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).
Several of Britain's aircraft manufacturers took interest in this relatively advanced specification, Bristol Aircraft being specifically invited to tendered by ministry officials. 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.
A fused-quartz windscreen and canopy and cockpit refrigeration system were designed and fitted, but were never tested in the environment for which they had been designed. The pilot was provisioned with a conventional ejector seat. All of the flight controls, along with elements such as the undercarriage and four-part air brakes, were hydraulically powered. The Type 188 was originally intended to be powered by a pair of Rolls-Royce Avon engines, however, these were substituted for a pair of De Havilland Gyron Junior engines (each of which was half a ton lighter) in June 1957. This change of engines necessitated some configuration changes, including the mounting of the engines further forwards along with elongated nacelles and jet pipes. The Gyron Junior was then under development for the Saunders-Roe SR.177 supersonic interceptor and incorporated a fully variable reheat arrangement, which achieved a smooth variation in thrust between dry and full reheat, so being one of the first engines in the world to give continuous variation in thrust from idle to max reheat. This choice of powerplant resulted in the Type 188 having a typical endurance of only 25 minutes, not long enough to conduct the high-speed research tests that were required of it. Chief Test Pilot Godfrey L. Auty reported that while the Type 188 transitioned smoothly from subsonic to supersonic flight, the Gyron Junior engines were prone to surging beyond that speed, causing the aircraft to pitch and yaw.
In order to solve the aerodynamic and flutter problems identified, a large number of scale models were produced and tested. Some of these models were mounted on converted rocket boosters and used to conduct free-flight investigations, multiple such launches were conducted from RAE Aberporth. As a result of these tests, along with wind tunnel testing, various aerodynamic refinements and alterations were made to the Type 188's design. As a result, a largely rectangular wing plan was adopted between the engine nacelles alongside horn-balanced ailerons on the compact outer wings; the all-moving tailplane was also raised to the top of the fin while the chord was also extended to accommodate single-engine failure during take-off.
Across 51 flights, the Type 188 reached a top speed of Mach 1.88 at 36,000 ft (11,000 m). The longest subsonic flight lasted only 48 minutes, which was largely due to 70 percent of the aircraft's total fuel capacity being consumed just to attain its operational altitude.
Measurements during testing were collected and, in addition to being recorded onboard, were transmitted to a ground station for live review as well as being recording and subsequently analysed. The ground station was typically manned by both an engineer and a "ground pilot"; the extent of the flight information transmitted permitted the ground pilot to comprehensively advise the pilot of the aircraft in real time, although it was convention for only key information to be communicated as such to avoid excessive distraction to the pilot flying. By the end of the programme, considered the most expensive to date for a research aircraft in Britain, XF923 had to be "cannibalised" in order to keep the other airframe flightworthy.
Surviving aircraft
In April 1966, both Type 188 fuselages were transported to the Proof and Experimental Establishment at Shoeburyness, Essex to act as targets for gunnery trials, but during 1972, XF926 was dismantled and moved to RAF Cosford (without its engines) to act as instructional airframe 8368M, and is preserved at the Royal Air Force Museum Cosford in Shropshire.
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Notable appearances in media
Bristol 188 XF923 was prominently featured in Some People (1962), a feature film primarily shot in Bristol.