Armstrong Whitworth Whitley
The Armstrong Whitworth A.W.38 Whitley was a British medium/heavy bomber aircraft of the 1930s. It was one of three twin-engined, front line medium bomber types that were in service with the Royal Air Force at the outbreak of the Second World War. Alongside the Vickers Wellington and the Handley Page Hampden, the Whitley was developed during the mid-1930s according to Air Ministry Specification B.3/34, which it was subsequently selected to meet. In 1937, the Whitley formally entered into RAF squadron service; it was the first of the three medium bombers to be introduced.
Following the outbreak of war in September 1939, the Whitley participated in the first RAF bombing raid upon German territory and remained an integral part of the early British bomber offensive. In 1942 it was superseded as a bomber by the larger four-engined "heavies" such as the Avro Lancaster. Its front-line service included maritime reconnaissance with Coastal Command and the second line roles of glider-tug, trainer and transport aircraft. The type was also procured by British Overseas Airways Corporation as a civilian freighter aircraft. The aircraft was named after Whitley, a suburb of Coventry, home of Armstrong Whitworth's Whitley plant.
Development
Origins
In July 1934, the Air Ministry issued Specification B.3/34, seeking a heavy night bomber/troop transport to replace the Handley Page Heyford biplane bomber. This combination bomber/transport was part of the RAF's concept of fighting wars in distant British Empire locations, where the aircraft would fly into the theatre of action carrying troops and then provide air support.John Lloyd, the Chief Designer of Armstrong Whitworth Aircraft, chose to respond to the specification with the AW.38 design, which later was given the name Whitley after the location of Armstrong Whitworth's main factory. The design of the AW.38 was a development of the Armstrong Whitworth AW.23 bomber-transport design that had lost to the Bristol Bombay for the earlier Specification C.26/31.
Lloyd selected the Armstrong Siddeley Tiger IX radial engine to power the Whitley, which was capable of generating. One of the novel features of the Whitley's design was the adoption of a three-bladed two-position variable-pitch propeller built by de Havilland; the Whitley was the first aircraft to fly with such an arrangement.
As Lloyd was unfamiliar with the use of flaps on a large heavy monoplane, they were initially omitted from the design. To compensate, the mid-set wings were set at a high angle of incidence to confer good take-off and landing performance. Flaps were included late in the design stage, but the wing incidence remained unaltered; as a result, the Whitley flew with a pronounced nose-down attitude when at cruising speed, resulting in considerable drag.
The Whitley holds the distinction of having been the first RAF aircraft with a semi-monocoque structure in its fuselage, which was built slab-sided to ease production. This replaced the tubular construction method traditionally employed by Armstrong Whitworth, who instead constructed the airframe from light-alloy rolled sections, pressings and corrugated sheets. According to aviation author Philip Moyes, the decision to adopt the semi-monocoque fuselage was a significant advance in design; many Whitleys surviving severe damage on operations.
In June 1935, owing to the urgent need to replace biplane heavy bombers then in service with the RAF, it was agreed to produce an initial 80 aircraft, 40 being of an early Whitley Mk I standard and the other 40 being more advanced Whitley Mk IIs. Production was initially at three factories in Coventry; fuselages and detailed components were fabricated at Whitley Abbey, panel-beating and much of the detailed work at the former Coventry Ordnance Works factory, while wing fabrication and final assembly took place at Baginton Aerodrome. During 1935 and 1936, various contracts were placed for the type; the Whitley was ordered "off the drawing board" - prior to the first flights of any of the prototypes.
On 17 March 1936, the first prototype Whitley Mk I, K4586, conducted its maiden flight from Baginton Aerodrome, piloted by Armstrong Whitworth Chief Test Pilot Alan Campbell-Orde. K4586 was powered by a pair of Armstrong Siddeley Tiger IX 14-cylinder air-cooled aircraft radial engines. The second prototype, K4587, was furnished with a pair of more powerful medium-supercharged Tiger XI engines. The prototypes differed little from the initial production standard aircraft; a total of 34 production Whitley Mk I were completed.
Further development
After the first 34 aircraft had been completed, the engines were replaced with the more reliable two-speed-supercharged Tiger VIIIs. K7243, the 27th production Whitley, is believed to have served as a prototype following modifications. The resulting aircraft was designated as the Whitley Mk II. A total of 46 production aircraft were completed to the Whitley Mk II standard. One Whitley Mk II, K7243, was used as a test bed for the 21-cylinder radial Armstrong Siddeley Deerhound engine; on 6 January 1939, K7243 made its first flight with the Deerhound. Another Whitley Mk I, K7208, was modified to operate with a higher gross weight.K7211, the 29th production Whitley, served as the prototype for a further advanced variant of the aircraft, the Whitley Mk III. The Whitley Mk III featured numerous improvements, such as the replacement of the manually operated nose turret with a single powered Nash & Thompson turret and a powered retractable twin-gun ventral "dustbin" turret. The ventral turret was hydraulically-powered but proved to be hard to operate and added considerable drag, thus the Whitley Mk III was the only variant with it. Other changes included increased dihedral of the outer wing panels, superior navigational provision and the installation of new bomb racks. A total of 80 Whitley Mk III aircraft were manufactured.
