Sør Korea utvikler ny fighter som likner F-35/F-22 - AW&ST

South Korean KF-X Design Approved, First Flight Due In 2022
Bradley Perrett and Kim Minseok 

The Korea Aerospace Industries (KAI) KF-X fighter program is moving into detail development, following the defense ministry’s approval of the company’s final preliminary design. The ministry has also reaffirmed the program schedule, with the first KF-X to fly in June 2022. Having grown in size in successive preliminary design iterations, the twin-engine KF-X has arrived at a weight category halfway between the Eurofighter Typhoon and Lockheed Martin F-35 Lightning. The ministry’s Defense Acquisition Program Administration (DAPA) says it reviewed and confirmed KAI’s preliminary design on June 28-29. The agency also has cleared a design for an indigenous radar for the KF-X with an active, electronically scanned array (AESA). ·            The fighter is sized between the Typhoon and F-35 ·            The design for its AESA radar has also been cleared The KF-X’s critical design review, to validate the detail design ahead of prototype manufacturing, will be held in September 2019, according to the head of the acquisition program, Jeong Kwangsun. The first prototype should be rolled out in June 2021 and fly 12 months later, DAPA says; the agency had previously said the first flight would happen sometime in 2022. Completion of development in 2026 has been scheduled, but that target was not restated in the announcement of design approval. The KF-X has the basic shape of a stealth fighter but not the detail features needed to prevent radio energy reflecting back to a radar. Most notably, it has protrusions for various antennas and lacks a weapon bay, though the design allows for one to be included. A later version of the fighter is supposed to incorporate a weapon bay and other stealth features. The design DAPA approved is C109, the latest in a series that began with C101 years before the launch of full-scale development in late 2015. C109’s basic specifications are the same as those of the immediately preceding design, C108, that KAI published in June. Empty weight is 12 metric tons (26,500 lb.), compared with 10.9 metric tons for the Typhoon and 13.2 metric tons for the F-35A. Maximum takeoff weight is 26 metric tons and payload 7.6 metric tons. The aircraft is therefore considerably larger than first envisaged. C103, prepared before the launch of full-scale development, had an empty weight of 10.9 metric tons and maximum takeoff weight of 24 metric tons; it was 1.3 m (4 ft.) shorter than C109 as well. KAI has not explained why its fighter has grown in development. The company chose the General Electric F414 engine for the KF-X in 2016. The specific version will be the F414-GE-400K. Thrust with afterburning, 22,000 lb., will be the same as generated by the F414-GE-400 version installed in the Boeing F/A-18E/F Super Hornet, but dry thrust will be greater, at 14,400 lb. According to the U.S. Navy, the F414 in the Super Hornet has a dry thrust of 14,000 lb. An option for the KF-X program, apparently rejected, was a version of the F414 that GE calls the F414 Enhanced Engine. This generates 18% more afterburning thrust than the standard F414-GE-400. C108 was dimensionally close to a  2017 iteration, C107. It is clear, then, that KAI’s project leaders over the past year have been increasingly sure of what they wanted—as is normal toward the end of a process of iterative design. KAI did not bother to prepare C110, which a year ago was supposed to be the design presented for the June 2018 review; its nonappearance is another sign that the KF-X has been fairly stable since C107 was drawn up.

In this official drawing, KF-X preliminary design C109 carries navigation and targeting pods. Credit: KAI

The span of C109 is (and for C108 was) 11.2 m, unchanged from C107’s. Its length is 16.9 m, up 10 cm (4 in.) from C107, and height 4.7 m, down 10 cm. The wing area is 500 ft.2 (46 m2). Its leading edge sweep is 40 deg. and aspect ratio, a measure of wing slenderness, 2.7; those latter two figures have appeared in a succession of preliminary designs. Even as the KF-X has grown, the wing’s proportions have been steady. Another consistent wing feature has been a 10-deg. forward sweep on the trailing edge, but this is not confirmed for C109. Following the preliminary design review, KAI published pictures of C109, and small changes from C107 are evident. One is the elimination of small forward extensions at the roots of the mainplane that blended it with the fuselage; these were introduced after iteration C105. The leading edge now meets the fuselage with a sharp angle, as it did in C105 and earlier designs. The fins of C109 extend a little farther aft and may be broader than those of C107, perhaps compensating for the reduction in height. And the tailplane shape has been revised, with a kinked trailing edge; in C107 the trailing edge was straight. The changes to the tail may account for the slight increase in length. Wide separation of the engines, a survivability feature that appeared after C105, appears to have been retained.

The KF-X design appears to have changed little over the past year. Credit: KAI

The shape of the KF-X follows what researchers Michael Pelosi and Carlo Kopp have called F-22 design rules, with such features as chines on the forward fuselage, a flat underside and aligned edges. The KF-X has diverters to take the boundary layer from the engine inlets. The Lockheed Martin F-22 has such features, possible sources of radar reflections, but in the F-35 the company uses diverterless supersonic inlets, which handle the boundary later aerodynamically. The KF-X will be armed with MBDA Meteor long-range and Diehl Iris-T short-range air-to-air missiles. These are shown in one of the official drawings of C109. South Korea has also planned to equip KF-X with the most equivalent U.S. weapons, the Raytheon AIM-120 Amraam and AIM-9 Sidewinder.  The same drawing shows the aircraft with a pair of navigation and electro-optical targeting pods mounted on the lower corners of the fuselage; these are like the U.S. AAQ-13 and AAQ-14 systems developed in the 1980s. Inclusion of the navigation pod is surprising, because its function should be available from a fighter’s AESA main radar, saving weight and drag. With the reception performance of a large antenna, a main radar could also emit with less power, and therefore be less detectable, than a small terrain-following radar in a pod. Inclusion of the navigation pod is therefore a hint that KAI thinks that the radar developers have enough challenges in providing basic fighter functions for the sensor and that software for terrain-following should come later. In May, DAPA approved the preliminary design of the radar, which the ministry’s Agency for Defense Development and contractor Hanwha are working on. It will have 1,024 transmitting and receiving modules, the Seoul Economic Daily reports. Approval of the radar followed an investigation by a DAPA committee in 2017 and 2018 into whether South Korea could feasibly develop such a sensor; it reported the country could. The committee was set up in response to a directive to DAPA from parliament to reduce the risk of radar development.