Invitations to tender for R.156T (which was worked up around Operational Requirement (OR) 330) were issued to A.V. Roe, English Electric, Handley Page and Vickers, in 1954. All responded with proposals to produce a high-speed reconnaissance platform for the RAF and ultimately a bomber aircraft to replace the RAF's V bombers in the late 1960s.
As a reconnaissance platform, the OR.330 aircraft was to carry a suite of optical and radar sensors to provide targeting intelligence and post strike assessment for the V-force. With a specified speed of M2.5 with M3.0 dash speed over the target at an altitude of 70000ft, OR.330 was to be immune to Soviet fighter defences.
The RAF had been conducting reconnaissance operations over the Soviet Union with impunity since the early 1950s. The Canberra light bomber had been used for this work, with single aircraft used for what were effectively one-off reconnaissance missions. By 1954 it was thought that for a viable strategic reconnaissance force to support the V-bomber force, a dedicated platform was required. Whereas the Americans were working concurrently on a subsonic high flying platform, the U-2, the Ministry of Supply plumped for a high altitude, high speed aircraft with an extensive sensor suite. As time progressed the specification was modified to include a bombing role as RB.156, which in turn was evolved from OR.336, a supersonic bomber requirement. The contractors went to their drawing boards and submitted their designs. All the contenders used a canard configuration, mainly as a means to retain stability in the high-speed sections of the flight profile.
A.V. Roe of Manchester had provided the RAF with its bomber aircraft for many years, the most famous being the Lancaster. Avro, as they were usually known as, were developing the Vulcan for the RAF and this had entered Squadron service in 1957. Development of its possible successor was underway by that time and the experience of bringing the Vulcan to service entry must have helped Avro with its OR.330 submission, the 730.
The Avro 730 started off as a four jet unswept canard, with the Armstrong Siddeley P.159 engines mounted in vertical pairs, in pods, at the tips of the trapezoidal wings. The undercarriage utilised a single main bogie with four wheels, along with nose wheels and a pair of outriggers in the engine nacelles. For high weight take offs, an extra four wheels could be attached to the main bogies. These would be jettisoned just after take off.
When the OR.330 specification was modified to include the bomber role, the 730 was modified to meet the new targets. As well as increasing the diameter of the fuselage, the engine type was changed to the Armstrong SiddeleyP.176 and their numbers doubled. Each quad of engines was mounted in a new nacelle, with a shock cone intake, at approximately 2/3 span of a redesigned wing. The wing gained a highly swept section outboard of the engine nacelles. The intention was to develop the Avro 730 with the aid of a 3/8 scale manned analogue, the 731. The Avro 731 shared the basic planform of the original 730, but with a single crew station and Gyron Junior engines. The 731 was not proceeded with, but when the definitive planform for the 730 was settled, it was tested on the Bristol 188. Bristols used the same planform as the Avro 730, but opted for a more conventional T tail.
The English Electric Company provided the most innovative of all the submissions for OR.330. The P.10 was powered by a pair of ramjets which were to be integrated into low aspect ratio, unswept wings. This integration reduced drag and produced a smaller, more efficient airframe which EECo believed was the only way to meet the range and speed targets. The ramjets would be unable to generate static thrust so a pair ofRB.123 auxiliary turbojets was installed in the rear fuselage. These would provide power for take-off and low speed flight as well as generating electrical power for the reconnaissance sensors
With a length of 108.75ft (33.1m) P.10 carried only 2 crew rather than the three specified, which the Ministry perceived as increasing the crew workload. The downside of the smaller airframe was reduced internal fuel capacity and inability to meet the specified range. English Electric intended gaining sufficient range to meet the specification by fitting auxiliary fuel tanks as detachable wing extensions. These extensions increased the take off weight of P.10 and would put additional strain on the undercarriage. To alleviate this, English Electric proposed fitting further wheels which were to be jettisoned after take off, with the auxiliary wing tanks jettisoned shortly after. These techniques prompted a sceptical response from the Ministry of Aviation, who considered the additional wheels to be a probable cause of aborted missions, as the landing gear could not be retracted until the auxiliary wheels had been jettisoned.
