In 1947 Avro proposed a bomber shaped like nothing the Royal Air Force had ever bought: a vast tailless delta with no fuselage worth the name, meant to carry a nuclear weapon at high altitude across a continent. It became the Avro Vulcan.

There was a problem. In the late 1940s nobody knew how a thick delta wing behaved at low speed, which is precisely the regime in which an aircraft takes off, lands and kills its crew. So Avro built a small one first, and a test pilot died finding out.

A scale model you could sit in

The 707 was principally the work of Stuart Davies, Avro's chief designer. It was small, simple and built quickly — so quickly that the canopy of the first prototype was lifted straight off a Gloster Meteor. The wing carried about 50 degrees of sweep, with inboard elevators and outboard ailerons on the trailing edge, a conventional fin and rudder, and retractable airbrakes above and below the wing.

Avro had also planned a half-scale aircraft, the Avro 710. It was cancelled once it became obvious that developing a faster version of the little 707 would be quicker.

Twenty-six days

The first 707, VX784, flew from Boscombe Down on 4 September 1949 in the hands of Squadron Leader Samuel Eric “Red” Esler, Avro's deputy chief test pilot, who had been made responsible for all flying on the type in the chief test pilot's absence.

Twenty-six days later, on 30 September, VX784 crashed near Blackbushe and Esler was killed. The investigation pointed to a suspected control circuit failure that left the airbrakes locked open, causing the aircraft to stall.

It is worth being precise about what that did and did not prove. The accident was traced to a system fault, not to the delta wing. But it cost Avro its pilot and its first aircraft within a month of first flight, and the programme had to start again.

The aircraft that taught the Vulcan to fly

It did start again. The second aircraft, VX790, was completed to a revised 707B standard with a longer nose, a different canopy, 51 degrees of sweep and a lengthened nose leg to sit the aircraft at a higher angle for take-off and landing. The third, the first 707A, took on the higher-speed work from late 1953.

Crucially, the second and third aircraft flew before the Vulcan did. Most of what Avro learned about how its delta would behave came from those two small jets, and it fed directly into the leading edge and the control surfaces of the full-size bomber.

The four surviving 707s went on flying long after the Vulcan was sorted out, doing general research for the Royal Aircraft Establishment and, later, for the Aeronautical Research Laboratories in Australia. Britain also used them as showpieces: the little deltas appeared at the Farnborough airshows through the early 1950s, at exactly the moment the country wanted to look like it was winning the jet age.

Why it still matters

The Avro 707 is a reminder of how aviation actually advanced before computational fluid dynamics: you built a small one, you flew it, and sometimes it killed somebody. The Vulcan went on to serve for more than three decades and to fly the longest bombing mission in history at the time. It could do that partly because four little research jets had already found the edges of its wing.

The last 707 was grounded in 1967. Three survive in museums, and they look exactly like what they are: a Vulcan that someone left in the wash.

Sources: Wikipedia, BAE Systems Heritage, Aviation Safety Network, and Aeroflight.