Avro Vulcan

The Avro Vulcan (later Hawker Siddeley Vulcan from July 1963) is a jet-powered, tailless, delta-wing, high-altitude, strategic bomber, which was operated by the Royal Air Force (RAF) from 1956 until 1984. Aircraft manufacturer A.V. Roe and Company (Avro) designed the Vulcan in response to Specification B.35/46. Of the three V bombers produced, the Vulcan was considered the most technically advanced, hence the riskiest option. Several reduced-scale aircraft, designated Avro 707s, were produced to test and refine the delta-wing design principles.

The Vulcan B.1 was first delivered to the RAF in 1956; deliveries of the improved Vulcan B.2 started in 1960. The B.2 featured more powerful engines, a larger wing, an improved electrical system, and electronic countermeasures, and many were modified to accept the Blue Steel missile. As a part of the V-force, the Vulcan was the backbone of the United Kingdom's airborne nuclear deterrent during much of the Cold War. Although the Vulcan was typically armed with nuclear weapons, it could also carry out conventional bombing missions, which it did in Operation Black Buck during the Falklands War between the United Kingdom and Argentina in 1982.

The Vulcan had no defensive weaponry, initially relying upon high-speed, high-altitude flight to evade interception. Electronic countermeasures were employed by the B.1 (designated B.1A) and B.2 from around 1960. A change to low-level tactics was made in the mid-1960s. In the mid-1970s, nine Vulcans were adapted for maritime radar reconnaissance operations, redesignated as B.2 (MRR). In the final years of service, six Vulcans were converted to the K.2 tanker configuration for aerial refuelling.

After retirement by the RAF, one example, B.2 XH558, named ''The Spirit of Great Britain'', was restored for use in display flights and air shows, whilst two other B.2s, XL426 and XM655, have been kept in taxiable condition for ground runs and demonstrations. B.2 XH558 flew for the last time in October 2015 and is also being kept in taxiable condition.

Development

Origins

The origin of the Vulcan and the other V bombers is linked with early British atomic weapon programme and nuclear deterrent policies. Britain's atom bomb programme began with Air Staff Operational Requirement OR.1001 issued in August 1946. This anticipated a government decision in January 1947 to authorise research and development work on atomic weapons, the U.S. Atomic Energy Act of 1946 (McMahon Act) having prohibited exporting atomic knowledge, even to countries that had collaborated on the Manhattan Project. OR.1001 envisaged a weapon not to exceed in length, in diameter and in weight. The weapon had to be suitable for release from .

In January 1947, the Ministry of Supply distributed Specification B.35/46 to UK aviation companies to satisfy Air Staff Operational Requirement OR.229 for "a medium range bomber landplane capable of carrying one bomb to a target from a base which may be anywhere in the world." A cruising speed of at altitudes between was specified. The maximum weight when fully loaded should not exceed . Alternatively, the aircraft was to be capable of carrying a conventional bomb load of . The similar OR.230 required a "long-range bomber" with a radius of action with a maximum weight of when fully loaded; this requirement was considered too exacting. Six companies submitted technical brochures to this specification, including Avro.

Required to tender by the end of April 1947, work began on receipt of Specification B.35/46 at Avro, led by technical director Roy Chadwick and chief designer Stuart Davies; the type designation was ''Avro 698''. As was obvious to the design team, conventional aircraft could not satisfy the specification. No worthwhile information about high-speed flight was available from the Royal Aircraft Establishment (RAE) or the US. Avro were aware that Alexander Lippisch had designed a delta-wing fighter and considered the same delta configuration would be suitable for their bomber. The team estimated that an otherwise conventional aircraft, with a swept wing of 45°, would have doubled the weight requirement. Realising that swept wings increase longitudinal stability, the team deleted the tail (empennage) and the supporting fuselage, it thus became a swept-back flying wing with only a rudimentary forward fuselage and a fin (vertical stabilizer) at each wingtip. The estimated weight was now only 50% over the requirement; a delta shape resulted from reducing the wingspan and maintaining the wing area by filling in the space between the wingtips, which enabled the specification to be met.Gunston, W.T
"The Vulcan Story."
''Flight'', 31 January 1958, p. 143. Although Alexander Lippisch is generally credited as the pioneer of the delta wing, Chadwick's team had followed its own logical design process.Laming 2002, pp. 23, 24. The initial design submission had four large turbojets stacked in pairs buried in the wings on either side of the centreline. Outboard of the engines were two bomb bays.

In August 1947, Chadwick was killed in the crash of the Avro Tudor 2 prototype, and was succeeded by Sir William Farren.Laming 2002, p. 26. Reductions in wing thickness made incorporating the split bomb bays and stacked engines impossible, thus the engines were placed side by side in pairs on either side of a single bomb bay, with the fuselage growing somewhat. The wingtip fins gave way to a single fin on the aircraft's centreline. Rival manufacturer Handley Page received a prototype contract for its crescent-winged HP.80 B.35/46 tender in November 1947. Although considered the best option, the contract award for Avro's design was delayed while its technical strength was established.Buttler 2003, p. 31. Instructions to proceed with the construction of two Avro 698 prototypes were received in January 1948. As an insurance measure against both radical designs failing, Short Brothers received a contract for the prototype SA.4 to the less-stringent Specification B.14/46. The SA.4, later named Sperrin, was not required. In April 1948, Vickers also received authority to proceed with their Type 660, which, although falling short of the B.35/46 Specification, but being of a more conventional design, would be available sooner. This plane entered service as the Valiant.

Avro 707 and Avro 710

As Avro had no flight experience of the delta wing, the company planned two smaller experimental aircraft based on the 698, the one-third scale model 707 for low-speed handling and the one-half scale model 710 for high-speed handling. Two of each were ordered. The 710 was cancelled when it was considered too time-consuming to develop; a high-speed variant of the 707 was designed in its place, the 707A. The first 707, VX784, flew in September 1949, but crashed later that month, killing the Aeroplane and Armament Experimental Establishment's chief test pilot Squadron Leader Samuel Eric Esler, DFC, AE. The second low-speed 707, VX790, built with the still uncompleted 707A's nose section (containing an ejection seat) and redesignated 707B, flew in September 1950 piloted by Avro test pilot Wg Cdr Roland "Roly" Falk. The high-speed 707A, WD480, followed in July 1951.Blackman 2007, p. 21.

Due to the delay of the 707 programme, the contribution of the 707B and 707A towards the basic design of the 698 was not considered significant, though it did highlight a need to increase the length of the nosewheel to give a ground incidence of 3.5°, the optimum take-off attitude. The 707B and 707A proved the design's validity and gave confidence in the delta planform. A second 707A, WZ736, and a two-seat 707C, WZ744, were also constructed, but they played no part in the 698's development.

Prototypes and Type Certification

First Prototype VX770 and Name

More influential than the Avro 707 in the 698's design was wind-tunnel testing performed at RAE Farnborough. This necessitated a wing redesign incorporating a cranked and drooped leading edge and vortex generators

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