The Hirth HM 506 was a six-cylinder air-cooled inverted inline engine that was developed from the earlier four-cylinder HM 504.^[1] The HM 506 was a popular engine for light aircraft of the 1930s to 1940s and powered the Bücker Bü 133A model trainer. The engine featured a cast magnesium alloy crankcase.

Applications

• Bücker Bü 133 A
• Fieseler Fi 99
• Fieseler Fi 157 (UAV prototype)
• Fieseler Fi 158 (UAV prototype)
• Gotha Go 241
• Klemm Kl 35 B (D-ERLQ)

Specifications (HM 506A)

Data from Jane's All the World's Aircraft 1938,^[2] Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944^[3]

General characteristics

• Type: 6-cylinder air-cooled inverted inline
• Bore: 105 mm (4.13 in)
• Stroke: 115 mm (4.53 in)
• Displacement: 5.976 L (364.68 cu in)
• Length: 1,276 mm (50.2 in)
• Width: 490 mm (19.3 in)
• Height: 735 mm (28.9 in)
• Dry weight: 149 kg (328 lb) dry, unequipped

174 kg (384 lb) wet, equipped

Components

• Valvetrain: 1 inlet and 1 exhaust valve per cylinder, operated by push-rods and rockers
• Fuel system: 2x SUM 713/1 down draught carburetters, automatic mixture control and suitable for inverted flight.
• Fuel type: 80 Octane
• Oil system: Fresh oil, metered for each cylinder. Rockers in oil bath.
• Cooling system: air

Performance

• Power output:
  

• 160 PS (158 hp; 118 kW) at 2,500 rpm (5 minutes) at sea level
• 145 PS (143 hp; 107 kW) at 2,420 rpm (30 minutes) at sea level
• 130 PS (128 hp; 96 kW) at 2,330 rpm (max. continuous / cruise) at sea level

• Specific power: 26.8 PS/L (0.43 hp/cu in; 19.71 kW/L)
• Compression ratio: 6.2:1
• Specific fuel consumption: 0.220 kg/PSh (0.492 lb/(hp⋅h); 0.299 kg/kWh) at max continuous
• Oil consumption: 0.003 kg/PSh (0.007 lb/(hp⋅h); 0.004 kg/kWh) at max continuous
• Power-to-weight ratio: 1.075 PS/kg (0.481 hp/lb; 0.791 kW/kg)
• B.M.E.P.: 9.65 atm (9.78 bar; 141.8 psi)