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History
The P.1154 story

This page consists a slightly modified version of an article that first appeared in the Spring 2000 edition of the Air Britain journal Aeromilitaria - some illustrations have been changed and some minor amendments made to the text. All black and white photographs are copyright © Brooklands Museum.

The Hawker Siddeley P.1154

It can justifiably be said that the Harrier is Britain's greatest post-war aviation success. However, it had originally been the RAF's intention to introduce a far more formidable 'jump-jet' to the front line - the Hawker Siddeley P.1154. The cancellation of this project in February 1965 was a huge blow to the prospects of the British aircraft industry, with long-term consequences more damaging than the cancellation of the TSR 2. The opportunity to provide the world's first supersonic V/STOL fighter was lost, a capability that will now be provided by the Joint Strike Fighter programme, in which Britain has only a minority stake.

Artist's impression of an RAF P.1154
Artist's impression of an RAF P.1154

Competition and Commonality

The P.1154 originated in the rejection of subsonic V/STOL aircraft, such as the Hawker P.1127, by both the RAF and NATO in the early 1960's. In 1959 both institutions had drafted requirements, GOR345 and GOR-2 respectively, for a subsonic strike fighter based around the P.1127. Further study resulted in both seeing such an aircraft as unattractive, due to its limited payload-range and apparent vulnerability to supersonic interceptors. With interest in an operational subsonic aircraft waning, despite flight tests having only just begun, Hawker Aircraft at Kingston began design work in early 1961 on a stretched, supersonic derivative of the P.1127, under the direction of Ralph Hooper.

Designated P.1150, this used a Pegasus engine incorporating plenum chamber burning (PCB) in the bypass air delivered to the front nozzles. However, Hawker did not actively promote the P.1150 to potential users in case it led to all remaining interest in the P.1127 evaporating. Despite the loss of service interest in the latter, it needs to be borne in mind that the practical experience gained from the P.1127 and Kestrel continued to 'pour design knowledge' into the supersonic aircraft.

During August 1961 Hawker received specification AC/169 for a supersonic V/STOL strike fighter to meet NATO Basic Military Requirement 3. This called for a single-seat aircraft capable of flying strike missions, with additional reconnaissance and interception capabilities. The key mission was a lo-lo sortie of 250nm radius at Mach 0.92 with a 2,000 lb weapon load. The prospect of providing the NATO alliance with a common fighter soon attracted most major aircraft companies in Western Europe and America to enter the biggest international design competition ever held. The Hawker entry was the P.1150/3, using a Bristol Siddeley BS.100/9 vectored thrust engine, the aircraft being re-designated P.1154 before final submission to NATO in January 1962. The full results of the competition became known in May, the P.1154 being declared technical winner, but when financial and work-sharing considerations were added in the French Mirage IIIV was judged to be of equal merit. As NATO had insufficient funds for full development this was seen to rely on the member countries moving ahead on their own initiative. Nevertheless, the P.1154 did receive some financial support from NATO until December 1963, in the shape of 50% funding of PCB development for the Pegasus and BS.100.

In Britain, the RAF saw that the NBMR-3 competition could lead to the kind of aircraft they needed to replace the Hawker Hunter from 1968, in contrast to the subsonic GOR345/P.1127 aircraft already studied. The Royal Navy also had a requirement for a Sea Vixen replacement, to enter service after 1970. The Ministry of Aviation saw an opportunity to develop the P.1154 for both Services and to break the NBMR-3 impasse at the same time; Hawker received the draft of a new joint requirement, OR356/AW406, in April 1962. It was soon clear to the design staff that the two Services needed very different aircraft, the RAF requiring essentially the NBMR-3 design while the Royal Navy wanted a two-seat, high altitude interceptor to be catapult launched from their carriers. Nevertheless, the prospect of saving 150 million in development costs, which was earmarked to pay for a new aircraft carrier, kept the Royal Navy from opposing the goal of commonality. Similarly, the Hawker directors, including Sir Sydney Camm, wanted to keep the aircraft common to both Services, as this would provide larger orders for the company. This led them to play down the technical difficulties that the firm's designers saw would occur in joint development.

