Hawker Hunter - 50th Anniversary
By Brett R Palfrey
Sidney Camm became Chief Designer of Hawkers in 1926, and remained in that post until his death in 1966. This is a stunning achievement particularly given the technological advances made in aircraft design during this period. Sidney Camm was a prolific designer who seemed to produce new fighter (or bomber) designs effortlessly on almost an annual basis. "Very nice, Sidney, we will take a hundred of those…" - this is how fighter procurement must have seemed to a casual observer throughout the 1930's. Hawker Aircraft were one of the leading producers of cutting edge, state of the art fighters during this period and the Second World War, but by 1948 Hawker and its Chief Designer found that they had time on their hands. The end of the war had reduced the pressure on aircraft development, and budgets were cut to a tiny percentage of their wartime levels.
By this stage, the jet age had arrived, and the RAF employed 2 main types of fighter, the Gloster Meteor and the De Havilland Vampire. Both were designed during World War 2, and neither of them were Hawker designs. These particular aircraft, although excellent machines, had started to show definite limitations, particularly in performance terms and especially when compared to the latest American fighters, which had been developed with the aid of German wartime research. The Meteor had a top speed of about 580 mph, if it flew faster compressibility became a problem as Mach 1 was approached.
Hawker built several jet prototypes in the immediate post-war period, the only one going into production was the Sea Hawk for the Royal Navy. The Sea Hawk itself was rejected by the RAF because they did not consider it to be sufficiently advanced over existing fighters. The series jet of prototypes, such as the P.1052 and P.1081, did however provide Hawker's with a great deal of experience in high speed fighter design.
All Camm's early jet aircraft designs used engines with centrifugal compressors, a feature common to all early jet engines, but the axial flow compressors which were in their infancy resulted in a much slimmer and more powerful generation of engines. Camm therefore went back to the drawing board, and designed a new fighter around this novel style of jet engine, specifically the Rolls Royce Avon and the Armstrong Siddeley Sapphire. These engines promised much better performance than anything already in service.
Development and first flight
Camm and his team set to work, and the new design, given the company designation Type 1067, took shape in late 1948. Metal was cut for the first prototypes in late 1949, the first aircraft being finished in July 1951. It was obvious from the outset that this aircraft's sleek lines, swept wings and tail, would promise good performance. Indeed the overall look of the fighter was more aesthetically pleasing than anything previously seen.
The new aircraft took shape around some design features necessitated by the intended equipment for the fighter's role. The radar ranging units had to be positioned in the nose, meaning the air intakes were moved to the wing roots. The armament associated with the ranging equipment was also entirely novel, in both type and arrangement. The future of fighter armament at this time was unclear, so four 30 mm Aden cannon were chosen as being likely to fullfil any Govenement requirement, unprecedented firepower for the day. The cannon were mounted in a single pod in the forward fuselage, the whole unit being removable. This meant the Hunter could be re-armed very quickly, as a full pod could be substituted for the empty one in around a minute by a trained crew. The first flight of the Hunter, as this aircraft was now named, was on 20th July 1951. It flew from Boscombe Down with Hawker's new Chief test pilot, Sqn Ldr Neville Duke, at the controls.
After some initial handling difficulties, and the addition of fairings over the tailplane and fin junction, the aircraft proved itself to be a true fighter thoroughbred from the Hawker stable. Even before flight testing was completed orders poured in for 200 Mk 1 Hunters, with the Rolls Royce Avon engine, from Hawkers at Kingston. A further 200 Mk 2 Hunters were ordered from Armstrong Whitworth at Coventry, fitted with the Armstrong Siddeley Sapphire engine.
Even while prototype testing was continuing, the Ministry of Supply added the requirement for an air brake that would not affect the aiming of the weapons, but that could also be deployed at all altitudes and all airspeeds. The optimum position for the brake took time to evaluate, and deliveries of the new fighter to the RAF were delayed as a result. The air brake was eventually built into the underside of the rear fuselage.
