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Aviation History
1988
1988 - 0021.PDF
Top Principal new technologies employed on the T-4. Above Typical training progression for JASDFpilots—from T-3 to F-15. The T-4 will replace the T-1, T-33, and eventually some elements of the T-2 syllabus tailplane wake during spins, and consequently it has to be quite large: A high aspect ratio was selected to gain the height necessary to allow a large propor tion of the fin and rudder to remain in "clean" air, even at extreme angles of attack when the fuselage is shedding a disturbed wake. The dorsal root extension restores the fin-stall sideslip angle to a reasonable value. The XT-4 is exhibiting the excellent high-angle-of-attack and spin character istics predicted from free-flight model tests and vertical windtunnel trials, according to Air Proving Wing personnel, who confirm that hands-off spin recovery has been demonstrated in the clean configuration. The JASDF regards predictable recovery characteristics as essential, so there is no inhibition on pilots receiving sufficient spin training before they are faced with less forgiving FLIGHT INTERNATIONAL, 2/9 January 1988 front-line types such as F-4. Gen Hiroyasu Takao, director for air development of the TRDI and previously commander of the Air Proving Wing, shares the widespread enthusiasm for the reliability of the Ishikawajima-Harima XF-3 turbofans which power the XT-4. Developing the aircraft around indige nous engines was an important plank in the JDA's long-term technological devel opment strategy, and the associated risks were accepted. In the event, the reliability of the XF-3 has surpassed expectations. This is fortuitous, because only 14 have been available for the four flight-test aircraft. Gen Takao says he raised a few eyebrows at the US Air Force Arnold Engineering Development Centre in 1982 when he took only two XF-3s for altitude- chamber trials, and returned to the United States for the second phase of testing with only one. Design policy Design policy of the XT-4 for the "medium jet trainer mission" demanded easy handling character istics to simplify the transition of trainees from the piston-powered T-3 after 70hr, together with sufficient performance to cover "secondary" training and "support" missions. Econ omy of operation had to be comparable with that of competitors such as Hawk and Alpha Jet, while development costs had to be held on a tight rein. It was considered important to match the airframe to a domestic engine—the first all-Japanese prod uction turbofan—a decision vindicated by the reliable performance of the IHI XF-3. Considerable emphasis was also placed on low-distortion intakes to facilitate spin training. The XT-4 also had to incorporate new technology to help extend its service life into the next century. Accordingly, some 4-5 per cent of the structure, by weight, is composite. Carbonfibre is used for the fin, rudder, ailerons, and speed-brakes, as well as for the trailing edge of the all-moving tailplane. Carbonfibr^/Kevlar compo nents include the rear-wing skins, the wing/fuselage fairing, the radome, flap trailing edges, nose undercarriage doors, and tailcone. The rest of the structure (which is designed and built using CADCAM) is almost entirely of conventional alumi nium alloys, produced in Japan. The main wing panels, which form integral fuel tanks inboard of the dogteeth, are milled from the solid and, for the first time in Japan, creep-formed at the dogteeth to adjust washout angle. Bulkheads are also milled, but most other structures consist of chemically etched skins, riveted to stringers. No bonding is used. Avionics are digital for small size, low weight, and high reliability. They are "designed and produced in Japan under American basic technology," according to Gen Takao, although UHF communications, Tacan, and intercom are indigenous. The attitude and heading reference system at the core of the XT-4's instrument system incorporates Honeywell laser gyros— their strapdown design, devoid of moving parts, being appropriate for such a highly manoeuvrable aircraft, which also features a Hud "built under Kaiser basic technology", and an air data computer incorporating Sperry transducers. Most systems, such as the 3,0001b/in2 duplicated hydraulics and the air-cycle air-conditioning, are conventional, but the US-licensed onboard oxygen generation system (Obogs) is unusual in a trainer. Signifi cant Japanese development work was nefeessary to suit it to the XT-4. The zero-zero rocket seats are built under Stencel licence, and the US-designed explosive cord, which facilitates ejec tion, is made in Japan, as are com ponents of the British q-feel system. 19
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