In 1954, NATO publicised the specifications for the project through the Mutual Weapon Development Programme, announcing a competition which would involve major European aerospace industries. The theme of the contest was obviously the design of a fighter intended to undertake close air support, reconnaissance and light interdiction missions, NMBR/1. Empty weight should not exceed 8 000 lbs (3,630 kg) and the fighter should be easily maintained, with high manoeuvrability and reasonable speed at low level. Fundamental to the project was the capability to operate from grass strips, semi-prepared runways and small airfields. The aim of the project was to release close air support fighters from dependence on traditional large air bases which would surely be amongst the first targets to be destroyed in any conflict. The Italian design emerged as the winner from a number of submissions and would be produced by Fiat Aviazione. It was assigned the designation G-91. An order was placed in June 1955 for three prototypes and 27 pre-production aircraft.
Designed by Giuseppe Gabrielli, the first prototype flew on August 9, 1956, powered by a 1837-kg (4050-1b) st Bristol Orpheus B Or.1 turbojet. Control problems arose later during a high-speed level run, and the struc-tural failure of the tail caused the pilot to eject. After exhaustive tests on the tail unit the second prototype was fitted with a larger tailplane and a small ventral keel; the cockpit was also raised by some 63-mm (2.5-in). Powered by a 2200-kg (4850-1b) st Bristol Orpheus B Or. 3 turbojet, this aircraft flew for the first time in July 1957. It was equipped with one of the basic sets of armament: four 0.50-in (12.7-mm) Colt-Browning machine-guns, two mounted on each side below the cockpit and each having 300 rounds of ammunition. Alternative installations were two 20-mm (0.79-in) or two 30-mm (1.18-in) cannon (one each side), with 200 or 120 rounds respectively. The guns could be sup-plemented by two underwing packs of 25 51-mm (2in), 15 70-mm (2.75-in) or six 127-mm (5in) rockets, or two 250-kg (551 lb) bombs.
Construction was conventional and simple. There was an all-metal semimonocoque fuselage built in three sections, with an armoured cockpit fitted with a Martin-Baker Mk 4 ejection seat. The nosewheel retracted rearward under the cockpit, the main under-carriage inward into a central fuselage bay. A braking parachute was fitted at the base of the rudder. The first of the preproduction G91s was flown in February 20, 1958, and in August of that year the 103O Gruppo Caccia Tattici Leggeri (Light Tactical Fighter Group) of the Italian air force was formed for operational evaluation. After limited squad-ron service, 16 of the preproduction aircraft were modified in 1964 for use by the Italian aerobatic team, receiving the new designa-tion G91PAN (Pattuglia Acrobatica Nazionale).
Two basic service versions of the original G91 were developed: the 1959 G91R single-seat reconnaissance-fighter and the G91T tandem two-seat combat trainer/tactical fighter. Both had shortened and revised nose housings for three Vinten aerial cameras for forward and lateral oblique photography. Twenty-four G91R/Is and the same number of R/IAs (with improved navi-gational aids) were delivered to the Aeronautica Militare Italiano, together with 50 G91R/111 fighter-bombers. These models all carried the armament of four 0.50-in (12.7-mm) machine-guns, as did the 101 G91T/1 trainers also delivered. It was, however, the Federal German Luftwaffe which employed the largest number of G91s, receiving 344 G91R/3s, nearly 300 of which were built in that country by Dornier, Heinkel and Messerschmitt. Fifty Italian-built G91R14s and 66 Fiat/Dornier-built G91T/3s, all with twin 30-mm (1.18-in) DEFA cannon, also served with the Luftwaffe. The German G91Rs (transferred later to the Portuguese air force) had two additional underwing pylons inboard, each capable of carrying 227 kg (500 lb) of stores.
The initial production variant was the G91R-1 which entered service with the Italian air force at the beginning of the 1960s, this air arm eventually acquiring over 100 similar aircraft. However, it was West Germany which proved to be the major customer, receiving a sizeable batch of Fiat-built G91R-3 aircraft plus a substantial number built under licence by a consortium comprising Dormer, Messerschmitt and Heinkel. The first German-built example of the G91R-3 made its maiden flight from Oberpfaffenhofen during July 1961, and the type entered service with Aufklärungsgeschwader 53 at Leipheim during 1962.
