectives for those areas, Issues regarding potential effects on cultural resources are also primarily related to accumulation and aesthetics, or, in the case of Native American resources, are indirectly associated with effects on physical and biological resources. The findings related to biological resources and visual resources, therefore, indicate that adverse effects are unlikely. While little is known about the potential for chemical effects f?om chaff on archaeological or architectural resources, they are considered to be remote, since chaff is composed of common, non-destructive materials.
The effects of releases of chaff, dud flares, and flare ash on the environmental depend on a variety of factors, including the quantity of material released, the propensity of these materials to leach toxic chemicals under given conditions, and the sensitivity of receiving environments to contaminants of concern. In that vein, the material likely to generate the highest volume of debris is chaff, which eventually precipitates totally to the surface. Dud flares are rare and incidental events, so it is extremely unlikely that any location would experience a "build-up" of dud flare material in the environment. Flare ash is a by-product of combustion and is widely dispersed by winds. The likelihood that a sufficient quantity of chaff or flare ash would fall into a particular pond, stream, or estuary, to measurably affect its chemical makeup is remote.
Esterline Defense Group is the sole qualified producer of chaff in the United States. Esterline's North Carolina chaff facility is the largest fully-integrated production operation in the world, including fiberizing and metalizing of raw glass, cutting and loading dipoles to the desired frequency and packing of the finished product. Esterline produces nearly one million pounds of chaff and integrate over two million chaff cartridges annually. Esterline's chaff products offer high reliability, multiple broadband frequency protection, excellent operational radar cross section and a rapid bloom with minimal birds-nesting. Variations of products are available to suit user requirements.
Chaff type Service Weight Composition\a Inventory\b ------------ --------------- --------------- --------------- --------------- RR-72B/AL Air Force Unknown Foil 37,800 RR-72C/AL Air Force Unknown Fiber 210,360 RR-112A/AL Air Force 7.0 oz. Fiber 372,720 RR-129/AL Navy\c 4.7 oz. Fiber Classified RR-136C/AL Air Force 14.4 oz. Fiber 939,990 RR-141E/AL Air Force 6.9 oz. Foil 207,557 RR-144/AL Navy\c 4.8 oz. Fiber Classified RR-149/AL Air Force 5.9 oz. Foil 1,440 RR-149A/AL Air Force Unknown Fiber 412 RR-170A/AL Air Force 6.4 oz. Fiber 23,606,750 RR-171/AL Navy\c 41-43 lbs. Fiber Classified RR-179/AL Navy\c 40 lbs. Fiber Classified RR-180/AL Air Force 6.4 oz. Fiber 830,786 RR-181/AL Navy\c 16 lbs. Fiber Classified RR-182/AL Navy\c 8.5 lbs. Fiber Classified MK-182 mod 1 Navy\d 16 lbs. Fiber 4,841 MK-182 mod 2 Navy\d 24 lbs. Fiber 4,909 RR-184/AL Navy\c 1.4 oz. Fiber Classified RR-185 Air Force Unknown Fiber 235,767 RR-188/AL Air Force 6.4 oz. Fiber 1,881,503 RR-189/AL Navy\c 1.4 oz. Fiber Classified MK-214 Navy\d 24.3 lbs. Fiber 50,163 MK-216 Navy\d 16.8 lbs. Fiber 24,118 M-1 Army 3.5 oz. Fiber 310,000 \a Fiber: aluminum-coated silica glass fibers; foil: aluminum foil. \b Air Force data as of May 8, 1998; Navy data as of March 3, 1998; and Army data as of February 23, 1998. \c Launched from airplanes. \d Dispensed from ships.
Chaff Used by ACC Units
|Aircraft||B-52||B-52||various||B-52||B-52 C-130||A-10, B-l, C-5, C-17, C-130, C-141, F-15, F-16, F/A-18E/F||A-10, C-130, F-15, F-16||A-10, F-15, F-16||B-52|
|Composition||Aluminum coated glass||Foil||Aluminum coated glass||Foil||Aluminum coated glass||Aluminum coated glass||Aluminum coated glass||Aluminum coated glass|
|Configuration||Rectangular aluminum foil laminate Kraft paper box with 2 Polystyrene supports||Rectangular aluminum foil laminate Kraft paper box with 2 Polystyrene supports||Rectangular aluminum foil laminate Kraft paper box with 2 Polystyrene supports||Rectangular aluminum foil laminate Kraft paper box with 2 Polystyrene supports||Rectangular tube cartridge||Rectangular tube cartridge with dual longitudinal cartridge||Rectangular tube cartridge||Rectangular plastic box held together with metal clips|
|Size||2.8 x 4.8 x 0.8 inches (10.75 cubic inches)||2.8 x 4.8 x 0.8 inches (10.75 cubic inches)||2.8 x 4.8 x 0.8 inches (10.75 cubic inches)||2.8 x 4.8 x 0.8 inches (10.75 cubic inches)||8 x l x l inches|
(8 cubic inches)
|8 x 1 x 1 inches|
(8 cubic inches)
|8 x l x l inches |
(8 cubic inches)
|2.8 x 4.8 x 0.8 inches (10.75 cubic inches)|
|No. of Dipoles||11 million||0.55 million or 1.1 million||Unknown||1.78 million||3.12 million||2.72 million||5.46 million||Classified|
|Dipole size (x-section)||1 mil (diameter)||0.45 x 8 mils||1 mil (diameter)||0.45 x 6 mils||1 mil (diameter)||0.7 mil (diameter)||1 mil (diameter)||1 mil (diameter)|
|Other Comments||Box ejected||Older type; box ejected||Box ejected||Older type; box ejected||Cartridge stays in aircraft||"Superfine" type;||Less interference with FAA radar (no D and E bands) replaces R-170 for training||Special order for Desert Storm|
|Join the GlobalSecurity.org mailing list|