Although the RAF had not selected the Fo 141 Gnat for service in a front-line role, it did have a requirement for an unarmed, two-seat advanced trainer to replace the de Havilland Vampire T.Mk 11. Folland had already considered a training version of the Gnat as a private venture, and this was shown to be able to meet Air Ministry requirements including a 100 knot (185 kph) landing speed.

Folland Fo.144 Gnat Article

To make the Gnat a two-seater, it was necessary to remove the standard fixed gun armament of two 30 mm ADEN cannon located in the cheek intake fairings, and relocate the fuel tanks, but no major structural alterations were required. The most significant change was a new wing, increased in area by 3.72sq.m and with additional fuel capacity, which reduced the fuel storage requirement in the fuselage, making room for additional equipment. The forward fuselage was increased slightly in length, the tail surfaces enlarged, and outboard ailerons and conventional inboard flaps replaced the inboard ailerons of the fighter version. Power was to be supplied by a 1919kg thrust Orpheus 100.

Follands had already designed and built a new wing for a proposed development of the Gnat fighter for naval use, with improved low speed performance. By adopting the simpler and more efficient construction of this wing, which was reduced in thickness from the eight per cent t/c ratio of the original Gnat, to a mean value of seven per cent, while retaining the symmetrical R.A.E. 102 (mod.) section, Follands were able to offer a larger area for the trainer to give the necessary reduction in landing speed without a major weight penalty. It had the additional facility of increased fuel capacity.

A Ministry of Supply design study contract was awarded to Specification T.185D in the autumn of 1956 and a prototype contract was negotiated during 1957.

Apart from performance, one of the main requirements was for the inclusion of an advanced level of equipment, comparable to that in operational aircraft under development although not then in service. This included new flight and navigational instrument presentation to OR.946, provision of engine anti icing, centralised failure warning system, installation of liquid oxygen facilities and many other very advanced items.

The OR.946 flight instrumentation occupied space on the instrument panel than in the earlier Gnat by the deletion of the gun sight and bullet proof windscreen framing. OR.946 concentrates all essential flight information on two display units occupying the entire centre of the panel. On the left is the roller blind F.4 attitude indicator, which takes the place of the normal artificial horizon, and provides a non toppling reference in all flight conditions, while on the right is the Mk.1 display unit for TACAN and other navigational equipment.

Additional space for the “black boxes” making up the Gnat T.l’s sophisticated equipment, including TACAN, ILS and the Air Data Computer, was found by enlarging the spine fairing of the original fighter behind the cockpit canopy. The canopy itself, as well as the windscreen, was completely new, the former being of the aft hinged clamshell type, blown from a single piece of Perspex. To protect the rear occupant in case of canopy jettison, the Gnat trainer has an additional internal windscreen over the duplicated instrument panel.

An ejection escape system was developed specially for the trainer by Folland, using two of the company’s own lightweight seats. Work on these was started by Folland in 1953, using a SAAB type seat layout as the original basis, but development had since continued entirely independently. The Mk. 4GT1 (front) and 4GT2 (rear) ejection seats in the Gnat have 80 ft/sec (24.4 m/sec) telescopic guns for adequate fin clearance at all airspeeds, and are cleared for use down to runway level at speeds of 90 650 knots (106 1204 km/h). They are used in conjunction with GQ Mk 35 back type parachutes, plus Type X personal survival packs in the seat pans, and have 6 ft (1.82 m) diameter drogues for man stabilisation if ejection takes place above 10,000 ft (3050 m). An extractor ‘chute on the seat helps immediate separation, with a drogue sock pulled off by a static line as the seat leaves the aircraft. After initiation by face blind or seat pan handle, operation of the seats is fully automatic.
Engine installation was not changed from the original Gnat except that a slightly de rated Bristol Siddeley Orpheus was adopted in the interests of improved fuel economy and longer overhaul times. Secondary modifications provided intake anti¬-icing from hot air tapped from the engine compressor through to the entry guide vanes and bullet, and drive for a larger electric generator. In its standard RAF form, the Gnat trainer was powered by an Orpheus 101 developing 4230 lb (1920 kg) thrust for take off, but it is offered in addition with the higher powered (4,720 lb (2135 kg) Orpheus 501 if extra altitude performance is required. A Gnat trainer (XM698) has also flown with the fighter engine, which is the Orpheus 701, with a similar thrust to the 500 series.

