The Vickers Wellesley has its origins in Air Ministry Specification G.4/31 which called for a general-purpose bomber and torpedo aircraft. Vickers-Amstrongs originally submitted an officially-sponsored biplane design against the requirement, the Type 253 (described separately).
At the same time, Barnes Wallis argued that a monoplane design, fully incorporating his ideas around geodetic construction, was likely to result in superior performance and the company were sufficiently confident that they developed the private venture monoplane Type 246 in parallel, to compete for the same requirement.
In a geodetic design (as used in the R100 Airship) the structural members form a light, robust and damage tolerant lattice work. The name geodetic arises from the designer creating load paths along geodesics – a geodesic being the shortest distance between two points on a curved surface.
The Type 246 prototype was flown for the first time by Chief Test Pilot Joseph 'Mutt' Summer at Brooklands on 19th June 1935.
In the meantime, the Air Ministry had already ordered 150 examples of the biplane Type 253 whilst in practice, the monoplane immediately demonstrated higher performance on the same power, whilst offering a greater payload, due to having a lighter, cleaner airframe.
As a result, the production order for the Type 253 was cancelled in favour of an initial order of 96 Type 246 monoplanes, with the service name Wellesley. Ultimately the RAF ordered 176 Wellesley aircraft, incorporating the newly-written specification 22/35. The first production aircraft (K7713) was flown for the first time on 30th January 1937 whilst full production at Weybridge ran between March 1937 and May 1938.
The original private venture prototype aircraft suffered an accident on 23rd July 1935 due to an undercarriage mechanical jam on take-off. It was repaired however, incorporating several modifications, and it emerged as the pre-production Wellesley (K7556 - Vickers Type 281).
Changes to the design had included the adoption of enclosed cockpits and a hydraulically operated (rather than manual) retractable undercarriage whilst panniers carried on wing-mounted pylons served as bomb carriers. Power was provided by a single Bristol Pegasus X engine although continuing engine developments resulted in the final production aircraft (Vickers Type 287) being fitted with the 835 hp Bristol Pegasus XX engine.
The Wellesley entered RAF service in April 1937 with 76 Sqn at RAF Finningley and went on to equip 6 Bomber Command Squadrons in the UK.
After entering service, the decision was taken to introduce a third crew station mid-fuselage to accommodate a navigator for long-range development flights.
The RAF had selected the Wellesley for long-range flight trials, creating a Long Range Development Unit at Upper Heyford in January 1938. After trials with one aircraft (K7717) all long-range aircraft were fitted with Pegasus XXII engines, having a higher compression ratio but a smaller supercharger, more suited to their optimum cruising altitude of 10,000ft.
Their efforts bore fruit in the form of a 48-hour non-stop world record-breaking flight of 7,158 miles by two aircraft between Ismailia, Egypt and Darwin, Australia in early November 1938. These aircraft were equipped with three-axis autopilots, constant speed propellers, and automatic engine boost and mixture controls to ensure optimum operation.
The five long-range Wellesley aircraft could be recognised by their adoption of a long chord NACA-style low-drag engine cowling, replacing the Townend ring of the standard production aircraft.
During the Second World War, the Wellesley saw service in North and East Africa, serving with 14, 47 and 223 Squadrons.
The type continued in operational service until September 1942 and whilst the Wellesley could never be described as a major combat aircraft, it did contribute significantly to the design principles of the Vickers Wellington medium bomber which played such an important role in Bomber Command operations during World War II.
Variants & Numbers
|Wellesley Mk.1||One pre-production prototype K7556 and 176 production aircraft. Some aircraft fitted with an extended canopy were informally (but not officially) known as Wellesley Mk.2. Five aircraft modified for long-range duties with long-chord engine cowlings, and autopilots for the RAF Long Range Development Unit.|
|Powerplant||One Bristol Pegasus XX, take-off rating 835 hp at sea level and 2,260 rpm, maximum power 925 hp at 10,000ft and 2,600 rpm.|
|Span||74 ft 7 in|
|Maximum Weight||11,100 lb|
|Capacity and armament||Three crew (pilot, navigator, gunner), One fixed forward-firing 0.303 Browning machine gun and one Vickers ‘K’ gun in rear cockpit. Maximum bomb load 2,000 lb in underwing bomb carriers|
|Maximum Speed||228 mph at 19,680 ft|
|Cruising Speed||180 mph at 15,000 ft|
|Endurance / Range||1,220 miles at 15,000 ft|
No examples of the Vickers Wellesley survive.