The Armstrong Whitworth A.W.41 Albemarle was a twin-engine transport aircraft developed by the British aircraft manufacturer Armstrong Whitworth and primarily produced by A.W. Hawksley Ltd, a subsidiary of the Gloster Aircraft Company. It was one of many aircraft which entered service with the Royal Air Force (RAF) during the Second World War.
The Albemarle had been originally designed as a medium bomber to fulfil Specification B.9/38 for an aircraft that could be built of wood and metal without using any light alloys. The aircraft was passed over as a bomber role in favour of aerial reconnaissance and transport, leading to the aircraft being extensively redesigned mid-development. Performing its maiden flight on 20 March 1940, its entry to service was delayed by the redesign; 295 Squadron at RAF Harwell, did not receive the type in quantity until January 1943. As superior bombers, such as the Vickers Wellington, were already in use in quantity, plans for using the Albemarle as a bomber were abandoned.
The Albemarle was used by the RAF primarily for general and special transport duties, paratroop transport, glider towing and other secondary duties. Albemarle squadrons participated in Normandy landings and the assault on Arnhem during Operation Market Garden. While the Albemarle remained in service throughout the conflict, the final examples in RAF service were withdrawn less than a year after war's end. During October 1942, the Soviet Air Force also opted to order 200 aircraft; of these, only a handful of Albemarles were delivered to the Soviets prior to the Soviet government deciding to suspend deliveries in May 1943, and later cancelling the order in favour of procuring the American Douglas C-47 Skytrain instead.
Development Background The origins of the Albemarle can be traced back to the mid-1930s and the issuing of Specification B.9/38 by the British Air Ministry.Tapper 1988, p. 276. This sought a twin-engine medium bomber of wood and metal construction, without the use of any light alloys, in order that the aircraft could be readily built by less experienced manufacturers from outside the aircraft industry. Furthermore, the envisioned aircraft had to be engineered in a manner that would allow it to be divided into relatively compact subsections, all of which had to fit on to a standard Queen Mary trailer to facilitate the adoption of a dispersed manufacturing strategy. At the time, the Air Ministry was particularly concerned that, in the event of a major conflict arising, there would be restrictions on the supply of critical materials that could undermine mass production efforts.Tapper 1988, pp. 276–277.
Several aircraft manufacturing firms, including Armstrong Whitworth, Bristol and de Havilland, were approached to produce designs to meet the specification. Bristol proposed two designs – a conventional undercarriage and an wingspan capable of 300 mph and a tricycle undercarriage design with span with a maximum speed of . Both designs, known as the Type 155, used two Bristol Hercules engines. The rival Armstrong Whitworth AW.41 design used a tricycle undercarriage and was built up of sub-sections to ease manufacture by firms without aircraft construction experience. The AW.41 was designed with Rolls-Royce Merlin engines in mind, but also with provisions for the use of Bristol Hercules as an alternative powerplant.
In June 1938, mock-ups of both the AW.41 and Bristol 155 were examined, while revised specifications B.17/38 and B.18/38 were drawn up for the respective designs; de Havilland opted against submitting a design. The specification stipulated at economical cruise while carrying of bombs. Bristol was already busy with other aircraft production and development and stopped work on the 155. Changes in policy made the Air Staff reconsider the Albemarle as principally a reconnaissance aircraft capable of carrying out bombing. Among other effects, this meant more fuel to give a range. An upper dorsal turret and a (retractable) ventral turret for downward firing were added.
Into production In October 1938, 200 aircraft were ordered "off the drawing board" (i.e. without producing a prototype). The aircraft had a positive reputation and there were initially high hopes for its performance, however it never quite lived up to expectations. Furthermore, according to aviation author Oliver Tapper, the brief was a relatively difficult one for any company to fulfil. Initially, physical work centred around the construction of a pair of lead aircraft, which were to be test flown prior to the commencement of full-rate manufacture of the type. The first Albemarle, serial number P1360, was assembled at Hamble Aerodrome by Air Service Training; the aircraft performed its maiden flight on 20 March 1940.Mason 1994, pp. 335–337.
This first flight had actually been unintended, the test pilot having picked up too much speed during a ground taxi run, and had only taken off with the barest margin after traversing the entire runway. Months later, P1360 was damaged after a forced landing during the test flight programme, but was promptly repaired. Early flights of the type by test pilots typically described it as being relatively average and being free of flaws.Tapper 1988, pp. 279–280. A number of modifications were made to the design during this late stage of development, including the extensive redesign of the aircraft's structure by Lloyd at Coventry. Further measures were made to improve the Albemarle's take-off performance, such as the adoption of a wider span wing, and the thickening of the rudder's trailing edge to correct a tendency to over-balance. Occurrences of the engines overheating were never fully resolved, the main change in this area being the raising of the maximum permissible operational temperature from 280C to 300C.Tapper 1988, pp. 280–281.