As the design of the P.1154 was adapted to meet the needs of the two Services the respective variants diverged from each other to an ever-greater degree. The preliminary brochure submitted in August 1962 saw the RAF and Royal Navy aircraft as being 80% common. By the time of the more detailed brochure of May 1963 the situation had reversed, with only 20% commonality between the two designs. This growing divergence was mostly caused by the Royal Navy's demands. AW406's insistence on two seats, large AI radar and two-shock inlets to achieve Mach 2 at altitude led to considerable weight growth, necessitating larger wings, while the catapult requirement led to a new undercarriage layout. The waters were further muddied by a Rolls-Royce proposal to substitute twin Spey engines, modified to use vectored thrust and PCB, in place of the BS.100. Despite all this, the design for the RAF remained fairly constant, being essentially the same as that proposed for NBMR-3. While the naval aircraft remained fluid, Hawker began detail design and mock-up construction of the RAF variant.

Detail of the P.1154 mock-up Lower aft view of the mock-up
Detail of the P.1154 mock-up at Kingston,May 1964, showing the engine nozzles in the vertical position.
Lower aft view of the mock-up, with the engine nozzles horizontal. .

By June 1963 it was clear that the divergence between the two versions meant that, in effect, two separate aircraft were being proposed, with the airframes, avionics and systems differing between them. The Defence Research Policy Committee therefore ordered that a wholly common, Bi-Service version of the P.1154 be designed. A brochure for this was hastily submitted in August 1963 and it quickly became obvious that it was unacceptable to both Services. The Royal Navy had to give up the second crewmember and two-shock inlets, while the provision of wing folding and catapult facilities increased weight, to the detriment of range and weapon load, in RAF missions. The P.1154 had reached crisis point, with complete cancellation on the cards. Numerous alternative aircraft purchases were investigated from November 1963 to January 1964, including a developed P.1127 for the RAF or dissimilar P.1154 variants tailored to the needs of each Service. The eventual decision, announced in February 1964, was to adapt the McDonnell F-4 Phantom with Spey engines for the Royal Navy and to develop a version of the P.1154 specifically for the RAF, this being seen as the most cost effective solution to the two Service's requirements.

New Beginning

The re-focussing of the P.1154 as a single seat strike fighter for the RAF allowed Hawker Siddeley to concentrate their efforts on a firm objective after the trials of the previous two years. It meant large reductions in development costs, and clearer planning for the manufacture and flight-testing of the development batch aircraft, could be envisaged. Both the RAF and Hawker Siddeley's technical staff were relieved by the elimination of the commonality requirement, and the P.1154 now began to make real progress, moving from design to development.

By early 1964 the industrial base of the project had been strengthened by the formation of Hawker Siddeley Aviation as a consolidated company. The P.1154 was to be developed by the Hawker Blackburn Division, with John Fozard as Chief Designer and Barry Laight (former leader of the Buccaneer team) as Chief Engineer. This division had been specifically formed in 1963 to allow the aircraft to benefit from the experience of the 'weapons system' approach that had been used in the Buccaneer programme, the P.1154 being expected to follow a similar development path. While Hawker Siddeley questioned the degree of control that the Ministry of Aviation had over areas such as the avionics, believing they could perform these functions much better themselves, they agreed to appoint a Programme Controller to oversee the project and to adopt the PERT management system. Both measures were recent innovations, aimed at avoiding the financial errors and timescale overuns that had afflicted the TSR 2 programme.

While the industrial organisation was taking shape, the RAF was refining its requirements. The key features they wanted from the P.1154 were V/STOL and supersonic speed. Outside of these they were willing to simplify the aircraft considerably, to save time and money. While being designed to fulfill essentially the same mission as that of the NBMR-3 submission, much use was made of the work undertaken during the commonality debacle. The airframe was basically that of the Bi-Service design, with all the naval features removed. Once the project received the green light in February 1964 it was constantly reviewed in order to keep the design as simple as possible. The previously projected use of digital computing was dropped, in favour of an analogue nav-attack system that would be 20% cheaper to produce. Manual, rather than automatic, terrain following was adopted while the requirement for the aircraft to carry AS.30, Bullpup and T.V. guided AJ.168 (Martel) missiles was dropped later in the year. The need for the P.1154 to be fully nuclear capable was also relaxed in order to further simplify the aircraft. By April 1964 the RAF had issued a revised OR356 and Hawker Siddeley had begun manufacture of assembly jigs and detail parts for the development batch aircraft at its Kingston and Hamble factories.