The Hunter F Mk.1 entered service with the Air Fighting Development Squadron at West Raynham in July 1954. These aircraft were quickly used in Air defence exercises, intercepting high flying Canberra bombers, surprising them with attacks from above, something the hitherto immune Canberras were not used to! The development trials were closely followed by Squadron service with No. 43 Sqn, at Leuchars. The only other 2 squadrons to receive the Mk.1 were No. 54 at Odiham, and No. 222 at Leuchars. The remainder of the 139 Mk 1s went to Operational Conversion Units. The Avon RA7 was starting to show problems with engine surges and flameouts, particularly when the aircraft's 30mm cannon were fired. This led to restrictions on gunfiring of 25,000 ft being introduced, a serious limitation in performance.
These particular problems were not evident in the Mk.2 with the Sapphire engine, although both marks were prone to a phenomena known as 'pitch-up'. The Mk.2 Sapphire engined aircraft could fire its guns beyond 40,000ft without problems. However, only 45 of these excellent aircraft were produced, equipping just 2 squadrons, Nos. 257 and 263, both based at Wattisham. Interestingly, the political clout of Rolls Royce was so strong, that despite the problems, most development was based on their engine, rather than the snag-free Sapphire. Bearing in mind that the endurance of the first two marks was very short, the Mk.2 did at least show everyone what the Hunter could do. It quickly became a favourite with Service pilots, because of its' crisp handling and great strength.
Only one Hunter Mk.3 was built, this was WB188, the first prototype Hunter. It was rebuilt with aerodynamic refinements, and a reheated Avon engine. This engine, the Avon RA7R, developed 7,130lb of thrust dry and up to 9,600lb of thrust with the afterburner lit. On 7 September 1953, Sqn Ldr Neville Duke took the Mk.3 to a new World Absolute Speed Record of 727.6 mph, off the Sussex coast at Rustington. On the 19th of the same month, Duke took the aircraft to a new 100 Km closed circuit record of 709.2 mph. This unique aircraft is still in existence, at RAF Cosford aerospace museum.
The mass-produced marks
The Mark 4 was the first really successful version. It took the Hunter from a useful point defence day fighter to a truly multi role fighter, with greater endurance and hardpoints for bombs and rockets. Drop tanks could also be carried to extend range even further, making the Hunter F Mk 4 a very capable fighter. Aircraft were produced initially as modified F Mk 1s, and later as new build aircraft. 365 F Mk 4 Hunters were produced, the first 156 with Avon 113 engines, and the remainder with Avon 115s. These had modified compressors to alleviate many of the surge problems that bedevilled the Hunter Mk.1.
The modified engines were retrofitted to most of the earlier airframes. The wing was also redesigned with 'sawtooth' extensions to the leading edge to alleviate the 'pitchup' phenomena, and internal fuel capacity was increased. The first Hunter F Mk 4 flew on 20th October 1954, and first deliveries were to No. 54 at Odiham, and No. 111 (F) at North Weald, in March 1955. In this same year, Hunter F Mk 4s were delivered to RAF Germany too, and by 1956, Hunters equipped 7 squadrons at home and 13 overseas in Germany.
Hunter F Mk 4s were also delivered to several NATO countries, and aircraft were built under licence in Belgium by Avions Fairey, and in the Netherlands by Fokker. These were for service in their respective air forces. After replacement in squadron service by the F Mk 6, many F Mk 4s served on OCUs, and later many were converted to two-seater T Mk 7 or T Mk 8 trainers. Still more were repurchased by Hawkers for refurbishment and resale overseas.
The Hunter F Mk 5 was essentially similar to the F Mk 4, the exception being that it was powered by the Armstrong Siddeley Sapphire Mk 101 engine, as fitted to the F Mk 2. Production was simply continued on the production line at the Coventry works of Armstrong Whitworth, aircraft number 46 in the production run was the first F Mk 5 off the line. Hunter F Mk 5s served with 5 squadrons of Fighter Command, No.s 1, 34, 41, 56 and 263. Deliveries commenced in 1955, and when the Suez crisis erupted in late 1956, Nos. 1 and 34 were deployed to Cyprus to escort British bomber operations over Egypt.
