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The advanced nature of the aircraft meant that 12% chromium stainless steel with a honeycomb centre was used for the construction of the outer skin, to which no paint was applied, but problems with the new Argon arc welding technique known as puddle welding caused long delays and was less than satisfactory. The W. G. Armstrong Whitworth company gave much technical help and support to Bristol during this period.
A quartz-lined windscreen and canopy and cockpit refrigeration system were designed and fitted but were never tested in the environment for which they had been designed.
Rolls-Royce engines were at first selected to power the 188, but five engine combinations were evaluated: two with Rolls Royce Avon 200s, two with the de Havilland Gyron Junior and one with an AJ.65, the latter disintegrating on test. But the final choice for the 188 were two 10,000 lbf (44 kN) thrust Gyron Junior DGJ10Rs developing 14,000 lbf (62 kN) of thrust on reheat at sea level and 20,000 lbf (89 kN) at Mach 2 at 36,000 ft (11 km). Unfortunately this choice of powerplant resulted in the 188 having an endurance of only 25 minutes, which was too little time for any serious high speed research. Test pilot Godfrey Auty reported that while the 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.
The project suffered a number of problems; the main being - as mentioned above - that the fuel consumption of the engines didn't allow the aircraft to fly at high speeds long enough to evaluate the "thermal soaking" of the airframe, which was one of the main research areas it was built to investigate. Also, the takeoff speed was nearly 300 mph.