Bristol Type 138

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Contents

Type Description

• Type 138
• Proposed purpose-built single-seat high-altitude research monoplane with retractable undercarriage and a supercharged Pegasus powerplant. Not built.

• Type 138A
• Purpose-built single-seat high-altitude research monoplane to meet the requirements of Specification 2/34, capable of carrying an observer when necessary. Weight saving was a priority and the airframe, other than the steel tube engine mount and cowling, used a wood shell. A plywood skin was glued to the mahogany longerons and struts that formed the internal structure, which was faired throughout to reduce drag. A conventional fixed undercarriage was used as it was more important to reduce the weight than the drag The wings were constructed in three sections with a centre section integral with the fuselage. Three spars with plywood webs and mahogany flanges were used, covered with plywood sheeting.
  The pilot was seated in a spacious cockpit, which was heated by air directed from the oil coolers set within the wings, which could be adjusted. Instrumentation included fore-and-aft levels, oil pressure gauges, airspeed indicator and fuel gauge, engine speed indicator and a pyrometer. Purpose-built recording altimeters, developed by the RAE, were housed within the wings, while a separate altimeter was installed in the cockpit. In order to cope with the extreme altitudes, the pilot used a specially-developed two-piece suit. The 138 had an internal fuel capacity of 82 imp gal, split between a 70 imp gal lower tank and a 12 imp gal upper tank. A specially-developed fuel, known as S.A.F.4, was used for the altitude record flight, derived from standard grade Shell Ethyl aviation gasoline. One 500 h.p. Bristol Pegasus P.E.6S powerplant. This engine featured a highly powered supercharger, which was a critical element enabling the engine to deliver the required performance in order to attain the envisioned altitude performance. The supercharger's installation, the detail work of which having been performed by Clifford Tinson, was a two-stage system; the first-stage compressor was permanently engaged, but the second-stage incorporated clutches which enabled it to be manually engaged by the pilot upon attaining the correct height. This arrangement was necessary to avoid administering an excessively dense mixture to the cylinders when flown at low altitudes. The supercharger arrangement employed an intercooler between the first and second stages.

• Type 138B
• Two-seat development of the Type 138A powered by a 500 h.p. Rolls-Royce Kestrel S powerplant fitted with a similar two-stage supercharger installation.

Type 138A Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Endurance	Service Ceiling
66 ft	44 ft	10 ft 3 in	568 sq ft	4391 lb	5310 lb		123 mph/ 107 kn	2 hr 15 min	54000 ft
20.12 m	13.41 m	3.12 m	52.77 m2	1992 kg	2409 kg		198 km/h		16459 m

Production Details

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Production Summary

Production References

1. Bristol Aircraft Since 1910, C.H. Barnes (Putnam, 1964, 1970 and 1988)
2. The K File, The Royal Air Force of the 1930s, J.J. Halley (Air-Britain Publications, 1995)
3. Royal Air Force Aircraft L1000 - N9999, RAF Aircraft Register Series (Air-Britain Publications, 1993)

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