The de Havilland DH.110 Sea Vixen is a British twin-engine, twin boom-tailed, two-seat, carrier-based fleet air-defence fighter flown by the Fleet Air Arm of the Royal Navy from the 1950s to the early 1970s. The Sea Vixen was designed by the de Havilland Aircraft Company during the late 1940s at its Hatfield factory in Hertfordshire, developed from the company's earlier first generation jet fighters. It was later called the Hawker Siddeley Sea Vixen after de Havilland was absorbed by the Hawker Siddeley Corporation in 1960.
The Sea Vixen had the distinction of being the first British two-seat combat aircraft to achieve supersonic speed, albeit not in level flight. Operating from British aircraft carriers, it was used in combat over Tanganyika and over Yemen during the Aden Emergency. In 1972, the Sea Vixen was retired in favour of the American-made McDonnell Douglas Phantom FG.1 interceptor. There have been no flying Sea Vixens since 2017.
Development
Origins In 1946, the de Havilland Aircraft Company conducted discussions with the British Admiralty on its requirements for a future jet-powered all-weather, radar-equipped fighter. From these talks, it became clear that the aircraft would need a crew of two to handle its radar and navigation equipment, as well as to fly the fighter, and that two engines were required for safety over the ocean, and that swept wings were desirable. The fighter would also have a moderate wing loading for manoeuvrability at altitude and acceptable takeoff and landing performance from aircraft carriers. Highly effective wing flaps would be needed for landing and taking off. de Havilland decided to pursue development of a design to meet the Navy requirements. The proposed aircraft, the DH.110, was a twin-engined all-weather fighter.Neal 1960, p. 179.
The design of the DH.110 uses the twin-boom-tail design layout of the de Havilland Vampire and de Havilland Venom. It has an all-metal structure, 45-degree swept wings, and an armament of four 30 mm ADEN cannons. The DH.110 was to be powered by a pair of Rolls-Royce Avon turbojets, each capable of generating of thrust, which would allow the aircraft to become supersonic in a shallow dive. The DH.110 had the distinction of being the first British two-seat combat plane to achieve supersonic speed."British two-seat fighter to attain speed of sound." Popular Mechanics, March 1955, p. 97.
In January 1947, specifications N.40/46 and F.44/46 were issued by the British Air Ministry for similar night fighters to equip the Fleet Air Arm (FAA) and Royal Air Force (RAF). de Havilland submitted its proposal for the DH.110 to both services. As initially submitted the RAF version had Metrovick F.9 engines, although these would soon be known as the Armstrong Siddeley Sapphire when Metrovick sold its engine division. Nine DH.110 prototypes were ordered for the RAF (together with four of the competing Gloster Javelin) and four prototypes for the Fleet Air Arm.Birtles 1991, p. 194.Jackson 1987, p. 470.
By early 1949 the DH.110 design was expected to fulfil four requirements: F4/48, F5/49 (a long range RAF fighter), N.40/46 (naval night fighter) and N.8/49 (naval strike aircraft). Three prototypes were needed for F.4/48, four for common RAF and RN development, and two each for the other three roles and by July the authorities were ready to order the 13 prototypes Buttler British Secret Projects revised edition, p77
In 1949 the Royal Navy decided to procure the de Havilland Sea Venom which, as a development of an existing aircraft, was cheaper, and would be available sooner to meet its immediate needs for a jet-powered night fighter to replace its fleet of piston-engined de Havilland Sea Hornets and Vought F4U Corsairs. The RAF decided to cut its order to two prototypes. Despite this setback, de Havilland elected to continue work on the DH.110 while trying to regain official interest in the type.Birtles 1991, pp. 195, 198. On 26 September 1951, an initial prototype was completed and conducted its maiden flight from the Hatfield Aerodrome, flown by the test pilot John Cunningham."British Unveil Twin-Boom Jet." Popular Science, Vol. 159, No. 6. December 1951. p. 123. Early flight tests of the prototype demonstrated that the aircraft's performance exceeded expectations. By the following year, the prototype was regularly flying in excess of the speed of sound.
Tragedy struck while the first prototype DH.110 (serial number WG236) was demonstrated at the Farnborough Airshow on 6 September 1952."On This Day – 1952: Dozens die in air show tragedy." BBC News, 2008. Following a demonstration of its ability to break the sound barrier during a low level flight the aircraft disintegrated and debris landed in the midst of spectators, killing 31 people including the crew of two, the test pilot John Derry and his flight-test observer, Tony Richards."1952: 'The crowd parted like the Red Sea'." BBC News, Retrieved: 25 September 2016.
Subsequent investigation of the accident traced the failure to faulty design of the wing leading edge section ahead of the main spar. The design had been satisfactory for the earlier Vampire and Venom but not for the higher stresses induced by the rolling pull-out manoeuvre at flown by the DH.110 prototype at Farnborough. The leading edge skin, without the extra reinforcing structure that would be added later, buckled, which resulted in the outer portions of the swept-back wings being torn off (similar display routines had been flown on preceding days by the other prototype DH.110 which had an aerodynamic fence providing external stiffening for the skin over the area where the buckling originated.Jones 1985, p. 95). The subsequent shift in the DH.110's centre of pressure caused the aircraft to pitch up, the cockpit and tail sections breaking away and the engines being torn from the airframe by the g loading.Brookes 1991, p. 80. One of the engines hit an area crowded with spectators at the end of the runway, causing the majority of the deaths. Sixty other spectators were injured by debris from the cockpit landing close to the main spectator enclosures along the runway. This incident led to new safety regulations for air shows in the UK, and no member of the public died as a result of a British airshow flight for more than 62 years, until the crash of a Hawker Hunter warbird killed 11 people during the Shoreham Air Show on 22 August 2015.
