[Source: Vectorsite.net] While fighter aircraft tend to become larger and more expensive as their users demand more of them, there have always been a few aircraft designers who believe that a simple, lightweight fighter might find a useful niche. One of the more interesting of these lightweight fighters was the British Folland (later Hawker-Siddeley) "Gnat". Although it was never used as a fighter by the British Royal Air Force (RAF), it did achieve success with the RAF in its "Gnat T.1" trainer version, as well as wide recognition as the mount for the RAF Red Arrows aerobatic team. The Gnat also achieved export success, particularly with India, which manufactured the aircraft under license. In fact, the Indians found the Gnat so capable that they designed and built their own improved version, the "Ajeet". This document provides a history and description of the Gnat and AJeet.
ORIGINS / FO-139 MIDGE
The Gnat was the creation of W.E.W. "Teddy" Petter, a British aircraft designer who had gained wide recognition for his design of the English Electric Canberra bomber and Lightning supersonic interceptor. Petter had grown suspicious of the trend towards bigger and more expensive combat aircraft, and he felt that a small, simple fighter would offer the advantages of low purchase and operational costs. New lightweight turbojet engines were being developed that would be able to power such small fighters.
Petter was unable to pursue this vision at English Electric, so he left to become managing director of Folland Aircraft. In 1951, using company funds, he began work on his lightweight fighter concept, which he designated the "Fo-141 Gnat". The Gnat was to be powered by a Bristol BE-22 Saturn turbojet with 16.9 kN (1,724 kgp / 3,800 lbf) thrust. However, the Saturn was cancelled, and so Petter's unarmed proof-of-concept demonstrator for the Gnat was powered by the less powerful Armstrong Siddeley Viper 101 with 7.3 kN (744 kgp / 1,640 lbf) thrust. The demonstrator was designated the "Fo-139 Midge". The Midge first flew on 11 August 1954 with Teddy Tennant at the controls, and proved to be an excellent aircraft.
The Midge had a number of advanced features, such as hydraulically powered "flaperons", main gear that could be used as airbrakes, and a one-piece canopy that hinged over an inner armored windscreen. Despite the underpowered engine, the little jet could break Mach 1 in a dive and was very agile.
FOLLAND FO-139 MIDGE:
The Midge was evaluated by pilots from Canada, India, Jordan, New Zealand, and the US Air Force, and was almost universally praised. The Midge had performed a total of 220 flights when it was destroyed in a fatal crash on 26 September 1955, with a Swiss pilot at the controls. However, the Midge had demonstrated that Petter's lightweight fighter concept had much going for it. Folland went on to develop a full-scale Gnat prototype, also using company funds.
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spec metric english
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wingspan 6.30 meters 20 feet 8 inches
wing area 11.61 sq_meters 125 sq_feet
length 8.76 meters 28 feet 9 inches
height 2.82 meters 8 feet 1 inch
MTO weight 2,041 kilograms 4,500 pounds
maximum speed 986 KPH 600 MPH / 522 KT
service ceiling 11,580 meters 38,000 feet
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FO-145 GNAT FIGHTER / FO-144 GNAT T.1 TRAINER
The full-scale aircraft, designated the "Fo-145 Gnat", performed its initial flight on 18 July 1955, again with Tennant at the controls. It was very similar to the Midge, but had a maximum takeoff weight about twice as great. It was powered by a preproduction Bristol Orpheus turbojet with 14.6 kN (1,490 kgp / 3,285 lbf) thrust.
FOLLAND FO-145 GNAT:
The Gnat was armed with two 30 millimeter Aden revolver-type cannon, firing from the outer edge of the air intakes. While this arrangement might have suggested that the Gnat would be prone to engine flameouts from muzzle gas ingestion, that did not prove to be the case, suggesting that the muzzle system had been carefully designed to deflect the gases out to the sides. The Gnat also had two stores pylons for drop tanks, 225 kilogram (500 pound) bombs, or unguided rocket pods.
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spec metric english
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wingspan 6.73 meters 22 feet 1 inch
wing area 12.65 sq_meters 136.1 sq_feet
length 9.04 meters 29 feet 8 inches
height 2.46 meters 8 feet 1 inch
empty weight 2,180 kilograms 4,800 pounds
max loaded weight 4,100 kilograms 9,040 pounds
maximum speed 1,120 KPH 695 MPH / 605 KT
service ceiling 13,720 meters 45,000 feet
combat radius with drop tanks 800 KM 500 MI / 435 NMI
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The Gnat prototype was refitted with an uprated preproduction Orpheus engine to put on flight displays at the Farnborough air show that year. While the RAF had no requirement for such a machine, the government wanted to encourage Folland in their work, and so the British Ministry of Supply (MoS) ordered six prototypes of the full-development aircraft for evaluation.
