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Avro 730

From Alfawiki
Avro 730
Company typeProposed military aircraft project
IndustryAerospace
Founded1954
FounderAvro Aircraft
FateCancelled in 1957
Headquarters
United Kingdom
ProductsMach 3-capable reconnaissance aircraft and strategic bomber (proposed)


Template:Infobox aircraft

The Avro 730 represented a proposed Mach 3-capable reconnaissance aircraft and strategic bomber developed by Avro Aircraft intended for service with the Royal Air Force (RAF). Initially conceived as an extremely fast reconnaissance platform aligned with the criteria outlined in Air Ministry Specification OR.330, Avro later adapted the design to incorporate nuclear armament. This modification enabled the aircraft to fulfill a combined nuclear strike and reconnaissance role, responding to Air Ministry Specification RB.156T which called for a high-speed reconnaissance-bomber.

Had it entered operational service, the Avro 730 would have succeeded the V bomber fleet as the primary delivery system within Britain's nuclear deterrent. However, in early 1957, the project was abruptly terminated alongside several other manned aircraft developments following directives from the 1957 Defence White Paper. Contributing factors to its cancellation included concerns that advancements in Soviet air defence technology would render the aircraft ineffective by its projected deployment date, and a strategic shift favouring missile technology over piloted aircraft. A subsequent initiative to produce a supersonic low-level bomber designed to evade radar detection, fulfilling Air Ministry Specification GOR.339, resulted in the BAC TSR-2; this program was also eventually discontinued.

Origins

In the aftermath of the Second World War and amid escalating tensions of the Cold War, the Royal Air Force (RAF) sought not only to maintain but enhance its strategic capabilities.[1] Specifically, RAF Bomber Command aimed to replace its existing wartime bomber fleet with more advanced aircraft that leveraged emerging technologies such as jet propulsion and nuclear weaponry. Throughout the late 1940s and early 1950s, a new generation of jet-powered bombers—the Vickers Valiant, Avro Vulcan, and Handley Page Victor—collectively known as the V-bombers, were developed and introduced into RAF service. These platforms were purpose-built to carry Britain's initial nuclear arsenal, designated Blue Danube, serving as key components of the nation's airborne nuclear deterrent for many years.[1]

While deploying the V-bombers, the RAF concurrently recognised a requirement for an extended-range supersonic strategic reconnaissance aircraft to support offensive operations.[2] Consequently, an Operational Requirement was formulated, leading to the issuance of Specification OR.330 in 1954 which detailed stringent performance objectives.[3] The intended reconnaissance platform needed to penetrate Soviet airspace while evading sophisticated enemy defences.[4] Criteria included sustaining speeds of Mach 2.5 at altitudes around 60,000 ft (18,000 m), achieving maximum speeds near Mach 3, and possessing an operational range extending up to approximately 5,754 mi (9,260 km). Operating at such high altitudes and velocities combined with advanced onboard electronic countermeasures was expected to enable successful avoidance of Soviet interceptors and emerging surface-to-air missile threats.[3]

At its introduction, Specification OR.330 represented one of the most demanding high-performance aircraft requirements globally.[4][lower-alpha 1] At that time, Britain had no operational supersonic combat aircraft; thus, fulfilling this requirement necessitated pioneering advances in aerodynamics, materials science, and propulsion technology.[3] Three British manufacturers submitted proposals: Handley Page with the HP.100, Vickers presenting the SP4, and Avro proposing the Type 730.[3][4] All designs featured delta or needle-shaped configurations powered by multiple engines—12 on the HP.100 and sixteen arranged horizontally at the rear for Vickers’ entry. The HP.100 progressed to full-scale mockup construction along with extensive wind tunnel testing.[3] In mid-1955, Avro received a development contract from the Ministry of Supply to advance their design.[4]

Development efforts and redesign

The Avro 730 featured an unswept canard configuration, extensively utilizing stainless steel and powered by four Armstrong Siddeley P.176 turbojet engines.[5] To support its development, the Bristol Type 188 was constructed to evaluate the compound-delta wing design and later to examine the metal's endurance during extended supersonic flights.[6] Plans called for up to ten prototypes, a necessity partly driven by a mid-development decision to incorporate bombing capabilities into the aircraft.[7] [8]

