Wellington Mark I aircraft with the original turrets; anticipating war, the New Zealand
government loaned these aircraft and their aircrews to the RAF in August 1939
In October 1932, the British Air Ministry invited Vickers to tender for the recently issued Specification B.9/32, which sought a twin-engine medium daylight bomber. In response, Vickers conducted a design study, led by Chief Designer Rex Pierson Early on, Vickers' chief structures designer Barnes Wallis proposed the use of a geodesic airframe, inspired by his previous work on airships and the single-engined Wellesley light bomber. During structural testing performed at the Royal Aircraft Establishment, Farnborough, the proposed structure demonstrated not only the required strength factor of six, but reached 11 without any sign of failure, proving the geodesic airframe to possess a strength far in excess of normal levels. This strength allowed for the structure design to be further developed to reduce the size of individual members and adopt simplified standard sections of lighter construction.
Vickers studied and compared the performance of various air and liquid-cooled engines to power the bomber, including the Bristol Pegasus IS2, Pegasus IIS2, the Armstrong Siddeley Tiger, and the Rolls-Royce Goshawk I. The Pegasus was selected as the engine for air-cooled versions of the bomber, while the Goshawk engine was chosen for the liquid-cooled engine variant. On 28 February 1933, two versions of the aircraft, one with each of the selected powerplants, were submitted to the tender. In September 1933, the Air Ministry issued a pilot contract for the Goshawk-powered version. In August 1934, Vickers proposed to use either the Pegasus or Bristol Perseus engines instead of Goshawk, which promised improvements in speed, climb rate, ceiling, and single-engine flight capabilities without any major increase in all-up weight; the Air Ministry accepted the proposed changes.
Other refinements of the design had also been implemented and approved, such as the adoption of variable-pitch propellers, and the use of Vickers-produced gun turrets in the nose and tail positions. By December 1936, the specification had been revised to include front, rear, and midship wind-protected turret mountings. Other specification changes included modified bomb undershields and the inclusion of spring-loaded bomb bay doors. The proposal had also been developed further, a mid-wing arrangement was adopted instead of a shoulder-mounted wing for greater pilot visibility during formation flight and improved aerodynamic performance, as well as a substantially increased overall weight of the aircraft. Design studies were also conducted on behalf of the Air Ministry into the adoption of the Rolls-Royce Merlin engine.
In spite of a traditional preference of the establishment to strictly adhere to the restrictive tare weight for the aircraft established in the tender, both Pierson and Wallis firmly believed that their design should adopt the most powerful engine available. Perhaps in response to pressure from Vickers, the Air Ministry overlooked, if not openly accepted, the removal of the tare weight restriction, as between the submission of the tender in 1933 and the flight of the first prototype in 1936, the tare weight eventually rose from 6,300lb to 11,508lb. The prescribed bomb load and range requirements were routinely revised upwards by the Air Ministry; by November 1935, figures within the Ministry were interested in the possibility of operating the aircraft at an all-up weight of 30,500lb, which aviation author C.F. Andrews stated to be "a very high figure for a medium bomber of those days".
During the development phase of the aircraft, the political and military situations in Europe drastically transformed. With the rise of fascist dictatorships in Germany and Italy, the British government had become keen to reevaluate the capabilities of the nation's armed forces, including the Royal Air Force (RAF). By 1936, the need for a high priority to be placed on the creation of a large bomber force, which would form the spearhead of British offensive power, had been recognised; accordingly, a new command organisation within the RAF, Bomber Command, was formed that year to deliver upon this requirement.
Prototype and design revision
In early 1936, an initial prototype, K4049, which was originally designated as a Type 271, was assembled. The prototype could accommodate a payload of nine 250lb or 500lb bombs, and both nose and tail gun positions were fitted with hand-operated turrets furnished with a single gun in each, provisions for a third retractable gun in a dorsal position were also present. It had provisions for a crew of four, along with a fifth position for performing special duties.
On 5 June 1936, the name Crecy was initially chosen for the type, and it was publicly displayed as such. On 15 August 1936, the aircraft was accepted for production. On 8 September 1936, the name Wellington was adopted for the type; Pierson later explained that this was due to Air Ministry nomenclature and also followed the tradition set by the Vickers Wellesley of possessing names referring back to the Duke of Wellington. On 12 December 1936, a corresponding works order was issued for the Wellington.
On 15 June 1936, K4049 conducted its maiden flight from Brooklands. Vickers chief test pilot Joseph Summers flew K4049 on its first flight, accompanied by Wallis and Trevor Westbrook. The aircraft soon came to be largely regarded as being an advanced design for its era and proved to have considerable merit during its flight trials. On 19 April 1937, K4049 was destroyed by an accident during a service test flight by Maurice Hare. The cause was the failure of the elevator's horn balance due to excessive slipstream exposure, leading to the aircraft inverting and rapidly descending into terrain. It was completely destroyed in the crash, which also resulted in the death of Smurthwaite the navigator. The horn balances would later be deleted, and thus not feature on production aircraft.