Like A.V. Roe, Handley Page at Cricklewood had a long pedigree in designing bombers for the RAF and for its predecessor, the Royal Flying Corps. During the Great War O/400 and V/1500 aircraft had been developed to meet a requirement for a "Bloody paralyser" of an aircraft to conduct a strategic bombing campaign against Germany. Trenchard's independent air force was to pursue a bombing campaign against the German homeland with Avro aircraft. In the Second World War Halifaxes had made up a high proportion of Bomber Command's strength. Handley Page's HP 98 Victor was the most advanced large aircraft ever designed in the UK, a track record that must have seen Handley Page in with a shout for the OR.330 contract. The HP 100 was a 70 degree canard delta design with a single fin and fitted out with stations for three crew.
At 185ft (56.4m) long, the HP.100 was the largest of the contenders, while the wingspan of 59.3ft (18.1m) was comparable with the Avro and Vickers submissions. Power was supplied by no less than twelveRB.121 turbojets. These were arranged, six on each side, in a pair of fairings under the wing's trailing edge.
Like Handley Page, Vickers at Weybridge had also provided bombers for the RAF, the Valiant being the latest example. Their Wellington and Warwick had pioneered the innovative geodesic construction method, while the Windsor had been imaginative, but showed the drawbacks to geodesic construction in modern, high performance aircraft. Despite this setback, Vickers had become the main designers and constructors of large aircraft in Britain. Experience gained with the Viscount and Vanguard airliners and the Valiant V-bomber also stood them in good stead for the OR.330 aircraft.
Vickers' submission was unusual to say the least with sixteen RB.121 turbojets grouped in quartets in four fairings under the wings.
One innovative feature of the SP4 was its use of endplate fins on the wings. This planform with the endplate fins appears again and again in high speed configuration in the years since OR.330 was drawn up.
Of all the tenders for OR.330 the Shorts study looks most conventional, being a tailed delta. In fact it looks pretty much like a scaled up Bristol Type 188, with a wing not unlike that ultimately settled on for the Avro 730.
Perhaps the Shorts bid was like its Sperrin forebear, an insurance against the failure of the more innovative studies.
...and the winner is...
The Ministry of Supply, while lauding the technically advanced English Electric design, deemed it too unconventional and foresaw difficulties in service use. The area where the Ministry was particularly scathing was the size of the airframe. The reconnaissance component of the specification for OR.330 stated that a K-band SLAR would be fitted, requiring a 50ft antenna. English Electric believed that by the time of entry into service, J-band, requiring a 35ft antenna, would be the sensor of choice. Similar criticism of the two crew was again countered by English Electric's faith in future systems improvement. Despite all this the P.10 was not capable of conversion to a bomber, its airframe was just too small. English Electric had been too advanced with the P.10, with the probable in service date of 1965 deemed too late for the RAF and their 1960-62 "deterrent gap".
P.10 and its innovations would not go away. It was suggested that it should be used as the basis for a fighter (check) and more interestingly, as a "clandestine reconnaissance" aircraft. An interesting development of what had originally been intended as a reconnaissance aircraft with OR.336 coming full circle.
The Vickers SP4, with its very unconventional configuration and no less than 16 engines probably fell at the maintenance hurdle.
This left the two large contenders, HP.100 and the Avro 730. Both designs underwent extensive wind tunnel testing and eventually a full scale mock up of the HP.100 was built.
The Avro 730 was selected in May 1955, meeting the specification with less innovation than the P.10, but more than the HP.100. By this time the specification had changed to place much more emphasis on the bomber role, with the specification becoming RB.156D, to meet OR.336. The Avro 730 was under construction at Avro's Chadderton plant when it ultimately fell to Duncan Sandys' axe in 1957. With the end of OR.330/OR.336 and the Avro 730, large high speed military aircraft development in Britain was dead.
Or was it? Sandys' axe may have been prompted by a realisation that the OR.336 aircraft would have been vulnerable to Soviet air defence systems then in the pipeline. It was also believed that the V-force, armed with stand-off missiles to meet OR.1149 would provide a superior deterence than the Avro 730. Avro, of course had a finger in that pie as well. In fact they had more than one finger in the pie.
Images from PRO ref ADM 199/1925, Photo image by Adrian Mann
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