Hispano-Suiza 12Z
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The 12Z was the final evolution of the series of Hispano-Suiza V-12 aircraft engines, which had just entered production when France fell to the Germans during World War II. A small number were produced during the war but the German occupation government would not allow production to start. After the war small numbers were built to equip new designs, but the rapid introduction of the jet engine ended further development.
The 12Z differed from the earlier 12Y primarily in the use of four valves per cylinder operated by dual overhead cams. This gave the cylinders considerably better volumetric efficiency, allowing the compression ratio to rise from the 12Y's 5.8:1 to the 12Z's 6.75:1, the rpm from 2,400 to 2,700, and the power from 1,000 to 1,300 hp (750 to 970 kW) at sea level. Unfortunately the engine continued to use a single-stage, single-speed supercharger, and therefore didn't have the same sort of performance as German and British designs. But by tuning the supercharger for a different critical altitude the engine improved high altitude performance considerably, delivering 1,500 hp (1,120 kW) at 21,000 ft (6,400 m), as opposed to 930 hp (690 kW) at 2,950 ft (900 m) for the 12Y.
Small prototype runs started in 1939, and were fitted to the French Armée de l'Air's front-line fighter aircraft, the M.S.410 and D.520, creating the M.S.450 and D.520Z respectively. Production of the main model, the 12Z-17, was just starting when France fell. Production was undertaken in Hispano-Suiza's Spanish factories, but these engines had many problems and were never used in any numbers.
After the war a new version tuned to operate with 92 octane fuel, as opposed to the -17's 100/130, was built in limited numbers as the 12Z-89. Compression ratio was raised slightly to 7:1, but with the lower grade fuel the power dropped slightly to 1,280 hp (950 kW) at 2,600 rpm (1,479 hp (1,100 kW) maximum take-off). These engines apparently had the same sorts of reliability issues as the earlier -17's made in Spain, and the type never entered production.
Specifications
For 12Z-17:
- Layout: 12-cylinder two-row vee
- Bore by stroke: 150 by 170 mm
- Displacement: 36 L (2,197 in³)
- Compression ratio: 6.75:1
- Power: 1,300 hp (970 kW) at 2,650 rpm MTO, 1,500 hp (1,120 kW) at 2,700 rpm at 21,000 ft (6,400 m)
- SFC at cruise: 0.48 lb/hp.h (0.29 kg/kWh)
- Weight: 690 kg (1,520 lb)
See also
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