One design choice hiding a bomb somewhere can be the difference between life and death in today’s air war. For South Korea’s KF-21EX, moving to internal bays for its weapons is not just a superficial design revision; it is a rational engineering choice that is a stamp of approval on the country’s aspiration to become one of the world’s stealth leaders.
1. Internal Weapons Bays: The Stealth-Payload Equation
The KF-21EX’s most dramatic innovation is the use of twin internal weapons bays, a design that puts it alongside the F-35, Su-57, and J-20. The bays are specifically designed to carry 2,000-pound-class guided bombs, presumably the GBU-31 Joint Direct Attack Munition (JDAM) with BLU-109 penetrator warheads, allowing the aircraft to attack hardened targets like bunkers while maintaining a low radar cross-section.
As KAI officials have pointed out, “internal weapons carriage for the KF-21EX is particularly important because the ‘loyal wingman’-type unmanned aerial vehicle under development to fly alongside it will not be able to carry missiles in the 2,000-pound class.” Internalization has a cost: while stealth is optimized, overall payload is limited relative to external carriage, necessitating structural redesigns like a deeper, and possibly wider, center fuselage to contain the bays.
2. Structural and Aerodynamic Engineering Challenges
Fitting internal bays into a fighter airframe is an engineering accomplishment in structural and aerodynamic design. Internal storage minimizes drag, which improves fuel efficiency, maximum speed, and mission range without compromising the aircraft’s lift-to-drag ratio during high-energy maneuvers and supersonic flight. However, the complication of these bay’s mechanical doors, gun ejection systems, and the necessity to handle heat and vibration requires considerable airframe redesign. The KF-21EX’s slender profile, with reprofiled radome and canopy, not only facilitates stealth but also enhances energy retention and stable flight under stressful combat conditions characteristic of fifth-generation aircraft.
3. Stealth vs. Payload: A Calculated Trade-Off
Although the F-35 is still the standard for radar invisibility, its signature is said to be “smaller than a metal golf ball.” The KF-21EX closes the gap by combining radar-absorbing materials, stealth-shaped exhaust, and conformal sensors. The shift to internal transport “dramatically lower[s] radar cross-section, similar to the F-35’s dual internal bays concealing smart bombs and missiles within the airframe’s sleek lines.” But the KF-21EX’s stealth is a calculated trade-off; it will not match the F-35’s levels, perhaps, but it provides a balance between survival and strike power that is uncommon beyond the world’s top-tier air forces by merging stealth and heavy payloads.
4. Next-Generation Sensors and Electronic Warfare: The Digital Cutting Edge
Under its skin, the KF-21EX is a demonstration of the next-generation sensors and electronic warfare. The new Electro-Optical Targeting System (EOTS) in the aircraft replaces the previous IRST and provides both air-to-ground targeting and infrared search and track. The sensor suite is completed by an Electro-Optical Distributed Aperture System (EODAS) and an Active Electronically Scanned Array (AESA) radar, both with Automatic Target Recognition (ATR) and Non-Cooperative Target Recognition (NCTR). These are combined through high-speed optical and satellite-connected datalinks, all controlled by an AI-equipped mission computer that delivers real-time targeting support, threat prioritization, and optimized flight path for the pilot.
5. DRFM Decoys: Revolutionizing Electronic Warfare
The employment of disposable Digital Radio Frequency Memory (DRFM) decoys like Leonardo’s BriteCloud represents a survivability quantum leap. DRFM systems record, rewrite, and retransmit adversary radar signals, generating authentic fakes or “spoofs” that have the potential to deceive even the most advanced radar-guided missiles. “BriteCloud, for instance, is an all-in-one DRFM jammer diminutive enough to be dropped by fighter aircraft like a conventional flare.” After it has been deployed, it sends advanced jamming signals that deceive radar-guided missiles into targeting the decoy instead of the plane.” This technology, which is now considered obligatory for contemporary air fighting, is a pillar of the KF-21EX’s electronic warfare suite and puts it on par with EW innovation.
6. Manned-Unmanned Teaming: The MUM-T Combat System
The KF-21EX is tailored from the ground up to function as the central manned component in South Korea’s Next Air Combat System (NACS) distributed operating environment that comprises manned-unmanned teaming (MUM-T). The Performance Improvement and MUM-T Combat System will provide secure datalink connectivity and AI-controlled sensor fusion, enabling the KF-21EX to interface with stealthy ‘loyal wingman’ unmanned aerial vehicles like the Low Observable Unmanned Wingman System (LOWUS). In Suppression or Destruction of Enemy Air Defenses (SEAD/DEAD) missions, the manned fighter may be an escort jammer, and drones play the role of stand-in jammers, exchanging real-time sensor tracks for distributed threat analysis and targeting. “Crewed and uncrewed aircraft will exchange real-time sensor tracks, enabling distributed targeting and threat analysis.” A two-seat KF-21EX model is being considered, providing a dedicated operator for drone operation and electronic warfare in intense situations to achieve maximum operating flexibility.
7. Roadmap and Technical Specifications
The KF-21EX carries on the tested twin-engine configuration, powered by two General Electric F414-GE-400K afterburning turbofans, each capable of delivering up to 22,000 pounds of thrust. The airframe can carry a maximum of 25,600 kilograms of takeoff weight and a payload of close to 7,700 kilograms. The plane measures 16.9 meters in length and has an 11.2-meter wingspan. It flies at Mach 1.8 and has fly-by-wire controls, a glass cockpit, and a modular design with the option of future upgrade. Block I production opened in 2024, with delivery scheduled through 2032. Block II will see a multirole upgrade by 2028, and Block III, the mature KF-21EX, is forecasted to achieve operational readiness by 2039 as the backbone of South Korea’s air combat fleet.
The KF-21EX’s combination of stealth, fifth-generation sensors, digital warfare, and manned-unmanned teaming makes it a serious player in the international arms market and a quantum jump for South Korea’s defense sector.
