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All visitors with an interest in the Sea Vixen should visit Martyn Dean's excellent site, the address of which is in our favourite links page. It may also be accessed by clicking HERE. 

From the November 2004 issue                                  Back to index

De Havilland Sea Vixen De Havilland's mighty Sea Vixen was the first British aircraft to be designed as an integrated weapons system, and the Fleet Air Arm's first swept-wing all-weather fighter. Despite a tragic � and very public � accident to its predecessor, the D.H.110,the type completed a highly successful career. TONY BUTTLER traces the development of the radical twin-boomer.


"On February 20,1952,WG236 was taken beyond Mach 1, becoming the first operational-type aircraft, the first two-seater and the first twin-engined aircraft to break the 'sound barrier'"


T HE ROYAL NAVY'S (RN) post-war quest for a radar-equipped all-weather fighter was a long-drawn-out affair. A new Naval Staff Requirement, NR/A.14, and Specification N.40/46 were issued for proposals in January 1947, calling for a twin-jet naval nightfighter to replace the de Havilland Sea Hornet piston fighter, with a top speed of at least 500kt from sea level to 20,000ft and a maximum all-up-weight of 30,000lb. The highest possible    
manoeuvrability was requested, and it had to be able to land and take off from carriers by day or night. Proposals were received from Blackburn, de Havilland, Fairey, Gloster and Westland.
De Havilland's project, given the type number D.H.110, was a variant of a design first submitted in March 1947 in response to RAF nightfighter specification F.44/46. The RAF D.H.110 had two 7,000lb-thrust Metropolitan-Vickers F.9 engines (later the Armstrong Siddeley

Sapphire), four cannon and airborne interception (Al) Mk 9D radar. Its span was 49ft 6in, length 47ft 11 in, gross wing area 640ft. all-up-weight 26,3501b and estimated top speed 570kt (Mach 0-86) at sea level and 543kt (Mach 0-90) at 25,000ft, The D.H.110 was eventually selected as the winner of the RAF requirement, but a Gloster design was also accepted, later becoming the Javelin (see Database, January 2003 Aeroplane). Three RAF D.H.110s were planned, but by

(continued below left column)



ABOVE Arthur Bowbeer's magnificent cutaway illustration of the Sea Vixen from the February 5, 1960, issue of Flight.



January 1948 the armament and radar requirements were under drastic review; F.44/46 was replaced by F.4/48, and by July the Rolls-Royce Avon had become the D.H.110's lead engine.
The RAF and RND.H.110s were essentially the same apart from specific naval equipment and some alterations made during 1947. The navalised D.H.110 was proposed in September with a swept-forward tail surface expected to be better structurally and aerodynamically than the RAF version's "straight tail". The two crew were seated side-by-side and slightly staggered, and four 20mm Hispano cannon were housed under the cabin floor. De Havilland's Vampire and D.H.108 experience had led to the conclusion that wing sweep was essential to achieve the Mach 0-87 required by the RAF nightfighter, so a sweep angle of 40� at the quarter chord would easily cover the Mach 0-82 requirement in N.40/46.
An N.40/46 Design Study