In addition to the prototype, refinement of the Wellington's design was influenced by the issuing of Specifications B.1/35 and B.1/35, the latter of which had led to the parallel development of a larger bomber aircraft, the Vickers Warwick. According to Andrews, the Wellington was practically redesigned to form the first production model of the aircraft, during which extensive details attributed to the Warwick were added, such as the deepening of the fuselage, the lengthening of the nose, a reshaped horizontal tail unit, and an increased crew complement for four to five members. Other changes made included the adoption of a retractable tailwheel and constant-speed propellers; the Air Ministry also requested the adoption of a Nash & Thompson-design ventral turret in place of the Vickers design.
On 23 December 1937, the first production Wellington Mk I, L4212, conducted its first flight; L4212 subsequently participated in an intensive flight programme. Flight trials with L4212 confirmed the aerodynamic stability initially encountered by K4049, but also revealed the aircraft to be nose-heavy during dives, which was attributed to the redesigned elevator. Accordingly, modifications, including the interlinking of the flaps and the elevator trim tabs, were successfully trialled on L4212 to resolve the issue.
A war time poster using a cutaway of a Vickers Wellington to illustrate how scrap and salvage was recycled for use in the production of war material. The poster expands on how different materials were used to make specific components of the bomber.
In August 1936, an initial order for 180 Wellington Mk I aircraft, powered by a pair of 1,050 hp (780 kW) Bristol Pegasus radial engines, was received by Vickers; it had been placed so rapidly that the order occurred prior to the first meeting intended to decide the details of the production aircraft. In October 1937, another order for a further 100 Wellington Mk Is, produced by the Gloster Aircraft Company, was issued; it was followed by an order for 100 Wellington Mk II aircraft, which were instead powered by a pair of Rolls-Royce Merlin X V12 engines. Yet another order was placed for 64 Wellingtons produced by Armstrong Whitworth Aircraft. With this flurry of order and production having been assured by the end of 1937, Vickers set about simplifying the manufacturing process of the aircraft and announced a target of building one Wellington per day.
Wellington Mark X HE239
of No.428 Sqn.
RCAF. It completed its bomb run despite losing the rear turret and then flew back home for a successful landing with its bomb bay doors stuck open due to lack of hydraulic power
Construction took longer to build due to the geodesic fuselage in comparison to other designs using monocoque approach, leading to criticism of the Wellington. In particular, it was difficult to cut holes in the fuselage for access or equipment fixtures; to aid manufacturing, the Leigh light was deployed through the mounting for the absent FN9 ventral turret. In the late 1930s, Vickers built Wellingtons at a rate of one per day at Weybridge and 50 a month at Broughton in North Wales. Many of the employees on the production lines were only semi-skilled and new to aircraft construction. Peak wartime production in 1942 saw monthly rates of 70 at Weybridge, 130 at Broughton and 102 at Blackpool. Shadow factories were set up to produce parts for the Wellington all over the British Isles.
In October 1943, as a propaganda and morale-boosting exercise, workers at Broughton gave up their weekend to build Wellington number LN514 rushed by the clock. The bomber was assembled in 23 hours 50 minutes, and took off after 24 hours 48 minutes, beating the record of 48 hours set by a factory in California. Each Wellington was usually built within 60 hours. It was filmed for the Ministry of Information for a newsreel Worker's Week-End, and was broadcast in both Britain and America. It was the first time in the world that a British aircraft manufacturer had attempted such a feat with a metal aircraft of this scale.
A total of 180 Wellington Mk I aircraft were built; 150 for the RAF and 30 for the Royal New Zealand Air Force (RNZAF) (which were transferred to the RAF on the outbreak of war and used by 75 Squadron). In October 1938, the Mk I entered service with 9 Squadron. The Wellington was initially outnumbered by the Handley Page Hampden (also ordered by the Ministry to B.9/32) and the Armstrong Whitworth Whitley (to B.34/3 for a 'night' bomber) but outlasted both rival aircraft in service. The Wellington went on to be built in 16 separate variants, in addition to two training conversions after the war. The number of Wellingtons built totalled 11,462 of all versions, a greater quantity produced than any other British bomber. On 13 October 1945, the last Wellington to be produced rolled out.
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The Wellington Mk I was quickly superseded by several successive variants featuring various improvements. Improvements to the turrets and the strengthening of the undercarriage quickly resulted in the Wellington Mk IA. According to Andrews, the IA model bore more similarities to the later Wellington Mk II than to its Mk I predecessor. Due to armament difficulties encountered that left the Wellington with weaker than intended defences, the Wellington Mk IB was proposed for trials, but appears to have been unbuilt. Further development of various aspects of the aircraft, such as the hydraulics and electrical systems, along with a revision of the ventral turret gun, led to the Wellington Mk IC.
In January 1938, design work on what would become the Wellington Mk II formally commenced. The principal change on this model was the adoption of the Merlin engine in place of the Pegasus XVIII; other modifications included hydraulic and oxygen system revisions along with the installation of cabin heating and an astrodome. On 3 March 1939, L4250, the prototype Mk II, performed its maiden flight; this had been delayed due to production delays of its Merlin X engines. Stability and balance issues were encountered during flight tests of the prototype, resulting in further changes such as the enlargement of the tailplane. By late 1939, the Mk II was capable of delivering superior performance to the Mk IC, such as higher cruising and top speeds, increased all-up weight or alternatively greater range, and a raised ceiling.