The Bristol Aeroplane Company Type 138A was a single engine, low-wing monoplane of large span and generous area.
It was designed to break the aircraft world’s altitude record at a time of intense competition within the British aircraft industry and much prestige was awarded for its record breaking. The Bristol 138A project also had the subsidiary benefit of achieving publicity for the Bristol Pegasus engine.
The early 1930s saw an active period of altitude record breaking, the height being raised by the Germans to 41,790 ft in May 1929. This was successively increased to 43,166 ft by the US Navy in 1930) and then to 43,976 ft by Cyril Uwins flying a Cmdr. Renato Donati established the new mark while flying his specially modified Caproni 113 AQ biplane in 1932. This was then pushed to a ceiling of 47,352 ft by Cmdr. Renato Donati flying his specially modified Caproni 113 AQ biplane
Air Ministry interest following the successful first flight over Everest led to Specification 2/34 and Bristol were invited to tender. They proposed a special high-altitude monoplane using a highly supercharged Pegasus engine with a view to taking the height record to above 50,000 ft.
The aircraft, designed by Frank Barnwell, was of wooden construction to minimise weight and the Bristol Type 138A (K4879) was first flown on 11th May 1936. It featured a standard Pegasus engine, driving a three-bladed propeller and was piloted by Cyril Unwins, who was already well-known following his world record flight in the Vickers Vespa.
After 2 further test flights, the aircraft was transferred for high-altitude flights from the RAE at Farnborough, who commenced their program in September 1936. On its very first flight from the Hampshire aircraft research facility, the Type 138A achieved a new record of 49,967 ft on 28th September 1936 although the pilot (Squadron Leader FRD Swann) suffered from oxygen starvation and had to break the windows in his pressure helmet once he had descended to a safe height.
After this flight, a number of small modifications were made to save weight and improve the supercharging and the Type 138A returned to 50,000 feet on 6 further occasions. Italy moved quickly to recapture the record with a flight to 51,364 ft in early 1937 whilst on 30th June 1937, the Bristol 138A increased the record yet again to 53,937 ft. A number of issues occurred during that flight (which took 2½ hours) including a major crack appearing in the canopy. Flt Lt Adams only survived due to the major development work that had been carried out on his personal pressure suit and helmet.
After this, no further record flights were attempted although it is rightly acknowledged that the increase in scientific data regarding pressurisation during these early flight was invaluable.
The height record was broken a further 9 times within ten years from 1928, once using a Bristol Jupiter engine and five times with a Bristol Pegasus and this proved hugely significant for Bristol engines.
A Bristol Type 138B was ordered in 1935 as a two-seater with a Rolls-Royce Kestrel S engine. Although the airframe was delivered to Farnborough in 1937, the engine was never fitted and the airframe was used for ground instructional training.
|Powerplant||One 500 hp Bristol Pegasus PE6|
|Span||66 ft 0 in|
|Maximum Weight||5,310 lb|
|Maximum Speed||123 mph|
|Design ceiling||More than 50,000 ft|