Bristol 37 Tramp

Designed for the Royal Mail Steam Packet Company, the Bristol Tramp was a British steam-powered passenger and airmail transport triplane aircraft. The Royal Mail Steam Packet Company only had limited experience with internal combustion engines, but extensive operating knowledge of steam turbine powerplants. As a result, the Tramp was to be powered by a steam turbine, housed in an engine room in the fuselage, driving propellers on the wings via clutches and driveshafts.

Two prototypes were completed in 1921, but the clutches gave continual trouble and neither ever flew. They were utilised as ground test rigs for several years before being broken up.