The Airspeed AS.4 Ferry was three-engined ten-seat biplane airliner designed and built by the British aircraft manufacturer Airspeed Limited. It was the company's first powered aircraft to be produced. It was proposed for development in April 1931, shortly following Airspeed's founding. The Ferry was designed specifically for Alan Cobham's National Aviation Day events, performing 'air-experience' flights for the general public. On 5 April 1932, the prototype performed its maiden flight. Only four examples were produced at the company's facilities in York during the early 1930s. Two aircraft served with the Royal Air Force during the opening years of the Second World War, although largely being used as instructional airframes. The Airspeed AS.4 Ferry was an unusual biplane airliner designed around the needs of Alan Cobham, one of the company's directors. It featured an unorthodox configuration, particularly the mounting of its third engine in the centre section of the upper wing, an arrangement which was principally adopted to provide the pilot with superior external visibility, although it also presented some aerodynamic benefits as well. The three engines installed upon the Ferry consisted of a pair of de Havilland Gipsy IIs mounted upon the upper surface of the lower wing, while the engine installed upon the upper wing was an inverted de Havilland Gipsy III instead. While the fuel tanks of the Ferry had sufficient size for around five hours of flight at cruising speeds, to best suit its air-experience role, the tanks were only ever partially filled, else it wouldn't be able to carry its maximum capacity of ten passengers. The Ferry was a biplane with equal-span wings, both of which were positioned high relative to the fuselage, with the lower wing being aligned with the top of the fuselage. According to Alan Cobham, this arrangement was to provide the passengers with an unobstructed view of the ground. The structure of the aircraft was conventional and largely composed of spruce and plywood, featuring monocoque construction across the fuselage. The wings were supported by box spars paired with wooden flanges and steel tubes for key areas such as the compression drag struts. While the Ferry had been designed specifically for short-haul pleasure flying, the design team made provisions towards its use in other roles, such as a longer distance airliner carrying five or six passengers with luggage. Despite having ten seats, which necessitated the fitting of a radio under British regulations of the era, it was certified for local flying without any radio present. To enable a faster turnaround, relatively rapid refuelling was facilitated via a pipeline to the tank from the side of the fuselage. An unusual feature of the design, believed to provide a beneficial ground-cushioning effect as well as possibly additional lift, was the aerofoil-section fairings present on the split-axle undercarriage. For details of development and operational istory, click here.