Following the finalisation of the design, a contract for fourteen development aircraft to spec T.185P was placed 7 January 1958, and the first prototype Fo.144 Gnat trainer made its initial flight in the hands of Sqdn. Ldr. E. A. Termant on August 31, 1959 from Chilbolton airfield. The first eight of these aircraft were mainly employed for per¬formance testing and development of the various systems, including improved longitudinal control. The Ministry did not at first place a production order as they were concerned about the size and ability of the company to take on a large order. Following the take-over of Folland by Hawker Siddeley Aviation (becoming the Hamble division), after successful evaluation by the various official bodies concerned, a production order was placed in July 1960 for thirty aircraft for use as advanced trainers, and an additional twenty were ordered a year later. A further order for forty one followed in March, 1962. These were being turned out at the requested rate of four per month. The last Gnat T.1 for the RAF was delivered in May 1965.The Gnat trainer was then being offered on the overseas sales market.

Yugoslavia ordered two Gnat F.1s for evaluation; the first aircraft flew on 7 June 1958 and both were delivered to Yugoslavia by rail. The aircraft were flown by the flight test centre but no further aircraft were ordered. One aircraft was destroyed in a crash in October 1958 while the other is preserved and on display in Serbia.

Hydraulic power is used as the primary means of operating ailerons and the all flying tailplane, with manual reversion in case of failure of the hydraulic system. Compared with the original Gnat, which had combined inboard ailerons and flaps, the trainer has a conventional flap and outboard aileron arrangement. The ailerons have automatic control stops which just about halve their range of movement to eight per cent at speeds above 150 knots IAS (278 km/h) to limit the rate of roll and prevent inertia coupling.
Effective longitudinal control results from the hydraulic¬ally powered flying tailplane, which like the ailerons has spring¬feel. A “Q” gearing mechanism reduces the amount of tailplane movement for a given stick displacement as speed increases, which improves handling at high indicated airspeeds, but the stick force per g is still very light above 400 knots (741 km/h). Tailplane trimming is via an electric actuator and thumb switch on the control column. In the event of hydraulic failure, the rear portion of the tailplane may be unlocked to act as elevators, with tailplane trimming still available from a stand by electric motor in the Hobson unit. Stick forces in manual are apparently not heavy, but because of the small size of the elevators, their effectiveness is only about one fifth of that of the tailplane. Speed is then restricted to 400 knots (741 kph) or M0.85.
The Orpheus 101 was up rated to 4,400 lb (1995 kg.) thrust to improve the high altitude performance.
With its simple and rugged structure designed for a minimum fatigue life of 5,000 hours and characterised by the absence of complicated castings and forgings, the Gnat is not difficult to build or maintain.
It became clear, however, that no production order would be placed while Folland remained outside the major manufacturing groupings which the government favoured; thus the company was taken over by Hawker Siddeley Aviation, becoming its Hamble Division.

Contracts for 30, 20 and 41 aircraft were awarded in February 1960, July 1961 and March 1962 respectively.
The last production Gnat T.Mk 1 flew on 9 April 1965 and was delivered to the RAF on 14 May, in the all-red scheme of the Red Arrows team. The Central Flying School, then at Little Rissington, first introduced the type in February 1962 but the major operator was No. 4 Flying Training School at Valley, which took its first aircraft on strength in November 1962 and which, in 1964, introduced the Gnat to the formation aerobatic scene, operating five all-yellow Gnats known as the Yellowjacks.

The team reformed as the Red Arrows in 1965, under the control of the Central Flying School, and its Gnats were withdrawn finally at the end of the 1979 display season, to be replaced in 1980 by the British Aerospace Hawk T.Mk 1. No. 4 FTS retired its Gnats on 24 November 1978.

