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155-557: 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 ,

310-416: A i r + m ˙ f ) V j − m ˙ a i r V {\displaystyle F_{N}=({\dot {m}}_{air}+{\dot {m}}_{f})V_{j}-{\dot {m}}_{air}V} where: If the speed of the jet is equal to sonic velocity the nozzle is said to be " choked ". If the nozzle is choked, the pressure at the nozzle exit plane

465-464: A propelling nozzle . The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine (that drives the compressor). The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust. Two engineers, Frank Whittle in

620-458: A trainer and a combat aircraft in ground-attack and day-fighter roles. The cockpit offered many features expected in standard fighter aircraft: full pressurisation , climate control , and an ejection seat . According to Folland, the Gnat offered advantages over conventional fighter aircraft in terms of cost, man-hours, handling, serviceability, and portability. Its tricycle landing gear let it operate from austere grass airstrips, thanks to

775-534: A Gnat at Lake Luonetjärvi . Gnat F.1 proved initially problematic in the harsh Finnish conditions. Finland was the first operational user of Gnat F.1, and the plane still had many issues yet to be resolved. All Gnats were grounded for half a year on 26 August 1958 after the destruction of GN-102 due to a technical design error in its 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

930-478: A conventional tail – for a multipurpose fighter/strike/trainer, designated the Fo.147. The design used a unique mechanism to sweep the wings; this mechanism used a combination of tracks positioned on the fuselage sides, the centerline, and on the underside of the wings, and was actuated by hydraulically -driven ball screws positioned at the inner ends of the wings. The wings could be swept from 20 degrees to 70 degrees; at

1085-659: 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

1240-677: 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

1395-585: A gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume . His engine was to be an axial-flow turbojet, but was never constructed, as it would have required considerable advances over the state of the art in compressors. In 1928, British RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbojet to his superiors. In October 1929 he developed his ideas further. On 16 January 1930 in England, Whittle submitted his first patent (granted in 1932). The patent showed

1550-542: A landing field, lengthening flights. The increase in reliability that came with the turbojet enabled three- and two-engine designs, and more direct long-distance flights. High-temperature alloys were a reverse salient , a key technology that dragged progress on jet engines. Non-UK jet engines built in the 1930s and 1940s had to be overhauled every 10 or 20 hours due to creep failure and other types of damage to blades. British engines, however, utilised Nimonic alloys which allowed extended use without overhaul, engines such as

1705-515: A local indentation of the fuselage above and below the wing root. This proved to not be very effective. During the development of the Douglas DC-8 airliner, uncambered airfoils were used in the wing root area to combat the unsweeping. Swept wings on supersonic aircraft usually lie within the cone-shaped shock wave produced at the nose of the aircraft so they will "see" subsonic airflow and work as subsonic wings. The angle needed to lie behind

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1860-612: 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

2015-462: A means of creating positive longitudinal static stability . For a low-speed aircraft, swept wings may be used to resolve problems with the center of gravity , to move the wing spar into a more convenient location, or to improve the sideways view from the pilot's position. By 1905, Dunne had already built a model glider with swept wings followed by the powered Dunne D.5 , and by 1913 he had constructed successful powered variants that were able to cross

2170-454: 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

2325-422: A pair of proposed fighter aircraft equipped with swept wings from Hawker Aircraft and Supermarine , the Hawker Hunter and Supermarine Swift respectively, and successfully pressed for orders to be placed 'off the drawing board' in 1950. On 7 September 1953, the sole Hunter Mk 3 (the modified first prototype, WB 188 ) flown by Neville Duke broke the world air speed record for jet-powered aircraft, attaining

2480-431: A potential overseas purchaser. 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

2635-555: 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. Folland sought to develop more capable versions of

2790-592: A record-breaking speed of Mach 1.06 (700 miles per hour (1,100 km/h; 610 kn)). The news of a successful straight-wing supersonic aircraft surprised many aeronautical experts on both sides of the Atlantic, as it was increasingly believed that a swept-wing design not only highly beneficial but also necessary to break the sound barrier. During the final years of the Second World War, aircraft designer Sir Geoffrey de Havilland commenced development on

2945-453: A reflex curve at the trailing edge. This results in a much weaker shock wave towards the rear of the upper wing surface and a corresponding increase in critical mach number. Shock waves require energy to form. This energy is taken out of the aircraft, which has to supply extra thrust to make up for this energy loss. Thus the shocks are seen as a form of drag . Since the shocks form when the local air velocity reaches supersonic speeds, there

3100-459: A second generation SST engine using the 593 core were done more than three years before Concorde entered service. They evaluated bypass engines with bypass ratios between 0.1 and 1.0 to give improved take-off and cruising performance. Nevertheless, the 593 met all the requirements of the Concorde programme. Estimates made in 1964 for the Concorde design at Mach 2.2 showed the penalty in range for

3255-411: A significant impact on commercial aviation . Aside from giving faster flight speeds turbojets had greater reliability than piston engines, with some models demonstrating dispatch reliability rating in excess of 99.9%. Pre-jet commercial aircraft were designed with as many as four engines in part because of concerns over in-flight failures. Overseas flight paths were plotted to keep planes within an hour of

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3410-405: A small helicopter engine compressor rotates around 50,000 RPM. Turbojets supply bleed air from the compressor to the aircraft for the operation of various sub-systems. Examples include the environmental control system , anti-icing , and fuel tank pressurization. The engine itself needs air at various pressures and flow rates to keep it running. This air comes from the compressor, and without it,

3565-522: A speed of 727.63 mph (1,171.01 km/h) over Littlehampton , West Sussex . This world record stood for less than three weeks before being broken on 25 September 1953 by the Hunter's early rival, the Supermarine Swift, being flown by Michael Lithgow. Turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with

3720-420: A swept wing as it travels through the air. The airflow over a swept wing encounters the wing at an angle. That angle can be broken down into two vectors, one perpendicular to the wing, and one parallel to the wing. The flow parallel to the wing has no effect on it, and since the perpendicular vector is shorter (meaning slower) than the actual airflow, it consequently exerts less pressure on the wing. In other words,

