Design and Development
The aircraft was designed to a BEA requirement for a 100-seat aircraft to replace their Viscounts. The original Type 870 design was then modified when TCA expressed their interest in the design as well, and Vickers returned the updated Type 950 that filled both requirements. The main difference between the Viscount and Vanguard was the construction of the fuselage. The Vanguard started with the original Viscount fuselage, but cut it off about half of the way up from the bottom, and replaced the top section with a larger-diameter fuselage to give it a double bubble cross-section (similar to the Boeing Stratocruiser). The result of the larger upper portion was a roomier interior, with increased cargo capacity below the floor.
With this larger, and heavier, fuselage came the need for a new engine to lift it. Rolls-Royce delivered their new Tyne design with a nominal 4,000 hp/3,000 kW (as compared to the Viscount's Dart of about 1,700 hp/1,300 kW). This allowed for a much higher service ceiling and cruising speed; the Vanguard had a service ceiling almost twice that of the Viscount. The Vanguard was one of the fastest turboprops ever and was faster than the present day Saab 2000 or de Havilland Canada Dash 8. A pilot report describes maintaining 10,000 ft altitude with three engines feathered and the port outer at maximum cruise power; weight at start of that flight was about 112,000 lb. This is notably better performance than a Lockheed C-130, an airplane of similar weight and power that cannot maintain any altitude on one engine. Nevertheless, the Vanguard was certainly overpowered.
The first Type 950 prototype G-AOYW flew on 20 January 1959 The flight, a transfer to Wisley 3 miles away, had been planned for December but the engines were returned to Rolls-Royce for minor work. Proper flight testing was then carried out from Wisley.
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