While the Tiger VIII engine used in the Whitley Mks II and III was more reliable than those used in early aircraft, the Whitley was re-engined with Rolls-Royce Merlin engines in 1938, giving rise to the Whitley Mk IV. Three Whitley Mk I aircraft, K7208, K7209 and K7211, were initially re-engined to serve as prototypes. The new engines are credited with producing greatly improved performance. Other changes made included the replacement of the manually operated tail and retractable ventral turrets with a Nash & Thompson powered tail turret equipped with four.303 in Browning machine guns, the increasing of fuel tankage capacity, including two additional fuel tanks in the wing. A total of 40 Whitley Mk IV and Whitley Mk IVA, a sub-variant featuring more powerful models of the Merlin engine, were completed.
The decision was made to introduce a series of other minor improvements to produce the Whitley Mk V. These included the modification of the tail fins and rudders, the fitting of leading edge de-icers, further fuel capacity increases, a smaller D/F loop in a streamlined fairing being adopted, and the extension of the rear fuselage by 15 in to improve the rear-gunner's field of fire. The Whitley Mk V was by far the most numerous version of the aircraft, with 1,466 built until production ended in June 1943.
The Whitley Mk VII was the final variant to be built. Unlike the other variants, it was developed for service with RAF Coastal Command and was thus furnished for maritime reconnaissance rather than as a general purpose bomber. A Whitley Mk V, P3949 acted as a prototype for this variant. A total of 146 Whitley Mk VIIs were produced, additional Whitley Mk V aircraft being converted to the standard. It had a sixth crew member to operate the new ASV Mk II radar system along with an increased fuel capacity for long endurance anti-shipping missions. Some Whitley Mk VII were later converted as trainer aircraft, featuring additional seating and instrumentation for flight engineers.
Early marks of the Whitley featured bomb bay doors, fitted on the fuselage and wing bays, that were held shut by bungee cords; during bombing operations, these were opened by the weight of the bombs as they fell on them and closed again by the bungee cord. The short and unpredictable delay for the doors to open led to highly inaccurate bombing. The Mk.III introduced hydraulic doors which greatly improved bombing accuracy. To aim bombs, the bomb aimer opened a hatch in the nose of the aircraft, which extended the bomb sight out of the fuselage but the Mk IV replaced this hatch with a slightly extended transparent plexiglas panel, improving crew comfort.
Design
The Armstrong Whitworth Whitley was a twin-engined heavy bomber, initially being powered by a pair of. Armstrong Siddeley Tiger IX radial engines. More advanced models of the Tiger engine equipped some of the later variants of the Whitley; starting with the Whitley Mk IV variant, the Tigers were replaced by a pair of Rolls-Royce Merlin IV V12 engines. According to Moyes, the adoption of the Merlin engine gave the Whitley a considerable boost in performance.The Whitley had a crew of five: a pilot, co-pilot/navigator, a bomb aimer, a wireless operator and a rear gunner. The pilot and second pilot/navigator sat side by side in the cockpit, with the wireless operator further back. The navigator, his seat mounted on rails and able to pivot, slid backwards and rotated to the left to use the chart table behind him after take-off. The bomb aimer position was in the nose with a gun turret located directly above. The fuselage aft of the wireless operator was divided horizontally by the bomb bay; behind the bomb bay was the main entrance and aft of that the rear turret. The bombs were stowed in two bomb bays housed within the fuselage, along with a further 14 smaller cells in the wing. Other sources state there were 16 "cells", two groups of two in the fuselage and four groups of three in the wings, plus two smaller cells for parachute flares in the rear fuselage. Bomb racks capable of holding larger bombs were installed on the Whitley Mk III variant.
The early examples had a nose turret and rear turret, both being manually operated with one Vickers 0.303 machine gun apiece. On the Whitley Mk III this arrangement was substantially revised: a new retractable ventral 'dustbin' position was installed mounting twin.303 in Browning machine-guns and the nose turret was also upgraded to a Nash & Thompson power-operated turret. On the Whitley Mk IV, the tail and ventral turrets were replaced with a Nash & Thompson power-operated tail turret mounting four Browning.303 machine guns; upon the adoption of this turret arrangement, the Whitley became the most powerfully armed bomber in the world against attacks from the rear.
The fuselage comprised three sections, with the main frames being riveted with the skin and the intermediate sections being riveted to the inside flanges of the longitudinal stringers. Extensive use of Alclad sheeting was made. Fuel was carried in three tanks, a pair of tanks in the leading edge of each outer wing and one tank in the roof of the fuselage, over the spar center section; two auxiliary fuel tanks could be installed in the front fuselage bomb bay compartment. The inner leading edges contained the oil tanks, which doubled as radiant oil coolers. To ease production, a deliberate effort was made to reduce component count and standardise parts. The fuselage proved to be robust enough to withstand severe damage.
The Whitley featured a large rectangular-shaped wing; its appearance led to the aircraft receiving the nickname "the flying barn door". Like the fuselage, the wings were formed from three sections, being built up around a large box spar with the leading and trailing edges being fixed onto the spar at each rib point. The forward surfaces of the wings were composed of flush-riveted, smooth and unstressed metal sheeting; the rear 2/3rds aft of the box spar to the trailing edge, as well as the ailerons and split flaps was fabric covered. The inner structure of the split flaps was composed of duralumin and ran between the ailerons and the fuselage, being set at a 15–20 degree position for taking off and at a 60 degree position during landing. The tailplanes employed a similar construction to that of the wings, the fins being braced to the fuselage using metal struts; the elevators and rudders incorporated servo-balancing trim tabs.