The Bristol Type 188 is a supersonic research aircraft designed and produced by the British aircraft manufacturer Bristol Aeroplane Company. It was nicknamed the Flaming Pencil in reference to its length and relatively slender cross-section as well as its intended purpose.

The Type 188 was developed as part of supporting research efforts for the Avro 730, a later-cancelled bomber capable of Mach 3 flight. Its purpose was to explore high-speed, high-temperature flights; for the latter purpose, it made use of unconventional materials, such as large quantities of stainless steel, as well as the incorporation of an active refrigeration system. To work with this material, relatively exotic puddle welding fabrication techniques were employed along with extensive technical support from external companies. As part of its intended test programme, the Type 188 was designed with flexible engine installations that allowed for the fitting of different air intakes, engines, and propelling nozzles. It was also furnished with extensive electronic sensors, data recording, and telemetry apparatus. A total of three aircraft were constructed – a single static test frame along with two (constructor numbers 13518 and 13519) flight-capable aircraft; various scale models were also produced.

During May 1960, the first airframe was delivered to the Royal Aircraft Establishment (RAE) at Farnborough. The maiden flight of the Type 188 occurred on 14 April 1962. Flight testing encountered numerous problems, including the excessive fuel consumption of the De Havilland Gyron Junior engines used, which did not permit the aircraft to fly at high speeds long enough to evaluate the "thermal soaking" of the airframe, one of the main research areas of the project. Across 51 flights, the Type 188 attained a maximum speed of Mach 1.88 (1,240 mph; 2,000 km/h) at 36,000 ft (11,000 m).

During early 1964, it was announced that all activity involving the Type 188 was to be terminated. The project had cost £20 million by the end of the programme, making it the most expensive research aircraft ever developed in Britain at that time. The technical data and knowledge garnered from the Type 188 was put to use in other British high-speed aerospace efforts, most notably the development of Concorde supersonic transport, as well as the Bristol (later Rolls-Royce) Olympus 593 powerplant, which powered both Concorde and the BAC TSR-2 bomber. During the late 1960s, it had been intended for both of the Type 188 fuselages to be used as targets for gunnery trials at the Proof and Experimental Establishment at Shoeburyness, Essex; however, XF926 was subsequently transported to RAF Cosford, initially to act as instructional airframe 8368M, it has since been preserved at the Royal Air Force Museum Cosford in Shropshire.

The Bristol Type 188 had its genesis in Operational Requirement 330, which sought a high speed (Mach 3) reconnaissance aircraft, which eventually developed into the Avro 730. Air Ministry officials recognised that, as the Avro 730 was expected to operate at high speeds for extended periods of time, more data was needed on high speed operations; to fulfil this need, the follow-on Operational Requirement ER.134T was issued in February 1953; it called for a flying testbed capable of attaining speeds in excess of Mach 2. This aircraft was expected to run at these speeds for extended periods of time, allowing it to study kinetic heating effects on such an aircraft. Furthermore, it was also expected to operate for a considerable amount of time with a skin temperature around 300 Celsius.

Several of Britain's aircraft manufacturers took interest in this relatively advanced specification, Bristol Aircraft being specifically invited to tendered by ministry officials. The company's design team opted to produce a clean sheet aircraft design, which was assigned the internal designation of Type 188. The submitted design was somewhat vague and even speculative in several aspects, the aircraft's layout was not firmly decided upon until as late as 1955. Nevertheless, following a competitive review of submissions, the associated contract 6/Acft/10144 was awarded to Bristol during February 1953.

The advanced nature of the aircraft meant that new construction methods had to be developed. Several materials were considered for construction and two specialist grades of steel were selected: a titanium-stabilized 18-8 austenitic steel and a 12%-Cr steel used in gas turbines (Firth-Vickers Rex 448). These had to be manufactured to better tolerances in sufficient quantities for construction to start. The 12% chromium stainless steel with a honeycomb centre was used for the construction of the outer skin, to which no paint was applied. However, simply procuring sufficient amounts of stainless steel sheeting was a challenge, only compounded by factors such as the desired strength and uniformity.

While traditional riveting was considered to be a potential construction method, however, this posed substantially difficulties as every rivet, bolts, and screws used would have had to be specially manufactured out of compatible materials to ensure the necessary tolerances were met. Instead, a relatively cutting-edge technique of arc welding using an argon gas shield, known as puddle welding, was used. Another British aircraft manufacturer, the W. G. Armstrong Whitworth company, provided substantial technical help and support to Bristol during this period; they had also explored the use of puddle welding for advanced aerospace purposes. Armstrong Whitworth produced major sections of the airframe as a subcontractor. North American Aviation used the same methods of argon welding of stainless steel honeycomb sheet metal for the XB-70 Valkyrie bomber.^{[citation needed]}