The Hunter training variants
The idea of developing a two-seat Hunter started to emerge as a private venture by Hawkers in early 1953, for use as an advanced trainer. The Hunter's performance was sufficiently beyond that of exisiting training aircraft, such as the Balliol and Vampire, to warrant such an aircraft. The layout was a subject of much discussion at first, both tandem and side-by-side layouts were advocated. In the end the side-by-side layout prevailed, and the first of 2 prototypes flew on 8 July 1955.
These were essentially single seat Hunters, with a new front fuselage. The first aircraft was a modified F Mk 4s, powered by the types original Avon RA 21. However, all was not well with the trainer variant, the new nose and cockpit caused airflow instability, and a long programme of trials began to develop the shape of the new canopy and the fairing behind it. By the summer of 1956 the airflow problems were solved, and the Ministry of Supply placed a production order for the trainer, now termed Hunter T Mk 7.
Even though the second prototype had been powered by the Avon 203 and based on the F Mk 6, it was planned for the production aircraft to be fitted with the Avon 121 engine, not the so called 'big Avon' 200 series. This was because it was intended that some F Mk 4 aircraft be converted to T Mk 7s, although this did cause great problems with spares in later years. Apart from the two-seat nose section and fairing, the only other structural difference between the F Mk 4 and T Mk 7 was the addition of a fairing in the tail for a braking parachute.
Altogether 55 aircraft were new-build T Mk 7s, although the last 10 were built as T Mk 8s for the Royal Navy with arrestor hooks and other associated naval equipment. Several of the Royal Navy T Mk 8s were reconverted in 1980, to become radar trainers for Sea Harrier student pilots. The reconversion included the addition of Blue Vixen radar in the nose for interception training. Deliveries of the T Mk 7s were to most front line squadrons, one apiece, and the remainder to 229 OCU at Chivenor, in 1958. These aircraft served in the advanced trainer role and as weapons trainers for over 20 years.
In late 1951, an improved Hunter with increased wing sweepback was conceived. This aircraft was powered by a reheated Avon engine and it was anticipated that this aircraft would be a truly transonic aircraft, capable of Mach 1+ in level flight. Although construction got underway, the project, designated P.1083, was cancelled in 1953, due to changes in Air Staff preferences for large un-reheated engines.
The centre section was used as a basis for the next version of Hunter, called the F Mk 6, with an Avon 200 engine and 10,500 lbs thrust. Nevertheless these engines were still experiencing problems, particularly during fast throttle-ups, and the engine was derated to 10,000 lbs thrust in an effort to alleviate this. Ultimately, the problem was traced to compressor blade fatigue. Rolls Royce were starting to iron out the problems with the Avon engine by this time, and reliability improved when the Hunter F Mk 6 entered service at the end of 1956. The Avon 200 engine (often called the 'big Avon') gave the Hunter F Mk 6 a very good rate of climb, making it a superlative interceptor.
The Hunter's wing was its' Achilles heel, and no amount of power could make it truly supersonic, without a major redesign. By 1958, all RAF day fighter squadrons in Europe were equipped with the Hunter Mk.6. Initially this was as an excellent interceptor, but when deployed in NATO duties, it was out performed by the supersonic American F-100 Super Sabre. However, the Hunter found increasing favour as a ground attack aircraft. This was just as well, considering what was about to happen in British defence thinking.
Bombshell - The 1957 Defence White Paper
The progress that had been made in guided missiles in the 1950's led Whitehall to believe that the time had come for manned aircraft to be replaced by missiles. Bombers were to be replaced by tactical and strategic missiles, the fighters would be superseded by surface to air missiles (SAMs). All future development of manned aircraft was to cease.
