Bristol Type 138
| Type 138 High Altitude Monoplane | |
|---|---|
 |
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| The Type 138A over Farnborough c. 1937 | |
| Role | High-altitude research aircraft |
| Manufacturer | Bristol Aeroplane Company |
| Designer | Frank Barnwell |
| First flight | 11 May 1936 |
| Primary user | Royal Aircraft Establishment |
| Number built | 1 (+1 Type 138B airframe not completed) |
The Bristol Type 138 High Altitude Monoplane was a British high-altitude research aircraft of the 1930s. It was a single-engine, low-wing monoplane with a fixed, tailwheel undercarriage.
The Type 138 was born of a period of intense competition between aviation manufacturers in the 1920s and 1930s. There was much prestige, as well as technological progress, to be gained from breaking any of the major aviation records: airspeed, distance and altitude. By the 1930s absolute speed and distance records were beyond the resources of individual companies, and required the involvement of national governments.
Bristol was well placed to compete in this field but in the event they found themselves lagging. Between 1929 and 1934, there were a number of altitude records established by rival machines including a Junkers W.34, a Vickers Vespa and a Caproni Ca.113 biplane, as well as the first flight over Everest by a pair of Westland Wallaces in 1933; all these aircraft used Bristol or Bristol-designed engines.
Sensing Air Ministry interest resulting from the success of the Everest flight, Barnwell proposed a purpose-built high-altitude research aircraft in November 1933. This, the Type 138, was a large single-engine, single-seat monoplane with retractable undercarriage and a supercharged Pegasus engine. Nothing came of this until Renato Donati set a new record in April 1934; public opinion demanded a new, government-sponsored record attempt. In June, the Air Ministry issued Specification 2/34 for two prototypes capable of reaching 50,000 ft (15,030 m). Barnwell revised the Type 138 to produce the Type 138A. This was of the original size and configuration but had a special, two-stage supercharged Pegasus and, although remaining basically a single-seater, had provision for an observer's cockpit to be fitted if required. Weight-saving was a priority; the airframe, other than the steel tube engine mount, was a wooden monocoque and the retractable undercarriage was replaced with a lightweight, fixed assembly.
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