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Aviation History
1988
1988 - 0020.PDF
They derive equal pleasure from having brought both the airframe and its twin Ishikawajima-Harima XF-3 turbofans to the verge of production deliveries within the cost target. Minimisation of military expenditure is the subject of perennial political pressure in Japan, and since only 2 per cent of that budget is currently allocated for research and development, tight control of programmes is a necessity, according to Ryozo Tsutsui, director-general of the Japan Defence Agency's Technical Research and Development Institute (TRDI). He says that the United States spent five times more developing the abor tive T-46 than Japan has allocated for the XT-4 and its engine. In common with many air forces, the JASDF relies on a mixture of aircraft for training. Pupils start on the piston- powered Fuji T-3 (based on the Beech Mentor) before progressing to the Fuji T-l (a two-seat Sabre lookalike), and thence to the Lockheed T-33, before moving on to the twin-Adour-powered Mitsubishi T-2 advanced supersonic trainer. Why do old straight-wing T-33s follow the swept-wing T-ls in the syllabus? The answer would be the same in many air forces: "Because we happen to have them". Pragmatism will begin to give way to planning, however, as the first production model of Kawasaki's new XT-4 trainer flies next July, ready to enter service in September. Eleven more will join it by March 1989, with a second batch of 20 scheduled for delivery during the year. Known by then as the T-4 (having lost its experimental status), the aircraft will gradually replace both the T-33 and the T-l, whose performance it outstrips with consummate ease, as Flight witnessed at the JDA Air Proving Wing's base, adja cent to Kawasaki's Gifu factory near Nagoya. Eventually the T-4 will also allow the supersonic T-2 to be phased out of some parts of the training syllabus, so the abil ity to demonstrate transonic aerodynamic effects was a major design requirement. Consequently, although the aircraft is designed for high manoeuvrability, low operating cost, and high reliability, it also boasts level-speed capability in excess of Mach 0 • 9, compared with Mach 0 • 86 for the Alpha Jet and the Hawk's Mach 0 • 88. The XT-4's published initial climb rate of "more than 10,000ft/min" (at normal take-off gross weight) is also fairly competitive with the ll,000ft/min to 12,000ft/min of Hawk and Alpha Jet. Given the XT-4's lower wing loading and 20 per cent greater thrust-to-weight ratio, however, Flight believes that it climbs considerably faster than the Japanese are prepared to admit in the brochure. This would appear to be confirmed by Ryozo Tsutsui, who cites climb rate as the XT-4's most significant performance advantage over the competitors. It has also demonstrated a ceiling of more than 50,000ft. The XT-4 is no flimsy device, trading structural longevity for performance. Airframe integrity has been proved by static and fatigue tests, which have now been completed on two separate airframes, giving clearance for a 7,500hr life (Hawk 6,000hr plus), assuming multiple touch- and-goes during lhr 20min sorties. Subsequent damage-tolerance tests of the fatigue specimen have also been carried out. Vertical dives to the dynamic pressure limit of 560kt calibrated airspeed were being flown during Flight's visit to Gifu. When clean, the XT-4 will pull an instantaneous 7 • 33g, aided by vortex lift from its small knife-edged leading-edge root extensions (lerxes), and can sustain 3g at 20,000ft between Mach 0 • 6 and 0 • 7. It is said by Air Proving Wing flight-test personnel to be more manoeuvrable than their F-15s in the subsonic regime. Although the XT-4's thick-section, almost flat-topped, transonic aerofoil was developed jointly by Kawasaki and the TRDI for low drag at high speed, impec cable high-angle-of-attack handling and spinning characteristics were among the top design priorities for the aircraft. Camber and washout have been care fully controlled along the span, while the leading-edge dogteeth enhance high-g departure characteristics, suppressing wing drop and pitch-up at the stall, while throwing vortices to energise airflow inboard of the ailerons for enhanced post- stall lateral control. Vortex generators have proved to be unnecessary. The XT-4's fin is set well forward on the fuselage to minimise interference from In addition to engine trials, the first XT-4 has conducted flutter tests. The second has been devoted to airframe load analysis and stability and control, while number four has flown the spinning trials. Number three is a production-standard two-seater XT-4 Development schedule 1981 Design • Rollout • First flight No1 • No2« No3)» No4 1986 1987 Delivery of prototypes Manufacture of prototypes Production deliveries begin Flight test Static test Fatigue test 18 FLIGHT INTERNATIONAL, 2/9 January 1988
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