Several projects were cancelled at this time, including a supersonic replacement for the Hunter, the P.1121, sometimes called the Hurricane. This was to be capable of Mach 2 performance, and the prototype was 85 per cent complete when the defence axe fell. It was to have been powered by a reheated engine, either a de Havilland Gyron, a Rolls Royce Olympus or Conway. One can only guess at the capability of this aircraft, but it would have been broadly similar to an American F-4 Phantom, ordered 10 years later for the RN and RAF.
By 1957, English Electric were flying the prototype Lightning fighter, which had Mach 2 performance, and this was allowed to continue into service, because it was too advanced by this stage to cancel. The Lightning replaced the Hunter as the RAF's principal interceptor, but the Hunter's stability, handling and load carrying capability gave it the potential to become a very good ground attack aircraft, and development concentrated in this area. Many F Mk 6s were returned to Hawkers for modification as dedicated ground attack aircraft, for service with the RAF and foreign air forces.
From air to ground - the Ground Attack Hunters
Around 1960, just as the Hunter was being replaced by the Lightning in service as the RAF pricipal interceptor, it was simultaneously being increasingly used as a ground attack aircraft, especially in Germany on NATO duties. The Hunter had been outclassed at altitude by the new generation of supersonic fighters, such as the Lightning, the American F-4 Phantom and the Russian MiG 21. All of these had Mach 2+ performance at altitude, but they were only about 30 knots faster than the Hunter in the denser air of the lower atmosphere. So, despite the limitations of it's older design, the Hunter was far from obsolete at low level.
Even today, strike aircraft are unable to fly much faster than 750 kt near sea level. So with the service already in possession of large numbers of Hunters and in order to utilise existing stocks of aircraft, Hawker undertook a major conversion programme to rebuild the Hunter F Mk 6 into the ground attack FGA 9. Modifications included tail parachutes for short runway performance, strengthened inner wing pylons to carry 230 gallon drop tanks, along with extra fittings beneath the wings for the carriage of an increased weapons load. The new weapons in the Hunter's inventory included 1000 lb bombs, 2 in and 3 in rockets and 100 gallon napalm bombs. The Hunter's fixed armament of 4 x 30mm cannon in the nose was retained.
The introduction into service of these modified FGA 9's was with 8 Sqn, in the Aden Protectorate, in January 1960. The new Hunters also served in East Africa, and the Far East. At home, Transport Command was forming a fighter wing for quick deployment around the world, known as 38 Group. Hunter FGA Mk.9's were the principal aircraft type of the new Group, to support these short-notice overseas deployments. These relatively unsophisticated aircraft gave sterling service for over 10 years in front line use, and were retained for some time after as weapons trainers in the Tactical Weapons Units (TWU's) of Brawdy and Chivenor. No. 8 Sqn finally gave up its FGA 9's in December 1971. The RAF maintained a ground attack training wing at RAF Wittering until August 1976, and the TWU's finally gave up their Hunters in the early 1980's, replacing them with Hawks.
One further version of the Hunter saw service in the RAF, this was the tactical reconnaissance FR 10. This was similar to the FGA 9 except that it had three cameras fitted in the nose along with other specialised equipment for the reconnaissance role. The Hunter FR 10 replaced the Swift FR 5 in service in RAF Germany with No. 2 Squadron in March 1961. These aircraft served until the end of the 1960's and were replaced by various types, such as the Harrier and the Jaguar.
Hunter F4 in 3 Squadron markings
Hunter F4 in IV Squadron markings
Hunter F6 in 14 Squadron markings
Hunter F6 in 41 Squadron markings
Hunter F6 in 67 Squadron markings
Hunter F6 in 111 Squadron "Black Arrows" Aerobatic Team markings
Hunter T 7 in Royal Aircraft Establishment markings
Hunter T 12 in Royal Aircraft Establishment markings
Hunter FGA9 in 8 Squadron markings
Hunter FR10 in II(AC) Squadron markings