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Aviation History
1968
1968 - 0975.PDF
fLIGHT International, 20 June 1968 Str931 7/ie first prototype Fiat G.9IY has now almost completed the airframe/ engine development flight trials that began 18 months ago. Pro- duction aircraft will have the Milplane raised an inch, and a slimmer rear fuselage to eliminate buffet at high speed. The two dorsal fins have been found superfluous end will not be retained Fiat G.91Y TWIN JETPIPES, set close together, in place of one is theonly feature which readily distinguishes the new FiatG.91Y strike/reconnaissance aircraft from its well known predecessors. This is deceptive because, as well as a 60 per cent total increase in thrust from two engines instead of one, the G.91Y has a completely re-engineered structure for greater efficiency and higher weights, is fitted with an up-to-date, fully automatic nav/ attack flight system, and has greatly improved manoeuvrability conferred toy the addition of wing leading-edge automatic slats. Thus, without going .beyond the existing subsonic envelope, the G.91 has been stretched to produce this most useful new mini-strike aircraft with all the advantages of being based on a well-proven design. Almost through the manufacturer's tests, the G.91Y is about to begin the official acceptance trials of the Italian Air Force. Meanwhile, Fiat is building op the production line for the airframe, engine (under licence from General Electric) and the installation of the flight system—with the promise of IAF squadron service next spring and export deliveries in just over a year for orders placed now. At $1.7 million (£710,000) each for a fully equipped G.91Y it is no surprise that many air forces are interested. A two-seat G.91 YT could be flying in less than two years but so far this has not been ordered. The best prospects at present are the Luftwaffe (already a big user of the G.91) and the Swiss Air Force (in competition with the Mirage 5, the Northrop F-5 and others as a Venom replace- ment). Israel and South Africa are also keen on the type but for the moment the Italian Government has vetoed these politically charged sales. The Turin Show saw the first public flying demonstrations of the G.91Y prototypes (002 was displayed only statically at Paris last year). Fiat also announced the results of 18 months' flight testing and pre-service operational trials. The first pre- production aircraft (003, to fly in July) was displayed in an outwardly complete state on the Fiat stand in the town^centre exhibition, with 001 (used for airframe/engine development) and 002 (for operational systems and weapons trials) flying in the show at Caselle. Twenty pre-production G.91Ys are on order for the Italian Air Force; all are to be delivered by next spring and it is expected that production will continues ^aight into a batch of 55 for the IAF. The two prototypes have accumulated over lOOhr in the course of some 79 flights, and 001 is 90 per cent through the fosic airframe/engine development. The nav/attack flight system and weaponry (but not the reconnaissance camera) was fi installed in 002; and the initial trials of this equipment are complete, and the aircraft is to be delivered shortly to the lAF operational test centre, the Reparto Experimentale atp ratica di Mare near Rome. No 003 will complete the manu- facturer's trials on the equipment before delivery to the RE, ^ the next three aircraft will be sent directly they have flown. The first IAF operational squadron of G.91Ys will be formed in March or April next year. Squadrons already experienced on the G.91 will be first to receive the -Y, but it is highly likely that the type will in time replace the F- and RF-84Fs in IAF service. Development of the G.91Y is financed by the Italian Government who will also continue to promote the type in export markets—both the supply of complete aircraft and licence production. The IAF procurement is under the banner of the requirement for a lightweight tactical strike/reconnais- sance aircraft. The nearest relative of the G.91Y is the G.91T two-seat trainer (the first two prototype -Ys are actually modified -Ts). A fuel tank occupies the second-seat space of the -T, and this doubles the tankage of the G.91 for an increase in range, despite the higher fuel consumption of the two J85-13As (thrust, 2,720lb dry, 4,0901b with reheat) compared with the one Orpheus (5,0001b thrust dry). The structure of the produc- tion -Y differs mainly in the wing (now largely of chemically machined panels) and in the main undercarriage, which has a larger shock strut, additional sideways bracing and larger- section tyres and wheels plus bigger brakes. For a 24 per cent increase in empty weight, compared with the equivalent- mission G.91R, the -Y has up to 60 per cent higher gross weight, and up to 73 per cent more payload. The revised undercarriage makes the -Y equally capable of the well-known rough-field abilities of the G.91, and JATO again gives an almost STOL performance from a semi-prepared surface. Compared with the F-84F, for instance, the G.91Y can perform an equal sortie but from a 4,000ft-long semi-prepared runway instead of a 10,000ft concrete runway, and with twin-engined security. To go with the doubling of the warload capacity and operational range of the G.91Y has been the adoption of an integrated nav/attack flight system with a head-up display •for the pilot. Basis of the system is a two-axis gyroscopic platform and Doppler feeding a position and homing indicator (PHI) computer. An air-data computer is stand-by for the Doppler. Up to 12 pre^fixed stations can be dialled into the nav /attack system during any moment of flight, with track-to- steer and distance-to-go presentation. The gyroscopic gunsight computer is also linked to the system, and a radio altimeter is provided to assist in the low-level attack primary mission. The main elements of the system, and their manufacturers, are as follows: Sperry SYP twin-axis gyro platform licence-made n Italy by Salmoiraghi; Computing Devices of Canada PHI 5C-15 licence-made by OMI; Bendix DRA-12 Doppler licence-made by FIAR; Garrett^AiResearch air-data computer licence-made by Microtecnia; Ferranti ISIS B gyro-gunsight computer; Honeywell AN/APN-471 radio altimeter licence-made by Fiat; Specto head-up display licence-made by OMI; and
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