3875-540: A swept wing the wing panels on the Douglas DC-1 outboard of the nacelles also had slight sweepback for similar reasons. 2. to provide longitudinal stability for tailless aircraft, e.g. Messerschmitt Me 163 Kometuu . 3. most commonly to increase Mach-number capability by delaying to a higher speed the effects of compressibility (abrupt changes in the density of the airflow), e.g. combat aircraft, airliners and business jets. Other reasons include: 1. enabling

4030-513: A turbojet application, where the output from the gas turbine is used in a propelling nozzle, raising the turbine temperature increases the jet velocity. At normal subsonic speeds this reduces the propulsive efficiency, giving an overall loss, as reflected by the higher fuel consumption, or SFC. However, for supersonic aircraft this can be beneficial, and is part of the reason why the Concorde employed turbojets. Turbojet systems are complex systems therefore to secure optimal function of such system, there

4185-512: A turbojet engine is always subsonic, regardless of the speed of the aircraft itself. The intake has to supply air to the engine with an acceptably small variation in pressure (known as distortion) and having lost as little energy as possible on the way (known as pressure recovery). The ram pressure rise in the intake is the inlet's contribution to the propulsion system's overall pressure ratio and thermal efficiency . The intake gains prominence at high speeds when it generates more compression than

4340-494: A turbojet is high enough at higher thrust settings to cause the nozzle to choke. If, however, a convergent-divergent de Laval nozzle is fitted, the divergent (increasing flow area) section allows the gases to reach supersonic velocity within the divergent section. Additional thrust is generated by the higher resulting exhaust velocity. Thrust was most commonly increased in turbojets with water/methanol injection or afterburning . Some engines used both methods. Liquid injection

4495-487: A two-stage axial compressor feeding a single-sided centrifugal compressor . Practical axial compressors were made possible by ideas from A.A. Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). Whittle later concentrated on the simpler centrifugal compressor only, for a variety of practical reasons. A Whittle engine was the first turbojet to run, the Power Jets WU , on 12 April 1937. It

4650-412: A wing carry-through box position to achieve a desired cabin size, e.g. HFB 320 Hansa Jet . 2. providing static aeroelastic relief which reduces bending moments under high g-loadings and may allow a lighter wing structure. For a wing of given span, sweeping it increases the length of the spars running along it from root to tip. This tends to increase weight and reduce stiffness. If the fore-aft chord of

4805-434: A wing is generated by the airflow over it from front to rear. With increasing span-wise flow the boundary layers on the surface of the wing have longer to travel, and so are thicker and more susceptible to transition to turbulence or flow separation, also the effective aspect ratio of the wing is less and so air "leaks" around the wing tips reducing their effectiveness. The spanwise flow on swept wings produces airflow that moves

Folland Gnat - Misplaced Pages Continue

4960-483: A world speed record. On 12 April 1948, a D.H.108 did set a world's speed record at 973.65 km/h (605 mph), it subsequently became the first jet aircraft to exceed the speed of sound. Around this same timeframe, the Air Ministry introduced a program of experimental aircraft to examine the effects of swept wings, as well as the delta wing configuration. Furthermore, the Royal Air Force (RAF) identified

5115-410: Is a certain " critical mach " speed where sonic flow first appears on the wing. There is a following point called the drag divergence mach number where the effect of the drag from the shocks becomes noticeable. This is normally when the shocks start generating over the wing, which on most aircraft is the largest continually curved surface, and therefore the largest contributor to this effect. Sweeping

5270-413: Is a component of a turbojet used to divert air into the intake, in front of the accessory drive and to house the starter motor. An intake, or tube, is needed in front of the compressor to help direct the incoming air smoothly into the rotating compressor blades. Older engines had stationary vanes in front of the moving blades. These vanes also helped to direct the air onto the blades. The air flowing into

5425-523: Is greater than atmospheric pressure, and extra terms must be added to the above equation to account for the pressure thrust. The rate of flow of fuel entering the engine is very small compared with the rate of flow of air. If the contribution of fuel to the nozzle gross thrust is ignored, the net thrust is: F N = m ˙ a i r ( V j − V ) {\displaystyle F_{N}={\dot {m}}_{air}(V_{j}-V)} The speed of

5580-573: Is modelled approximately by the Brayton cycle . The efficiency of a gas turbine is increased by raising the overall pressure ratio, requiring higher-temperature compressor materials, and raising the turbine entry temperature, requiring better turbine materials and/or improved vane/blade cooling. It is also increased by reducing the losses as the flow progresses from the intake to the propelling nozzle. These losses are quantified by compressor and turbine efficiencies and ducting pressure losses. When used in

5735-589: Is more commonly by use of a turboshaft engine, a development of the gas turbine engine where an additional turbine is used to drive a rotating output shaft. These are common in helicopters and hovercraft. Turbojets were widely used for early supersonic fighters , up to and including many third generation fighters , with the MiG-25 being the latest turbojet-powered fighter developed. As most fighters spend little time traveling supersonically, fourth-generation fighters (as well as some late third-generation fighters like

5890-507: Is normally used to mean "swept back", but variants include forward sweep , variable sweep wings and oblique wings in which one side sweeps forward and the other back. The delta wing is also aerodynamically a form of swept wing. There are three main reasons for sweeping a wing: 1. to arrange the center of gravity of the aircraft and the aerodynamic center of the wing to coincide more closely for longitudinal balance, e.g. Messerschmitt Me 163 Komet and Messerschmitt Me 262 . Although not

6045-429: Is placed in an airstream at an angle of yaw – i.e., it is swept back. Now, even if the local speed of the air on the upper surface of the wing becomes supersonic, a shock wave cannot form there because it would have to be a sweptback shock – swept at the same angle as the wing – i.e., it would be an oblique shock. Such an oblique shock cannot form until the velocity component normal to it becomes supersonic." To visualize

