Airspeed AS.57 Ambassador: 1947 жылғы британдық қос поршеньді ұшақ

British twin piston engined airliner, 1947

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team in 1943, which initially worked on a smaller proposal powered by Bristol Hercules radial engines; this was quickly superseded by a larger capacity design aimed at better fulfilling the expansion in postwar civil air travel, although several entities doubted Airspeed's projected growth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. 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. 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. 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. 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 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. 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. During the latter stage of development, some issues were uncovered. Quantity production of the Ambassador commenced during 1950, leading to the first production standard aircraft, destined for BEA, performing its first flight on 12 January 1951.

The Airspeed Ambassador was an all metal twin engine airliner, designed to serve short to medium haul routes. It was relatively advanced for the era, being relatively aerodynamically clean, having a high aspect–ratio wing with hoped for near Laminar flow characteristics, a tricycle undercarriage, a steerable nosewheel, integral fuel tanks, and other recent innovations. Distinctive external features of the Ambassador included its three low tailfins and a long pointed nose, giving it a resemblance to the larger transcontinental Lockheed Constellation. Its tricycle gear gave it a more modern appearance than contemporaries such as the DC 3, Curtiss Commando, Avro Lancastrian and Vickers Vikings that were common on Europe's shorter airline routes. In a standard configuration, the Ambassador could accommodate up to 47 passengers; somewhat unusually, its passenger cabin could be either pressurised or not as the customer preferred. It was typically powered by conventional Bristol Centaurus radial engines, although individual aircraft were reengined with various powerplants, including turboprops. To increase cruise performance, designers made great efforts to minimise drag, using a NACA laminar flow wing section. The predicted low drag performance was not completely realized, however, due to structural features for wing construction, propeller slipstream over the inner wing, and increased skin roughness in actual service conditions. The engine nacelles were initially designed with inwardly opening louvres for exhaust gases and cooling air rather than the usual outwardly opening "gills". However, these proved inadequate for cooling the engine, thus the gills were reinstated. Engine out climb performance was enhanced by being able to feather the propeller using a zero torque signal from the engine.

During 1952, British European Airways (BEA) introduced the first of its 20 strong fleet of Ambassadors to revenue service, the airline referred to them as the "Elizabethan Class" in honour of the newly crowned Queen Elizabeth II. The first "Elizabethan" scheduled flight was from Heathrow Airport to Paris Le Bourget on 13 March 1952, soon the type was used across BEA's main the airline's key UK routes. According to Taylor, the Ambassador's performance gave BEA a competitive edge over its rivals. One example of de Havilland's undermining of potential sales was the recall of the Sales Director to de Havilland's headquarters at Hatfield Aerodrome (Hertfordshire, England) from Australia, despite his reportedly being near to finalizing an order from Trans Australia Airlines for 12 Ambassadors. Taylor observed that prospective customers were often sceptical that Airspeed, being a relatively small company, could be relied upon for technical support and components. Following the type's disposal by BEA, secondhand Ambassadors helped to establish the scheduled and charter flight operations of Dan Air, an important airline in the development of the package holiday. The type was also used in the UK by Autair and BKS Air Transport. Secondhand Ambassadors were also flown for short periods by other airlines including Butler Air Transport (Australia), Globe Air (Switzerland) and Norrønafly (Norway). Multiple entities, such as Royal Dutch Shell and the Royal Jordanian Air Force, also procured Ambassadors for private purposes. The initial popularity of the Ambassador, with its pressurised cabin and good soundproofing, was soon eclipsed by the arrival of turboprop powered aircraft such as the Vickers Viscount and, some years later, the Lockheed Electra, which featured more reliable engines and faster speeds.

AS.57 Ambassador 1
Prototype aircraft with Bristol Centaurus 130 engines, two built. AS.57 Ambassador 2
Production version with Bristol Centaurus 661 engines, 21 built including the production prototype.

AS.59 Ambassador II
Project for either a twin engined variant with Bristol Proteus or Bristol Theseus engines or a four engined variant with Napier Naiads or Rolls Royce Darts. AS.60 Ayrshire C.1
Proposed variant to meet Air Ministry Specification C.13/45 for a medium range military transport with a rear fuselage loading ramp. Ten were ordered in October 1946 but were not built, after a review of the design's projected performance produced figures lower than the Air Ministry's requirements. AS.64
Proposed military transport variant for the Royal Air Force to meet Air Ministry Specification C.26/43, not built. 6 February 1958: G ALZU, Lord Burghley, also of BEA, in what became known as the Munich air disaster, crashed on takeoff after a refuelling stop at Munich while operating a charter flight from Belgrade, Yugoslavia, to Manchester, England. This crash received tremendous public attention in the UK as it involved team members and staff of Manchester United Football Club, together with representatives of the national press. Of the 44 people on the plane, 21 died in the crash and 2 died later, including eight Manchester United players. The investigation eventually focused on runway slush adversely affecting the speed of the plane as it attempted to take off. 14 April 1966: G ALZX of Dan Air was damaged beyond repair when its undercarriage collapsed on landing at Beauvais, France. 14 September 1967 G ALZS of Autair was damaged beyond repair on landing at Luton Airport, UK. The aircraft overran the runway and ended up in soft clay. 3 July 1968: G AMAD of BKS Air Transport crashed at London Heathrow Airport. All but two of its crew as well as several horses which were being transported and their grooms, were killed. A parked Trident airliner was damaged beyond repair (G ARPT) and another Trident had its tail torn off before the airliner hit terminal buildings and came to rest. The accident was caused by a failed flap actuating rod in the left wing. The Trident which suffered the damaged tail (G ARPI) was subsequently repaired and later involved in an unconnected fatal accident in June 1972. 30 September 1968: G AMAG of Dan Air was damaged beyond repair in a wheels up landing at Manston, United Kingdom.

Butler Air Transport – operated three units. Norrønafly – proposed to operate two aircraft but they never entered service. South Seas Airways – bought one aircraft but failed to gain an operators licence; the aircraft was not delivered to New Zealand. Globe Air – operated three aircraft.