Rule the Sky-(1) How Aircraft Flares Were Developed

[Lee Jun-woong, former senior researcher at the Agency for Defense Development] Various flares are used in military operations, one of which is the LUU-2 aircraft-deployed flare developed by Thiokol, a leading American defense contractor at the time. This flare, when dropped from aircraft such as helicopters at night, descends slowly under a parachute for about 5 minutes, illuminating a 50-meter radius on the ground as bright as daylight (15 lux). In the 1980s, researchers at the Agency for Defense Development attempted to reverse-engineer this aircraft-deployed flare.

▲ Difficult flare filling achieved, followed by combustion test failure= The aircraft-deployed flare consists of a parachute, an ignition device, and an aluminum canister containing the flare composition. While we possessed the technology to manufacture key hardware such as the ejection device, parachute deployment device, ignition device, and flare composition, we did not know the process to safely fill the flare composition into the aluminum canister. The flare composition must be properly filled to emit 1.8 million candlepower of light and burn for more than 5 minutes.

The first essential task in development was to develop a method for filling the flare composition. Thiokol used a tamping machine, which operates as follows: as the flare composition is supplied into the aluminum canister, a tamping rod strikes it, increasing the density of the composition inside the canister until a certain value is reached, at which point the tamping rod automatically slides upward. The key to this device is a clutch holding the tamping rod, which is lined with leather; when the pressure on the tamping rod increases, the leather causes the rod to slip. Although it was possible to manufacture the device according to Thiokol’s design, there were several drawbacks. In particular, repeated operation weakened the friction between the clutch and leather, requiring frequent disassembly and replacement of the leather, which was a critical disadvantage. To address this, instead of using Thiokol’s method of slipping the tamping rod, we firmly fixed the tamping rod to the clutch and connected an oil tank and hydraulic control valve to the bottom of the flare canister so that oil would leak slightly whenever a certain pressure was applied to the tamping rod.

Based on this design and through trial and error, we finally succeeded in filling the flare composition at the correct density. After inventing the flare filling device, we focused on filling the flare composition using it. To verify whether the filled flare would emit 1.8 million candlepower of light and burn for more than 5 minutes, we began combustion tests. Avoiding the full moon, we conducted the test late at night with an ambulance and fire truck on standby. Upon ignition, the flare emitted brilliant light and began burning. However, after a few minutes, an unexpected result occurred. The flare burned for about 4 minutes and then went out, leaving about 10 cm of partially burned flare composition on the ground. Since the project would fail if the flare did not burn for more than 5 minutes, we faced a new challenge.

▲ Solution found in a simple sentence= After reviewing various materials related to the flare, a simple sentence?“The asbestos board attached as insulation inside the flare canister should be adhered over as narrow an area as possible”?became the starting point for the solution. Before this, the research team had firmly adhered the entire asbestos board inside the aluminum canister before filling the flare composition. Conversely, we concluded that if the asbestos board was not adhered to the aluminum canister, an air layer between the asbestos and aluminum would enhance insulation, preventing premature combustion of the aluminum. Previously, heat generated by the burning flare composition was directly transferred to the aluminum, igniting it. As a result, the aluminum burned faster than the flare composition, completely burning away after 4 minutes, leaving only the remaining flare composition to fall to the ground.

The research team completed a flare with the asbestos board attached inside the canister according to the newly discovered method. A few days later, we selected a pitch-dark night for the experiment. After the ignition signal, the flare burned with a brightness barely visible to the naked eye and surpassed the critical 4-minute barrier, burning for 5 minutes and 10 seconds. While everyone was elated, an unexpected accident occurred. One researcher observing the test was dragged tens of meters by a rope trailing behind the fire truck as it withdrew, resulting in hospitalization for over three months.

▲ Another twist= Subsequent repeated tests fully verified the flare’s performance. All technical issues were resolved, and the project reached the stage where only assembly of parts such as the parachute and ignition device remained. However, a defense contractor that had predicted the research team’s failure signed an MOU to adopt all of Thiokol’s production technologies and was commissioned by related agencies for mass production. As a result, although the research team succeeded in developing independent technology, they failed in mass production deployment, and all activities, including the project, were halted.

▲ Lessons learned from developing the aircraft-deployed flare= Nevertheless, the flare development left many lessons for the research team. First, there is no problem that cannot be solved with scientific knowledge and passion. Second, as demonstrated in the insulation adhesion, many technical know-hows arise from shifts in perspective, and since such technologies are often simple, they must be actively protected. Lastly, no matter how excellent the technology developed, if close contact and communication with related departments fail to persuade them, mass production and deployment are difficult. This was a valuable lesson for the research team and helped in subsequent nationally important weapons system development tasks.

This content was produced with the assistance of AI translation services.