Avro 707A (WZ736) [@ Manchester Museum of Science & Technology]
The origins of the Avro 707 are intertwined with those of the Avro Vulcan. In 1947 the Avro design team were busy working on the design of the Type 698 Vulcan. The layout eventually decided upon was that of a delta-shaped wing, with no tail-plane. This configuration had many performance advantages, but had never been flown on a British aircraft before. The high speed characteristics of delta-shaped wings were at least theoretically well understood by the late 1940s but little was known about their behaviour at low speeds, where various aerodynamic factors made analysis very difficult.
Avro decided that a number of flying scale models of the delta wing would be built to help provide detailed data for the Vulcan project. Two one-third scale aircraft were proposed for low speed research, designated Avro Type 707, and two half-scale aircraft for high speed high altitude research, designated Avro Type 710. After further discussion, the Type 710 design was dropped and replaced by a single one-third scale aircraft under the designation Type 707A. All Type 707s were powered by a single Rolls Royce Derwent centrifugal turbojet engine.
The first Type 707 aircraft (VX784) as a relatively simple design using many components from existing aircraft types and construction proceeded quite rapidly. It featured a rather unusual bifurcated dorsal air intake behind the cockpit for the Derwent engine, a clear-view canopy taken from a Gloster Meteor and a sharply tapered nose cone. The short stubby-looking aircraft made its maiden flight on the 4th September 1949 at Boscombe Down. Unfortunately, the aircraft crashed at low speed on the 31st September killing the test pilot. The probable cause was a sudden control circuit failure causing the air brakes to be locked open and thus provoking a stall.
The loss of the first prototype resulted in work on the second Type 707 aircraft being suspended for a time while modifications were made. The long pointed nose section intended for the Type 707A was grafted onto the fuselage, resulting in the new aircraft being 3.66 m (12 ft) longer. Other changes included a different degree of wing leading edge sweep, modified elevators and air brakes. A Gloster Meteor cockpit canopy, Avro Athena main undercarriage and a lengthened Hawker P.1052 (a swept-wing development of the Sea Hawk) nose leg were incorporated in the design. Re-designated Type 707B (VX790), the maiden flight took place at Boscombe Down on the 5th September 1950.
Apart from restoring Avro's faith in the delta wing and its relatively docile handling characteristics, the contribution of the Type 707B to the Vulcan programme was rather limited because a great deal of time was spent on modifications which were relevant only to the 707B itself. Eventually VX790 was used for general research duties with the Royal Aircraft Establishment (RAE) and the Empire Test Pilots School (ETPS) before undergoing a serious accident and was then used for spares for the remaining 707A and 707C aircraft.
Avro 707A (WD280) [@ RAAF Laverton]
Avro 707A (WD280) [@ Royal Australian Air Force Museum]
The third aircraft in the series was the Type 707A (WD280) and first flew at Boscombe Down on 14th June 1951. This aircraft was designed to fly at high subsonic Mach numbers and differed from the 707B in having a scaled-down Vulcan wing, complete with wing root engine intakes, cropped wing tips and hydraulically powered flying control surfaces. The absence of a dorsal air intake allowed an elegant extended dorsal fin to be fitted. For high altitude work the cockpit was partially pressurised. Again a lot of flight time was spend in eliminating some of the problems with the new flying control system and the eventual contribution to the Vulcan programme amounted to very little. In 1954 WD280 was fitted with a modified wing with a kinked leading edge and after successful testing this later became the Vulcan 'Phase Two' wing modification. In 1956 WD280 was shipped to Australia on board the aircraft carrier HMAS Melbourne. Arriving in Sydney in May 1956 WD280 was assigned to the Australian Aeronautical Research Council (AARC) based at RAAF Laverton, Melbourne, for low speed flight trials. On the 10th February 1967 WD280 was struck off charge and sold on to the private market. Finally in 1999 WD280 was purchased by the RAAF museum at Point Cook and placed on display. The photographs of WD280 are by the kind permission of Barry Maclean and Alf Batchelder of the RAAF museum.
Avro 707C (WZ744) [@ RAF Cosford]
On 13th November 1951, three additional aircraft were ordered. These comprised a second Type 707A (WZ736), which received an orange finish, and the first two of four planned side-by-side conversion trainers designated Type 707C (WZ739 and WZ744). The 707Cs were intended to familiarise pilots with the characteristics of delta-winged aircraft, but the early Vulcans proved easy to fly and WZ739 was cancelled. The two remaining aircraft were assembled at Avro's at Bracebridge Heath, just south of Lincoln. WZ736 was first flown from nearby RAF Waddington on 20th February 1953 and WZ744 followed on 1st July 1953. Neither aircraft was directly involved in the Vulcan development programme and spent their time involved in general research with the Royal Aircraft Establishment (RAE) at Farnborough and Bedford. WZ736 was involved in auto-throttle development trials until withdrawn in 1964 and WZ744 flew nearly 200 hours in the development of fly-by-wire electrically signalled hydraulic flying controls before being retired in January 1967. WZ736 struck off charge at Farnborough on 9th May 1962 and used as a source of spares for WZ744.
Although the Avro 707 family of research aircraft did not contribute significantly to the Vulcan programme they did give the British aircraft designers early confidence in the general handling characteristics of the delta-wing, which lead to its adoption on other aircraft types (several of which where cancelled in the 1957 White Paper), and some of the systems tested found a direct application on other military aircraft programmes.