cockpit. It was powered by a single Bristol Siddeley Viper turbojet; up to 150 gallons of fuel could be accommodated within the wing's interior across three separate tanks. The engine was positioned above the wing and set into the base of the tailfin. This fin had a bullet fairing at the top to accommodate a cine-camera to record airflow visualisation experiments, some of which employed smoke generators mounted on the wing leading edges. Both the tailfin and rudder were swept at an angle of 60°, save for a slight up-turning near to the engine exhaust to minimise thrust-related pitching movements. Testing and evaluation On 17 August 1961, the single aircraft HP.115, XP841, conducted its maiden flight at the Royal Aircraft Establishment Bedford, piloted by J.M. Henderson, who reported his enthusiasm for this initial flight. This flight had been preceded by extensive ground taxying trials, during which the optimum takeoff trim was determined. In advance of the flight, Henderson had undergone extensive simulator training which, according to Barnes, had projected more pessimistic handling characteristics than those that presented themselves in real world flight. All pilots selected to pilot the HP.115 underwent many hours of simulated flight prior to operating the actual aircraft. Only one month following its maiden flight, the HP.115 performed an aerial display at the 1961 Society of British Aerospace Companies (SBAC) airshow; on 29 September of that year, the contractor's trials were completed. The aircraft was quickly put to use for its intended low-speed research work, supporting the supersonic transport development programme that would ultimately lead to Concorde. In parallel to the HP.115, a separate aircraft, the BAC 221, (a modified Fairey Delta 2) was used to perform high-speed flight research. The HP.115 proved to be very capable aircraft; pilots were able to demonstrate rapid changes of bank while still safely retaining control at speeds as low as 69 mph (60 kn, 111 km/h), about that of the contemporary Lockheed F-104 Starfighter. Neil Armstrong was at one point scheduled to fly the HP.115 as a test pilot in 1962, but after his selection as an astronaut, NASA refused him permission to fly the aircraft. He eventually flew it on 22 June 1970. Despite its involvement in a pair of separate but minor mishaps, the experimental programme was a relatively lengthy one, continuing up to its final flight on 1 February 1974. It provided substantial data on the characteristics