Wing assemblies at Hamble The first P.1154 fuselage
Wing assemblies at Hamble, February 1965.
The first P.1154 fuselage in the jig at Kingston, February 1965.

August saw Hawker Siddeley submit their detailed design to the Ministry of Aviation, as called for under holding contract KC/3B/5. This outlined a development programme involving eight aircraft, with first flight two years from the instruction to proceed (ITP) and initial CA release five years from ITP. It was agreed in October 1964 that, in the light of the work already done, the ITP could be regarded as having been reached in July 1964. Rolls-Royce were allocated 9 million of development work on the BS.100, including conversion of the Vulcan B.1A test-bed, XA896. Two Hunters were to be converted to test the nav-attack system, designated HS.1172. Hawker Siddeley and the Ministry of Aviation continued to discuss detail points that affected the programme, the most important being the continuing lack of orders for the radar and inertial nav-attack system. Both these items had been awarded to Ferranti, but contract signature was suspended until the company could pay back excess profits gained on the Bloodhound missile programme. This hold-up was causing serious worry to Bob Lickley, Chief Executive of the Hawker Blackburn Division, as he thought it could delay the full release of the P.1154 weapons system by up to 18 months from the planned service entry date of July 1969.

Nevertheless, the RAF continued to refine its scheme for the deployment of the P.1154, the name Harrier having been provisionally chosen for the aircraft. Plans went ahead for eight operational squadrons, two each in the UK, Germany, Middle East and Far East. The aircraft would operate from both main and forward bases, such as short airstrips or stretches of road, with four or six aircraft operating from the latter. Unsupported forward sites could also be used, reducing mission capability. Although it would have been capable of true vertical take-off, the normal means of operation would have been to use a short take-off, in order to minimize ground erosion and hot gas re-ingestion problems, and to maximise payload. Rolling vertical landing, with the engine throttled back, was to be employed at the end of each mission, with vectoring of the engine nozzles in forward flight envisaged to increase maneuverability, at the cost of significant deceleration. All of these techniques were to be explored 'in the field' during the Tripartite trials of the Kestrel in 1964-65. In the ferry mission extended wing tips were added to the aircraft, the 'combat tips' being stored in the rear fuselage. RAF P.1154s were to be capable of operating from all Royal Navy carriers, the aircraft having a folding nose to help it fit their deck lifts.

Definitive Design

All the design and operational characteristics worked out during 1964 were embodied in specification SR250D, issued in October. The P.1154 submitted to this specification had a length of 57ft 6in, span of 28ft 4in and height of 12ft 6 in. The low aspect ratio, 269 sq. ft wing used a 'peaky' aerofoil, with a leading edge sweep of 41.2 degrees. The airframe was stressed to 7.5g for combat and 3g for ferry missions. The aluminium and titanium structure was designed for a 3,000hr fatigue life; extensive use of chemical etching, integral machining and bonded honeycomb helped to keep down weight. To cope with bird-strikes at low level the windscreen and leading edges were designed to withstand a 1lb bird impacting at 600 kts. The bicycle undercarriage, stressed for descent rates of 10 ft/sec, employed low-pressure tyres, with the outriggers taking a significant proportion of the aircraft's weight in order to increase stability during ground maneuvering.

The heart of the P.1154 was its Bristol Siddeley BS100/8 Phase II vectored-thrust engine, at the time the most powerful jet engine in the Western world. This was installed around the aircraft's centre of gravity and could be removed via a detachable 'tray' underneath the fuselage. An electronic control system was provided for the engine's main functions. The four engine nozzles had 16 degrees anhedral to improve propulsive efficiency, with the PCB equipped front pair discharging past variable area ramps. Peak temperature of the front jets was 1,400K, the rear jets having a maximum of 1,000K.

