 {|  |} the hispano-suiza 12y was an aircraft engine produced by hispano-suiza for the french air force in the pre-wwii period. the 12y became the primary 1,000 hp (750 kw) class engine and was used in a number of famous aircraft, including the morane-saulnier m.s.406 and dewoitine d.520. its design was based on the earlier and somewhat smaller, 12x. a further development was under way, the 12z, but ended due to the german occupation of france. the 12y was also produced under hispano-suiza licence in the soviet union as the klimov m-100. this design later spawned the highly successful klimov vk-105 series that powered the yakovlev and lavochkin fighters as well as the petlyakov pe-2 bomber. licensed production of the early models was also undertaken in czechoslovakia as the avia hs 12ydrs. ==design and development== ===early development=== the 12y was a fairly traditional in construction, a 36-litre water-cooled v-12 with the two cast aluminium cylinder banks set at 60 degrees to each other. the cylinder heads were not removable, instead the entire block could be quickly removed from the engine. this made it somewhat famous for being leak-proof, a design feature that was considered by other designers and almost became a part of the rolls-royce merlin. the major design change from the earlier 12x was to use a master-articulated connecting rod system, instead of the fork-and-blade type. a single overhead camshaft (sohc) drove the valves, which were filled with liquid sodium for cooling. only a single intake and exhaust valve were used, unlike most designs of the era which had moved to three or four valves per cylinder. a single-stage, single-speed supercharger was standard, although the art of designing a useful intake was not as well developed as in other countries, and high altitude performance was always lacking. the first 12y test articles were constructed in 1932, and almost immediately the entire french aviation industry started designing around it. at the time the engine developed only 760&nbsp;hp (570&nbsp;kw), but it was clear it had potential to the 1,000&nbsp;hp (750&nbsp;kw) class. an early modification led to the hispano-suiza 12ycrs which used a hollow propeller shaft 
Aircraft_piston_engines_1930a1939 Hispano-Suiza_aircraft_engines Klimov_aircraft_engines