Bristol Tramp

Type 37 Tramp Type 44 Tramp Boat
Role	Passenger aircraft
National origin	United Kingdom
Manufacturer	Bristol Aeroplane Company
Designer	Frank Barnwell
Number built	2
Developed from	Bristol Pullman

The Bristol Tramp was a British steam-powered passenger and airmail transport aircraft designed by the Bristol Aeroplane Company. It was built but never flew.

The Tramp was a development of Bristol's earlier Pullman passenger aircraft. In 1919, Frank Barnwell entered discussions with the Royal Mail Steam Packet Company about the feasibility of using flying boats as auxiliaries to ocean liners. The Royal Mail Steam Packet Company had very limited experience with internal combustion engines, but long-term and deep knowledge of steam turbine powerplants, and so suggested the use of a steam turbine to power the aircraft. As Bristol's heavy bomber, the Braemar – the progenitor of the Pullman – had originally been designed to have a central engine room with driveshafts to wing-mounted propellors, the Pullman seemed a suitable candidate as a testbed for the installation of a steam turbine engine room.

The powerplant was to consist of two 1,500 hp (1,120 kW) steam turbines of the Ljungstrøm type, with closed-circuit high-pressure flash boilers. The unprecedented 3,000 hp (2,240 kW) would be delivered though driveshafts and clutches to four-bladed tractor propellers mounted on each middle wing (the Braemar/Pullman/Tramp family were triplanes). In the end, the only problem encountered with the steam turbine itself was that it delivered far too much power for the Tramp airframe, which had been designed to handle the 1,600 hp (1,190 kW) of four 400 hp (300 kW) Liberty L-12 engines. The main problem turned out to be designing a reliable lightweight closed-circuit boiler and condenser.

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