The Albemarle's production run was principally undertaken by A.W. Hawksley Ltd of Gloucester, a subsidiary of the Gloster Aircraft Company, which was specifically formed to construct the Albemarle. Originally, Gloster was to have undertaken this work itself at its Brockworth facility. Both Gloster and Armstrong Whitworth were member companies of the Hawker Siddeley group, one of the largest aircraft manufacturing interests in Britain. Individual parts and sub-assemblies for the Albemarle were produced by in excess of 1,000 subcontractors.Tapper 1988, p. 277."British Aircraft of WWII." jaapteeuwen.com. Retrieved: 15 March 2007. Amongst the companies that were subcontracted were MG Cars, to produce the forward fuselage, Rover, which constructed the wing centre section, and Harris Lebus, which built the tailplane units. Production of the Albemarle was terminated during December 1944, by which point 602 aircraft had been completed.
Design The Armstrong Whitworth Albemarle was a mid-wing cantilever monoplane with twin fins and rudders. The fuselage was built in three primary sections; the structure being composed of unstressed plywood over a steel tube frame, including four circular steel longerons; most elements were bolted together via gusset plates.Flight 27 January 1944, p. 89.Tapper 1988, pp. 277–278. The structure was intentionally divided in order that it might readily permit individual sections to be removed and replaced in the event of battle damage being sustained. The centre section of the wing was a single piece that ran through the fuselage, being built around a steel tube girder; it formed the attachment points for the central and nose fuselage sections, as well as the engines, main undercarriage legs, and extension wings.Tapper 1988, p. 278. Aside from a portion of the leading edge that used light alloys, the majority of the wing was covered in plywood. The extension wings were almost entirely made of wood, save for the bracing of the two spars by steel tubing; the Frise-type ailerons and tailplane were also composed of wood. The structure of the forward section used stainless steel tubing as to reduce interference with magnetic compasses.Flight 27 January 1944, p. 90.
The Albemarle featured a Lockheed-designed hydraulically-operated, retractable tricycle undercarriage, the main wheels retracting back into the engine nacelles, and the nose wheel retracting backwards into the front fuselage, while the tail wheel was fixed in position, albeit semi-concealed by a "bumper" configuration. It was one of the particularly notable design features of the Albemarle, according to Tapper, it was the first British-built aircraft with a retractable nose-wheel to be built in quantity for the Royal Air Force. Power was provided by a pair of Bristol Hercules XI air-cooled radial engines, each capable of 1,590 hp and driving a three-blade de Havilland Hydromatic propeller unit. Fuel was typically stored in four tanks, two in the center fuselage and two within the wings centre section; in circumstances where extended range would be required, a maximum of additional auxiliary tanks could be installed within the aircraft's bomb bay. This sizeable bomb bay was equipped with hydraulically-operated doors and spanned from just aft of the cockpit to roughly halfway between the wings and the tail.
The two pilots sat side by side in the forward portion of the cockpit, while the radio operator was seated behind the pilots. The navigator's position was in the aircraft's nose, and thus was forward of the cockpit. The bomb aimer's sighting panel was incorporated into the crew hatch in the underside of the nose. In the rear fuselage, several glazed panels were present so that a "fire controller" could help coordinate the aircraft's defensive turrets against attackers. The dorsal turret was a Boulton-Paul design, which was electrically operated and originally armed with four Browning machine guns.Tapper 1988, pp. 278–279. A fairing forward of the turret automatically retracted as the turret rotated to fire forwards.Flight 27 January 1944, p. 88. The original bomber configuration of the Albemarle required a crew of six including two gunners; one in the four-gun dorsal turret and one in a manually operated twin-gun ventral turret but only the first 32 aircraft, the Mk I Series I, were produced in such a configuration.Williams 1989, p. 37.Tapper 1988, p. 279.
As a bomber, the Albemarle was commonly considered to be inferior to several other aircraft already in RAF service, such as the Vickers Wellington;Williams 1989, p. 36. according to aviation author Ray Williams, the type was only used ever used as a bomber on two occasions. Accordingly, later built aircraft were configured as transports, called either "General Transport" (GT) or "Special Transport" (ST). Amongst the modifications made was the elimination of the ventral turret, while the dorsal unit was downgraded to a manually operated twin gun arrangement; the internal space was heavily altered by the elimination of bomb-aiming apparatus and the rear fuselage tank. Additions also included a quick-release hook, installed at the rearmost part of the fuselage for the towing of gliders. When used as a paratroop transport, a maximum of ten fully armed troops could be carried; these paratroopers were provided with a dropping hatch in the rear fuselage along with a single large loading door in the starboard side of the fuselage.Bridgman, Leonard. Jane's Fighting Aircraft of World War II. New York: Crescent Books, 1988. .
Operational history Ambitions to use Albemarle in the bomber role were dropped almost immediately upon the type reaching service; this was due to it not representing an improvement over current medium bombers (such as the Vickers Wellington) and possessing inferior performance to the new generation four-engined heavy bombers that were also about to enter service with the RAF. However, the aircraft was considered to be suitable for general reconnaissance and transport duties, and thus was re-orientated towards such missions.