ABOVE The first D.H.110 prototype, WG236, which made its maiden 46min flight at Hatfield in the hands of John Cunningham on September 26,1951, and which threw the whole D.H.110 programme into jeopardy after its fatal crash at Farnborough the following year.
LEFT Designer J.P. "Phil" Smith, responsible for the Sea Vixen at Hatfield until its move to Christchurch. He was also co-designer of the pre-war Moth Minor.
public during the following month. The observer was now housed inside the fuselage, with just a small window to look through. At this time the screens for the new airborne radars needed dark conditions for ideal viewing, which sentenced the operator to a world devoid of much light and also resulted in an offset canopy for the pilot.
Conference held on December 15, 1947, agreed that further investigation of the D.H.110 and Fairey's designs should continue. After F.44/46 was updated to F.4/48 in June 1948 the three D.H.110 nightfighter prototypes were ordered, together with four examples of Gloster's design. Then, on January 3. 1949, it was proposed to acquire four more F.4/48 D.H. 110s for a common RAF/RN development programme on armament, radar and instrument clearance, and two each to N.40/46, F.5/49 (for an RAF long-range fighter) and N.8/49 (for a naval strike aircraft), bringing the total to 13 prototypes. In March the NR/A.14 requirement was brought up to date under a new specification, N.14/49. Four months later three naval D.H.110s were ordered (two nightfighters, one strike), leading to concern over the financial implications of procuring so many prototypes. A joint trials programme for the RN and RAF was agreed, but in November 1949 the naval D. H. 110s were dropped for economy, leaving N.14/49 to Fairey's project. The twin-boom design seemed a logical advance over its ancestors, the Vampire and Venom, both of which were conventional aeroplanes in which the twin booms carried the tail rather than having it fitted to the end of the fuselage, thus permitting a very short and efficient jetpipe. In


 Neither D.H.110 received any radar or armament. The first had 6,500lb-thrust Avon RA.3s, while WG240 had 7,500lb RA.7s, intended to be typical of the Service version but without reheat.
Initial test flying with WG236 revealed flight characteristics that were much more pleasant than had been experienced in the D.H.108. There was none of the ghastly high-speed pitching oscillation that had made the D.H.108 such a horror; the biggest problem was found to be "snaking" at high speeds, which was traced to aeroelasticity (flexing) in the twin booms. As a result WG236 had its fin area increased, and the tail-booms were stiffened with steel reinforcing strips riveted on to the outside surfaces. The curved fin extensions were faired into the line of the rudder trailing edge under the rear of the booms to give extra stability (WG240 had modified booms of thicker-gauge aluminium alloy).
On February 20, 1952,WG236 was taken beyond Mach 1 for the first time, in a dive, by John Derry and Tony Richards. It thus became the first operational-type aircraft, the first two-seater and the first twin-engined aircraft to break the "sound barrier". During 1952 it was decided to develop and fit a fully-powered all-moving tailplane to provide good transonic handling. There was no known practical method of moving a
ABOVE A sketch of the original D.H.110 concept, designed to RAF nightfigher Specification F.44/46, with side-by-side seating and unusual forward-swept tail surface, both of which would be changed for the prototype D.H.I 10s.
ABOVE The second D.H.110 prototype, WG240, at the SBAC show at Farnborough in 1953.This head-on view illustrates well the distinctive offsetting of the canopy to port, which remained on the later Sea Vixen
comparison, the D.H.110's swept wing was similar to that of the tailless D.H.108 research aircraft, while the tail was set high and much closer to the wing. The tail had to be added to counteract several problems suffered by tailless aeroplanes (as distinct from deltas), particularly a gradual loss in longitudinal stability as the speed dropped. Designer J.P. "Phil" Smith led the D.H.110 project until it was transferred from Hatfield to Christchurch.
After the naval machines were cancelled the surviving RAF order
comprised five F.4/48 nightfighters (WG236, WG240, WG247, WG249 and WG252). The contract for these machines was dated May 26,1950, but WG247 (to be Sapphire-powered), WG249 and WG252 were all cancelled on June 14,1952. The surviving two were built in the experimental shop at Hatfield, and WG236's taxying trials began on September 16,1951. On September 26 chief test pilot John Cunningham made the first flight, with Tony Fairbrother as his observer, and the new fighter was first revealed to the




