Armstrong Whitworth Whitley - Design and Development

Design and Development

The Whitley was designed by John Lloyd, the Chief Designer of Armstrong Whitworth Aircraft to meet Air Ministry Specification B.3/34 issued in 1934 for a heavy night bomber. The AW.38 design was a development of the Armstrong Whitworth AW.23 bomber-transport design that had lost to the Bristol Bombay for specification C.26/31 partly due to its Armstrong Siddeley Tiger engines. The Whitley carried a crew of five and was the first aircraft serving with the RAF to have a (semi‑)monocoque fuselage, using a slab-sided structure which eased production. As Lloyd was unfamiliar with the use of flaps on a large heavy monoplane, they were initially omitted. To compensate, the mid-set wings were set at a high angle of incidence (8.5°) to confer good takeoff and landing performance. Although flaps were included late in the design stage, the wing remained unaltered. As a result, the Whitley flew with a pronounced nose-down attitude, resulting in considerable drag. This "nose down" attitude was also seen in the design of the Armstrong Whitworth Ensign pre-war airliner.

The first prototype Whitley Mk I (K4586) flew from Baginton airfield on 17 March 1936, piloted by Armstrong Whitworth's Chief Test Pilot Alan Campbell-Orde and was powered by two 795 hp (593 kW) Armstrong Siddeley Tiger IX radial engines. The second prototype was powered by more powerful Tiger XI engines.

Owing to the urgent need to replace biplane heavy bombers still in service with the RAF, an order for 80 aircraft had been placed in 1935, "off the drawing board", before the Whitley had flown. These had medium-supercharged engines and manually operated drum magazine single machine guns fore and aft. After the first 34 aircraft had been built, the engines were replaced with more reliable two-stage supercharged Tiger VIIIs, resulting in the Whitley Mk II, that completed the initial order. One Whitley Mk II, K7243, was used as a test bed for the 1,200 hp 21-cylinder radial Armstrong Siddeley Deerhound engine, first flying with the Deerhound on 6 January 1939. The replacement of the manually operated nose turret with a powered Nash & Thomson turret and a powered retractable two-gun ventral "dustbin" turret resulted in the Whitley Mk III. The turret was hydraulically powered but it was hard to operate and added considerable drag.

While the Tiger VIIIs used in the Whitley Mks II and III were 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. These demonstrated greatly improved performance and the decision was made to introduce a series of other minor upgrades to produce the Whitley Mk V. The modifications included modified fins, leading edge de-icing, manually operated tail and retractable ventral turrets replaced with a Nash & Thompson powered turret equipped with four .303 in (7.7 mm) Browning machine guns, tail fuselage extended by 15 in (381 mm) to improve the field of fire. The Mk V would be the most numerous version of the Whitley, with 1,466 built until production ended in June 1943.

Early marks of the Whitley had bomb bay doors - the eight bays were in fuselage compartments and wing cells - that were kept closed by bungee cords and opened by the weight of the released bombs falling on them. Even the tiny random delay in time that it took for the doors to open led to highly inaccurate bombing. The Mk.III introduced hydraulically actuated doors which greatly improved bombing accuracy. To aim bombs, the bomb aimer opened a hatch in the nose of the aircraft which extended the bombsight out of the fuselage but to everyone's comfort, the Mk IV replaced this hatch with a slightly extended transparency.

The bomb aimer position was in the nose with a gun turret above. The pilot and second pilot/navigator were sat by side by side in the pilot cockpit. The navigator rotated so they could use the chart table behind. Behind the pilots was the wireless operator. The fuselage aft of the wireless operator was divided horizontally by the bomb bay. Aft of the bomb bay was the main entrance and aft of that the rear turret.