Sacheon on South Korea’s southern coast is breeding the country’s next defense ambitions. The problem is they are missing a crucial element for liftoff.
"We are currently focusing on mass production of the LAH, and we're aiming to produce around three aircraft a month," said Kim Bong-jin, a general manager in KAI’s production engineering team, during a factory tour on Oct. 23.
"But because of the engine issue, some aircraft have piled up."
Asked whether deliveries were continuing, he was unequivocal.
"We cannot make deliveries at the moment."
The aircraft is the LAH Miron, a light armed helicopter developed to replace the South Korean Army’s aging 500MD and AH-1S Cobra helicopters.
Its stalled deliveries expose a constraint behind the country’s growing defense capabilities: assembling an aircraft at home does not put every critical technology or supply decision within the manufacturer’s control.
In June, figures disclosed by a South Korean lawmaker showed corrosion in 47 of 57 engines inspected and cracks in 38. The two categories overlap. The Defense Acquisition Program Administration had identified engine problems in April, and the military subsequently suspended flights of affected helicopters.
The engines use technology from France’s Safran and are assembled domestically by Hanwha Aerospace. The defects were found in diffusers, components that regulate airflow inside the engine.
Questions arose over the assembly process, although Hanwha maintained that its procedures met the original manufacturer’s requirements.
The disruption was still visible on the factory floor at the time of the visit. An industry analysis published Oct. 20 reported no Miron deliveries during the third quarter and forecast a resumption of engine supplies in November. Even then, aircraft would still need to complete inspections and acceptance procedures before reaching the military.
"We used to produce fixed-wing aircraft and helicopters together, but we ran out of assembly-line space, so we built this rotary-wing facility," Kim said.
Two aircraft families now share the building. The larger KUH-1 Surion is a utility helicopter designed to carry troops and cargo. The smaller Miron is built for armed reconnaissance and attack missions.
The Surion has a maximum takeoff weight of about 8.7 metric tons and can accommodate up to 13 people, including two pilots. The Miron’s maximum takeoff weight is about 4.9 tons, with armament including a 20-millimeter turret gun and air-to-ground weapons.
Kim described an assembly operation arranged in three rows, with the second generally assigned to the Surion and the third to the Miron. The layout can change with production needs.
"We start structural assembly on the right and move toward the left," he said.
The pale colors across the unfinished bodies offered clues to their construction.
The patchwork marks different materials rather than successive stages of painting. Before the final exterior coating gives a helicopter its uniform appearance, the factory floor reveals how much of it is built from separate structures and systems.
The Surion, South Korea’s first domestically produced utility helicopter, has evolved into versions for troop transport, medical evacuation and Marine Corps amphibious operations. Police, coast guard, fire and forestry agencies also use variants of the platform.
Each mission brings its own equipment. Police helicopters may carry surveillance systems, weather radar and loudspeakers. Rescue aircraft need hoists to lift people from inaccessible terrain. Firefighting versions can carry water tanks.
Maritime operations demand further changes, including additional fuel and, on some versions, emergency flotation equipment.
"Without the external fuel tanks, the helicopter can fly for a little less than three hours," Kim said. "With the additional tanks, we can extend that to around five hours."
Such requirements must be settled before the aircraft reaches the line.
"Before starting a project, we have to carefully review and decide on all the requirements," he said. "If we build an aircraft and then have to change it, the cost of doing so is enormous."
The variety of missions also helps explain the workload behind aircraft that receive less attention than KAI’s fighter jets.
A helicopter must turn engine power into the precise movement of its rotors. Transmissions and gearboxes carry that power through the aircraft, adding mechanical complexity to the task of integrating its structure, electronics and mission equipment.
"The basic manufacturing methods are not that different between fixed-wing and rotary-wing aircraft," Kim said. "But helicopters use turboshaft engines, and that power has to be converted into rotational force to turn the rotor."
He described the Surion’s arrangement of main, intermediate and tail gearboxes. The Miron uses main and tail gearboxes without a separate intermediate gearbox in the configuration he outlined.
At the rear of the Miron, another distinction is immediately visible: its tail rotor sits inside a circular enclosure rather than turning in the open.
Known as a Fenestron, the design helps reduce the danger posed by exposed spinning blades.
"Because the tail rotor is enclosed, it has advantages in terms of noise and the safety of maintenance personnel," Kim said.
The fuel tanks are designed to limit leaks if struck by gunfire. Kim described layers of rubber-like material that swell when exposed to fuel, helping seal a puncture.
"If the aircraft is hit and fuel starts leaking, the material between the rubber layers comes into contact with the fuel and swells," he explained. "That's how the self-sealing fuel tank works."
Making the Miron an effective armed helicopter also requires its weapons and sensors to work precisely with an aircraft that is constantly moving and vibrating.
"If you designate a target, the system can continue tracking it," Kim said. "For accurate firing, the gun, targeting system and the aircraft's position all have to work together."
Vibration is a particular concern.
"To fire the 20-millimeter gun accurately, you need to minimize vibration," he said.
That places exacting demands on the rotor assembly. The heavier Surion uses four main rotor blades, while the smaller Miron has five. Blade count alone does not determine lifting performance or smoothness of flight; rotor size, aircraft weight, engine power and other design choices all matter.
Both aircraft use composite rotor blades. KAI said these are designed with computer-aided software and made by laying composite materials, including carbon fiber, into molds to achieve the required strength, flexibility and durability.
Installation is just as exacting as manufacture.
"The rotor is installed during the final stage of aircraft production," KAI said. "Precise horizontal and vertical alignment must be checked, because improper alignment can cause vibrations when the rotor spins."
The same care is needed when rotor components are removed and reinstalled during maintenance.
Beyond the assembly line lie ground inspections, functional checks and flight tests. A helicopter that looks complete is not yet ready for delivery.
"Even if both engines fail, helicopter pilots train to land using autorotation," Kim explained.
During autorotation, airflow through the rotor as the helicopter descends keeps the blades turning without engine power, allowing the pilot to attempt a controlled emergency landing.
For the Mirons waiting at Sacheon, however, the immediate challenge was getting reliable engines into aircraft that could then be cleared for service.
Kim has spent his career working through the demands of aircraft production. He recalled starting on fixed-wing programs, including the KT-1 trainer and work associated with Boeing’s F-15, before joining the Surion program.
Helicopters may attract less public attention than fighters, he said, but their demands on engineers and technicians are no lighter.
"The amount of work and effort is just as great, if not greater," he said.
His pride in the range of Surion variants was accompanied by frustration over the resources available to produce them.
"Look at how many different versions of the Surion we've produced and delivered in such a short period of time," Kim said. "But we had fewer people. To be honest, I do feel somewhat unfairly treated."
Around him, helicopters continued to take shape along the assembly rows. The breadth of work was visible in their unfinished bodies, from protective coatings to the systems that would allow them to carry troops, rescue survivors or engage a target.
For the Miron, the next step depended on something outside that steady progression from right to left: the arrival of engines that would allow the waiting aircraft to leave the factory.
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