"The Farnborough crash was a great tragedy, but should never be allowed to cloud the fact that the three D.H.110s proved to be fine flying machines, and valuable research tools for the Sea Vixen"
"slab tail" manually owing to the very high loads involved, so any failure of the hydraulic system had to be safe�guarded against by full duplication and partial triplication. In 1954 the manual rudders were changed for fully-powered alternatives using the same system duplication. It was then found that many of the troubles associated with yaw autostabilisation on manually-operated controls were now eliminated and the rudder power was greatly increased due to the removal of the large balance tabs. Development of the D.H.110 with fully-powered controls was largely completed by the end of 1955.
On July 25,1952, WG236 was followed into the air by WG240, and the extra power available to the second aircraft was impressive. It was also lighter than WG236, so WG240 was selected as the flying display aircraft for the September 1952 SBAC show at Farnborough. It flew throughout the week, but on the Saturday went unserviceable owing to engine problems. John Derry and Tony Richards went to Hatfield to collect WG236 as a substitute, and flew this aircraft direct to Farn�borough for their display. During a manoeuvre WG236 broke up in the air, killing both crew, and an engine landed in the crowd, killing another 27 people and injuring 63. The inquiry into this accident was extensive. The flight had included a supersonic dive from 40,000ft, with the pull-out close to the airfield. After a fast pass, Derry turned to port and made a tight left-hand circuit at low
(Continued RH column)
ABOVE The second prototype in 1952 in its striking all-black colour scheme, which made quite an impression on the public during its dynamic displays. LEFT John Derry in the cockpit of Vampire W218, which he demon�strated masterfully at the SBAC show in 1948. At the time of his death he was D.H. chief test pilot.
level. While straightening out from this turn about 1.5 miles north-west of the public enclosure, WG236 disintegrated.
A film taken by a spectator revealed what had happened. As WG236 banked to the left towards the crowd its starboard outer wing detached, immediately followed by the port outer wing. With only the inner wing sections left, the rapid nose-up change of trim following the wing failures caused the cockpit, engines and tail to detach in secondary failures under an abnormal g loading. All of this occurred within about a second. It was found that WG236 had succumbed to the twisting forces produced while undertaking a manoeuvre that combined a turn and a climb. The accident report, dated April 8,1953, stated that the cause was a combined effect of pull-up acceleration (associated with turning) and the loads produced by upward aileron (appropriate to straightening out from a turn), which had created instability in the structure. The D.H.110's wing form was the problem. The unusual D-nose leading-edge arrangement had proved fine for the lightweight Vampire and Venom but could not cope with the heavier stresses experienced with the much bigger D.H.110.
Before WG240 flew again, in June 1953, its wing structure was substantially redesigned. It was fitted with a front spar web and thicker wing ribs, while the inter-spar stringers between ribs eight and
(contd. below left)



ABOVE The awful aftermath of the crash of WG236 on September 6, 1952.The subsequent crash report determined that the joint actions of torsion, shear and bending loads on the starboard outer wing caused it to twist off, initiating catastrophic failure of the entire airframe.
Test pilots John Cunningham (left), who made the D.H.I 10's first flight, and "Jock" Elliot, who flew the maiden flight of the navalised XF828.


seven were reinforced (all of these modifications were retained on the Sea Vixen). Early in 1954WG240 was taken in hand to receive the all-moving "flying" tail instead of the original fixed tailplane and hinged elevator (at the time it was the only British aircraft so equipped). The powered rudders, plus cambered "droop-snoot" leading edges on the outer wings and improved aileron controls, were also fitted, and it made its first flight in this form on June 11.
After the loss of WG236, Gloster's Javelin nightfighter had become the favoured candidate for the RAF requirement and was eventually ordered in quantity. The RN's N. 14/49 requirement was withdrawn on July 19,1950, and Fairey's project was abandoned. A new specification, N.114T, was intended to replace it but, as a stop-gap, the RN ordered a navalised de Havilland Venom (Sea Venom) to fill the unacceptable gap between the Sea Hornet and the new programme. In January 1952 each of the tenders to N.114T was found to be unsuitable, leaving the new all-weather fighter requirement unfilled. R.E. Bishop at de Havilland designed an improved Venom, the D.H.116 Super Venom, and a mock-up was built, but Bishop informed the Admiralty that his company could not cope with the project because of a shortage of design staff. In November 1952 he suggested a navalised D.H.110 as an alternative.
The D.H.110 was assessed by the Ministry of Supply (MoS) on March 5, 1953, to see how far a navalised version could solve the navy's problems. There were doubts whether the Al Mk 18 radar could be installed, even with a small scanner, and the strength factors provided by D.H. were on the bottom limit for fighter duties and would need modifying for ground-attack operations. The Admiralty also wanted four Blue Jay air-to-air missiles (AAMs). The D.H.110 could be adapted to new requirement, NA.38, and on July 14 the Naval Aircraft Design Committee recorded formal acceptance of the type to this specification.
   The changes required to the


