In the post-World War 2 (1939-1945) period, both conventional and extreme aircraft developments were en vogue and not solely confined to the United States and the Soviet Union for the powers of Europe were also busy in presenting all-new forms for review. Case-in-point the Handley Page "HP.115", developed as a delta-winged aircraft for the purpose of detailing low-speed handling characteristics for a possible future supersonic passenger hauler. The vehicle was a true technology demonstrator, living its entire career as a research platform, and was instrumental in helping to bring about the famous British-French BAe/Aerospatiale "Concord" supersonic passenger airliner.
The HP.115 was primarily operated by the Royal Aircraft Establishment (RAE) research arm for its time in the air.
In the latter part of the 1950s, British researchers were already understanding that a Mach 2-capable passenger airliner would be relying on a delta-winged planform and considered various sub-designs of this very wing configuration, ultimately settling on the "ogival" approach. - a more elegantly-shaped platform which saw smoother leading edges coupled to straight-lined trailing edges. To prove its low-speed handling qualities on a flyable design, the wings were constructed to fit on a single-seat, single-engined (jet-powered) technology demonstrator offered by Handley Page, the model HP.115. Meanwhile, Fairey worked on the "Delta 2" to prove the high-speed qualities of the same passenger airliner proposal.
A contract in December of 1959 was drawn up to cover the Handley Page work on its powered aircraft after thoughts of an unpowered glider form were abandoned. Off-the-shelf components would be used in the construction of the research aircraft in an effort to get it into the air as quickly (and cheaply) as possible. The resulting design was of very conventional appearance save for its engine powerplant fitted at the base of the vertical tail fin (to clear the wings for pure data use/collection).
As a delta-wing-configured aircraft, there were no horizontal tailplanes for the mainplanes took up all of the horizontal surface area, offering the required controlling, drag, and lift properties. The single-seat cockpit was positioned at the front of the slim fuselage in the traditional way and offered excellent vision for the pilot. For ground-running, a tricycle undercarriage configuration was used - the legs were fixed in flight and not retractable to retain operating/maintenance simplicity. Beyond its engine placement, one of the more unique aspects of the aircraft's design was its fuselage which was cinched along its ventral line between cockpit and center mass - this was obvious when the aircraft was viewed in the side profile. Lightweight alloys were used throughout its construction and the wing mainplanes had a feature where leading edges could be exchanged with different shapes for "quick-testing" purposes. The engine-of-choice became the Armstrong Siddeley "Viper" ASV.9 jet engine - this installed in a streamlined, fin-mounted nacelle.
The HP.115 made it into the air for the first time on August 17th, 1961 and the product was put on display at the various Farnborough aviation gatherings from 1961 into 1964 for public consumption. Testing continued uninterrupted for the most part and proved the technologically-laden research aircraft through-and-through.
The active flying phase for this exceptional aircraft was largely trouble-free save for an undercarriage incident taking place on November 20th, 1964. During its take-off (following a rolling landing test), structural fatigue in the port-side landing gear member left it damaged and at an awkward angle. Rather amazingly, the test pilot returned the experimental aircraft safely to the ground intact after following proper crash landing procedures and using skill at the controls. This proved a relatively minor setback for the aircraft which remained in repair until May of 1965.
In total, the specimen completed 1,060 total test sorties with its final flight recorded in August of 1973 - no fewer than sixty-one test pilots were part of the aircraft's history which helped to pave the way for the classic Concorde.