Once pilots graduated from basic training on the BAC Jet Provost and gained their wings they were selected for one of three streams: fast jet, multi-engined, or helicopter. Those selected for fast jets were posted to RAF Valley for advanced training on the Gnat T.1, typically 70 hours of flying. Students would then move on to operational training using the Hawker Hunter, followed by a posting to an operational conversion unit for the type of aircraft to be flown.

Following the introduction of the Hawker Siddeley Hawk into the training role as a replacement the Gnats were withdrawn from service. The largest operator 4 FTS retired its last Gnat in November 1978. Most of the retired Gnats were delivered to No. 1 School of Technical Training at RAF Halton and other training establishments to be used as ground training airframes. When the RAF had no need for the Gnats as training airframes they were sold off. Many were bought by private operators and are still flying in 2014.

Including licence built models, India received 238 plus 79 similar Ajeets. The first 13 aircraft for the Indian Air Force (IAF) were assembled at Hamble-le-Rice, they were followed by partly completed aircraft and then sub-assemblies as Hindustan Aircraft slowly took over first assembly, and then production of the aircraft. The first flight of an Indian Air Force Gnat was in the United Kingdom on 11 January 1958, it was delivered to India in the hold of a C-119, and accepted by the Air Force on 30 January 1958. The first Gnat squadron was the No. 23 (Cheetah), which converted from Vampire FB.52 on 18 March 1960 using six Folland-built Gnats. The first aircraft built from Indian-built parts first flew in May 1962. The last Indian-built Gnat F.1 was delivered on 31 January 1974.

The Gnat is credited by many independent and Indian sources as having shot down seven Pakistani Canadair Sabres in the 1965 war, while two Gnats were downed by PAF fighters. During the initial phase of the 1965 war, an IAF Gnat, piloted by Squadron Leader Brij Pal Singh Sikand, mistakenly landed at an abandoned Pakistani airstrip at Pasrur and was captured by the PAF. Two Lockheed F-104 Starfighters claimed to have forced the Gnat down. This Gnat is displayed as a war trophy in the Pakistan Air Force Museum, Karachi. After the ceasefire, one Pakistani Cessna O-1 was shot down on 16 December 1965 by a Gnat.

The Gnats were used again by India in the Indo-Pakistani War of 1971 against Pakistan. The most notable action was the Battle of Boyra where the first dogfights over East Pakistan (Bangladesh) took place. The Indian Air Force (IAF) Gnats downed two PAF Canadair Sabres in minutes and badly damaged one. The Pakistan Air Force claims that one Gnat was shot down, which was proved incorrect. Another notable dogfight involving a Gnat was over Srinagar airfield where a lone Indian pilot held out against six Sabres, scoring hits on two of the Sabres in the process, before being shot down. Gnat pilot Nirmal Jit Singh Sekhon was posthumously honoured with the Param Vir Chakra (India’s highest gallantry award), becoming the only member of the IAF to be given the award.

By the end of 1971, the Gnat proved to be a frustrating opponent for the larger, heavier and older Sabre. The Gnat was referred to as a “Sabre Slayer” by the IAF since most of its combat “kills” during the two wars were against Sabres. The Canadair Sabre Mk 6 was widely regarded as the best dogfighter of its era. Tactics called for Gnats taking on the Sabres in the vertical arena, where the Sabres were at a disadvantage. As the Gnat was lightweight and compact in shape, it was hard to see, especially at the low levels where most dogfights took place. Apart from air defence operations, they performed multiple roles in the Bangladesh Liberation War, including anti-shipping operations, ground attack, bomber/transport escort and close air support.

The IAF was impressed by the Gnat’s performance in the two wars, but the aircraft had problems including hydraulics and unreliable control systems. To address these issues, the IAF issued a requirement for an improved “Gnat II” in 1972, at first specifying that the new version was to be optimized as an interceptor, but then expanding the specification to include the ground-attack role. Over 175 of the Hindustan Aeronautics Limited-built licensed version, the Ajeet (“Unconquerable”), were produced in Bangalore. Several Gnats remain in use in private hands. Some IAF Gnats, one of which had participated in the 1971 war in East Pakistan (present day Bangladesh), were presented to the Bangladesh Air Force.

