The Hirth HM 512 was a 12-cylinder development of the earlier, 6-cylinder HM 506, produced in the late 1930s. Both were supercharged, inverted V, air-cooled engines.
Design and development
The HM 512 shared the same bore and stroke (105 mm × 115 mm) and 6:1 compression ratio with the rest of the HM500 series air-cooled engines. Other shared features were Hirth's use of roller bearings in the crankshaft and at both ends of connecting rods. The crankshaft was of typical Hirth multipart design, the 12-cylinders requiring 7 roller bearings. Like the HM 508, the drive was geared down by 1:1.5.
HM 512A
Initial version; take off power 400 hp (300 kW), continuous 360 hp (270 kW)
HM 512B
Take off power 450 hp (335 kW), continuous 360 hp (270 kW)
Dornier Do 212
Data from Grey 1972, p. 61
Type: Inverted 60° V-12-cylinder air-cooled piston
Bore: 105 mm (4.128 in)
Stroke: 115 mm (4.52 in)
Displacement: 11.94 L (728.6 cu in)
Length: 1,507 mm (59.33 in)
Width: 680 mm (26.87 in)
Height: 853 mm (33.58 in)
Dry weight: 270 kg (595 lbs)
Supercharger: Light alloy centrifugal type, driven at 3.86 times crankshaft speed.
Fuel system: Supercharger drew through twin Pallas 65VH2 carburetters with automatic mixture control and equipped for inverted flight. One Bosch double magneto with automatic advance.
Oil system: Metered fresh oil to cylinder barrels and crankshaft bearings. Splash lubrication for supercharger and camshaft. Stökicht Sun and planet reduction gear lubricated by high pressure oil.
Cooling system: Air
Power output: maximum 270 kW (360 hp) at 3,000 rpm, rated 224 kw (300 hp) at 2,810 rpm, take off 300 kW (400 hp)
Compression ratio: 6.0:1