Originally, the aircraft was designed solely for aerial reconnaissance, employing its "Red Drover" side-looking airborne radar system to locate targets for the forthcoming V bomber fleet. As development advanced, it was discovered that a smaller radar antenna could be used, significantly increasing available internal volume.[8] Consequently, the RAF introduced a secondary bombing function, equipping the aircraft with both radar and an elongated bomb bay capable of housing either munitions or extra fuel. Concurrently, a high-speed bomber specification, OR.336, was under review; these initiatives merged into the RB.156 requirement in October 1955.[8] This integration prompted a substantial redesign of the Avro 730.[7] Avro had anticipated such changes in their initial proposal.[8]

The proposed testing regime was comprehensive, involving full-scale aircraft being exposed to extreme temperatures associated with Mach 2.5 speeds inside a specially designed heat chamber. The flight testing phase aimed for prototypes to accumulate approximately 1,400 hours of flight time.[9] The first prototype, internally designated Avro 731, was a three-eighths scale model intended for preliminary trials and scheduled to fly in 1959.[10] [8] Two Avro 731 prototypes were planned to precede the construction and flight of full-scale models.[11]

Construction of the initial prototype was underway when in 1957 air minister Duncan Sandys announced the program’s cancellation.[12] Concerns had arisen that by its projected operational date a decade later, advancements in Soviet anti-aircraft missile technology would render the aircraft vulnerable.[13] Resources were redirected towards the Blue Streak medium-range ballistic missile, and the only test fuselage of the Avro 730 was dismantled.[11] Despite this cancellation, work on the Bristol 188 continued. Elements derived from the Avro 730 project influenced research at the Royal Aircraft Establishment, Farnborough, into supersonic transport designs, which ultimately played a role in advancing efforts that led to Concorde.[14][15]

Design

The Avro 730 was initially conceived exclusively as a high-speed aerial reconnaissance aircraft. To meet the stringent speed requirements, its design featured a long, slender fuselage characterized by a high fineness ratio and a compact, tapered wing of nearly rectangular shape, centrally attached to the fuselage.[16] The relatively short and straight wing allowed the installation of an extended antenna for the primary reconnaissance instrument, the Red Drover X-band radar, entirely within the fuselage.[16] Propulsion was provided by four Armstrong-Siddeley P.156 engines, arranged in pairs stacked vertically within pods located at the extreme wingtips. These engine nacelles incorporated variable-geometry air intakes, while the engines themselves were fitted with convergent-divergent nozzles.[16] Additionally, options for two or three shock cones on each nacelle were considered.[17]

The aircraft employed a canard layout, which significantly minimized trim-drag and enhanced lift during low-speed flight.[16][18] Control around the longitudinal axis (roll) was managed by elevators on the nose-mounted tailplane’s trailing edges, pitch control was handled by ailerons situated on the wing’s trailing edge, and yaw control utilized a conventional rudder. All primary flight control surfaces were operated through a quadruple-redundant electro-hydraulic system developed by Boulton Paul.[16] The design also incorporated fly-by-wire electrical controls alongside automatic flight management systems. The landing gear, engineered by Dowty Group, featured a single main unit with four wheels located centrally under the fuselage, a two-wheel nose unit, and outrigger units mounted on the engine nacelles.[16]

To preserve the aircraft's aerodynamic fineness ratio, the Avro 730 did not have a traditional canopy; instead, its cockpit included just two small side-facing windows. Early prototype models were planned to have a raised canopy to allow direct external vision; however, production variants would rely exclusively on an electrically operated retractable periscope to provide outside visibility during all phases of flight, including takeoff and landing.[19] The crew complement was originally set at three: pilot, navigator, and radar operator.[7] All personnel were housed within a single pressurized and refrigerated compartment designed for comfort; lightweight ejection seats were to be installed for each crew member.[16] Thanks to advanced automatic flight control and stabilization systems, the pilot’s responsibilities extended to overseeing some engineering functions such as fuel management, cooling systems, and control system monitoring.[16]