6200-447: Is rare and the wing must be unusually rigid. There are two sweep angles of importance, one at the leading edge for supersonic aircraft and the other 25% of the way back from the leading edge for subsonic and transonic aircraft. Leading edge sweep is important because the leading edge has to be behind the mach cone to reduce wave drag. The quarter chord (25%) line is used because subsonic lift due to angle of attack acts there and, up until

6355-487: The Sabre dance in reference to the number of North American F-100 Super Sabres that crashed on landing as a result. Reducing pitch-up to an acceptable level has been done in different ways such as the addition of a fin known as a wing fence on the upper surface of the wing to redirect the flow to a streamwise direction. The MiG-15 was one example of an aircraft fitted with wing fences. Another closely related design

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6510-566: The Bangladesh Liberation War , Gnats flew anti-shipping operations, ground attack , bomber/transport escort and close air support operations. The IAF was impressed by the Gnat's performance in the two wars, but the aircraft had many technical problems including hydraulics, a temperamental pair of Aden 30 mm cannons which often failed in-flight, significant 'bent thrust' on take-off, leading to many aborted take-offs and an unreliable control system. To address these failings,

6665-656: The English Channel . The Dunne D.5 was exceptionally aerodynamically stable for the time, and the D.8 was sold to the Royal Flying Corps ; it was also manufactured under licence by Starling Burgess to the United States Navy amongst other customers. Dunne's work ceased with the onset of war in 1914, but afterwards the idea was taken up by G. T. R. Hill in England who designed a series of gliders and aircraft to Dunne's guidelines, notably

6820-621: The F-111 and Hawker Siddeley Harrier ) and subsequent designs are powered by the more efficient low-bypass turbofans and use afterburners to raise exhaust speed for bursts of supersonic travel. Turbojets were used on Concorde and the longer-range versions of the Tu-144 which were required to spend a long period travelling supersonically. Turbojets are still common in medium range cruise missiles , due to their high exhaust speed, small frontal area, and relative simplicity. The first patent for using

6975-704: The Gloster Meteor , entered service in 1944, towards the end of World War II , the Me 262 in April and the Gloster Meteor in July. Only about 15 Meteor saw WW2 action but up to 1400 Me 262s were produced, with 300 entering combat, delivering the first ground attacks and air combat victories of jet planes. Air is drawn into the rotating compressor via the intake and is compressed to a higher pressure before entering

7130-485: The Hawker Siddeley Hawk . In October 1950, W. E. W. "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

7285-588: The Heinkel HeS 3 ), or an axial compressor (as in the Junkers Jumo 004 ) which gave a smaller diameter, although longer, engine. By replacing the propeller used on piston engines with a high speed jet of exhaust, higher aircraft speeds were attainable. One of the last applications for a turbojet engine was Concorde which used the Olympus 593 engine. However, joint studies by Rolls-Royce and Snecma for

7440-461: The Junkers Ju 287 or HFB 320 Hansa Jet . However, larger sweep suitable for high-speed aircraft, like fighters, was generally impossible until the introduction of fly by wire systems that could react quickly enough to damp out these instabilities. The Grumman X-29 was an experimental technology demonstration project designed to test the forward swept wing for enhanced maneuverability during

7595-483: The Ministry of Supply . 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

7750-527: The North American XB-70 Valkyrie , each feeding three engines with an intake airflow of about 800 pounds per second (360 kg/s). The turbine rotates the compressor at high speed, adding energy to the airflow while squeezing (compressing) it into a smaller space. Compressing the air increases its pressure and temperature. The smaller the compressor, the faster it turns. The (large) GE90-115B fan rotates at about 2,500 RPM, while

7905-488: The Rolls-Royce Welland and Rolls-Royce Derwent , and by 1949 the de Havilland Goblin , being type tested for 500 hours without maintenance. It was not until the 1950s that superalloy technology allowed other countries to produce economically practical engines. Early German turbojets had severe limitations on the amount of running they could do due to the lack of suitable high temperature materials for

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8060-424: The Tu-144 , also used afterburners as does Scaled Composites White Knight , a carrier aircraft for the experimental SpaceShipOne suborbital spacecraft. Reheat was flight-trialled in 1944 on the W.2/700 engines in a Gloster Meteor I . The net thrust F N {\displaystyle F_{N}\;} of a turbojet is given by: F N = ( m ˙

8215-553: The United Kingdom and Hans von Ohain in Germany , developed the concept independently into practical engines during the late 1930s. Turbojets have poor efficiency at low vehicle speeds, which limits their usefulness in vehicles other than aircraft. Turbojet engines have been used in isolated cases to power vehicles other than aircraft, typically for attempts on land speed records . Where vehicles are "turbine-powered", this

8370-590: The Westland-Hill Pterodactyl series. However, Dunne's theories met with little acceptance amongst the leading aircraft designers and aviation companies at the time. The idea of using swept wings to reduce high-speed drag was developed in Germany in the 1930s. At a Volta Conference meeting in 1935 in Italy, Adolf Busemann suggested the use of swept wings for supersonic flight. He noted that

8525-418: The de Havilland Comet , which would become the world's first jet airliner. An early design consideration was whether to apply the new swept-wing configuration. Thus, an experimental aircraft to explore the technology, the de Havilland DH 108 , was developed by the firm in 1944, headed by project engineer John Carver Meadows Frost with a team of 8–10 draughtsmen and engineers. The DH 108 primarily consisted of

8680-412: The 1930s and 1940s, but the breakthrough mathematical definition of sweep theory is generally credited to NACA 's Robert T. Jones in 1945. Sweep theory builds on other wing lift theories. Lifting line theory describes lift generated by a straight wing (a wing in which the leading edge is perpendicular to the airflow). Weissinger theory describes the distribution of lift for a swept wing, but does not have

8835-857: The 1971 war in East Pakistan, were presented to the Bangladesh Air Force . The first production Gnat T.1s for the Royal Air Force were delivered in February 1962 to the Central Flying School at RAF Little Rissington . The major operator of the type was 4 Flying Training School at RAF Valley , the first aircraft being delivered in November 1962. In 1964 4 FTS formed the Yellowjacks aerobatic team with all-yellow painted Gnats. The team reformed in 1965 as part of