One of the six BS.100 engines built On the test-bed this engine had a 'short' rating of 35,900 lb thrust for 20 seconds using PCB, maximum 'normal' thrust being 33,900 lb. Water methanol injection was to be used to restore thrust in hot and high conditions. With PCB off maximum thrust was 26,200 lb. Mass flow was 490 lb/sec, by-pass ratio 0.9 and overall pressure ratio 11.45. The minimum specific fuel consumption of 0.6 lb/hr/lb was achieved at 14,400 lb thrust, SFC at maximum thrust being twice this figure. In order to reduce technical and financial risk, compared to the earlier 'all new' BS.100/9 proposal, the BS.100/8 used the high-pressure compressor of the Olympus B.Ol.22. The annular combustor and lightly loaded four-stage titanium fan were both based on Pegasus 5 experience, suitably scaled. For engine starting and prolonged ground loiter at dispersed sites a gas turbine starter/APU was fitted. The air intakes had variable geometry lips to provide optimum pressure recovery in all flight regimes, with blow-in doors operating at low speeds. A large ventral airbrake, mounted well forward, acted as a dam to alleviate hot-gas re-ingestion problems. Internal fuel capacity was 1,300 Imperial gallons.
One of the six BS.100 engines built - the garish colour scheme was due to the use of heat sensitive paint for tests.
 

Empty weight of the P.1154 was projected as 20,100 lb, maximum loaded weight being 40,050 lb in the ferry condition. Each wing had two pylons, rated at 2,000 lb inboard and 1,000 lb outboard, while the fuselage could take either a single centreline pylon rated at 2,000 lb or dual pylons of 1,000 lb each, maximum weapon load being 8,000 lb. For combat missions two 300 Imperial gallon tanks could be carried on the inboard wing pylons, replaced in the ferry role by 400-gallon tanks, a 200-gallon tank under the fuselage and a detachable flight refueling probe on the starboard air intake. The duplicated, fully powered flying control system was backed up in jet-borne flight by reaction controls in the wingtips and tailcone, using high-pressure air bled from the engine. Both autostabilisation and a simple autopilot were fitted. In case of engine failure, a ram air turbine could be extended from the rear fuselage to sustain electrical and hydraulic power. For emergency landings a 1.5g arrester hook was fitted under the tail.

Partial cutaway of the aircraft
Partial cutaway of the aircraft - note the airbrake mounted forward and the variable intake lips.

Capabilities and Costs

For strike missions the P.1154 would have carried low-drag and retarded 1,000 lb bombs, cluster bombs and napalm tanks. Stand off attack could be carried out using SNEB rockets and the anti-radar AJ.168 missile. In the air-to-air role up to four Red Top missiles could be carried on the wing pylons, with underfuselage 2in rockets or twin 30mm Aden guns as secondary armament in either role. In the reconnaissance mission a pod carrying optical linescan, sideways looking radar and a pair of oblique cameras was schemed, although this was thought to pose some problems and simpler equipment was looked into. The aircraft was to be permanently fitted with an F.95 camera in the nose, in addition to its monopulse radar. The latter was able to provide terrain avoidance information on the pilot's head-up display and ranging on surface and airborne targets. Allied with the inertial navigation system, air-data computer and moving map it would provide an accurate system for low-level, single pass attacks. The high speeds envisaged at low altitude led to the adoption of a single piece windscreen to increase the pilot's forward field of view; a Martin-Baker zero-zero ejection seat allowed for his escape at all airspeeds.

Radius of action was affected by both climate and the warload of the aircraft. In typical missions (I.S.A. + 15C at sea-level, 2,000 lb load) and utilising a rolling vertical take-off (500 ft to 50 ft, ground run 50 ft) a lo-lo radius of action of 210 nm was envisaged. With a short take-off (1100 ft to 50 ft, ground run 220 ft) and full internal fuel a lo-lo radius of 280 nm was possible, cruising at Mach 0.92. With combat tanks a radius of 405 nm was forecast in the same regime. If water injection was used in temperate climates it was hoped that an extra 25 nm could be added to the potential radius. A hi-lo profile could potentially double range, while in the air-to-air mission a loiter of 160 minutes, 100 nm from base was possible with maximum combat fuel and two Red Top missiles. Maximum speed at altitude with PCB on was Mach 1.7, falling to Mach 1.13 at sea level. Even in cold thrust the aircraft could achieve Mach 1.1 with two Red Tops, allowing it to 'supercruise' during interception missions.

