Hawker Siddeley (BAe), McDonnell-Douglas/Boeing Harrier AV-8S/TAV-8S & AV-8B/B+/TAV-8B

Senior project engineer Ralph Hooper at Hawker promptly set about establishing an initial layout for a theoretical aircraft to take advantage of the Pegasus engine, using data provided by Bristol. This proposed aircraft soon received the internal designation P.1127. In July 1957, a modification made to the design was the incorporation of a bifurcated tailpipe, similar to the Hawker Sea Hawk, which was equipped with rotatable nozzles for the hot exhaust, similar those already used for the cold exhaust. The switch from a single tailpipe meant that the initial tailwheel undercarriage could also be discarded in favour a conventional nose wheel-led undercarriage.  The design process extended throughout 1958, being financed entirely by Hawker, while approaches were made to NATO headquarters to better establish the tactical requirements sought, particularly between the conflicting demands for a lightly armed supersonic fighter and a simpler multipurpose subsonic one.
The development process had involved extensive use of physical models; for one series of blowing trials, mixtures of focused hot and cold air were directed onto ground platforms to simulate the ground effect upon take-off.  This work was considered to be critical to the project as there was very little knowledge of the adverse effects which could influence the aircraft during the vertical takeoff process; as there was no airflow over the ailerons, tailplane, and rudder while the aircraft was held in a stationary hover, wingtip control jets were experimented with as an alternative reaction control approach.  These research included the development of an all-new control response simulator which linked a series of simple flying controls to a computer. By the end of 1958, barely eighteen months after the start of the project, all the main features of the P.1127 were developed with one exception, that being the reaction control system, the development of which was completed by April 1959.


Throughout the development, Camm heavily emphasised the importance of the design’s simplicity, observing that “Sophistication means complication, then in turn escalation, cancellation, and finally ruination”. In 1958, the design centered around a single Pegasus engine capable of generating 13,000 lb of thrust; when fully equipped, the aircraft was to weight slightly less than the maximum thrust, thereby allowing vertical takeoffs to be performed under all nominal conditions. During late 1958, the rapid progress of the P.1127 project had been noticed by technical advisors at NATO, who began promoting the acceleration of the aircraft’s development and that member nations should skip over the next generation of support fighters in favour of the emergent P.1127 instead. In Britain, support for the program was also growing within the British Air Staff, from January 1959 onwards, rumours of a pair of P.1127 prototypes being ordered by the Ministry of Supply alongside those of a Air Ministry specification being drafted around the project frequently echoed.
As the P.1127 had been developed at a time of deep UK defense cuts, Hawker had to seek commercial funding, and significant engine development funding came from the U.S.  Research assistance was also provided by U.S.; including a series of wind tunnel tests conducted by NASA’s Langley Research Center using sub-scale models, which demonstrated acceptable flight characteristics.  Hawker test pilot Hugh Merewether went to the U.S. at NASA’s request to fly the Bell X-14.  In March 1959, the company’s board of directors (Hawker Siddeley then) decided to privately fund two P.1127 prototypes.
In February 1959, Hawker had completed practically all of the design work and thus passed the entirety of its manufacturing design work to the company’s Experimental Design Office at Kingston, London. In April 1959, the Ministry of Supply formally issued a contract for the completion of a pair of P.1127 prototypes. However, there were critics amongst the Air Staff of the project, typically disliking the P.1127 for its subsonic speeds, favouring supersonic-capable aircraft instead; Mason attributes this as having caused considerable delay in the issuing of a contract to Hawker. On 23 July 1959, Hawker authorised the application of maximum effort to complete the development of the P.1127.


On 15 July 1960, the first “P.1127 Prototype V/STOL Strike Aircraft”, serial XP831, was delivered to RAF Dunsfold, Surrey, to commence static engine testing. On 31 August 1960, the Pegasus engine was ran for the first time while inside the airframe. Some of the tests were performed from a purpose-built platform at the aerodrome, which functioned to deflect the hot exhaust gases away from the aircraft during early hovering trials while more powerful versions of the engine were developed. On 13 October 1960, the first Pegasus flight engine, capable of generating 11,300 lb of thrust, was delivered to Dunsfold.