In the event, Germany's Luftwaffe also operated some 50 or so G91R4 aircraft, originally being earmarked for equal distribution between Greece and Turkey, which eventually rejected them. After a fairly short career with the Luftwaffe, 40 of these aircraft were transferred to Portugal alongside a number of G91 R-3s made redundant when the Luftwaffe re-equipped its light attack units with DassaultBreguet/Dornier Alpha jets in the late 1970s and early 1980s.
In the spring of 1965 details were announced of the G91Y, a single-seat twin-jet tactical fighter-bomber developed as a follow-on type for the AMI. Based on the two-seat G91T airframe, it incorporated two 1235/1850-kg (2722/4078-1b) st General Electric J85-GE-13A afterburning jet engines, mounted side by side in the rear fuselage and giving 60% more total thrust. Two prototypes (converted G9ITs) were flown on December 27, 1966, and September 1967, respectively. In July 1968 the first of 20 preproduction G91Ys appeared, and orders for a further 45 followed. Delivery of these was completed by mid-1976, and they were in service with the 1O and 13O Gruppi in Italy. They have provision for JATO (jet assisted takeoff) units which can halve the distance required for takeoff, and three nose-mounted cameras are fitted as standard. Armament comprises two 30-mm (1.18-in) DEFA cannon in the nose, and four under-wing hardpoints for up to 1814 kg (4000 lb) of bombs, rockets or napalm canisters.
During the 1960s within the ranks of the AMI General Staff (Stato Maggiore), the idea began to emerge of a new type with higher performance than that offered by the G-91R. To avoid protracted development and coincident cost increases, Gabrielli based his design on the same aerodynamic formula as that adopted by the G-91R. Similarly, the requirements specified by the AMI were in part based on those of its predecessor and included high manoeuvrability, high subsonic speed (Mach 0.95) at low level, mechanical simplicity, high operational efficiency and the ability to operate from small fields. Payload and radius of action were greatly increased and a more complex electronic fit was embodied, although this was relatively simple to achieve since the G-91R carried only rudimentary equipment. The new aircraft would be equipped with a navigation and attack system, with a gyroscopic collimator as well as an inertial platform, which at the time constituted a useful electronics fit. Consistent with thinking of the period, no passive or active ECM package was planned. Adoption of a twin-engine formula using two general Electric J85-GE13A turbojets was planned to give the type good flight safety. Nevertheless, the configuration of the air intake system was designed in a way that later caused problems and the loss of some aircraft. The front air intake, shared by both power units, splits into a 'y' form near the cockpit and it was this layout which was to be the source of a number of failures.
In comparison with the G-91R, the G-91Y features a 24 per cent increase in empty weight, a 73 per cent improvement in payload, a 63 per cent increase in take-off power and double the fuel load. The J85 provides 1,235 kg of 'military' thrust, climbing to 1,850 kg when afterburner is selected. The G-91Y was also designed to accept JATO rockets and can utilise a catapult device for take-off, something that necessitated enlargement and strengthening of certain undercarriage components. Installation of a ventral hook allows the use of arrester barriers.
With regard to electronics, besides the normal communications equipment, the G-91Y possesses an inertial platform, a position and homing indicator (PHI), a doppler radar, an air data calculator, a radar altimeter, a radio compass and a gyroscopic calculator. Armament comprises two 30 min DEFA 552 cannon with 125 rounds each. External stores are fixed to four wing pylons, two on each side, with a maximum load 1,815 kg. The Yankee is also equipped for daylight tactical reconnaissance and carries three lateral TA-7M2 cameras and a forward-looking KA-60C camera with a rotating prism for panoramic work. All cameras are housed in the nose section.
The first prototype G-91Y made its maiden flight from Turin-Caselle on 27 December 1966 and was subsequently used to explore the flight envelope. The second prototype was used for weapons trials and electronic system tests and featured modifications to the windscreen as well as the nose contours. It also had a double engine cooling air intake replacing the original, which was located at the base of the dorsal fin.
The flight test programme was rapidly brought to a conclusion and in July 1968 the first production example was flown. Nevertheless, deliveries of the type to operational units only began two years later, as problems concerning the engines had first to be resolved. The first unit to receive the type was the 101st Gruppo of the 8th Stormo, which deployed temporarily to the experimental base at Pratica di Mare for transition to the new aircraft.
For nearly four years, the Gruppo was the only one to operate the G-91Y and it struggled to achieve operational status and overcome the problems that construction of only two prototypes had prevented the manufacturer from solving. Later, in 1974, the 13th Gruppo of the 32nd Stormo began transition to the new type which was at last adjudged to be fully operational.