While the first BS.100 engine went on test at Patchway in October 1964, the RAF had drawn up an additional requirement, ASR382, for an operational two-seat trainer version of the P.1154. The design that Hawker Siddeley submitted was modified to have a front fuselage with stepped tandem seating and a rear fuselage plug, bringing overall length to 61ft 1in. By relocating avionics from the nose to the rear equipment bay, and by reducing internal fuel to 1,174 gallons, the trainer's centre of gravity could be maintained. The RAF planned to buy 25 of these in addition to 157 single-seat aircraft, with training supported by simulators. Overall development costs were officially estimated (taking into account TSR.2 experience) at 170-200 million, with an additional 10 million for the two-seater. Unit costs were put at 1 million for the single-seat aircraft and 1.2 million for the trainer. Final approval was given for development, based on these figures, by the Weapons Development Committee in November 1964. Bristol Siddeley were planning to develop the BS.100 to 39,250 lb thrust by 1972, restoring any performance shortfalls caused by weight growth during development. This was estimated by the Ministry of Aviation to be potentially as high as 8.5%, although Hawker Siddeley hoped to limit weight growth to 4% over the August 1964 brochure figure.

Front fuselage Two-seat trainer P.1154
Front fuselage for the 'final installation model' P.1154.
Two-seat trainer P.1154 front fuselage mock-up.

Cancellation

In the same month that the BS.100 began bench tests, a Labour government came to office dedicated to making economies in defence expenditure. They initially focussed on equipment programmes, the high costs of combat aircraft drawing special scrutiny. Almost to a man the RAF was dedicated to preserving the TSR 2, as it was seen to provide the core capability that justified the Service's full independence. In the ongoing debate over the East of Suez commitment, in which they were striving to oust the Royal Navy's carrier task groups from their key role, the RAF saw the TSR 2 as their main weapon. With the further integration of the Service ministries under a centralised Ministry of Defence, the idea that the army might take over the tactical air support mission, and with it the future P.1154 squadrons, seemed a further possibility. The RAF decided not to oppose the cancellation of the P.1154 too vigorously and to gamble all on the TSR 2.

The reason given in the House of Commons for cancelling the P.1154, on 2nd February 1965, was that it would not be in service in time to replace the Hunter in 1969. Although this was probably true, the records show that the RAF had accepted the anticipated delay in introducing the P.1154 until 1970-71, with the Hunter being considered adequate until 1972 in any case. The 1969 date had continued to be publicly quoted merely as a way to keep Hawker Siddeley applied to the task after the commonality fiasco. The P.1154 was replaced in the RAF's plans by a combination of Spey engined Phantoms and a promise to develop, although not necessarily to procure, an operational P.1127/Kestrel derivative using much of the nav-attack system, and some detail design, from the P.1154. However, this subsonic V/STOL development was seen as very much a political consolation prize by the RAF and Hawker Siddeley. Both organisations were fully aware that the P.1127 had been rejected for operational purposes four years previously and, while it had matured a great deal since then, might only be developed in the short term to sweeten the bitter pill of the P.1154's cancellation.

By early 1965 over 5,000 men were directly employed on the P.1154, with more than 750,000 engineering hours expended and 25 million committed. With the development aircraft in assembly, and the forecast operational difficulties largely side-stepped, the cancellation of the P.1154 was a huge waste of potential. Although the TSR 2 was a triumph of 1950's technology, its prospects of being exported looked extremely poor due to its high costs and complexity. On the other hand, the P.1154 represented the last all-British entry in the key supersonic fighter market that has provided the bulk of exports for combat aircraft in the 1970's, 80's and 90's. At the time of its cancellation many countries were still pursuing the goal of survivable, effective airpower that aircraft such as the P.1154 offered. While the subsonic Harrier has proved modestly successful in the export field, the availability of the more capable P.1154 could have strengthened the customer base for V/STOL combat aircraft, providing a much greater success in the one area of aviation where Britain had genuinely led the world.

 

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