The Hirth HM 501 was a 6-cylinder air-cooled inverted in-line engine that was developed by Hirth Motoren GmbH in the late 1930s, from the 4-cylinder HM 500 and used principally on the submarine-born Arado Ar 231.

• Arado Ar 231

Data from Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944^[1]

• Type: 6-cylinder air-cooled inverted in-line aircraft piston engine
• Bore: 105 mm (4.13 in)
• Stroke: 115 mm (4.53 in)
• Displacement: 5.97 L (364.3 cu in)
• Length: 1,272 millimetres (50.1 in)
• Width: 485 mm (19.1 in)
• Height: 662 mm (26.1 in)
• Dry weight: 148 kg (326 lb) dry, unequipped

155 kg (342 lb) wet, equipped

• Valvetrain: one intake and one exhaust under-head valve per cylinder actuated pushrods and rockers
• Fuel system: SUM 698/2 carburetor
• Fuel type: 80 octane gasoline
• Oil system: Dry sump with one pressure and two scavenge pumps
• Cooling system: Liquid-cooled, ethylene glycol

• Power output:
  

• 160 PS (158 hp; 118 kW) at 2,550 rpm for takeoff
• 145 PS (143 hp; 107 kW) at 2,470 rpm (high performance) at sea level
• 130 PS (128 hp; 96 kW) at 2,380 rpm (max. continuous ) 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: 0.002–0.003 kg/PSh (0.004–0.007 lb/(hp⋅h); 0.003–0.004 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.: 9.46 atm (9.59 bar; 139.0 psi)

Wikimedia Commons has media related to Hirth aircraft engines.

• Nowarra, Heinz J. (1993). Die Deutsche Luftrüstung 1933-1945 Vola.4 - Flugzeugtypen MIAG-Zeppelin (in German). Koblenz: Bernard & Graefe Verlag. p. 101, 108-109. ISBN 3-7637-5468-7.