In total, production of the G-91Y amounted to some 65 aircraft (MM6441-MM6495 and MM6951-MM6960), to which should be added two prototypes (NIM579 and MMS80). The final batch of eight (MM6961-MM6968) was cancelled and the last Yankee was assigned to the 32nd Stornio in 1976.
In addition about 160 examples of the two-seat G91T trainer variant were also completed and this has also seen service with Italy, Portugal and West Germany.
The G-91 was also evaluated by the Schweizerische Flugwaffe (Swiss Air Force) as a possible Venom replacement. In the light of Swiss interest, Aeritalia modified a production example (MM6461, c/n 2023), transforming it into the prototype 'G-91YS'. These modifications comprised the addition of two underwing pylons capable of launching the AIM-9 Sidewinder and the replacement of the nose cameras by a Swedish-designed laser aiming system. The new nose was slightly elongated and two ventral fins were added to the two already present. Maximum takeoff weight rose from 8,700 kg to 9,000 kg, thereby increasing the take-off run by around 20 per cent. The new version was a finalist in a fly-off competition with the Vought/LTV A-7 Corsair II but negotiations were suspended and no other nation showed interest in buying the Aeritalia fighter.
Principal versions - G91 (initial light attack model), G91R/1 (attack and reconnaissance model), G91R/1A (version with improved navigation system), G91R/1B (strengthened and updated version of the G91R/ 1A), G91R/3 (West German model with two 30-mm cannon, Doppler navigation and other im-provements), G91R/4 (G91R/3 variant with the armament of the G91R/1), G91T/1 (Italian two-seat trainer with two 0.5-in/12.7-mm machine guns), and G91T/2 (West German version of the G91T/1).
Engine: one 5,000-lb (2,268-kg) thrust Fiat-built Rolls-Royce (Bristol Siddeley) Orpheus Mk 803 turbojet.
Maximum speed 675 mph (1,086 km/h) at 4,920 ft (1,500 m)
Initial climb rate 6,005 ft (1,830 m) per minute
Service ceiling 42,980 ft (13,100 m)
Radius 199 miles (320 km).
Empty weight: 6,834 lb (3,100 kg)
Maximum take-off weight: 12,125 lb (5,500 kg).
Wing span 28 ft 1 in (8.56 m)
Length 33 ft 9.5 in (10.30 m)
Height 13 ft 1.5 in (4.00 m)
Wing area 176.75 sq ft (16.42 sq.m).
Armament: four 0.5-in (12.7-mm) machine guns / 1,500 lb (680 kg) of disposable stores.
FIAT G 91 R3 Gina
Engine: Bristol Siddeley Orpheus 801, 22269 N / 2270 kp
Length: 33.05 ft / 10.06 m
Height: 12.992 ft / 3.96 m
Wingspan: 27.986 ft / 8.53 m
Max take off weight: 12502.4 lb / 5670.0 kg
Max. speed: 580 kts / 1075 km/h
Service ceiling: 42979 ft / 13100 m
Range: 999 nm / 1850 km
Armament: 4MG 12,7mm 2MK 30mm
Span: 8.60 m (28 ft 2.5 in)
Length: 11.70 m (38 ft 4.5 in)
Height: 14 ft 7.25 in / 4.45 m
Gross weight: 6050 kg (13338 lb)
Maximum speed: 1030 km/h (640 mph) at 5000 ft / 1525 m
Service ceiling: 40,000 ft / 12190 m
Engines: two General Electric J85GE-13A turbojet, 1851 kg (4080-1b) afterburning thrust.
Maximum speed 1110 km/h (690 mph) at SL
Maximum speed 1038 km/h (645 mph) at 30,000 ft / 9145 m
Cruise: 497 mph / 800 kph at 35,000 ft / 10670 m
Initial ROC: 17,000 fpm / 5180 m/min
Time to 42,000 ft / 12200m; 4 min 30 sec
Service ceiling 12500 m (41,000 ft)
Combat radius at sea level 600 km (372 miles)
Ferry range 3500 km (2,175 miles)
Empty weight 3900 kg (8,598 lb)
Maximum take-off 8700 kg (19,180 lb).
Wingspan 9.01 m (29 ft 6½ in)
Length 11.67 m (38 ft 3½ in)
Height 4.43 m (14 ft 6 in)
Wing area 16.42 sq.m (176.74 sq.ft).