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MJU-7A/B Infrared Decoy Flare
MJU-53/B Infrared Decoy Flare

The MJU-53/B Infrared Decoy Flare is an Infrared (IR) decoy providing aircraft survivability and protection against IR guided threats. It is intended as an improvement over the performance of the MJU-7A/B decoy when used either singly or in combination with other Infrared Countermeasure (IRCM) on the F/A-18E/F aircraft. This decoy is being derived (marinized) from the MJU-7A/B which incorporates features which will allow it to be used safely in a Naval operating environment. The decoy is sealed to prevent moisture and air contamination of the flare grain, and uses a BBU-36/B sized impulse cartridge. The MJU-53/B IR decoy flare consists of a rectangular case approximately 1x2 inches in cross section and 8.1 inches in length; therefore, it will be common for both Navy F/A-18E/F and Air Force aircraft. The IR payload is magnesium, Teflon«, Viton« (MTV) extruded flare grain.

With the MJU-7/B and A/B flare configuration, all versions of this flare measure 1 by 2 by 8 inches and have a nominal weight of 13 ounces. They use a BBU-36/B impulse cartridge. These are the most heavily used flares by ACC units, which employ an estimated 215,000 per year in the mid-1990s.

There are two versions of the MJU-7/B: a 'parasitic" and a "non-parasitic" type. The parasitic type is ignited in the aluminum case before it leaves the aircraft by holes in the piston that permit ignitor gases to contact the first fire mixture on top of the flare pellet. The non-parasitic type flare incorporates a mechanical mechanism (a safety and initiation device) to prevent ignition of the pellet in the case. This mechanism includes a G-weight, a locking bar and fork, a push button and spring, a firing pin, and primer assembly. When ignited by the firing pin, the primer assembly fires the ignition charge (15 mg of basic lead styphnate, lead azide, barium nitrate, antimony trisulfide, and tetracene) which fires the output charge (40 mg of zirconium, molybdenum trioxide, and potassium perchlorate), which ignites the flare pellet.

The MJU-7AB was designed to reduce the complexity of the non-parasitic type flare, improve its reliability, and reduce debris. In this flare, the mechanical mechanism is replaced with a slider assembly that incorporates an initiation pellet (640 mg of magnesium, Teflon, and Viton A or Fluorel binder). This pellet is ignited by the impulse cartridge, but its hot gases do not reach the flare until the slider exits the case, exposing a fire passage from the initiation pellet to the first fire mixture on top of the flare pellet.

The parasitic type flare is less likely to produce duds, and the only debris is the plastic end cap and the remains of the piston. However, there is an increased risk of fire damage to the aircraft, compared with the non-parasitic flare. The non-parasitic flare can be expected to produce the largest number of duds and the most debris, due to the complexity of the ignition process. The MJU-'IA/B provides a middle ground by igniting a small pellet inside the case, rather than the flare itself, thereby reducing both the safety risk and the quantity of debris. Since the complexity of the flare ignition process of the MJU-7AB falls between the parasitic and non-parasitic versions of the MJU-7/B, the dud rate can also be expected to fall between them. The MJU-7/B was being phased out of the inventory in the mid-1990s.

The MJU-7(T-I) is a simulator version of the MJU-7/B. It replaces the magnesium flare pellet with a smoke charge. The smoke charge is smaller than a flare (5 inches versus 8 inches long) and is held in place inside the flare case by cardboard spacers. It is composed - of doughnut-shaped pellets 0.75 inches in diameter with a 0.37 inch hole, 0.5 inches thick, encased in a cardboard tube. The charge material is 20 percent powdered sugar, 36 percent KClO,, 42 percent yellow dye (Chinoline Yellow-5), and 2 percent binder (Goodrich Hightemp, a dry rubber, and Teflon). It uses the M-796 impulse cartridge (Figure 4.2-4), which generates hot gases that push the piston down the case and simultaneously ignite a Quick Match cord (ME-Q-378) in the center of the pellets. Resulting debris includes the plastic end cap and the remains of the cardboard spacers and piston.

Lot acceptance testing for the MJU-7A/B, the most heavily used flare (approximately 57 percent of all ACC flare use), examines the success of ignition and burn, pellet breakup, and indication of dispenser damage. The specification requires that lots pass an ignition and ejection test in accordance with MIL-STD-105, Inspection Level I, Acceptance Quality Level (AQL) of 1 .O. In this test, with a sample size of 80, two failures would be acceptable, but three failures would not. This means that the reliability of flares must be greater than 96.25 percent. However, to. ensure that good lots are not erroneously rejected in these tests, the flares would have to be designed to a reliability of 99 percent (assuming a confidence level of 95 percent), which is consistent with an AQL of 1.0. Therefore, the reliability of the MJU-7A/B flare is expected to be closer to 99 percent.




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