Hispano-Suiza 12Y

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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 somewhat more modern 12Z, but production had not yet started when France fell.

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 cylinder rod system, instead of the fork-and-blade type. A single overhead camshaft 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 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 20mm cannon to fire through the propeller spinner (what the Germans called a motorkanone). 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 Armee de Air changed 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.

A real effort to improve the performance of the engine in 1938 resulted in the 12Y-45, which used the Polish-designed Szydlowski-Planiol S-39-H3 supercharger in place of the indifferent French 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 1,084 hp (808 kW) 12Y-51, which had just started into production when France fell in 1940. The -51 was the first version that came close to the performance limits of the engine, 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).

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 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 M-105, became one of the major Soviet engine designs during the war. In 1941 designers were allowed to attach their own names to their designs, and the engine became the VK-105.

[edit] Specifications (12Ydrs)

General characteristics

Type: 12-cylinder supercharged liquid-cooled 60° Vee piston engine
Bore: 150 mm (5.9 in)
Stroke: 170 mm (6.7 in)
Displacement: 36 L (2,197 in³)
Dry weight: 470 kg (1,036 lb)

Components

Valvetrain: One intake and one sodium-cooled exhaust valve per cylinder actuated via a single overhead camshaft per bank.
Supercharger: Gear-driven single-stage single-speed centrifugal type supercharger
Cooling system: Liquid-cooled

Performance

Power output:
- 664 kW (890 hp) at 2,400 rpm at sea level
- 700 kW (930 hp) at 900 m (2,950 ft)
Specific power: 19.44 kW/L (0.42 hp/in³)
Compression ratio: 5.8:1
Power-to-weight ratio: 1.49 kW/kg (0.90 hp/lb)