The Folland Gnat is a British compact swept-wing subsonic fighter aircraft that was developed and produced by Folland Aircraft. Envisioned as an affordable light fighter in contrast to the rising cost and size of typical combat aircraft, it was procured as a trainer aircraft for the Royal Air Force (RAF) as well as by export customers, who used the Gnat in both combat and training capacities.
Designed by W. E. W. Petter, the Gnat has its origins in the preceding private venture Folland Midge. The issuing of Operational Requirement OR.303 by the British Air Ministry served to motivate the type's development, the Gnat was later submitted to meet this requirement. Its design allowed for its construction and maintenance tasks to be carried out without specialised tools, making it suitable for use in countries that had not yet become highly industrialised. The Gnat has been viewed as a major motivating factor towards the issuing of the NATO NBMR-1 requirement, which sought to make available a common strike/attack light fighter with which to equip the air forces of the various NATO members.
Although never used as a fighter by the Royal Air Force (RAF), the Gnat T.1 jet trainer variant was adopted and operated for some time. In the United Kingdom, the Gnat became well known due to its prominent use as the display aircraft of the RAF's Red Arrows aerobatic team. The Gnat F.1 was exported to Finland, Yugoslavia and India. The Indian Air Force became the largest operator and eventually manufactured the aircraft under licence. Impressed by its performance during combat, India proceeded to develop the improved HAL Ajeet, a modified variant of the Gnat. In British service, the Gnat was replaced by the Hawker Siddeley Hawk.
In October 1950, WEW "Teddy" Petter, a British aircraft designer formerly of Westland Aircraft and English Electric, joined Folland Aircraft as its managing director and chief engineer. Almost immediately upon joining the firm, Petter conducted a study into the economics behind modern fighter manufacturing, and concluded that many combat aircraft entailed far too great a cost in terms of man-hours and material to be readily mass-produced during a major conflict. While the British Air Staff emphasised quality over quantity, the economics involved in the anticipated vast wartime production of many of the RAF's aircraft of the time, such as the Hawker Hunter and the Gloster Javelin interceptors, were viewed as questionable.
Petter examined the prospects for producing a more affordable but capable "light fighter", including a survey of available modern engines to power the type. Having identified suitable powerplant arrangements along with methods of making multiple key design aspects, such as the manufacturing of the fuselage and wings, more affordable, Folland promptly commenced work upon this lightweight fighter concept, financing the project using existing company funds. The light fighter project soon received the Fo-141 designation along with the name Gnat. Development of the Gnat and the specifics of its design were heavily influenced by the issuing of Operational Requirement OR.303, which sought a capable lightweight fighter aircraft. Work to develop the Gnat went ahead, irrespective of any external orders or financing; there was no funding provided to support the type's early development from any British government department, such as the Ministry of Supply.
Gnat F.1 single-seat fighter variant at the 1957 Paris Air Salon
Petter believed that a compact and simplified fighter would offer the advantages of low purchase and operational costs, and that the Gnat should be capable of being manufactured both cheaply and easily. The emergence of new lightweight turbojet engines, several of which were well advanced in their own development process, also enabled the envisioned light fighter concept to be realised. The Gnat was initially intended to be powered by a Bristol BE-22 Saturn turbojet engine, capable of generating 3,800 lbf (16.9 kN 1,724 kgp) of thrust. However, development of the Saturn was cancelled; in its place, the more capable but not immediately available Bristol Orpheus turbojet engine was adopted instead.
In order that the project would not be delayed before reaching the prototype stage, Petter's unarmed proof-of-concept demonstrator for the Gnat was instead powered by the less powerful Armstrong Siddeley Viper 101 turbojetengine, capable of generating 1,640 lbf (7.3 kN / 744 kgp) of thrust. While using a different powerplant from later-built prototypes and production aircraft, the demonstrator still used a nearly-identical airframe along with similar onboard systems so that these could be proved in advance of the Gnat itself being built. This demonstrator was designated Fo-139 Midge. On 11 August 1954, the Midge performed its maiden flight, piloted by Folland's chief test pilot E. A. Tennant. Despite the low-powered engine, the compact jet was able to break Mach 1 while in a dive and proved to be very agile during its flying trials. On 20 September 1955, the Midge was destroyed in a crash, which had possibly been due to human error.
The Midge, partly due to its nature as a private venture, had only a short lifespan, however had served as a proof-of-concept demonstrator for the subsequent aircraft. It had failed to interest the RAF as a combat aircraft at that time, but officers did issue encouragement of the development of a similar aircraft for training purposes. The larger Gnat, which was being developed in parallel with the Midge, was an improved version of the original fighter design; it was differentiated by larger air intakes to suit the Orpheus engine, a slightly larger wing, and provision for the installation of a 30 mm ADEN cannon in each intake lip. The first prototype Gnat was built as a private venture by Folland. Subsequently, six further aircraft were ordered by the British Ministry of Supply for evaluation purposes. On 18 July 1955, the Folland prototype, serial number G-39-2, first flew from RAF Boscombe Down, Wiltshire.[a]
Although the evaluation by the British brought no orders for the lightweight fighter, orders were placed by Finland and Yugoslavia. India placed a large order for the type, which included a licence for production by Hindustan Aeronautics Limited (HAL). Although the Gnat's development is considered a factor which motivated the Mutual Weapons Development Team to issue the NATO NBMR-1 requirement for a low level strike/attack light fighter, the Gnat itself was not evaluated in the competition, which was won by the Fiat G.91. However, the Gnat was evaluated in 1958 by the RAF as a replacement for the de Havilland Venom, as well as other light aircraft such as the BAC Jet Provost. The Hawker Hunter was selected as the eventual winner of the fly-off competition.
Operational Gnat T.1 of No. 4 Flying Training School RAF in 1971
Although RAF interest in the possibilities for using the Gnat as a fighter had waned, Folland identified another potential use for the type as a trainer aircraft. Accordingly, the aircraft was modified to conform with the requirements of Specification T.185D, which had called for an advanced two-seat trainer aircraft that could transition pilots between the current de Havilland Vampire T 11 and operational fighters, such as the supersonic English Electric Lightning.
Folland proposed the two-seat Fo. 144 Gnat Trainer. The trainer model featured several changes, including the adoption of a new wing with additional fuel capacity, which in turn allowed for more internal space within the fuselage to be allocated for additional equipment. A more powerful variant of the Orpheus engine was also used, while the length of the forward fuselage area was increased, and the tail surfaces were enlarged. The inboard ailerons of the fighter variant were reconfigured to an arrangement of outboard ailerons and conventional flaps. On 7 January 1958, an initial contract for 14 pre-production Gnat trainers was issued.
On 31 August 1959, the prototype Gnat Trainer conducted its maiden flight from Chilbolton airfield, Hampshire. 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), further orders for 30, 20 and 41 trainers were placed between February 1960 and March 1962, receiving the designation Gnat T Mk. 1. The final Gnat T.1 for the RAF was delivered in May 1965.