Armstrong Whitworth AW.681

AW.681 / HS.681
Manufacturer's model of the AW.681
Role	Projected VTOL Military transport
Manufacturer	Hawker Siddeley
Status	Project cancelled February 1965

The Armstrong Whitworth AW.681, also known as the Whitworth Gloster 681 or Hawker Siddeley HS.681, was a projected British long-range STOL military transport aircraft design of the early-1960s by Armstrong Whitworth Aircraft and was to be capable of development to VTOL performance. The AW.681 was designed to meet the NATO specification NBMR-4.

Operational Requirement 351 was issued to meet a requirement for the Royal Air Force for a medium-range freighter to replace the Beverley and Hastings. There were proposals from British Aircraft Corporation and Hawker Siddeley, the former offering the BAC.222 based on the Lockheed Hercules and the BAC.208 with deflected-thrust engines and lift fans. Armstrong Whitworth's design was selected.

The aircraft featured a swept shoulder-mounted wing and a high T-tail. The rear fuselage was upswept with loading doors and a ramp. Four Rolls-Royce RB.142 Medway engines with vectored thrust nozzles were to be mounted on pylons under the wings which were to feature boundary layer control with blown flaps, leading edges, and ailerons. The Medway engines would have given STOL performance only. The use of an additional 18 6,000 lbf (26.7 kN) RB.162-64 lift engines or replacement of the Medways with four Bristol Siddeley Pegasus ducted-flow turbofans was proposed to obtain VTOL capability. The Pegasus 5-6 would have been rated at around 18,000 lbf (80 kN).

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