Gallery

Folland Gnat Mk. 1
Engine: 1 x 4,230 lbs.t. (1919 kgp) Bristol Siddeley Orpheus 101
Wingspan, 24 ft. (7.33 m)
Length, 31 ft. 9 in. (9.7 m)
Height, 10 ft. (3.06 m)
Wing area, 175 sq. ft. (16.26 sq m)
Empty weight, 5,639 lb. (2 559 kg)
Crew weight, 360 lb. (163 kg)
Internal fuel, 265 Imp.ga1 (1200 litres)
AVTAG, 2,040 lb. (926 kg)
Gross weight, clean, 8,039 lb. (3 648 kg)
External fuel tanks, 118 gal. (536 litres), 908 lb. (412 kg)
Overload gross weight, 9,107 lb. (4 133 kg)
Max level speed: 610 kts EAS (1130 km/h) at sea level (Mach 0.93).
Max speed, 36,000 ft. (11 000 m), M= 0.95
Max speed, 636 mph (1024 kph) at 31,000ft (9 500 m)
Max dive speed, M 1.15
Cruise, 470 mph (756 kph)
Initial climb, 7,620 fpm (38.7 m/sec)
Climb to 26,000 ft. (8 000 m), 4 min. 40 sec.
Climb to 40,000 ft (12,000 m), 7 min 30 sec.
Service ceiling, 48,000 ft (14 600m)
Stalling speed, 115 mph (185 kph)
Take off distance to 50 ft (15 m), 2,550 ft (775 m)
Landing distance from 50 ft (15 m), brake parachute, dry surface, 2,210 ft (705 m)
Max range, internal fuel, 600 nm (1100 km)
Range with external fuel, 1,000 nm (1 850 km).
Armament: 2 x 30mm Aden cannon.
Crew: 1-2

Developed from the Fo 139 Midge, the Fo 141 Gnat was designed as a light fighter. The shoulder wing is swept back at 40 degrees. All tail surfaces are swept with a one-piece tailplane low-set on the fuselage. Ailerons are on the inner wings and can be drooped to act as flaps. The wheel fairing doors act as air-brakes when the undercarriage is partially lowered in flight. The tricycle undercarriage has single main wheels and twin nose wheels, all retracting rearwards into the fuselage.

Folland Fo 141 Gnat Article

The private-venture prototype Gnat G-39-2, piloted by Folland’s chief test pilot, Squadron Leader E. A. Tennant, first flew at the Airplane & Armament Experimental Establishment at Boscombe Down on 18 July 1955. The aircraft was powered by a newly developed 1490kg thrust Bristol Orpheus turbojet.

The Gnat, being developed in parallel with the Midge, was an improved version of the original fighter design, differentiated by larger air intakes for the Bristol Orpheus engine (the Midge had an Armstrong Siddeley Viper engine), a slightly larger wing, and provision for a 30 mm ADEN cannon in each intake lip.

A more powerful version, rated at 1814kg thrust, was installed on 30 August for the Gnat’s debut at that year’s SBAC flying display and exhibition at Farnborough.

Six development aircraft were ordered by the Ministry of Supply in August 1955, the first flying on 26 May 1956, and these were used for a variety of trials at Boscombe Down, including firing of the 30mm ADEN cannon, one of which was fitted in the lip of each intake. Evaluation in the ground-attack role was undertaken in Aden, in competition with a modified Hawker Hunter.

Although the Royal Air Force had lost interest in the Gnat as a fighter, the Finnish air force took delivery of 13 aircraft in 1958-59. The Finnish Air Force received the first of its 13 Gnats (11 fighters and 2 photo-reconnaissance planes) on 30 July 1958. It was soon found to be a problematic aircraft in service and required a lot of ground maintenance. In early 1957 a licence agreement was reached to allow Valmet to build the Gnat at Tampere in Finland, although in the end none was built.

