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Aviation History
1958
1958 - 0680.PDF
696 FLIGHT FIAT G.91 First-generation NATO Strike Fighter THE French, German and Italian governmentshave now definitely chosen the G.91 as thestandard LWSF (lightweight strike fighter) for NATO service "until 1961." It appears that this deci-sion was reached on the condition that, after 1961, a French aircraft—almost certainly a developedBreguet Taon—would replace the G.91. The "mission profile" required of the LWSF inthe original NATO specification is now well known. This and the associated operating requirementscalled for a simple, robust aircraft which could be easily serviced with the minimum of ground equip-ment, provide the greatest fire-power and operate from unprepared fields. A manned aircraft wasneeded to provide the flexibility in attacking targets of opportunity, with which a missile could not deal.NATO is still convinced that machine-guns consti- tute the most effective weapon against "soft-skinned" targets. The risk to the pilot is considered relatively low, because the fast low-level approachaffords an excellent opportunity of surprise. The G.91 fills the requirements well, for, with the leading-edgeslats of the G.91A version, it can take off or land on about 600 yd of grass, and its fire-power is equivalent to that of a large fighter.Its manoeuvrability allows it to operate in mountainous country, to position itself rapidly to attack a chance target and to escapefrom ground fire by climbing rapidly out of range. Great care has been taken to make the G.91 easy to maintain, for operation fromadvanced bases. As the type will be used by several air forces, it will be able to operate with almost any NATO command. Principal dimensions of the G.91 are: span, 27ft 1 lin; length,34ft 2in; height, 13ft lin; wing area, 177.5 sq ft; and sweep at 25 per cent chord, 37 deg. Horizontal tail-surface area is 26.8 sq ft.The Bristol Orpheus 3 confers on the G.91 a thrust/wing-area ratio of 26.6 lb/sq ft. At a gross weight of about 11,000 1b, whichincludes external stores, thrust/weight ratio is 2.35. With machine- guns and ammunition, but no external stores, the ratio is 2. Equip-ment and internal arrangement were laid down in close collabora- tion with the AGARD committee. Both cockpit and tank baysare protected by steel and the nine tanks are close to the e.g. Replacement of major components such as wings and engine canbe carried out by very small teams of men working in the field. Aileron and elevator control is by irreversible hydraulic jackswith spring feel and manual reversion, while the rudder is "manual" and carries a yaw-stabilizer. Cockpit equipment in-cludes pressurization, electronic temperature control, ventilation, oxygen, windscreen de-icing, anti-g suit and a Martin-Bakerlightweight, fully automatic seat. Cockpit dimensions have not been specially restricted. Engine-starting takes 40 sec and thehydraulic, powered wheel-brakes are used for steering. On take-off, rudder becomes effective at 50 kt, 40 deg of flap maybe used, and stability is positive in all three axes immediately after unsticking at about 100 kt. Initial acceleration on take-offwith full external load is over 0.4 g; and accelerations of this order can be obtained in the air. At 5,000ft, level speed can be increasedfrom 280 to 400 kt in 30 sec; and 460 kt are exceeded in less than a minute. The G.91 can reach 377 kt 90 sec after "brakes off." Both static and dynamic stability in all three axes and at varioustrimmed speeds remain positive. The stall comes at about 110 kt, Fiat G.91 fixed armament of four 0.5in machine guns and ammunition tanks is mounted on the hinged panels, as shown. External loads for each wing, in addition to the fuel tank shown at left, include 5in HVARs, honeycomb packs of 30 folding- finned unguided rockets, and six 3in rockets. It is also reported that Nord 5103 command-guided rockets can be fitted for ground attack. heralded by buffeting at over 130 kt. Little height is lost. TheG.91 may be trimmed "hands-off" at speeds below 1.3 Vsl. Maximum sea-level I.A.S. is about 580 kt and 0.91 Mach can bereached at 20,000ft. At 30,000ft Mach 1 is easily exceeded in a shallow dive. The yaw damper in the rudder circuit makes theG.91 a particularly good platform for both guns and bombs. Four-g pull-ups are regularly performed at Mach numbersbetween 0.96 and 0.98. Extension of the airbrakes, taking 4 sec, produces a positive acceleration of 0.4g at 350 kt; and nose-downtrim when retracting them can be_ held with a stick-force of 4£ to 6j lb. Bombs may be dropped with airbrakes extended. At cruising speed the G.91 can achieve a rate of roll of 250deg/sec, while at 150 kt 100 deg/sec are still available. Only slight adverse yaw results from rolling. The low wing is sensitiveto ground effect, considerably assisting landing. The above figures refer to fully loaded G.91s carrying two 500 lb bombs. Some 20 per cent of the gross take-off weight of the G.91consists of weapons; and 50 per cent of this gross weight is accounted for by fuel and armament combined. The range ofweapons includes 0.5in, 20 mm or 30 mm guns, tactical nuclsar weapons, air-to-ground rockets and missiles. The G.91 can remainairborne for one hour at sea level and, operating from fields close to the front, can spend most of that time ranging over enemyterritory. The aircraft can also be rapidly converted to carry a full range of still and motion cameras for oblique or verticalphotography at all altitudes. Single hydraulic jacks operate each undercarriage leg while afourth jack operates a cable linkage serving the main leg up-locks and fairing-door latches. All three legs are locked down by boltsoperated by main hydraulic pressure. In emergency, the nose- wheel is lowered by pressure tapped direct from the accumulator,while the mainwheels drop under gravity after doors and leeks have been unfastened. The nosewheel rotates during retractionto lie flat in the fuselage. Emergency braking power is also avail- able. The flaps are extended by screw-jacks operated from acommon flexible-shaft system by an electrical actuator. Nine tanks are included in the fuel system, transfer being by air pressure andbalancing by fuel flow-proportioner. (Left) a 500 kg bomb on the star- board pylon. Note how the pylon is "wrapped" round the leading edge. (Right) the Messier levered main- wheel suspension, hydraulic disc brake and Kleber Colombes low- pressure tyre.
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