Profile – Hawker Hunter

However, Camm and his skilled staff were not at first enthusiastic about making the transition to jet propulsion and swept wings. Their first venture into this area was the Hawker P. 1035 towards the end of 1944 built around a Rolls-Royce B. 41 (Nene) engine. It was a straight-wing design with bifurcated engine exhausts emerging from the trailing edge wing roots, a layout not favoured by officialdom.

Camm could see no real problem associated with a bifurcated jetpipe system and retained the layout in his P. 1040 design submitted to the Ministry of Aircraft Production in January 1946. The RAF. was not interested but the R. N. thought it could be a possible replacement for the Sea Fury. Three prototypes were ordered to Specification N. 7/46 on May 28, 1946. The first P. 1040 (VP40I) was flown at Boscombe Down on September 2, 1947, and the type eventually entered service with the Fleet Air Arm in March, 1953, as the Sea Hawk. An advantage of the bifurcated pipe was that it enabled an extra fuel tank to be placed behind the engine because the fuselage was left free of ducting. A total of 585 Sea Hawks were produced altogether.

While they were working with the P. 1040 the Ministry of Aircraft Production issued Specification F. 43/46 on January 24, 1947. This called for an interceptor fighter capable of destroying high-altitude jet bombers in daylight using either two 30mm cannons or a huge 4. 5-inch recoilless gun capable of firing a clip of 6-10 rounds as an eventual replacement for the Meteor.

Then, on October 1, 1947, at Edwards A. F. C. , California, the promising North American XP-86 Sabre took to the air for the first time, one month after the P. 1040’s first flight. British design was clearly lagging. The XP-86 was powered by a General Electric J35 axial-flow engine and it featured a wing sweep of 35°.

Some exploratory work on swept wings had already been done in the U. K. so Camm decided to join 35° swept wings onto the fuselage of his P. 1040 and two prototypes were put under construction. The first (VX272) was designated P. 1052 and flew for the first time on November 19, 1948, just over a year after the XP-86.

The P. 1052’s straight tail surfaces proved to be ineffective at high speed because of airflow separations caused by shock waves. Accordingly, the second prototype (VX279) was modified by giving it a swept tail. At the same time, Camm, mindful of the unfavourable opinion of the bifurcated engine exhaust layout, replaced the wing root nozzles with a single, straight-through jetpipe and redesignated the machine P. 1081. This first flew on June 19, 1950, and it was this aircraft that created such interest in R. A. A. F. circles.

Unfortunately, another feature not favoured by the Air Staff was the Whittle-style centrifugal Nene jet engine. This type of engine was expected to be superseded by engines with axial-type compressors, a view underlined by the promise shown by the J35-powered Sabre. It was the Air Staff’s dislike of centrifugal engines that eventually killed the P. 1052/P. 1081 series in spite of Camm’s arguments for the virtues of such engines as the Rolls Royce Tay with afterburner (advanced versions of this engine gave up to 8,750-lb thrust and were cheaper and more efficient than the heavy and cumbersome axial power plants such as the J35 and early Rolls Royce Avon. Be that as it may, after VX279 crashed in April 1951, there was no effort put into constructing another P. 1081. Something else was almost ready.

NEW SPECIFICATION

Camm had not put all his eggs into the one basket and while testing of the P. 1040, P. 1052 and P. 1081 aircraft was proceeding, another related type, the P. 1067, was under simultaneous development and receiving benefit from the valuable lessons learned.

Back in 1947, after specification F. 43/46 had been issued, Camm envisaged a trim, mid-wing aircraft with a cylindrical tubular fuselage incorporating a nose intake for an AJ-65 axial jet engine which exhausted out of the back under a T-shaped tail. It was to carry two 30mm Aden cannons under the fuselage. This concept did not exactly match F. 43/46 but when it was submitted for consideration as a private venture in January 1948, it was accepted. In March the same year, new specification F. 3/48 was prepared around the P. 1067 and an order for 3 prototypes followed. By May, when the order came through, Camm’s original proposal had undergone numerous modifications. Instead of having a nose intake he decided to use wing root inlets as he had done in the P. 1040/P. 1081 series. This meant a thickened wing root incorporating strong, sharply tapering spars with steel booms outside which the ruling thickness/chord ratio was 8. 5 per cent. Wing sweep was 40°. The tailplane was lowered on the fin to a position three-quarters down but still well clear of the fuselage. Armament had been increased to four 30mm Aden cannon mounted in an easily connected and disconnected gun pack, change time would be around five minutes.