On 31 July 1958, the Finnish Air Force Major Lauri Pekuri, a World War II fighter ace, broke the sound barrier for the first time in Finland at Lake Luonetjärvi with a Folland Gnat.

Gnat F.1 proved initially problematic in the Finnish harsh conditions. Finland was the first operational user of Gnat F.1, and the plane had still many issues yet unresolved. All Gnats were grounded for half a year on 26 August 1958 after the destruction of GN-102 due to a technical design error on hydraulic system, and the aircraft soon became the subject of severe criticism. Three other aircraft were also destroyed in other accidents, with two pilots ejecting and one being killed. Once the initial problems were ironed out, the plane proved to be extremely manouevreable and have good performance in the air, but also to be very maintenance intensive. The availability of spare parts was always an issue, and its maintenance a challenge to the conscript mechanics. The Gnats were removed from active service in 1972 when the Häme Wing moved to Rovaniemi, and when the new Saab 35 Drakens were brought into use.

The Finnish Air Force serial codes for Folland Gnat were GN-100 to GN-113 and its usual nickname Nutikka (“Stubby”). Several Finnish Gnat F.1s still survive either as museum pieces or memorials. One airframe, GN-113, is in private ownership.

The Yugoslav government also bought two but the major export order was from India: 40 airframes in various stages of completion were supplied from the UK, and licence-production was undertaken by Hindustan Aeronautics Ltd at Bangalore, local production accounting for 175 aircraft. The Gnat entered Indian Air Force service in the spring of 1958, when the Gnat Handling Flight was first formed, and ultimately eight squadrons were equipped.

The Indian Air Force (IAF) operated the Folland Gnat jet fighter from 1958, with over 200 aircraft being license built by Hindustan Aeronautics Limited (HAL). The aircraft proved successful in combat in both the 1965 and the 1971 War with Pakistan, both in the low-level air superiority role and for short range ground attack missions, while being inexpensive to build and operate, came to be called the Gnat Mk 2.
In the words of Late Air Cmde Jasjit Singh, “The Gnat was a very unforgiving aircraft and had the poorest safety track record in the IAF, despite having only Average plus pilots posted to it.” In his book, Indian Air Force: The Case for Indigenisation, Air Cmde Singh said, “It is not surprising the RAF never used it.”

The Gnat aircraft had a peculiar design with the ailerons also doubling as flaps, drooping 15 degrees from a normal aileron position with undercarriage in down position. The raising and lowering of the undercarriage made the ailerons (flaps) go up and down from their normal position. This involved excessive change in attitude and required proper handling by the pilot. All the pilots were briefed repeatedly on this aspect to control the excessive pitch-up after raising of the undercarriage after take-off. Not surprisingly, there were a few incidents because of this peculiar nature of the aircraft.

Although the RAF had not selected the Gnat for service in a front-line role, it did have a requirement for an unarmed, two-seat advanced trainer to replace the de Havilland Vampire T.Mk 11 and to follow the Hunting Jet Provost sections of the all-through jet training programme. Folland undertook a private-venture investigation of the changes necessary to install a second seat and to bring the landing speed down to less than 185km/h. The most significant of these changes was a new wing, increased in area by 3.72sq.m and with additional fuel capacity, which reduced the fuel storage requirement in the fuselage, making room for additional equipment. This became the Folland Fo 144 Gnat

Gallery

Fo 141
Engine: Bristol Siddeley Orpheus 701, 4520 lb
Wing span: 22 ft 2 in
Wing area: 135.5 sq.ft
Length: 29 ft 9 in
Height: 8 ft 10 in
MTOW: 8885 lb
Fuel capacity: 300 gal
External fuel: 2 x 66 gal drop tanks
Wheel track: 4 ft 1 in
Wheelbase: 7 ft 9 in
Max speed: 695 mph / M0.98 at 20,000 ft
Max ROC: 20,000 fpm
Service ceiling: 50,000 ft +
Max endurance: 2 hr 30 min
Armament: 2 x 30mm Aden cannon
Bombload: 2 x 500 lb bomb or 12 air-ground rockets