The evaluation Gnats were powered by the production-spec Bristol Orpheus 701 turbojet with 20.1 kN (2,042 kgp / 4,502 lbf) thrust. Most of the test flights were conducted in the UK, though ground-attack trials were performed in Aden (now Yemen). The report from the RAF evaluation generally praised the Gnat's performance, but there were criticisms of its flight-control systems, and there was no consensus that the Gnat was what the RAF needed. The Gnat fighter never served operationally in Britain, though the MoS did order two more Gnats on top of the original order for six.
However, the good press given the Gnat opened the way for export sales. Two were sold to Yugoslavia for evaluation, and thirteen were sold to Finland. The Finnish Gnats were delivered in 1958 and 1959, with two of them configured for reconnaissance, with noses carrying three 70 millimeter cameras. Finland operated its Gnats until 1972.
India was very interested in the Gnat, and in 1956 Folland and Hindustan Aircraft Limited (HAL) signed a license agreement, beginning a long love affair between India and the Gnat. 25 Folland-built Gnats, including two hand-me-downs from the RAF evaluation program, and 20 kits were sold to India through HAL. These machines were powered by the further uprated Bristol Orpheus 701-01 engine with 20.93 kN (2,134 kgp / 4,705 lbf) thrust.
The Gnat went into IAF service in the spring of 1958, with the first Gnat assembled by HAL from a kit flying in Bangalore on 18 November 1959. HAL then went on to build 195 Gnats themselves up to early 1974. The first completely HAL-built Gnat flew on 21 May 1962. IAF pilots were delighted with the nimble Gnat, which they felt was more than a match for Pakistani F-86s and MiG-19s, and nicknamed it the "Saber Slayer".
The RAF had shown no real interest in the Gnat fighter, but Teddy Petter was persistent, proposing the tandem-seat "Fo-144" trainer version of the Gnat. The RAF liked the idea, and a contract for 14 preproduction "Gnat T.1" trainers was placed in 1958. The first performed its initial flight on 31 August 1959.
The Gnat T.1 had no gun armament, but retained the twin stores pylons. It was powered by a Bristol Orpheus 4-100 engine with 18.8 kN (1,920 kgp / 4,230 lbf) thrust; a larger tail; and a bigger wing with integral fuel tanks, 40% greater wing area, and conventional ailerons and flaps instead of flaperons.
FOLLAND FO-145 GNAT T.1 TRAINER:
The RAF was pleased with the Gnat T.1 and ordered 91 more, for a total of 105. These were built between 1962 and 1965 by Hawker-Siddeley, which had bought out Folland since the government was strongly encouraging consolidation in the aviation industry.
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spec metric english
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wingspan 7.32 meters 24 feet
wing area 16.26 sq_meters 175 sq_feet
length 9.68 meters 31 feet 9 inches
height 2.93 meters 9 feet 8 inch
empty weight 2,331 kilograms 5,140 pounds
max takeoff weight 3,915 kilograms 8,630 pounds
max speed at altitude 1,024 KPH 636 MPH / 553 KT
service ceiling 14,630 meters 48,000 feet
range with drop tanks 1,852 KM 1,151 MI / 1,000 NMI
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Five yellow-painted Gnat T.1s fitted with smoke generators were used in 1964 by the RAF "Yellowjacks" aerobatic demonstration team, which was redefined a year later to become the RAF "Red Arrows", with red-painted aircraft. Their nine red Gnats, trailing smoke during precision maneuvers, pleased crowds at airshows in Britain and around the world until 1979, when they converted to the British Aerospace Hawk, which also replaced the Gnat T.1 in the advanced training role.
The Gnat T.1 served the RAF well, though it suffered from high operating costs. It had not been designed for maintainability, and some of its systems were not noted for their reliability. Its cockpit was also cramped and instructor's forward visibility was poor. The BAE Hawk was designed specifically to provide the utility of the Gnat T.1, while lowering operational costs and eliminating some of the Gnat's defects.
HAL AJEET / TWILIGHT OF THE GNAT
The Indians were very happy with the Gnat, but the little fighter did have its problems, the worst being that its hydraulics and some of its control systems were unreliable. In 1972, the IAF issued a requirement for an improved "Gnat II", 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.
HAL modified two Gnats to test subsystems for the new design, and the first example of the new type flew on 6 March 1975. The improved Gnat was named "Ajeet", Sanskrit for "Invincible / Unconquered / Unbeatable", and the two initial prototype Ajeets were modified from the last production Gnats built by HAL. The first production Ajeet flew on 30 September 1976, with deliveries to the IAF beginning in 1977. A total of 79 Ajeets were built by the time manufacture ended in 1982, and ten Gnats were upgraded to Ajeet standards.
The Ajeet was difficult to tell apart from a Gnat at a casual glance, but it incorporated many changes and improvements. The most visible change was that the Ajeet had four stores pylons, with a total carriage capacity of 900 kilograms (one ton), instead of the Gnat's two pylons. Other significant changes included:
- Improved hydraulics and controls.
- Fit of the Martin-Baker Mark GF4 ejection seat instead of the Folland-designed Type 2G seat.
- New avionics, including a modern Ferranti gunsight.
- A slab tailplane.
- Improved landing gear with an antiskid braking system.