The engine to be used for the first two prototypes was the Rolls Royce Avon RA. 2, a renamed AJ. 65, while the third was to be powered by an Armstrong Siddeley Sapphire.

The first prototype (WB188) was finished in June 1951, two months after the P. 1081 crash. It was shipped to Bascombe Down by road where, after it was assembled, S/Ldr. Neville Duke, now Hawker’s chief test pilot after S/Ldr. T. S. ‘Wimpey’ Wade’s death in the P. 1081, carried out taxi trials. On his first fast taxi run the brakes burned out and he only just managed to steer off the far end of the runway safely.

FIRST FLIGHTS

On July 20, 1951, Duke took the duck-egg green machine into the air for the first time. He found that the extreme sensitivity of the powered ailerons caused lateral rocking which could not be completely eliminated. Also, he needed to maintain a heavy force on the elevator controls because the elevator hydraulic boost had been disconnected for the first flight and a severe lack of tailplane trim obliged him to use both hands to pull back on the control column while landing 47 minutes later. Nevertheless, he had taken the plane up to 20,000 feet (6,100m) and to a speed of 350 knots and been impressed by it – he was convinced that Hawker had a winner. With elevator power restored, early test flights ran smoothly, so much so that, with only 11 hours in its logbook, Duke demonstrated WB188 at the SBAC show. At low level over the heads of the crowd, he hurtled at an impressive 700 mph (1,130 km/h). In January 1952, when he began taking the plane up to its limiting speed, Duke encountered heavy tail buffeting and vibration due to the compressibility effects near Mach 1. This was remedied by the introduction of an acorn-shaped tailplane anti-buffet fairing. On June 6 buffet free flight was achieved at an indicated Mach 1. 06.

The second prototype (WB195) flew on May 5, 1952. It was powered by a fully developed Avon RA. 7 Mk104 and carried almost all of its combat equipment including a radar ranging Mk5 gunsight, the gun pack, two VHF radios and Rebecca/Eureka and DME navaids.

Unlike the other two, the Sapphire-powered prototype (WB202) was painted silver and first flew on November 30, 1952, at Dunsfold. It was 7 1/2 inches (19. 1 cm) longer than the others and this became the standard length for production aircraft. It also proved to be a marginally better performer. After the usual test flights, this machine was used for gunnery trials which proceeded without a hitch.

Even before the first prototype had flown, production orders ‘ were being placed for the new aircraft. In October 1950, Hawker received an order for 200 Avon-powered aircraft, Armstrong Whitworth an order for 200 with the Sapphire engine but an order placed with Gloster for 151 machines was later cancelled because the company did not have the capacity to meet it. The impetus behind these orders was the Korean War and the fear that it could erupt into a wider conflict. Production was placed on a ‘super priority’ level. Tooling for the construction of the P. 1067 required 3,250 tool designs and more than 40,000 jigs and fixtures. Of these, more than 11,000 had to come from the continent, especially from Italy, together with over 1,800 special machine tools and much raw material. The former Wellington bomber factory at Squire’s Gate was reopened as Hawker Aircraft (Blackpool) and plans were made for assembly lines at Dunsfold and Bitterswell. On July 10, 1952, Neville Duke and WB188, now officially known as the ‘Hunter’, gave their first public demonstration of supersonic flying over Brussels. Present was a USAF evaluation team which was suitably impressed and recommended major Off-Shore Procurement Orders. Under this scheme the US government bought equipment from friendly NATO powers in order to boost their arms industries and distribute it to the various member air forces. At least 468 Hunters were built and distributed under this system. (Altogether 958 Hunters were funded wholly or partly by the U. S. ).

PRODUCTION PROBLEMS IN SERVICE

In spite of these promising beginnings, the Hunter’s introduction into service was delayed many months and when it did become operational its efficiency was seriously inhibited. There were two serious problems. The first to manifest itself concerned the airbrakes. As in Camm’s earlier designs, the P. 1052 and P. 1081, the main landing flaps of the Hunter were designed to act as airbrakes and remain fully open at speed stresses up to 620 knots IAS and above that speed to blow back via hydraulic relief valves so as to prevent any structure failure.

