The Boulton Paul P.111 is an experimental aircraft designed and produced by the British aircraft manufacturer Boulton Paul. It was amongst the first aircraft designed to explore the characteristics of the tailless delta wing configuration.
The development of the P.111 came as a response to the release of Specification E.27/46 by the Air Ministry shortly after the conclusion of the Second World War. To internally accommodate its Rolls-Royce Nene turbojet propulsion, a relatively broad fuselage was necessitated, giving it an unorthodox appearance. The wing featured removable wing tips that could be swapped to produce different wing shapes, a feature deemed to be highly desirable for the aerodynamic investigations it was built to perform. Other novel features beyond the wing included a Martin-Baker-built ejection seat and an early fully-powered flight control system. The P.111 performed its maiden flight on 10 October 1950.
Early flight testing of the aircraft revealed the flight controls to be highly sensitive, major trim shifts would also occur whenever the landing gear was deployed or retracted, and a relatively high landing speed was also necessary. Various modifications, including the addition of fuselage-mounted airbrakes, a rudimentary feedback arrangement for the flight controls, and redesigned undercarriage doors, were made during the flight test programme, the majority of these changes occurred following a minor landing accident. These modifications were so extensive that the aircraft was re-designated as the P.111A. Its final test flight occurred during 1958, after which the aircraft itself was transported to the Cranfield College of Aeronautics for use as a training airframe. The type should not be confused with the later Boulton Paul P.120, albeit the two aircraft do share considerable similarities.
Design and development
Throughout the late 1940s and early 1950s, the Allied Powers sought to maximise the capabilities of their militaries and industries by investigating and harnessing the wartime advances made in Nazi Germany during the Second World War. In particular, these nations were keen to explore and integrate numerous aerospace advances and theories acquired through activities akin to Operation Paperclip. In Britain, the Air Ministry issued Specification E.27/46, which called for an experimental aircraft to perform an investigation of the then-unfamiliar delta planform wing, particularly in terms of its stability and controllability. The aircraft manufacturer Boulton Paul opted to pursue this specification and tasked its chief designer, Dr S. C. Redshaw, with producing an appropriate aircraft.
The resulting aircraft, designated P.111, was a basic aircraft specifically designed for Delta wing research. In terms of its basic configuration, the P.111 was designed to be the smallest possible airframe that would accommodate both a single Rolls-Royce Nene turbojet engine, a Martin-Baker-built ejection seat and a delta wing. Because of the need to internally house the relatively wide Nene engine, which used a centrifugal compressor, the fuselage of the P.111 had a rather tubby appearance; air was supplied to the engine via a flattened oval nose intake. The inward-retracting landing gear had a noticeably wide track and a tall nosewheel leg placed it at 17° on the ground; sizable doors covered the recesses of the undercarriage while retracted. All-metal construction was used throughout the aircraft, with the exception of the wing extensions and the fin tip, which were of glass-reinforced plastic; the exterior skin of the aircraft typically used a stressed-skin approach.
The delta wing of the P.111 was relatively thin in comparison to contemporary wings and was swept at an angle of 45°. When not fitted with tip extensions, this wing was strongly cropped at about 75 percent of the pure delta shape, while the installation of the larger extensions resulted in an almost unbroken pure delta shape. The P.111 could be flown with these wings or with one of two pairs of extensions. The purpose of these tip extensions was to investigate the different aerodynamic effects that their fitting would have upon the delta wing without having to replace or reshape the whole wing to do so. The fin, which had an unswept trailing edge, also featured a removable and adjustable tip, though it is believed that the aircraft was always flown with the particularly pointed tip fitted. The fin accommodated a VHF aerial at its tip as well as a camera installed in its leading edge.