Delta-Wing Research Aircraft
The delta wing Avro Model 707 testbed flyer preceded the famous Avro Vulcan V-Bomber line for the British Royal Air Force.
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The classic British "V-Bomber" - the Avro Vulcan - incorporated a highly advanced, large-area delta wing planform which gave the jet-powered bomber its unique and very identifiable shape. However, to produce a sound and effective design, prior evaluation of more controlled designs and technologies would be required to prove the approach viable and this came in one form as the delta-winged Avro 707 technology demonstrator. The platform allowed for the collecting of data and institution of changes on a smaller, less costly scale rather than working on an expensive, full-sized bomber form. As the Avro 707 was to the Vulcan program, so too was the Handley Page HP.88 research plane to the other V-Bomber - the Handley Page Victor.
Before the full-scale, five-man-crew Vulcan prototypes had been ordered, two smaller-scale, single-seat aircraft were committed to as the Model 707 (a 1/3rd scale offering) and the Model 710 (a half-scale version). Each would serve separate program goals with the 707 intended for low-speed, low-altitude handling and performance. Two prototypes of the 707 then followed as VX784 and VX790 and these were to be originally constructed largely of wood for expediency as well as to keep resource costs in check. However, this design initiative was quickly abandoned in favor of an all-metal aircraft to better mimic the design of the Vulcan. The official specification - E.15/48 - appeared in October 1948 to officially drive the product along while specification E.10/49 coming in July 1949 covered development of an experimental offshoot of the 707 - this model pairing intended for high-speed research (models WD280 and WZ736).
On the whole, the 707 looked the part of the Vulcan with its delta wing planform. The wings were mid-mounted along the sides of a tubular fuselage with the cockpit sat ahead of the wing roots and aft of a short nose cone assembly. The cockpit position was raised which offered relatively good views around the frontal section of the aircraft. The wing assemblies were well-swept along their leading edges and straight along their trailing edges, ending in sharp points at the tips. The tail unit was of a single vertical fin while the delta wing planform also took the function of typical horizontal tailplanes. The sole engine was buried within the aft fuselage of the aircraft and, rather interestingly, aspirated through a semi-circular, split vent found along the fuselage dorsal spine near midships. This particular design quality was not at all reflective of the finalized Vulcan form which seated its air intakes at the wing leading edges. Some other design qualities for the 707 were selected simply to expedite its construction process and this included the nosewheel assembly and cockpit taken from a Gloster Meteor F.3 fighter and the main landing gear legs from an Avro Athena trainer mount.
After the requisite taxiing trials were completed, first flight of a 707 aircraft was recorded on September 4th, 1949 by model VX784 and the aircraft was then showcased at Farnborough 1949. Sadly, the aircraft then claimed the life of its test pilot during a routine test flight, crashing into the ground from a low-speed/low-altitude approach. The cause of this crash centered on the deployed air brakes which forced the aircraft's tail into the ground. Engineers then devised a new air brake arrangement for future 707 flights.
Model VX790 was brought along with a slightly lengthened fuselage - just over two feet - and a revised nose cone with a new nose leg taken from a Hawker Sea Hawk. The installation of this leg provided an increased "nose up" attitude to the airframe which helped to increase lift during take-off. The new air brake arrangement was also implemented into the model and the changes warranted a slight revision of the original 707 designation to become "707B". 707B made its maiden voyage on September 6th, 1950.
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.