Britain's First Delta-Wing 'Plane -- Seen in flight is Britain's first 'delta winged' aircraft, the Avro 707, which made its initial flight earlier this month. The stubby aircraft, performance details of which are still secret, will be used for examination of the qualities of delta-wing configuration powered with one Rolls-Royce Derwent gas turbine engine, it is an experimental research aircraft designed to permit controlled flight at and above the speed of sound. The Avro 707 measures 38 feet i