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Bristol Hercules XII Engine

Between 1994 and 1999, MAPSL undertook the preservation of this Bristol Hercules Mk VIII engine from the RAF Museum’s Halifax.  The 14-cylinder radial aircraft engine is air-cooled and has sleeve valves to increase the efficiency by eliminating the traditional valves in the cylinder heads.  The cylinders are in two banks of seven, rotated with respect to each other for optimal cooling and each bank has its own master connecting rod and six other connecting rods.  A reduction gearbox is mounted on the front as can be seen in these two images.


The Bristol Hercules was designed by Sir Roy Fedden and produced by the Bristol Engine Company starting in 1939.  It was the first of their sleeve valve designs to see widespread use, powering many aircraft in the mid-World War II time frame.

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