The Bristol High Altitude Monoplane (factory name Type 138)was a research aircraft manufactured by Bristol Aeroplane Company.
It was developed and built in particular to surpass the existing absolute altitude world record.
Already after the flight of two Westland biplanes over Mount Everest, the Air Ministry showed interest in supporting record flights.
In November 1933, Bristol proposed a large single-seat low-deckerwith the Type 138, but this was not implemented due to the high estimated costs.
Only after the record flight of Donati the development work was resumed. In June 1934, Bristol was asked to submit an offer in accordance with the tendering requirements (Air Ministry Specification) 2/34.
In September 1934, the design work on the Type 138A – which retained the dimensions and the design of the Type 138 – was completed.
The drive was a modified Bristol Pegasus with a two-stage mechanical loader that powered a rigid four-blade draught.
The first flight of type 138A (RAF serial number K4897) with Cyril Unwins at the wheel took place on 11 May 1936 in Filton.
The engine was a standard Bristol Pegasus with a three-bladed propeller.
In August 1936, the aircraft received the high-altitude engine and the four-blade dweller.
Squadron Leader F.R.D. Swain was able to bring the altitude world record back to England on 28 September with 15,230 m.
In May 1937, however, he was again outbid by an Italian Caproni Ca.161 with 15,665 m.
The Bristol 138A was modified again, so that Fl. Lt. M.J. Adam was able to set the new record at 16,440 m with her on June 3, 1937.
The two-seater Bristol 138B, which was ordered for comparison purposes in 1935 and equipped with a special Rolls-Royce Kestrel, was delivered to Farnborough in 1937, but the engine was no longer installed.
The cell of type 138 was designed as a wooden half-shell construction.
The cockpit was covered with a plastic hood.
In front of the pilot, a second place for an observer could be set up.
The machine also had a large wing span, also made of wood, and a fixed chassis.
There was no pressurized cabin. The pilot therefore had to wear a pressure suit during the flight.
Length 13.41 m
Span 20.12 m
Height 3.12 m
Wing area 52.77 m2
Weight 1996 kg
max. starting mass 2414 kg
Speed 285 km/h in 13715 m
Service peak height 16,500 m
Climbing rate 436 m/min in 12190 m
Range 2.25 h
Engines 1 x Bristol Pegasus PE.6S with 373 kW
Bristol Aircraft since 1910- C H Barnes.
Bristol Type 138. X-Planes and Prototypes- Jim Winchester.