8990-405: The 1980s. The Sukhoi Su-47 Berkut is another notable demonstrator aircraft implementing this technology to achieve high levels of agility. To date, no highly swept-forward design has entered production. The first successful aeroplanes adhered to the basic design of rectangular wings at right angles to the body of the machine. Such a layout is inherently unstable; if the weight distribution of

9145-414: The 70-degree position, longitudinal control was maintained by wing tip-mounted elevons , and at the 20-degree position by a retractable canard arrangement. Auto- stabilisation was also to be used. By providing trimming with the canard, a large tailplane was not needed, as would have been on designs without a canard configuration. The Fo.147 was to have been capable of speeds in excess of Mach 2, with

9300-662: The Central Flying School as the Red Arrows which operated the Gnat until 1979 as the RAF aerobatic demonstration team. On 14 May 1965 the last Royal Air Force Gnat T.1 to be built was delivered to the Red Arrows. 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

9455-493: 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

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9610-513: The Folland prototype, serial number G-39-2 , first flew from RAF Boscombe Down , Wiltshire . 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

9765-405: The Gnat 5 could be readied for operational service within four or five years. In 1960, Maurice Brennan joined Folland as its chief engineer and director. Hawker Siddeley wanted to use his knowledge of variable-geometry wings in future designs. Under his direction, a variable geometry wing was applied to the basic Gnat 5 design to produce two different configurations – one tailless and one with

9920-481: 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

10075-548: 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

10230-441: The Gnat was instead powered by the less powerful Armstrong Siddeley Viper 101 turbojet engine, 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

10385-456: The Gnat; one of the more substantial of these proposals was tentatively designated as the Gnat Mk.5. This model was to be capable of supersonic speeds and was intended to be made available in both single-seat and twin-seat configurations, enabling its use in the trainer and interceptor role. The Gnat 5 was to be powered by either a pair of Rolls-Royce RB153R engines or two Viper 20 engines; in

10540-672: The IAF issued a requirement for an improved "Gnat II" in 1972, at first specifying that the new version was to be optimised as an interceptor but then expanding the specification to include ground-attack. 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

10695-574: The Indian government signed a contract for the production of the aircraft and Orpheus engine in India. 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

10850-615: 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,

11005-496: 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

11160-707: The actual aircraft speed is, this becomes a problem during slow-flight phases, such as takeoff and landing. There have been various ways of addressing the problem, including the variable-incidence wing design on the Vought F-8 Crusader , and swing wings on aircraft such as the F-14 , F-111 , and the Panavia Tornado . The term "swept wing" is normally used to mean "swept back", but other swept variants include forward sweep , variable sweep wings and oblique wings in which one side sweeps forward and

11315-434: The air does have time to react, and is pushed spanwise by the angled leading edge, towards the wing tip. At the wing root, by the fuselage, this has little noticeable effect, but as one moves towards the wingtip the airflow is pushed spanwise not only by the leading edge, but the spanwise moving air beside it. At the tip the airflow is moving along the wing instead of over it, a problem known as spanwise flow . The lift from

11470-421: The air would be added to the previously perpendicular airflow, resulting in an airflow over the wing at an angle to the leading edge. This angle results in airflow traveling a greater distance from leading edge to trailing edge, and thus the air pressure is distributed over a greater distance (and consequently lessened at any particular point on the surface). This scenario is identical to the airflow experienced by

11625-414: The aircraft changes even slightly, the wing will want to rotate so its front moves up (weight moving rearward) or down (forward) and this rotation will change the development of lift and cause it to move further in that direction. To make an aircraft stable, the normal solution is to place the weight at one end and offset this with an opposite downward force at the other - this leads to the classic layout with

11780-464: The aircraft decreases the efficiency of the engine because it has been compressed, but then does not contribute to producing thrust. Compressor types used in turbojets were typically axial or centrifugal. Early turbojet compressors had low pressure ratios up to about 5:1. Aerodynamic improvements including splitting the compressor into two separately rotating parts, incorporating variable blade angles for entry guide vanes and stators, and bleeding air from

11935-422: The aircraft to reach speeds closer to Mach 1. One limiting factor in swept wing design is the so-called "middle effect". If a swept wing is continuous - an oblique swept wing - the pressure isobars will be swept at a continuous angle from tip to tip. However, if the left and right halves are swept back equally, as is common practice, the pressure isobars on the left wing in theory will meet the pressure isobars of

12090-404: The aircraft's low weight. The Gnat design used a conventional metal stressed-skin structure, with extensive flush- rivetting . To reduce workload and cost, intensive fabrication methods such as machining , forging , and casting were minimised. The airframe could be constructed using simple jigs without any specialised skills or tooling. The wing (for example) could be produced at a quarter of

12245-418: The airspeed over the wing was dominated by the normal component of the airflow, not the freestream velocity, so by setting the wing at an angle the forward velocity at which the shock waves would form would be higher (the same had been noted by Max Munk in 1924, although not in the context of high-speed flight). Albert Betz immediately suggested the same effect would be equally useful in the transonic. After

12400-413: The angle of attack at the tip, thus reducing the bending moment on the wing, as well as somewhat reducing the chance of tip stall. However, the same effect on forward-swept wings produces a wash-in effect that increases the angle of attack promoting tip stall. Small amounts of sweep do not cause serious problems, and had been used on a variety of aircraft to move the spar into a convenient location, as on

12555-401: The basic concept of simple sweep theory, consider a straight, non-swept wing of infinite length, which meets the airflow at a perpendicular angle. The resulting air pressure distribution is equivalent to the length of the wing's chord (the distance from the leading edge to the trailing edge). If we were to begin to slide the wing sideways ( spanwise ), the sideways motion of the wing relative to