Unfortunately, when they were applied they produced a nose-down pitching movement which was unacceptable except at slow speed. The RAF refused to accept the Hunter until a more satisfactory new combat air brake was developed. After experimentations, the problem was solved by the introduction of a clumsy-looking curved brake hinged under the rear fuselage. The effect of this modification on the ‘super priority’ production line caused delays but these were minimal in terms of changes needed and time lost, however, the slim, elegant line of the Hunter’s fuselage was marred by the addition. Even so, particularly when viewed from underneath, there was always something beautiful but shark-like about the Hunter with its graceful but menacing appearance.

As already mentioned, gun firing trials were initially carried out using WB202, the Sapphire-powered prototype, but it was found that when Avon-Hunters fired their four 30mm cannons in flight the engine would cough and surge severely. Gunfire concussion was causing the sudden, violently unstable breakdown of flow through the Avon’s compressor and the problem was not discovered until production aircraft and engines were rolling off the assembly lines in 1953 (the first Avon-Hunter F. 1, WT555, was completed on May 16, 1953, and the first Sapphire-Hunter F. 2. WN888 on October 1, 1953).

Actually, Rolls Royce had known that its engine was subject to surging since 1950 when it first occurred in the Avon 104. They tried unsuccessfully to correct it in the hot-air, anti-iced Avon 107 and the problem persisted in the Avon 113 (RA21 rating) which became the standard Hunter F. 1 engine. Surging could happen any time, especially about 10,000 feet (3,050m), resulting in damage to the engine and possible flameouts. It always occurred when the guns were fired. Sapphire-Hunters suffered from no such vice. The first F. 2’s, by 1955 used by 257 and 263 Squadrons were cleared to fire high-velocity ammunition to 48,000 feet (14,500m) and 550 knots IAS whereas Hunter F. 1’s, by 1955 used by 43, 54 and 222 Squadrons and 229 and 233 OCU’s, were limited to 25,000 feet (7,600m) and 250 knots IAS. The problem was not completely eliminated until Rolls Royce licence built the Sapphire compressor and combined it with their Avon engine, the union resulting in the excellent Avon 200 series which worked efficiently and gave greater power and was incorporated in the later Hunter F. 6. However, an interesting question remains why were not more of the trouble-free Saphire-Hunters produced?

Another problem associated with firing the Adens on all Hunters was that at high IAS the ammunition links, after they were ejected, often struck and damaged the protruding air brake and rear fuselage. Later, two large external blisters were added under the guns to collect the links – these were named ‘Sabrinas after a well-known female movie personality.

SPEED RECORD

There was only one Hunter Mk. 3 and it was something special This designation was given to the first prototype WB188 after it was fitted with an afterburning Avon RA. 7R of 6,900-lb (4,355- kg) thrust for a high-speed record attempt. The nose was pointed and the windscreen streamlined. With Neville Duke again at the controls, this machine, painted bright red for ease of camera definition, set a new official world speed record of 727. 48 mph (1,170. 76 km/hr)” on September 7, 1953, and twelve days later a new 100 km closed circuit record of 709. 2 mph (1. 141 km/hr)”. both in adverse weather conditions. Back on August 31, Duke had actually achieved an unofficial speed of 741. 5 mph (1,193. 33 km/hr)”. (“Figures from Guinness Book of Air Facts and Feats. )

LATER MODELS

Designed as a fast climbing interceptor, the Hunter’s main drawback was its extremely short endurance and there are a number of incidents recorded where they were lost or obliged to force land because of fuel shortage. A normal training sortie lasted around 35 minutes. The need for more internal fuel led to the introduction of fuel cells in the leading edge of the wings immediately outboard of the inlet ducts. This converted the F. 1 (139 produced) into the F. 4 and the F. 2 (45 built) into the F. 5 without disrupting the production lines. At the same time the wings were modified to carry 100-gallon (455-1) drop tanks as standard or up to a 1,000-lb (454 kg) bomb load on each pylon. Later modification doubled the external capacity and provided for eight racks of rocket projectiles. A total of 365 Avon 115/121 powered Hunter F. 4’s were constructed in the U. K. plus 96 in the Netherlands and 114 in Belgium. There were 105 Sapphire- Hunter F. 5’s built Meanwhile, under project designation P. 1099, the pale green prototype Hunter F. 6 (FX833), powered by a 10,000 lb (4,536 kg) thrust Avon 200-series engine, flew for the first time on January 22, 1954. This potent new variant proved to be the most prolific of the Hunter series, a total of 590 being built (including 93 in the Netherlands and 114 in Belgium). As the Mk. 56 export model, 160 were delivered to India and, as the Mk. 58 and Mk. 58A models, 152 went to Switzerland. It flew with no fewer than 19 RAF Squadrons from late 1958 when it entered service. The new machine also featured liquid-fuel starting instead of a triple-breach cordite starter used previously by Avon-Hunters (Sapphire-Hunters had only 2 cartridges but rarely needed the second to start). Camm also introduced a ‘flying tail”.

