Airspeed Ambassador

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 postwar 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 turbo-compound 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.

Into flight

On 10 July 1947, the first prototype, registered G-AGUA, conducted the type's maiden flight, flown by chief test pilot George B.S. Errington. After the generally successful first flight, the prototype underwent a month of alterations, including deleting the spring tab and replacing it with geared tabs fitted to the outer rudders and locking the inner rudder; reversible propellers were also installed. During September 1947, the prototype made its first public display alongside elements of the second prototype, including its cockpit and control system, at the Society of British Aircraft Constructors (SBAC) show at Radlett.

On 22 November 1947, the programme received a setback when the prototype was forced to perform a belly landing after the port undercarriage leg failed to deploy due to a loss of hydraulic pressure. This did not seemingly deter customer confidence, as the newly created operator British European Airways (BEA) continued to openly express their preference for the type, and in September they placed a £3 million order for 20 Ambassadors. This support was so impactful that, according to aviation author H. A. Taylor, rival aircraft manufacturer Vickers was close to cancelling development of the Viscount over fears that airlines held a preference for advanced piston-powered airliners over the unfamiliar turboprop.

During flight testing, it was found that the aircraft possessed particularly favourable low speed characteristics. Having been explored in depth beforehand, this was dramatically displayed at the 1948 Farnborough Airshow, becoming the only aircraft in history to perform such an aerial display with one engine out throughout. This was a deliberate choice, with the inactive engine's propeller being feathered prior to taking off and remaining so until after landing. The first prototype performed the majority of flight testing through late 1948.

A total of three prototypes were constructed for the test programme. The second Ambassador, G-AKRD, was the first to feature pressurisation and was equipped with a full passenger cabin configuration for demonstration flights. This second prototype was subsequently used by the Bristol Aeroplane Company from 1953 for flight-testing the Bristol Proteus 705 turbine engine. From March 1958, it was used by Rolls-Royce for testing the Dart and Tyne turboprops.