12710-412: The capability to include chordwise pressure distribution. There are other methods that do describe chordwise distributions, but they have other limitations. Jones' sweep theory provides a simple, comprehensive analysis of swept wing performance. An explanation of how the swept wing works was offered by Robert T. Jones : "Assume a wing is a cylinder of uniform airfoil cross-section, chord and thickness and

12865-410: The combustion chamber. Fuel is mixed with the compressed air and burns in the combustor. The combustion products leave the combustor and expand through the turbine where power is extracted to drive the compressor. The turbine exit gases still contain considerable energy that is converted in the propelling nozzle to a high speed jet. The first turbojets, used either a centrifugal compressor (as in

13020-432: The combustor and pass through to the turbine in a continuous flowing process with no pressure build-up. Instead, a small pressure loss occurs in the combustor. The fuel-air mixture can only burn in slow-moving air, so an area of reverse flow is maintained by the fuel nozzles for the approximately stoichiometric burning in the primary zone. Further compressed air is introduced which completes the combustion process and reduces

13175-421: The compressor enabled later turbojets to have overall pressure ratios of 15:1 or more. After leaving the compressor, the air enters the combustion chamber. The burning process in the combustor is significantly different from that in a piston engine . In a piston engine, the burning gases are confined to a small volume, and as the fuel burns, the pressure increases. In a turbojet, the air and fuel mixture burn in

13330-401: The compressor is passed through these to keep the metal temperature within limits. The remaining stages do not need cooling. In the first stage, the turbine is largely an impulse turbine (similar to a pelton wheel ) and rotates because of the impact of the hot gas stream. Later stages are convergent ducts that accelerate the gas. Energy is transferred into the shaft through momentum exchange in

13485-536: The compressor stage. Well-known examples are the Concorde and Lockheed SR-71 Blackbird propulsion systems where the intake and engine contributions to the total compression were 63%/8% at Mach 2 and 54%/17% at Mach 3+. Intakes have ranged from "zero-length" on the Pratt & Whitney TF33 turbofan installation in the Lockheed C-141 Starlifter , to the twin 65 feet (20 m) long, intakes on

13640-519: The cone increases with increasing speed, at Mach 1.3 the angle is about 45 degrees, at Mach 2.0 it is 60 degrees. The angle of the Mach cone formed off the body of the aircraft will be at about sin μ = 1/M (μ is the sweep angle of the Mach cone) When a swept wing travels at high speed, the airflow has little time to react and simply flows over the wing almost straight from front to back. At lower speeds

13795-473: The cost, with less than one-fifth the labour, required for the wings of other contemporary fighter aircraft. Similarly, the layout and construction techniques used allow the airframe to be rapidly disassembled into its major subsections, without the use of cranes or ladders ; the Gnat was vastly easier to service than most other aircraft. The Finnish Air Force received the first of its 13 Gnats (11 fighters and 2 photo-reconnaissance planes) on 30 July 1958. It

13950-421: 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

14105-407: 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

14260-412: The effects of compressibility in transonic and supersonic aircraft because of the reduced pressures. This allows the mach number of an aircraft to be higher than that actually experienced by the wing. There is also a negative aspect to sweep theory. The lift produced by a wing is directly related to the speed of the air over the wing. Since the airflow speed experienced by a swept wing is lower than what

14415-460: The engine in front and the control surfaces at the end of a long boom with the wing in the middle. This layout has long been known to be inefficient. The downward force of the control surfaces needs further lift from the wing to offset. The amount of force can be decreased by increasing the length of the boom, but this leads to more skin friction and weight of the boom itself. This problem led to many experiments with different layouts that eliminates

14570-554: The fastest aircraft of the era were only approaching 400 km/h (249 mph).The presentation was largely of academic interest, and soon forgotten. Even notable attendees including Theodore von Kármán and Eastman Jacobs did not recall the presentation 10 years later when it was re-introduced to them. Hubert Ludwieg of the High-Speed Aerodynamics Branch at the AVA Göttingen in 1939 conducted

14725-408: The fictional carrier-based "Oscar EW-5894 Phallus" tactical fighter bombers flown by US Navy pilots in the 1991 comedy Hot Shots! . Related development Aircraft of comparable role, configuration, and era Related lists The initial version of this article was based on a public domain article from Greg Goebel's Vectorsite . Swept-wing Swept wings have been flown since

14880-621: The first wind tunnel tests to investigate Busemann's theory. Two wings, one with no sweep, and one with 45 degrees of sweep were tested at Mach numbers of 0.7 and 0.9 in the 11 x 13 cm wind tunnel. The results of these tests confirmed the drag reduction offered by swept wings at transonic speeds. The results of the tests were communicated to Albert Betz who then passed them on to Willy Messerschmitt in December 1939. The tests were expanded in 1940 to include wings with 15, 30 and -45 degrees of sweep and Mach numbers as high as 1.21. With

15035-839: 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. Several Gnats survive including some airworthy examples (particularly in the United States and the United Kingdom) and others on public display. Data from Jane's All the World's Aircraft 1958-59, The Great Book of Fighters General characteristics Performance Armament Avionics Four privately owned Gnat T.1s together with an Ajeet portrayed

15190-442: The freestream conditions around the rest of the aircraft, and as the flow enters an adverse pressure gradient in the aft section of the wing, a discontinuity emerges in the form of a shock wave as the air is forced to rapidly slow and return to ambient pressure. At the point where the density drops, the local speed of sound correspondingly drops and a shock wave can form. This is why in conventional wings, shock waves form first after

15345-475: The high-temperature materials used in their turbosuperchargers during World War II. Water injection was a common method used to increase thrust, usually during takeoff, in early turbojets that were thrust-limited by their allowable turbine entry temperature. The water increased thrust at the temperature limit, but prevented complete combustion, often leaving a very visible smoke trail. Allowable turbine entry temperatures have increased steadily over time both with

15500-692: The immediate post-war era, several nations were conducting research into high speed aircraft. In the United Kingdom, work commenced during 1943 on the Miles M.52 , a high-speed experimental aircraft equipped with a straight wing that was developed in conjunction with Frank Whittle 's Power Jets company, the Royal Aircraft Establishment (RAE) in Farnborough , and the National Physical Laboratory . The M.52