Soon the more powerful F. 6’s began to encounter severe pitch-up problems at high speeds and altitudes. As with other fighters of the mid-1950s, this was remedied by extending and drooping the outside leading edges of the wings with a dog-tooth cut-off to generate a large vortex at the inboard ends. These changes were introduced after more than three-quarters of the Hunter F. 6’s had been produced but they were gradually applied as retroactive modifications to all preceeding aircraft. After the pitch-up problems had been solved the Hunter became an exceptionally stable gun platform Lessening of East-West tensions in the post-Korean War period decreased the pressing need for new fighters and in 1957 a British Defence White Paper cancelled the most recent Hunter orders. The only new version to reach production was the belated, private venture P. 1101, a side-by-side two-seat trainer powered by a small-bore Avon 122 and featuring two Aden cannons in bulges under the fuselage. The prototype (X2615) first flew on July 8, 1955, but there were problems in developing a satisfactory hood shape and dorsal fairing so the maiden flight of the first Hunter T. 7 was delayed until October 11, 1957. By fitting the more powerful 200-series Avon inside F. 6 airframes the trainer became the T. 66 of the Indian Air Force. At the same time, the R. N. ‘s equivalent of the T. 7 was the T. 8 which was fitted with an arrester hook and a naval radio. Production Hunter T. 7’s were built with only the starboard Aden cannon. A total of 73 were delivered plus a further 20 for the Netherlands. There were 41 Hunter T. B. ‘s.

After comparison trials with Folland’s Gnat, the Hunter was selected for the ground-attack role to replace the de Havilland Venom. This led to the FGA. 9, a ground-attack derivative of the F. 6, which had special provisions for long-range ferry flights including 230-gallon (1,046-1) drop tanks, extra oxygen, and modifications to the longitudinal controls and front transport joint, plus the addition of a braking parachute. Altogether 126 were made.

The last mark of Hunter used by the RAF was the FR. 10 based on an F. 6 airframe and similar to the FGA. 9 but featuring a new nose housing one forward and two oblique reconnaissance cameras – 34 were constructed.

RN equivalents of the GFA. 9 and FR. 10 were the GA. 11 and PR. 11 converted from F. 4 airframes and powered by Avon 113/ 122 engines. Use was made of them as operational trainers with the guns removed. A total of 40 were converted.

The Hunter Mk. 12 (XE531) was a one-off, two-seat test aircraft, powered by an Avon 207, used by the Royal Aircraft Establishment for trials of equipment specifically developed for the TSR-2 including such items as a head-up display (HUD) and a vertically-mounted survey camera in the nose.

FLYING THE HUNTER From the cockpit, acceleration during take-off was impressive, particularly in the later models, and in its time it had one of the fastest climb rates of any fighter in the world. The aircraft’s large wing area, originally designed for high-altitude performance, also enhanced its manoeuvrability for ground attack. Use of the large airbrake caused little change in trim. It was a strong and robust machine without vices whereas many other fighters of that time displayed dangerous handling in high-speed, low-level flight, departed viciously at high angles of attack and could not recover from spins. Although its poor longitudinal control at high Mach numbers was never completely cured it became well-loved by its pilots.

From 1966, BAe (incorporating Hawker) maintained a substantial business utilizing Hunter’s universal popularity by custom rebuilding scrapped airframes and existing aircraft for overseas customers. Through modifications and rebuilding, any previous mark could be converted into any other so that out of the 1,972 Hawker Hunters built, even in the 1980s, more than 550 remain in service in 13 countries including India, Switzerland and the UK itself. An impressive record for a design that dates back to Specification F. 3/48 issued in March 1948, and one which, it is anticipated, will continue into the next century.