Hispano-Suiza 12Y

The Hispano-Suiza 12Y was a French aircraft engine in the pre-WWII era. Developed from the earlier, and somewhat smaller, 12X, 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, Dewoitine D.520. The design was also widely used in other countries, and formed the basis for licensed production of a number of designs, most notably the Soviet Klimov VK-105 series. The 12Y design was further modified to create the more modern 12Z, but development was never fully completed due to the German occupation of France.


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. A unique feature was that the cylinder heads were not removable, instead the entire block could be quickly removed from the engine. This made it somewhat famous for being entirely leak-proof, a design 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 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 instantly the entire French aviation industry started designing around it. At the time the engine developed only 760 hp (570 kW), but it was clear it had potential to the 1,000 hp (750 kW) class. An early modification led to the 12Ycrs which used a hollow propeller shaft to allow a 20 mm cannon to fire through the propeller spinner (a combination known as a moteur-canon). All later designs shared this feature. The 12Ydrs was the next major series, with a basic rating of 836 hp (623 kW) at sea level with a compression ratio of 5.8:1.

The Armée de l'Air changed their nomenclature, so the next version was the 12Y-21, which increased the compression ratio to 7:1, running on 100 octane. This boosted power to 867 hp (647 kW). In 1936 the connecting rod design was changed slightly to create the 12Y-31, but the lower 5.8:1 compression ratio was retained and the power was increased only slightly over the drs model to 850 hp (630 kW). Nevertheless this became one of the most used engine designs of the pre-war era, used in almost all fighter designs and prototypes.

Late variants

A real effort to improve the performance of the engine in 1938 resulted in the 12Y-45, which used the S-39-H3 supercharger co-designed by André Planiol and Polish engineer Joseph Szydlowski. The Szydlowski-Planiol device was larger, but much more efficient than the indifferent Hispano-Suiza models. This allowed the compression ratio to be raised to that of the -21's 7:1, boosting power to 900 hp (670 kW), although requiring the use of 100 octane fuel. Combined with the fully-adjustable Ratier propeller, this allowed the D.520 to perform as well as contemporary designs from Germany and England. Another improvement in supercharging led to the 12Y-49, whose performance improved from 850 hp (630 kW) at sea level to 920 hp (690 kW) at just over 10,000 ft (3,000 m). This improvement in power with altitude was a common feature of many early engines, the result of the supercharger "robbing" power at low altitudes to provide boost that then had to be dumped to avoid overboosting the engine.

The final major version was the 1,085 hp (809 kW) 12Y-51, which had just started into production at the time of the Armistice with Germany. The -51 was the first version that came close to the performance limits of the engine, taking advantage of the 100-octane gasoline, although the single-stage supercharging meant that it was unable to compete with designs from England and Germany above 15,000 ft (5,000 m).

Foreign derivatives

In the mid-1930s, Russian engineer Vladimir Klimov was sent to France to obtain a license for local production of the 12Y. A series of design changes were added to cope with cold weather operation, and the engine entered production in 1935 as the Klimov M-100 with about 750 hp (560 kW). However a series of continual upgrades increased the allowable rpm from the 12Y's fairly low 2,400 to 2,700, thereby increasing power to 1,100 hp (820 kW). The resulting design, the Klimov M-105 (VK-105), became one of the major Soviet engine designs during the war, powering all Yakovlev fighters.

Specifications (12Ycrs)



12Y Derivatives


See also

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