15655-505: The initial problems were ironed out, the plane proved to be extremely manouevreable and had 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. In September 1956

15810-401: The interceptor role, it would be also equipped with a Ferranti AI.23 Airpass radar and armed with a pair of de Havilland Firestreak air-to-air missiles . Featuring an estimated maximum speed around Mach  2 (2,500 km/h; 1,500 mph) and a time to 50,000 ft (15,000 m) of 3 minutes, Folland estimated that a prototype could be flown as early as the end of 1962 and that

15965-538: The introduction of jets in the later half of the Second World War , the swept wing became increasingly applicable to optimally satisfying aerodynamic needs. The German jet-powered Messerschmitt Me 262 and rocket-powered Messerschmitt Me 163 suffered from compressibility effects that made both aircraft very difficult to control at high speeds. In addition, the speeds put them into the wave drag regime, and anything that could reduce this drag would increase

16120-494: The introduction of supercritical sections, the crest was usually close to the quarter chord. Typical sweep angles vary from 0 for a straight-wing aircraft, to 45 degrees or more for fighters and other high-speed designs. Shock waves can form on some parts of an aircraft moving at less than the speed of sound. Low-pressure regions around an aircraft cause the flow to accelerate, and at transonic speeds this local acceleration can exceed Mach 1. Localized supersonic flow must return to

16275-441: The introduction of superior alloys and coatings, and with the introduction and progressive effectiveness of blade cooling designs. On early engines, the turbine temperature limit had to be monitored, and avoided, by the pilot, typically during starting and at maximum thrust settings. Automatic temperature limiting was introduced to reduce pilot workload and reduce the likelihood of turbine damage due to over-temperature. A nose bullet

16430-401: The jet V j {\displaystyle V_{j}\;} must exceed the true airspeed of the aircraft V {\displaystyle V\;} if there is to be a net forward thrust on the airframe. The speed V j {\displaystyle V_{j}\;} can be calculated thermodynamically based on adiabatic expansion . The operation of a turbojet

16585-399: The maximum Thickness/Chord and why all airliners designed for cruising in the transonic range (above M0.8) have supercritical wings that are flatter on top, resulting in minimized angular change of flow to upper surface air. The angular change to the air that is normally part of lift generation is decreased and this lift reduction is compensated for by deeper curved lower surfaces accompanied by

16740-420: The need for the downward force. One such wing geometry appeared before World War I , which led to early swept wing designs. In this layout, the wing is swept so that portions lie far in front and in back of the center of gravity (CoG), with the control surfaces behind it. The result is a weight distribution similar to the classic layout, but the offsetting control force is no longer a separate surface but part of

16895-402: The opposite way to energy transfer in the compressor. The power developed by the turbine drives the compressor and accessories, like fuel, oil, and hydraulic pumps that are driven by the accessory gearbox. After the turbine, the gases expand through the exhaust nozzle producing a high velocity jet. In a convergent nozzle, the ducting narrows progressively to a throat. The nozzle pressure ratio on

17050-433: The other back. The delta wing also incorporates the same advantages as part of its layout. Sweeping a wing forward has approximately the same effect as rearward in terms of drag reduction, but has other advantages in terms of low-speed handling where tip stall problems simply go away. In this case the low-speed air flows towards the fuselage, which acts as a very large wing fence. Additionally, wings are generally larger at

17205-421: The pairing of the front fuselage of the de Havilland Vampire to a swept wing and small vertical tail; it was the first British swept wing jet, unofficially known as the "Swallow". It first flew on 15 May 1946, a mere eight months after the project's go-ahead. Company test pilot and son of the builder, Geoffrey de Havilland Jr ., flew the first of three aircraft and found it extremely fast – fast enough to try for

17360-458: The performance of their aircraft, notably the notoriously short flight times measured in minutes. This resulted in a crash program to introduce new swept wing designs, both for fighters as well as bombers . The Blohm & Voss P 215 was designed to take full advantage of the swept wing's aerodynamic properties; however, an order for three prototypes was received only weeks before the war ended and no examples were ever built. The Focke-Wulf Ta 183

17515-504: The pioneer days of aviation. Wing sweep at high speeds was first investigated in Germany as early as 1935 by Albert Betz and Adolph Busemann , finding application just before the end of the Second World War . It has the effect of delaying the shock waves and accompanying aerodynamic drag rise caused by fluid compressibility near the speed of sound , improving performance. Swept wings are therefore almost always used on jet aircraft designed to fly at these speeds. The term "swept wing"

17670-402: The presentation the host of the meeting, Arturo Crocco , jokingly sketched "Busemann's airplane of the future" on the back of a menu while they all dined. Crocco's sketch showed a classic 1950s fighter design, with swept wings and tail surfaces, although he also sketched a swept propeller powering it. At the time, however, there was no way to power an aircraft to these sorts of speeds, and even

17825-422: The problem. In addition to pitch-up there are other complications inherent in a swept-wing configuration. For any given length of wing, the actual span from tip-to-tip is shorter than the same wing that is not swept. There is a strong correlation between low-speed drag and aspect ratio , the span compared to chord, so a swept wing always has more drag at lower speeds. In addition, there is extra torque applied by

17980-493: 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

18135-483: 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 a number are still flying today. 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

18290-403: The right wing on the centerline at a large angle. As the isobars cannot meet in such a fashion, they will tend to curve on each side as they near the centerline, so that the isobars cross the centerline at right angles to the centerline. This causes an "unsweeping" of the isobars in the wing root region. To combat this unsweeping, German aerodynamicist Dietrich Küchemann proposed and had tested

18445-431: The root anyway, which allows them to have better low-speed lift. However, this arrangement also has serious stability problems. The rearmost section of the wing will stall first causing a pitch-up moment pushing the aircraft further into stall similar to a swept back wing design. Thus swept-forward wings are unstable in a fashion similar to the low-speed problems of a conventional swept wing. However unlike swept back wings,

