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History
Chapter 1 - The origins of the P.1127

History 1/1 History 1/3

2. Design

The first company that Bristol approached was Shorts in Northern Ireland. Not only were Shorts the most experienced in terms of VTOL aircraft design, they were also partly owned by Bristol's parent company, making such a move natural. However, Shorts were firmly committed to the SC1 and with it the concept of using lift engines to achieve vertical flight. Although they did scheme a design around the BE.53, Shorts' motive for this appear to have been to allow them to establish contact with MWDP. Once this contact was achieved, the Belfast-based firm concentrated on promoting the SC1. Although this first attempt at getting an airframe design for the BE.53 ended so discouragingly, prospects were soon to brighten for the Bristol team.

The source of these renewed prospects came from Hawker Aircraft Limited at Kingston upon Thames in Surrey. Hawker had an unmatched record of success, having had its aircraft in front line service with the RAF or Royal Navy since 1925 - and if the aircraft of its forebear, Sopwith Aviation, are included, this record stretched back to before the First World War. In the mid-1950s the company was enjoying worldwide success with the Hunter, while its Sea Hawk design was being built by Armstrong Whitworth, a sister company in the Hawker Siddeley group. However, 1957 was to be a watershed year for Hawker. Back in 1954 work had begun on a design to meet OR 329, a specification calling for an all-weather, missile equipped Mach 2+ interceptor for the RAF. Although their submission, the P.1103, was unsuccessful in meeting the RAF's requirement, Hawker saw the need for something to succeed the Hunter. To this end, they re-designed the P.1103 as a single-seat, general-purpose fighter-bomber, numbering it P.1121. Although not officially sanctioned by the RAF, Hawker went ahead with design and prototype construction of the P.1121 as a private venture, confident that customer interest would soon be stimulated. Then, in April 1957, the British Minister of Defence, Duncan Sandys, pulled the rug out from under the entire aircraft industry when he announced that most future fighter and bomber development was to be cancelled in favour of guided missiles. As fighters were Hawker's forte the future suddenly began to look much bleaker for the company.

However, despite Sandys' cancellation of the last 100 Hunters for the RAF, large export orders from India and Switzerland meant that the company had some breathing space. The P.1121 project went on, with the company arguing that it was the ideal aircraft to cover the transition period before the full introduction of the missile arsenal of the future. Nevertheless, with the clear pronouncement that fighters were out of favour with the RAF, Hawker realised that they might need an alternative product within a few years if they were not to go out of business when the Hunter ceased production.

P.1127 G.A. Pegasus gas flows
General arrangement of the Hawker P.1127 design, mid-1959.
Airflow in the Pegasus 2, showing the common inlet for both compressors.

It was against this background that the company received copies of Bristol's brochure for the BE.53, one from their agent in France (Gerry Morel) at the Paris airshow of 1957, the other as a result of a letter from Sir Sydney Camm, Chief Designer of Hawker, to Stanley Hooker enquiring as to what Bristol were doing about VTOL engines. In early June 1957 Ralph Hooper, a designer in the company's Project Office, received one of the BE.53 brochures. He was initially unimpressed by it. However, he quickly drew up a scheme for an aircraft around the engine proposal. The BE.53 outlined in the brochure was equipped with vectoring nozzles for the fan airflow only, all attempts at vectoring the core flow having been put aside. This severely hampered the kind of aircraft Hooper could design. His initial scheme recognised these limits by being a three seat observation/liaison aircraft with no warload, being forced to sit at a nose high angle on a tail wheel undercarriage in order to have any hope of vertical flight. This scheme was initially called the 'High Speed Helicopter' and given the company designation P.1127. In an attempt to reduce the estimated weight, Hooper quickly refined the design to incorporate two seats and a pair of lateral intakes in place of the original ventral one, as well as incorporating reaction controls at the aircraft's extremities that would use air piped from the engine for low speed control. However, the limits imposed by only vectoring 50% of the engine's thrust were still evident.

It was at this point that what Ralph Hooper calls "the blinding flash of the obvious" occurred. He realised that if the hot air from the engine core could be bifurcated, as on the Sea Hawk, an extra pair of nozzles could be added and 100% of the thrust would be available for vertical flight. This proposal was tentatively accepted by Bristol and Hooper drew up a new P.1127 design on the basis of this. This revised P.1127 was designed as a ground attack aircraft, capable of VTOL at a weight of 8,500 lb., while it could carry a 2,000 lb. warload from a 200 yard short take-off. Hawker prepared a brochure for this aircraft in August 1957, a copy being shown to Colonel Chapman from MWDP at the Farnborough airshow the following month. He approved of the general concept, but thought that greater warload-radius performance would be required. To this end Hawker and Bristol proposed water injection for the engine, allowing a near doubling of internal fuel from the 2,000 lb of extra thrust, a new P.1127 brochure with this feature added being produced in October. This brochure also proposed that the engine be re-designed to feature contra-rotating spools for the fan and core in order to eliminate gyroscopic effects in hovering flight. Bristol were resistant to this idea as it would mean that the fan could no longer use Olympus blades, but Hawker wanted to eliminate the need for auto-stabilisation and saw such a change as vital.

While such differences of opinion between engine and airframe designers existed, by late 1957 both companies were working closely together, with the P.1127 and BE.53 projects feeding ideas into each other. For both companies, however, V/STOL was by no means the most important prospect for the future. The only significant combat aircraft that Sandys had permitted the RAF to develop was a replacement for the Canberra to meet General Operational Requirement 339. It was in order to win this competition that Hawker stopped all work on the P.1127 in late 1957, to concentrate resources on their GOR 339 proposal, the P.1129. However, English Electric and Vickers were favourites for the contract right from the start, and despite further submissions based on a P.1129 incorporating features from the Avro 739, and on developed versions of the P.1121, Hawker was still faced with a dead end when Hunter production ended. With this in mind, P.1127 design was renewed in January 1958, with greater resources in design and other departments dedicated to it. Further contact with MWDP led to a variant being drawn up with the emphasis being put on VTO, the original 'bent-pipe' nozzles being replaced with shorter, lighter nozzles featuring cascades. The most important change to the P.1127 was, however, to come from Bristol, who informed Hawker in March 1958 of their decision to re-design the engine. This was now to feature a new fan whose two-stages were to supercharge the core, allowing the separate inlets to the Orpheus to be eliminated, and removing the main obstacle to counter rotation of the engine spools.

Ralph Hooper incorporated this revised engine, the BE.53/2, into a re-designed P.1127 by the end of March. He was forced to work over a weekend to meet a deadline for a meeting with MWDP the following week, and has commented that things became exciting when he realised that the design now "fitted together much better". The improved efficiency of the engine allowed the fuel load to be reduced, whilst inverting the engine allowed the accessories to be placed ahead of the wing box, reducing frontal area and weight. A further refinement was the addition of the familiar bicycle undercarriage with wing-tip outriggers, the cropped delta wings being given increased anhedral at the same time. The design was now essentially that of the P.1127 that was to fly in October 1960, although much work remained before that stage was reached.

 

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