ABOVE The third prototype, XF828, was navalised but without folding wings. During August 1954 the name Pirate was mooted for the type but was eventually dropped, approval for Sea Vixen being made on March 5,1957.
sanction was delayed until December 31,1954, when approval was given for 75 (later 78) aeroplanes.
The Instruction to Proceed with the full programme arrived in early January 1955, and the third prototype, the navalised XF828, was first flown, from Christchurch, on June 20 by "Jock" Elliot. Production aeroplanes were to be designated FAW Mk 20 (soon changed to FAW Mk 1. FAW � Fighter, All Weather) and receive the Avon 208; the intermediate XF828 was designated FAW Mk 20X. Four Blue Jay AAMs became the weapon choice, with the Aden guns removed and replaced by packs of Microcell 2in rockets.
On September 23,1954, WG240 made a series of preliminary approaches, overshoots and touch-and-go landings on the deck of HMS Albion, with the intention of showing the D.H.110's general handling to be adequate for carrier operation. Its behaviour was reported as out�standing. On April 5, 1956, XF828 made its first fully arrested deck landing, on HMS Ark Royal. By early 1957 the aircraft had received a large fixed in-flight refuelling probe, and the first successful in-flight refuelling with a tanker aircraft at 10,000ft was achieved on January 10. The Farnborough crash was a great tragedy, but should never be allowed to cloud the fact that the three D.H.110s proved to be fine flying machines and immensely valuable research tools for the Sea Vixen.                                   
ABOVE In September 1954, Jock Elliot made a series of touch-and-go landings aboard HMS Albion with WG240 painted in naval colours and fitted with modified long-travel undercarriage oleos. The results were very satisfactory.
existing D.H.110 were a folding wing, arrester gear and other normal navalisation fittings, RA.14 Avons, the Al Mk 18 radar, redesign of both main and nose undercarriages, changes to the cockpit layout and fitment of the all-moving tail and larger flaps. Converting the RAF D.H.110 into a naval aircraft required a lot of redesign, and most of the drawings had to be changed. By now D.H.110 design work had been transferred to Christchurch, and a new specification, N.139D&P, was written around the aircraft. The standard for the third prototype, to be constructed from spare F.4/48 components to a contract dated November 6,1953, was agreed in
August 1953. Specification N.139D&P stated that the D.H.110 was to operate from HMS Hermes and larger-class carriers, and its primary role was to be the destruction of enemy reconnaissance and strike aircraft. Minimum top speed was now set at 690 m.p.h. at sea level and 610 m.p.h. at 40,000ft, rate of climb at a minimum of 14,000ft/min (later 18,000ft/min) and service ceiling at 48,000ft. Production aircraft were to carry a mix of four Aden cannon and two Blue Jay (Firestreak) AAMs or two Aden and four Blue Jay.
An initial approach to the Treasury was made in October 1953 for 100 machines. However, Treasury
The prototype D.H.110, WG236, spent its brief life painted in a silver scheme with standard roundels and a swept fin-flash. Early trials with the first prototype showed the type to be well in advance of a number of its contemporaries, including the American Northrop F-89 Scorpion and Soviet MiG-17"Fresco"� 2004 JUANITA FRANZI