18600-404: The speed limit set by the temperature of the structure as a result of kinetic heating. It had a maximum all-up weight of 18,500 lb (8,400 kg), comparing well with the Gnat 5's more restrictive 11,100 lb (5,000 kg) maximum. According to aviation author Derek Wood, the Fo.147: "would have provided a first-class flying test-bed for variable geometry theories...even a VG conversion of

18755-402: The stagnation point on the leading edge of any individual wing segment further beneath the leading edge, increasing effective angle of attack of wing segments relative to its neighbouring forward segment. The result is that wing segments farther towards the rear operate at increasingly higher angles of attack promoting early stall of those segments. This promotes tip stall on back-swept wings, as

18910-488: The standard Gnat Mk 2 fighter would have been an invaluable research tool". However, neither the Fo.147 nor its successor, the Fo.148, would be developed to the prototype stage; the RAF showed little interest in the need for a variable-geometry trainer, although it intended to procure the General Dynamics F-111K strike aircraft. The Folland Gnat was a purpose-built light fighter aircraft, suitable as both

19065-468: The supersonic airliner, in terms of miles per gallon, compared to subsonic airliners at Mach 0.85 (Boeing 707, DC-8) was relatively small. This is because the large increase in drag is largely compensated by an increase in powerplant efficiency (the engine efficiency is increased by the ram pressure rise which adds to the compressor pressure rise, the higher aircraft speed approaches the exhaust jet speed increasing propulsive efficiency). Turbojet engines had

19220-554: The swept wing design used by most modern jet aircraft, as this design performs more effectively at transonic and supersonic speeds. In its advanced form, sweep theory led to the experimental oblique wing concept. Adolf Busemann introduced the concept of the swept wing and presented this in 1935 at the Fifth Volta Conference in Rome. Sweep theory in general was a subject of development and investigation throughout

19375-446: The temperature of the combustion products to a level which the turbine can accept. Less than 25% of the air is typically used for combustion, as an overall lean mixture is required to keep within the turbine temperature limits. Hot gases leaving the combustor expand through the turbine. Typical materials for turbines include inconel and Nimonic . The hottest turbine vanes and blades in an engine have internal cooling passages. Air from

19530-548: The thrust from a turbojet engine. It was flown by test pilot Erich Warsitz . The Gloster E.28/39 , (also referred to as the "Gloster Whittle", "Gloster Pioneer", or "Gloster G.40") made the first British jet-engined flight in 1941. It was designed to test the Whittle jet engine in flight, and led to the development of the Gloster Meteor. The first two operational turbojet aircraft, the Messerschmitt Me 262 and then

19685-411: The tips are most rearward, while delaying tip stall for forward-swept wings, where the tips are forward. With both forward and back-swept wings, the rear of the wing will stall first creating a nose-up moment on the aircraft. If not corrected by the pilot the plane will pitch up, leading to more of the wing stalling and more pitch up in a divergent manner. This uncontrollable instability came to be known as

19840-450: The tips on a forward swept design will stall last, maintaining roll control. Forward-swept wings can also experience dangerous flexing effects compared to aft-swept wings that can negate the tip stall advantage if the wing is not sufficiently stiff. In aft-swept designs, when the airplane maneuvers at high load factor the wing loading and geometry twists the wing in such a way as to create washout (tip twists leading edge down). This reduces

19995-404: The tips to bend upwards in normal flight. Backwards sweep causes the tips to reduce their angle of attack as they bend, reducing their lift and limiting the effect. Forward sweep causes the tips to increase their angle of attack as they bend. This increases their lift causing further bending and hence yet more lift in a cycle which can cause a runaway structural failure. For this reason forward sweep

20150-412: The turbines would overheat, the lubricating oil would leak from the bearing cavities, the rotor thrust bearings would skid or be overloaded, and ice would form on the nose cone. The air from the compressor, called secondary air, is used for turbine cooling, bearing cavity sealing, anti-icing, and ensuring that the rotor axial load on its thrust bearing will not wear it out prematurely. Supplying bleed air to

20305-408: The turbines. British engines such as the Rolls-Royce Welland used better materials giving improved durability. The Welland was type-certified for 80 hours initially, later extended to 150 hours between overhauls, as a result of an extended 500-hour run being achieved in tests. General Electric in the United States was in a good position to enter the jet engine business due to its experience with

20460-524: The two wars were against Sabres despite the Canadair Sabre Mk 6 being 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, in

20615-512: The undercarriage; almost all new pilots would find it difficult to control the anticipated pitch up. With sufficient experience, pilots would exploit the nimble mini-sized aircraft to its limits. The Gnat is credited by many independent and Indian sources as having shot down seven Pakistani North American F-86 Sabres in the 1965 war . During the initial phase of the 1965 war, an IAF Gnat, piloted by Squadron Leader Brij Pal Singh Sikand, landed at an abandoned Pakistani airstrip at Pasrur and

20770-472: The wing also remains the same, the distance between leading and trailing edges reduces, reducing its ability to resist twisting (torsion) forces. A swept wing of given span and chord must therefore be strengthened and will be heavier than the equivalent unswept wing. A swept wing typically angles backward from its root rather than forwards. Because wings are made as light as possible, they tend to flex under load. This aeroelasticity under aerodynamic load causes

20925-448: The wing experiences airflow that is slower - and at lower pressures - than the actual speed of the aircraft. One of the factors that must be taken into account when designing a high-speed wing is compressibility , which is the effect that acts upon a wing as it approaches and passes through the speed of sound . The significant negative effects of compressibility made it a prime issue with aeronautical engineers. Sweep theory helps mitigate

21080-402: The wing has the effect of reducing the curvature of the body as seen from the airflow, by the cosine of the angle of sweep. For instance, a wing with a 45 degree sweep will see a reduction in effective curvature to about 70% of its straight-wing value. This has the effect of increasing the critical Mach by 30%. When applied to large areas of the aircraft, like the wings and empennage , this allows

