Subsequent flights proved the viability of the tail-less delta wing design though one recurring issue became the engine's ability to take in enough airflow during flight. It was found that the raised cockpit structure ahead of the intake retarded airflow into the slit, the engine in turn not providing the necessary out power. The decision was made to added a "hump" along the fuselage spine at the intake structure to better induce the airflow coming over and behind the canopy. The work delayed further testing for a time and a landing accident on September 21st, 1951 added concern - the nose of the aircraft suffered some damage and the test pilot was injured but survived. Once repaired, the aircraft made a second showing at Farnborough 1952 but its history was marred yet again by a second landing accident during 1956. With no more flights to its name, 707B was officially scrapped in 1960.
The aforementioned high-speed WD280 and WZ736 models developed along their own lines from 1949 onwards. However, these airframes utilized an all-new delta wing design which incorporated wing leading edge intake openings ala the Vulcan bomber itself - losing the dorsal spine intake of the 707B. WD280 and WZ736 were collectively designated 707A and these aircraft better represented the finalized Avro Vulcan bomber form, much more than the unique 707B and its sister aircraft. First flight of the high-speed 707A was on June 14th, 1951.
However, the 707 research planes had all but reached their usefulness by now as the actual Vulcan bomber flyable prototypes were providing more of the needed data during their test phases. As such there proved little value in the smaller-scale 707 models while the Vulcan program more or less evolved without their help from 1952 onwards. Testing did continue of these research aircraft for a time and a two-seat "707C" (WZ744) was later added, this aircraft featuring a side-by-side cockpit seating arrangement. In a final show of strength, the four remaining 707 program contributors were flown together during Farnborough 1953.
With the four distinct Avro 707 forms completed, each aircraft showcased slightly different structural dimensions and performance. The original 707 was powered by a Rolls-Royce Derwent 5 turbojet engine of 3,500 lb thrust while 707B followed with a Derwent 5lb of equal thrust output. 707A was outfitted with a Derwent 8 turbojet slightly uprated to 3,600 lb thrust output and the two-seat 707C model incorporated the same engine installation. Gross weight was gradually increased from the 707 to the 707C, from 8,600 lb to 10,000 lb. Beyond these qualities, the aircraft were largely faithful to the original 707.
For a time, WD280 served over Australian soil through the Commonwealth Aeronautical Advisory Research Council (CAARC). It was carried over by HMAS Melbourne. It served there from 1956 to 1960.
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