Thermal management posed significant challenges for the Avro 730. At speeds reaching Mach 2, skin temperatures were expected to climb to approximately 190 °C, rising further to about 277 °C at Mach 2.7.[16] The airframe largely consisted of brazed stainless steel honeycomb structures.[3] Fuel served an additional function as a heat sink, while a fully duplicated freon-based refrigeration system supplied by Normalair was incorporated to maintain internal temperatures.[16]

During its development phase, modifications were made to transform the Avro 730 into a dual-role aircraft capable of both reconnaissance and bombing missions. Although it retained much of its original appearance, this revised model was larger overall and featured an altered wing configuration.[9] To increase wing surface area, supplementary “winglettes” were added outside the engine pods and the entire wing planform adopted a more traditional delta shape. Approximately two-thirds of the span inside the engine pods had a sweep angle near 45°, while the smaller outer wing sections were swept more steeply at about 60°. The forward sweep previously present on the trailing edge was eliminated. Engine pods were upgraded to house four Armstrong-Siddeley P.176 engines each, doubling total powerplants to eight.[7][11] These pods featured circular fronts with single large shock cones and transitioned to a squarer cross-section towards their rear ends where they aligned flush with the wing’s trailing edge. Much of the internal layout remained consistent with earlier designs, including rectangular canards, a buried cockpit, and a large cropped-delta vertical stabilizer at the tail.

In this bomber-reconnaissance variant, crew size was reduced to two members. The bomb bay was narrow but extended approximately 50 ft (15 m) in length and was designed to carry nuclear-armed stand-off missiles.[8] Development had commenced on an appropriate warhead known as Blue Rosette.[7]

Specifications

Orthographic projection diagram of the Avro 730.
Orthographic projection diagram of the Avro 730.

Template:Aircraft specs

See also

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Notes

  1. ↑ The well-known SR-71, exhibiting comparable overall capabilities, originated from discussions held in 1958—several years after this specification was issued.

References

Citations

  1. ↑ 1.0 1.1 Wood 1975, p. 130.
  2. ↑ Wood 1975, pp. 136-137.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Wood 1975, p. 137.
  4. ↑ 4.0 4.1 4.2 4.3 Polmar 2001, p. 9.
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wood 137 138
  6. ↑ Bud and Gummett 2002, p. 49.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Cite error: Invalid <ref> tag; no text was provided for refs named polmar 10
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Cite error: Invalid <ref> tag; no text was provided for refs named wood 139
  9. ↑ 9.0 9.1 Cite error: Invalid <ref> tag; no text was provided for refs named wood 139 140
  10. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lewis 388
  11. ↑ 11.0 11.1 11.2 Cite error: Invalid <ref> tag; no text was provided for refs named wood 140
  12. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named polmar 11
  13. ↑ Bartlett 1971, p. 134.
  14. ↑ Bud and Gummett 2002, p. 50.
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wood 141
  16. ↑ 16.00 16.01 16.02 16.03 16.04 16.05 16.06 16.07 16.08 16.09 Cite error: Invalid <ref> tag; no text was provided for refs named wood 138
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wood 138 139
  18. ↑ Buttler 2003, p. 75.
  19. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wood 132

Bibliography

  • Bartlett, Christopher John. "The Long Retreat: A Short History of British Defence Policy, 1945-70". Macmillan, 1971.
  • Brookes, Andrew J. "V-Force: The History of Britain's Airborne Deterrent". Jane's, 1982.
  • Bud, Robert and Philip Gummett. "Cold War, Hot Science: Applied Research in Britain's Defence Laboratories, 1945-1990". NMSI Trading Ltd, 2002. ISBN 1-900747-47-2.
  • Buttler, Tony. "British Secret Projects: Jet Bombers Since 1949". Midland, 2003. ISBN 1-85780-130-X.
  • Lewis, Peter M. H. "The British Bomber Since 1914: Sixty-Five Years of Design and Development". Putnam, 1980. ISBN 0-370-30265-6.
  • Polmar, Norman. "Spyplane: The U-2 History Declassified". Zenith Imprint, 2001. ISBN 0-7603-0957-4.
  • Wood, Derek. Project Cancelled. Macdonald and Jane's Publishers, 1975. ISBN 0-356-08109-5.

External links

Template:Avro aircraft

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