Redesign and navalisation In response to the loss of the first prototype de Havilland introduced modifications to the design which were implemented on the remaining second prototype. These changes included the adoption of an all-moving tailplane, and cambered leading edge extensions. The modified prototype did not return to flight until July 1954.Jackson 1987, p. 471. As a result of these changes the DH.110 was no longer able to exceed the speed of sound, only reaching Mach 0.95 in a steep dive where its controls were immovable until passing .Noble 2003, p. 29. By this time, the Royal Air Force announced the abandonment of its interest in the DH.110, after deciding to buy the Gloster Javelin instead.Neal 1960, pp. 179–180. The Fleet Air Arm had decided that it would adopt the aircraft as a replacement for its interim fleet of Sea Venoms.Polmar 2008, p. 183. In February 1955, an order was placed for 110 naval aircraft, which received the name Sea Vixen.
Along with tailoring the aircraft for carrier-based operation by the Royal Navy, de Havilland implemented major changes to the Sea Vixen during its redesign. Throughout the 1950s, when the DH.110 design was still being evolved, major advances had occurred in subsystems such as weaponry, fire-control systems, radar equipment, and cockpit instruments. The concept of an aircraft being an integrated weapons system had proliferated, where sensors such as the radar would be more directly tied to navigation and weapons systems. de Havilland included this concept in the design of the Sea Vixen. According to aviation author David Hobbs, it was the first British fighter aircraft to be designed in this manner.Hobbs 2014, p. 256.
In June 1955, a semi-navalised prototype, XF828, was completed for conducting carrier flight deck suitability trials. XF828 had several changes, including the alteration of the profile of the wing leading edges and the strengthening of the wings, as well as underwing fixture points for catapult launches, and a tailhook for arrested landings; the prototype lacked a wing folding mechanism, or racks for armaments.Neal 1960, p. 180. On 20 June 1955, this aircraft made its first flight from de Havilland's facility at Christchurch Airfield in Dorset. The following year, XF828 performed its first arrested deck landing on the Royal Navy's aircraft carrier .Birtles 1991, pp. 198–199.
In April 1956, the finalised production drawings were formally issued. The fully naval production Sea Vixen had improvements over earlier development models. These included the addition of a powered folding wing system, reinforcement of the landing gear to withstand the additional stresses of carrier landings, a steerable nose wheel, a revised tail unit, and the redesigning of the fuselage to carry armament. On 20 March 1957, the first true Sea Vixen, the Sea Vixen FAW.20 (fighter all-weather, later renamed FAW.1), performed its first flight. This aircraft was promptly used for clearance trials, in particular for addressing handling problems; the second production aircraft was used for engineering trials and the third aircraft for conducting radar trials.Neal 1960, pp. 180, 184. On 2 July 1959, the first Sea Vixen-equipped squadron was formed.Jackson 1987, p. 472.
Production Sea Vixens were manufactured at first by de Havilland at its former Second World War Airspeed Ltd. "shadow factory" at Christchurch near Bournemouth, starting in March 1957. In August 1962, all production was moved to another de Havilland factory at Hawarden, near Chester.
Further development
Beyond the initial FAW.1 model, de Havilland proceeded with the development of an improved variant, that became the Sea Vixen FAW.2. This served as the successor to the FAW.1 and included many improvements. As well as Firestreak missiles, it could carry the Red Top air-to-air missile, four RP-2 rocket pods, and the AGM-12 Bullpup air-to-ground missile.
Its enlarged tail boom allowed for additional fuel tanks in the "pinion" extensions above and in front of the wing leading edge, there was an improved escape system and additional room for more electronic countermeasures (ECM) equipment."de Havilland DH 110 Sea Vixen FAW.2." de Havilland Aircraft Museum, Retrieved: 25 September 2016. The changes in aerodynamics meant that the 1,000 lb bomb could no longer be carried. Visually the FAW.1 and FAW.2 could be distinguished by the tail booms which extended forward over the wing leading edges of the FAW.2.
In 1962, the Sea Vixen FAW.2 conducted its maiden flight; the type entered service with frontline squadrons in 1964. A total of 29 FAW.2s were newly built along with a further 67 FAW.1s that were rebuilt to FAW.2 standard. In 1966, the original FAW.1 begun to be phased out and in 1972, the career of the Sea Vixen FAW.2 came to an end.
The Sea Vixen FAW2 could be armed with up to four Red Top infrared-homing missiles. The Red Top could home on to heat sources generated by kinetic heating of a fast-approaching supersonic target such as the Tupolev Tu-22 bomber. The Red Top system was integrated into the AI 18R (R for Red Top) radar. From 1969 the Sea Vixen FAW2 practised intercepts of a supersonic target against the Concorde SST in flight tests over the Irish Sea.