The Airspeed AS.57 Ambassador is a British twin piston-engined airliner that was designed and produced by the British aircraft manufacturer Airspeed Ltd. It was one of the first postwar airliners to be produced.
The Ambassador was developed in response to a requirement identified by the Brabazon Committee for a twin-engined short-to-medium-haul airliner as a replacement for the ubiquitous Douglas DC-3. Airspeed assembled a design team in 1943, which initially worked on a smaller proposal powered by Bristol Hercules radial engines; this was quickly superseded by a larger-capacity design aimed at better fulfilling the expansion in postwar civil air travel, although several entities doubted Airspeed's projected growth in air travel. While outfitted with the new but conventional Bristol Centaurus radial engines, the Ambassador was designed to accommodate four Napier Nomad turbo-compound engines, a then-recent innovation. Its fuselage was compatible with pressurisation, this being an optional feature offered to customers.
On 10 July 1947, the first prototype Ambassador conducted its maiden flight; a total of three prototypes were built. Early on, British European Airways (BEA) emerged as a key customer for the type, having placed a £3 million order for 20 aircraft in September 1948. Introducing the Ambassador to service in 1951, BEA often referred to the aircraft as the "Elizabethans", as the aircraft were used for the airline's "Elizabethan Class" passenger service. However, the type was quickly outperformed by the turboprop-powered Vickers Viscount, with BEA opting to withdraw its Ambassadors in 1958.
Secondhand aircraft were operated by several other airlines, including Dan-Air and Northeast Airlines. Despite being produced in relatively small numbers, the Ambassador was operational for longer than had been anticipated by planners.
Development
Background
The origins of the Ambassador can be traced to 1943 and the work of the Brabazon Committee, which sought to define what types of aircraft would be desired by the post–war civil aviation sector. One of the committee's recommendations was a twin-engined short-to-medium-haul replacement for the Douglas DC-3, known as the Type 2. The British manufacturer Airspeed Ltd. was interested in this requirement and established a small design team to work on the project from a dispersed office in Fairmile Manor at Cobham in Surrey in 1943. This effort was headed by ex-de Havilland aeronautical engineer Arthur Hagg, who had joined the company earlier that year.
Early concepts included an unpressurised aircraft in the 14.5-ton gross weight class to be powered by a pair of Bristol Hercules radial engines. Work on the endeavour was taken as far as possible without impacting Airspeed's wartime production activity, as the Second World War was still raging. In response to changes in planner's preferences, dictating that the interim aircraft be procured so that airliners such as the in-development Ambassador had more development time, thus the design was revised substantially to expand its capacity. By 1944, it was a considerably larger design than the DC-3, with improved comfort and space.
While Airspeed's management believed that postwar demands would demand greater passenger capacities, several figures, including those within the British Overseas Airways Corporation (BOAC) and the Air Ministry, were less enthusiastic with their projections. The company also promoted the economics of higher utilisation rates and elevated cruise speeds, whereas conventional wisdom amongst airlines was to avoid increasing speeds to reduce fuel consumption. For the Ambassador, Airspeed opted to pursue a cruising altitude of 20,000 ft, relatively high for the era. A comprehensive mockup was completed by November 1944, largely for promotional purposes, while the projected operating cost figures were released during early 1945.
Immediately following the end of the conflict, the British Ministry of Aircraft Production placed an order with the company to produce a pair of prototypes. While the first prototype was to be unpressurised and powered by a pair of Bristol Centaurus radial engines, it was envisioned that the second prototype would feature a reinforced fuselage compatible with pressurisation and a wing that could accommodate four Napier Nomad turboprop engines. Several officials, including company chairman Alan Samuel Butler, favored the adoption of the new turbopropeller engines. By the end of 1945, work had commenced on building structural test sections and jigs.