The Boulton Paul Balliol and Sea Balliol are monoplane advanced trainer aircraft designed and produced by the British aircraft manufacturer Boulton Paul Aircraft. On 17 May 1948, it became the world's first single-engined turboprop aircraft to fly. The Balliol was operated primarily by both the Royal Air Force (RAF) and the Royal Navy Fleet Air Arm (FAA). Developed during the late 1940s, the Balliol was designed to fulfil Air Ministry Specification T.7/45, replacing the wartime North American Harvard trainer. Unlike previous trainer aircraft, which were powered by piston engines, it was specified for the aircraft to use newly developed turboprop propulsion instead. On 30 May 1947, the Balliol performed its maiden flight; the first preproduction aircraft would fly during the following year. Production examples were powered by the Rolls-Royce Merlin engine, while various prototypes and pre-production aircraft featured alternative powerplants such as the Rolls-Royce Dart and Armstrong Siddeley Mamba turboprop engines. The Balliol entered service with the RAF in 1950 and proved to be a relatively trouble-free trainer. However, a shift in attitudes towards turbojet-powered trainer aircraft would see orders being curtailed for the type by 1952. Despite this, a navalised version of the aircraft, the Sea Balliol, was also introduced for deck landing training. The type also saw some use in other capacities, such as for experimental flights. Only a single export customer, the Royal Ceylon Air Force, would procure the type. Origins During March 1945, the Air Ministry issued Specification T.7/45, which sought a new advanced trainer to succeed the Royal Air Force's (RAF) fleet of North American Harvards. Amongst the requirements specified was the use of the newly developed turboprop engine, as it was felt that the new generation of advanced trainers would better prepare pilots for flying jet-powered combat aircraft such as the newly emerged Gloster Meteor fighter aircraft. As a fallback measure in case of difficulties being encountered with engine development programmes, the envisioned trainer was also to readily accommodate a more conventional Bristol Perseus radial engine as well. A further stipulation by the ministry was the fitting of a three-seat cockpit in a configuration roughly akin to the contemporary Percival Prentice basic trainer. The pilot and instructor were sat in a side-by-side arrangement, while a second student could be accommodated in a third seat to the rear, positioned as to enable them to closely observe the pilot and the instructions being issued. The trainer was to be configured to perform various forms of training, being suitable for both day and night operations, featuring both guns and bombs for armament training, a glider-towing capability, and a general design that would be compatible with navalisation measures, such as a strengthened undercarriage and the fitting of arrestor gear. Within a month of the specification's issuing, Boulton Paul Aircraft had opted to produce multiple proposals in response, as large orders had been anticipated. Boulton Paul's P.108 proposal, which would become the Balliol, was that of a conventional low-wing monoplane, featuring retractable main undercarriage and a fixed tailwheel. Towards the end of August 1945, Boulton Paul received an order from the Air Ministry, calling for the production of a batch of four prototypes, which were to be powered by the Rolls-Royce Dart turboprop engine. During August 1946, this was followed by a larger order for 20 pre-production aircraft, with ten each to be powered by the Dart and the Armstrong Siddeley Mamba turboprop, with delays to development of the Dart meaning that the prototypes would now be fitted by the Mamba. Competing proposals from other manufacturers were also submitted, including Avro's Athena in particular. For more details of development, design, operational history and 4 variants, click here.