- Fuel tanks built into the wings, with each integral wing tank storing 250 liters (66 US gallons) of fuel.
The integral wing tanks meant that all four stores pylons could be used for weapons. The small size of the Gnat had meant limited range without drop tanks, and with the Gnat's two stores pylons, drop tanks meant no weapons other than cannon. The Ajeet was much better suited to the ground attack role than the Gnat.
HAL also designed a two-seat trainer version of the Ajeet, with a lengthened fuselage and a tandem dual-cockpit design. Two internal fuel tanks were deleted to accommodate the second cockpit. The two 30 millimeter cannon and the four stores pylons were retained, though the cannon could be removed and replaced with additional fuel tanks. The trainer used the same Orpheus 701 engine as the Gnat and Ajeet fighters.
The Ajeet trainer never reached production. One prototype was built in 1982 and crashed in that year, a second prototype flew in 1983, and then the program went into limbo and eventually died. Some sources claim that 30 Ajeet trainers were built, but this is hard to believe. The IAF's requirement for an advanced trainer became something of an infamous saga (or possibly endless raga), remaining unfilled through the 1980s and 1990s, until the service settled on the BAE Hawk.
The last Ajeets were phased out of IAF service in 1991. No Gnats or Ajeets remain in operational service. However, a number of Gnats, mostly ex-RAF T.1s, have ended up in private hands as a thrilling high-class toy, and make occasional appearances at airshows. A number of Gnat fighters are preserved as museum pieces; it is unclear if any are in flight condition.
The following table provides a production and user summary of the Gnat family:
variant built updated notes
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Midge 1 Subscale demonstrator.
Gnat (P) 9 Prototype Gnat fighters.
Gnat (Y) 2 Yugoslav evaluation machines.
Gnat (FF) 11 Finnish fighter variants.
Gnat (FR) 2 Finnish reconnaissance variants.
subtotal 25 Non-Indian single-seaters.
Gnat (IF) 23 2 Folland-built Gnats for India.
Gnat (IK) 20 Indian Gnats built from kits.
Gnat (IP) 195 Indian Gnats produced by HAL.
Ajeet 79 10 Improved HAL-built Gnat
subtotal 317 Indian single-seaters.
subtotal 342 All single-seaters.
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Ajeet (T) 2 Ajeet trainer, never produced.
Gnat T.1 105 Gnat trainer.
subtotal 107 Two-seaters.
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TOTAL 449
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The actual total may be somewhat less. Some of the aircraft listed here as new-build may have been recycled and so there may be a bit of "double counting"
COMMENTS, SOURCES, & REVISION HISTORY
There were a number of unbuilt Gnat concepts. A navalized Gnat, with the wing of the trainer, plus arresting gear and other carrier kit, was considered briefly. More consideration was given in the mid-1950s to the "Fo.143 Gnat Mark 2", which featured a thinner wing -- 6% thick instead of the 8% wing of the standard Gnat fighter -- plus an afterburning Orpheus engine in a longer fuselage, enlarged engine intakes, more internal tankage, and (in maturity) an AI.23 radar system in a fatter nose.
The Gnat Mark 2 would have been capable of Mach 1.28 at altitude and the Air Ministry was interested, with Folland going so far as to build a wing for a prototype. The project went no further, mainly because the RAF still didn't have a requirement for the Gnat, even one that was capable of cracking Mach 1.
Further refinements were considered along this line. The "Gnat Mark 4" had a redesigned 6% wing -- featuring full-span flaps to improve takeoff and landing handling -- and a top speed of Mach 1.5. The "Gnat Mark 5" was a series of designs, ultimately featuring twin afterburning Rolls-Bristol RB.153 engines, improved aerodynamics that resulted in only a general resemblance to the original Gnat, and a top speed of Mach 2.4. Nothing came of these notions.
The final and most spectacular redesign was a Mach 2 variable geometry ("swing wing") machine, the Folland "Fo.148", that was intended as a trainer, air superiority fighter, or light strike aircraft. The wings were to have full-span leading-edge flaps and slotted trailing edge flaps; there would be a single stores pylon on each side of the fuselage. It was to have been fitted with an afterburning RB.153 engine with a thrust reverser. The Fo.148 was said to have been the last aircraft design to bear a Folland designation before the company was absorbed into the Hawker-Siddely group. It was an interesting design and it is a bit of shame it never flew.
Sources include:
- THE ILLUSTRATED ENCYCLOPEDIA OF 20TH CENTURY WEAPONS AND WARFARE, edited by Bernard Fitzsimons, 1978 edition
- MODERN WARPLANES, by Doug Richardson, Crescent Books, 1982
- THE COMPLETE ENCYCLOPEDIA OF WORLD AIRCRAFT, edited by Paul Eden and Soph Moeng, Barnes & Noble, 2002
- BRITISH SECRET PROJECTS by Tony Buttler, Midland Publishing, 2000
Various small pieces of information were found in other sources such as JANE'S ALL THE WORLD AIRCRAFT, but no one of them added more than one or two pieces to the puzzle, and so I have not cited them
