KAI Proposes Smaller KF-X Design

By Minseok Kim, Bradley Perrett
Source: Aviation Week & Space Technology

Especially in the twin-fin version, the KFX-E has many external similarities with the C103, ADD's tail-aft design. (The C203 has horizontal stabilizers forward.) This is because KAI has used the same technical studies. The leading- and trailing-edge sweep angles of the main and tail planes are the same in the KAI and ADD designs, and various edges are similarly aligned. The same inlet duct design, with a boundary layer diverter, appears to have been used. However, fuselage width and volume are noticeably smaller for the KFX-E, reflecting the lower weight of the aircraft and perhaps F-16 design roots—though it takes a keen eye, and maybe some imagination, to see much of the F-16 in KAI's drawings. At 3.63 tons, the KFX-E's internal fuel capacity is only 14% more than that of the U.S. Air Force's current F-16C Block 40.

If the KFX-E carries an external tank on its center under-fuselage hard-point, it cannot use two stations on the corners of the fuselage. Altogether, it has nine hard-points; the C103 has 10. Depending on whether the chosen engine—either the Pratt & Whitney F100 or General Electric F110—can deliver more thrust than it does in the F-16, the KFX-E will accelerate more slowly than the U.S. fighter. The bigger wing will surely generate more drag, too.

The KFX-E borrows from the light-attack version of the T-50, the FA-50 of 8 tons empty. KAI Vice President Seongseop Jang told the Sept. 26 seminar at the Jungwon air force base that the designers proposed “using existing FA-50 parts with minimum modifications for the KFX-E development.” So the KFX-E would use or adapt the FA-50's flight control, auxiliary power, electrical, environmental control and oxygen systems, as well as the landing gear.

KAI stresses that the KFX-E is not an adapted FA-50 (or T-50). This is important because South Korea cannot modify the T-50 design without U.S. authorization. At the seminar, KAI did not address legal restrictions on its proposal. But the KFX-E has probably been designed with at least close reference to the T-50 family: A telling point is that a single fin is offered as standard, while the desirable twin-fin configuration is an option. The structure for the single fin could be derived from the T-50's.

Jinsoo Cho, president of the Korean Society for Aeronautical & Space Sciences, criticizes KAI's proposal, arguing that South Korea needs an indigenously designed aircraft to avoid foreign interference in international sales and upgrades. Cho, an influential figure in South Korean aerospace policy, seems to take for granted that the KFX-E is not entirely South Korean.

The role of foreign partners in the KF-X development is still in question. Indonesia has been working with ADD on the design. Its attitude to KFX-E is unclear. Also uncertain is how South Korea can acquire technology needed for a mainly indigenous KF-X. The F-X Phase 3 bidders instead offered updates of their own aircraft.

Whichever airframe and engine are chosen for KF-X, only one set of South Korean avionics is available. Following initial production with foreign avionics, the KF-X would switch to systems developed mainly by LIG Nex1. That would include an active, electronically scanned (AESA) radar that, according to the company and ADD, will perform about as well as the Northrop Grumman APG-80. The South Korean radar has around 1,000 transmitting-and-receiving modules. Software for functions including ground-moving-target indication is already developed, while 95% of technologies related to the antenna and 75% of test-related technologies have been acquired. Foreign help will be needed in testing.

LIG Nex1 has revealed plans to develop an electro-optical targeting system similar to Northrop Grumman's Litening II targeting pod. Signal-processing techniques and a high-resolution infrared camera are ready, but the company says it lacks the capability to develop an internally mounted targeting system, such as the F-35's.

The radar warning receiver for the KF-X will be similar to those in established fighters, such as the F-16. Technologies needed for that system are ready. It will be able to detect low-probability-of-intercept radars, says LIG Nex1. But antennas will not be conformal. The electronic warfare system of the indigenously developed ALQ-200K pod will be adapted for internal installation. A digital radio-frequency memory was developed in 2012. The KF-X will have no towed decoy.


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