LUU-2B/B AIRCRAFT PARACHUTE FLARE

The LUU-2B/B flare is the same size as the Mk 45 flare. It is 36 inches long, 4.9 inches in diameter, and weighs about 30 pounds. The flare is supplied only as an AUR, and it is shipped assembled with drogue trays for dispenser launch. The flare is hand launched, or configured for launching from IMER or ITER aircraft bomb racks. It replaces the Mk 24 Mods and Mk 45 Mods aircraft parachute flares.

Components

The LUU-2B/B flare (fig. 4-8) has four major components:

Figure 4-8.-LUU-2B/B aircraft parachute flare.

1. The mechanical timer assembly

2. The parachute suspension system

3. The out-of-line igniter

4. The case assembly with the tamped candle

The mechanical timer assembly consists of a mechanical timer and related hardware in a Lexan plastic housing. The nonexplosive mechanical timer functions like the explosive Mk 364 fuze on the Mk 45 flare. The mechanical timer is a three-gear timer, powered by a torsional mainspring. A phosphorescent plastic decal with calibrated markings from 250 to 11,000 feet of fall is located on the face of the timer cover. A white, plastic, dial timer knob is used to set the desired drop distance. Settings of 150,500, and 1,000 to 11,000 feet can be selected. A safe setting is also provided.

An 18-foot diameter cruciform-shaped canopy parachute suspension system is used for good stability. The riser cables connect the parachute to a bulkhead. The bulkhead separates the parachute compartment from the remainder of the flare assembly. One cable is attached to an explosive bolt for parachute dump at candle burnout, just like the Mk 45 flare.

In the ignition system, a lanyard is attached to one of the parachute riser cables. This lanyard is threaded through the bulkhead and past the candle in an internal raceway along the side of the aluminum case. This leads to the ignition assembly in the ignition housing near the candle's face. The lanyard is attached to a triggering mechanism, which consists of the out-of-line igniter (OLI-2/A). Upon ignition, the firing pin initiates the pyrotechnic firing train.

The aluminum case assembly contains a tamp-cast illuminating candle that consists of a composition of magnesium, sodium nitrate, and a polymer binder. The flare is designed so the outer aluminum case is partially consumed during candle burning.

Operation

A lanyard is attached to the timer knob on the flare timer during flare uploading procedures. The lanyard is also connected to the flare drogue tray or bomb rack, depending on the launch configuration. At launch, the timer knob is pulled out of the timer (requires approximately 30 pounds of force) by the lanyard, starting the clock mechanism. After the preset time (drop distance) ends, the three locking pawls in the timer assembly release, retracting and releasing the timer assembly. A spring, located between the timer assembly and the packaged parachute, expels the timer assembly, which, in turn, initiates removal of the parachute from the flare case. When the cord breaks, it separates the timer assembly from the parachute. As the parachute system deploys and its main cables are pulled taut, the ignition lanyard is pulled to activate the ignition system. The ignition lanyard must exert a pull force in excess of 90 pounds to pull the slider assembly in line. This, in turn, releases the firing pin against the primer. The primer ignites a propellant wafer that produces sufficient heat for candle ignition. Pressure buildup during candle ignition blows off the igniter housing, and the candle power reaches a nominal value. Just before candle burnout, the explosive bolt functions to release one of the suspension cables, causing the parachute to dump.

The LUU-2B/B flare has several advantages over the Mk 24 and Mk 45 flares. The most important advantage is that the candle is not ejected from the case on the LUU-2B/B. Only the parachute is removed from the case. This is accomplished by a mechanical timer instead of an explosive fuze, as is done in the Mk 24 and Mk 45. Therefore, if the timer knob should be accidentally pulled during handling when the timer is not on the SAFE setting, the timer and release mechanisms can be forcibly hand-held onto the flare housing to prevent ejection of the timer and release mechanisms. When the timer completes its cycle, the timer mechanism can be taped on the flare housing and marked for disposal. If the timer is ejected from the flare and a portion of the parachute comes out of the housing, the parachute can be stuffed back into the housing, taped, and marked for disposal.

Another advantage of the LUU-2 B/B flare is the increased pull force on the parachute lanyard to initiate the ignition sequence. If the parachute should accidentally deploy on the flight deck/line, the opening shock from deck winds or jet blast is not sufficient to ignite the candle.