Two-seat version and European weapons added to Seoul’s new fighter
The Korea Aerospace Industries (KAI) KF-X fighter keeps growing. What began as a concept design as big as the
has repeatedly gained length and wingspan and is now likely to be heavier than that earlier aircraft.
The indigenous fighter will have a two-seat version, developers have confirmed, following years of depictions of it with just one seat. And the type will be equipped with MBDA Meteor and Diehl IRIS-T air-to-air missiles, says South Korea’s defense procurement office, outlining a plan to avoid complete reliance on U.S. weapons.
The twin-engine KF-X is intended to fly in 2022. The Republic of Korea Air Force and KAI have said the service will receive its first unit in 2024, but KF-Xs delivered before 2026 must be developmental units. The first version is not due to be fully developed until 2026 and will lack features intended for later variants. Indonesia is a junior partner in the KF-X program.
The defense ministry’s Agency for Defense Development (ADD) led preliminary design and is still deeply involved as KAI works on detail development. The military procurement office, the Defense Acquisition Program Administration (DAPA), chose the
F414 engine for the KF-X in 2016.
The newest design, C107, is the latest in a series that began sometime before 2012. The iteration numbered C104 was chosen as the basis of the KF-X when
won the separate F-X Phase 3 import competition in 2013 with the
Lightning; the competition winner was required to support KF-X development.
This design series has featured tailplanes; an alternative concept with canard control surfaces would have been used had a European supplier won F-X Phase 3. Designs before C107 have been shown only as single-seaters, though a model of a two-seat version was glimpsed on a television report about KAI in 2016. In describing C107, officials have confirmed that a second seat will be available.
The extra place is unrelated to the increase in size. Rather, the aircraft has been enlarged to create more space and to give it a better aerodynamic shape, DAPA officials said at a briefing on the program.
Thanks to DAPA’s release of low-resolution plan drawings of the latest five design iterations, it is now possible to tell some of the story of the evolution of the KF-X since 2012. Although the aircraft has grown and the wing has been enlarged, the designers have stuck with the planform of the mainplane: It has 40 deg. of leading-edge sweep, 10 deg. of forward sweep on the trailing edge and an aspect ratio of 2.7.
The first design in the series was C101. By 2012, it had evolved to C103, which had the general configuration that has persisted until now. At the time of program launch, C103 was thought to be the current design, but in 2014 designers had proceeded to C104, adding conformal antennas and refining the placement of internal equipment. Low-resolution drawings suggest little change to the external shape, if any.
The dimensions of C104 are unknown, but C105, from 2016, was bigger than C103. Span rose to 11 m (36 ft.) from 10.7 m (see table) and length by 40 cm (16 in.). At least half of the lengthening was probably associated with enlargement of the wing, since the chord and therefore the carry-through structure in the fuselage had to be longer. The wing was moved back in relation to the fuselage, so its trailing edges were now behind the leading edges of the fins. The fuselage appears to have been slightly widened.
Also, the canopy shape changed to improve some unstated aspect of performance, perhaps stealth, while the F414 was incorporated and the intake design was revised. The F414 was the bulkiest and most powerful engine under consideration, so its selection may have had something to do with the enlargement of the design.
Despite these changes, empty mass rose only 2%, to 11.1 metric tons, suggesting weight savings had been found. The aircraft was still just a little lighter than the Typhoon, the fighter with which the KF-X has been most comparable in size.
Further growth appeared in C106: span, wing area and fuselage length all increased. The cockpit moved forward. The dimensions of C106 are unknown but C107, for which figures are available, is apparently about the same size. While C107’s span, up 20 cm, is only modestly greater than C105’s, the fuselage is considerably longer. The aircraft is now fully 1.2 m longer than it was in the C103 concept. Empty mass is unavailable, but it is now likely to be significantly greater than the Typhoon’s.
The shapes of the forward fuselage and the inlets have been improved in C107. The wing roots are extended forward, blending with the fuselage, while the tail fins have moved forward and, with trailing edges now swept forward at a greater angle than before, are almost cropped triangles. They have probably been heightened in compensation for the loss of moment arm caused by their relocation; the whole aircraft has gained 30 cm of height from C103’s 4.5 m.
The engines were closely spaced before C107; now they are farther apart, improving survivability and providing volume between them. The nose is blunter in plan, rather like that on designs for Japan’s proposed indigenous fighter. More changes can be expected, because three more design iterations will be prepared by June 2018.
The reason for the second seat has not been disclosed. Fighters designed before the 1990s routinely have two-seat versions. In some cases, the second seat is now used not just for training but for carrying another crew member in combat, as became popular during and after the Vietnam War. But the
Raptor, F-35 and Avic Chengdu J-20 have only single-seat versions, relying on advanced simulation to prepare pilots for solo flights. Provision for a second seat in the KF-X may indicate that the type’s avionics will not be sufficiently advanced to support the most demanding strike missions without two crew members.
MBDA and Diehl have agreed to supply Meteor and IRIS-T missiles, respectively, says DAPA, presumably meaning that terms have been settled. But South Korea still needs the permission of Germany to use the IRIS-T and from the countries behind the MBDA consortium—Britain, France and Italy—for the Meteor. There is no indication of when government authorization will be received. The Meteor and IRIS-T are long- and short-range air-to-air missiles, respectively.
South Korea also plans to use the most equivalent U.S. weapons, the AIM-120 Amraam and AIM-9 Sidewinder. Negotiations for integration of those missiles are not complete, DAPA says. Washington agreed in June to give technical information on its two air-to-air missiles and nine other U.S. weapons, but this will only be data of the level called 1A: size, weight and basic interface particulars. South Korea is still seeking level 1B information: full interface data needed for integrating and operating the weapons.
Full-scale development of the KF-X began in late 2015 after years of national debate. One objective is to free South Korea from depending on Washington’s permission in integrating weapons, as it must when it buys fighters straight from the U.S. and would if it equipped the KF-X with U.S. avionics.
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