21235-469: The wing to the fuselage which has to be allowed for when establishing the transfer of wing-box loads to the fuselage. This results from the significant part of the wing lift which lies behind the attachment length where the wing meets the fuselage. Sweep theory is an aeronautical engineering description of the behavior of airflow over a wing when the wing's leading edge encounters the airflow at an oblique angle. The development of sweep theory resulted in

21390-524: The wing, which would have existed anyway. This eliminates the need for separate structure, making the aircraft have less drag and require less total lift for the same level of performance. These layouts inspired several flying wing gliders and some powered aircraft during the interwar years. The first to achieve stability was British designer J. W. Dunne who was obsessed with achieving inherent stability in flight. He successfully employed swept wings in his tailless aircraft (which, crucially, used washout ) as

21545-421: Was an extremely difficult aircraft to handle in the early stages of training. Unlike the RAF, the IAF did not buy a trainer version. Inductees were brought in from Hunter aircraft squadrons, having gained experience on powered controls. They then flew dual checks on the Hunter trainer. The pilot would do a brief full throttle run on the runway before flying solo. The Gnat had a tendency to pitch up sharply on raising

21700-516: Was another swept wing fighter design, but was also not produced before the war's end. In the post-war era, Kurt Tank developed the Ta 183 into the IAe Pulqui II , but this proved unsuccessful. A prototype test aircraft, the Messerschmitt Me P.1101 , was built to research the tradeoffs of the design and develop general rules about what angle of sweep to use. When it was 80% complete, the P.1101

21855-555: Was captured by US forces and returned to the United States , where two additional copies with US-built engines carried on the research as the Bell X-5 . Germany's wartime experience with the swept wings and its high value for supersonic flight stood in strong contrast to the prevailing views of Allied experts of the era, who commonly espoused their belief in the impossibility of manned vehicles travelling at such speeds. During

22010-536: Was captured by the PAF. Two Lockheed F-104 Starfighters claimed to have forced the Gnat down. Sikand — who had a complete electrical failure on his Gnat while he got separated from the IAF flight to fight a Sabre — had to make an emergency landing at the PAF field at Pasrur. This Gnat is displayed as a war trophy in the Pakistan Air Force Museum, Karachi . After the ceasefire, one Pakistani Cessna O-1

22165-406: Was designated Fo-139 Midge . On 11 August 1954, the Midge performed its maiden flight , piloted by Folland's chief test pilot Edward 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 by a pilot from

22320-460: Was envisioned to be capable of achieving 1,000 miles per hour (1,600 km/h) in level flight, thus enabling the aircraft to potentially be the first to exceed the speed of sound in the world. In February 1946, the programme was abruptly discontinued for unclear reasons. It has since been widely recognised that the cancellation of the M.52 was a major setback in British progress in the field of supersonic design. Another, more successful, programme

22475-537: 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

22630-510: 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

22785-424: Was liquid-fuelled. Whittle's team experienced near-panic during the first start attempts when the engine accelerated out of control to a relatively high speed despite the fuel supply being cut off. It was subsequently found that fuel had leaked into the combustion chamber during pre-start motoring checks and accumulated in pools, so the engine would not stop accelerating until all the leaked fuel had burned off. Whittle

22940-415: Was selected as the eventual winner of the fly-off competition. Although RAF interest in the possibilities for using the Gnat as a fighter had waned, Folland identified a 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

23095-580: Was shot down on 16 December 1965 by a Gnat. The Gnats were used again by India in the Indo-Pakistani War of 1971 . The most notable action was the Battle of Boyra where the first dogfights over East Pakistan ( Bangladesh ) took place. IAF Gnats shot down two PAF Canadair Sabres and badly damaged one. Another notable dogfight involving a Gnat was over Srinagar airfield where a lone Indian pilot held out against six Sabres, shooting two Sabres in

23250-470: 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 were built. On 31 July 1958, Finnish Air Force Major Lauri Pekuri , a fighter ace of the Second World War , became the first Finnish pilot to break the sound barrier while flying

23405-640: Was tested on the Power Jets W.1 in 1941 initially using ammonia before changing to water and then water-methanol. A system to trial the technique in the Gloster E.28/39 was devised but never fitted. An afterburner or "reheat jetpipe" is a combustion chamber added to reheat the turbine exhaust gases. The fuel consumption is very high, typically four times that of the main engine. Afterburners are used almost exclusively on supersonic aircraft , most being military aircraft. Two supersonic airliners, Concorde and

23560-654: Was the US's Bell X-1 , which also was equipped with a straight wing. According to Miles Chief Aerodynamicist Dennis Bancroft, the Bell Aircraft company was given access to the drawings and research on the M.52. On 14 October 1947, the Bell X-1 performed the first manned supersonic flight, piloted by Captain Charles "Chuck" Yeager , having been drop launched from the bomb bay of a Boeing B-29 Superfortress and attained

23715-541: Was the addition of a dogtooth notch to the leading edge, used on the Avro Arrow interceptor. Other designs took a more radical approach, including the Republic XF-91 Thunderceptor 's wing that grew wider towards the tip to provide more lift at the tip. The Handley Page Victor was equipped with a crescent wing , with three values of sweep, about 48 degrees near the wing root where the wing

23870-471: Was thickest, a 38 degree transition length and 27 degrees for the remainder to the tip. Modern solutions to the problem no longer require "custom" designs such as these. The addition of leading-edge slats and large compound flaps to the wings has largely resolved the issue. On fighter designs, the addition of leading-edge extensions , which are typically included to achieve a high level of maneuverability, also serve to add lift during landing and reduce

24025-485: Was unable to interest the government in his invention, and development continued at a slow pace. In Germany, Hans von Ohain patented a similar engine in 1935. His design, an axial-flow engine, as opposed to Whittle's centrifugal flow engine, was eventually adopted by most manufacturers by the 1950s. On 27 August 1939 the Heinkel He 178 , powered by von Ohain's design, became the world's first aircraft to fly using

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