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Hirth HM 515
Type	Inline piston engine
National origin	Germany
Manufacturer	Hirth-Motoren GmbH, Stuttgart-Zuffenhausen
Major applications	Siebel Si 202C Hummel
Developed from	Hirth HM 500

The Hirth HM 515 was a four-cylinder air-cooled inverted inline engine, intended to power light aircraft of the 1940s. Due to World War II, demand for the light aircraft to be powered by the HM 515 dried up and only the Siebel Si 202C Hummel was powered by development engines before further work was abandoned.

The HM 515 closely followed the Hirth formula of Elektron (magnesium alloy) castings for the crank case and covers, with roller bearings and metered oil feeds for light weight, smooth running and low oil consumption. Only a small number were produced before the war precluded further production of the light aircraft class that the engine was intended to power. Flight testing was carried out in the Si 202Cs driving a 1.8 m (5 ft 11 in) propeller, but no production ensued.^[1]

Specifications (HM 515)

Data from Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944^[2]

General characteristics

Type: 4-cylinder air-cooled inverted in-line piston engine
Bore: 95 mm (3.74 in)
Stroke: 105 mm (4.13 in)
Displacement: 2.980 L (181.85 cu in)
Length: 976 mm (38.4 in)
Width: 334 mm (13.1 in)
Height: 570 mm (22.4 in)
Dry weight: 68 kg (150 lb) dry, unequipped

74 kg (163 lb) wet, equipped

Components

Valvetrain: 1 inlet and 1 exhaust under-valve per cylinder driven by pushrods and rockers
Fuel system: 1x Pallas MF 35 carburetor
Fuel type: 80 Octane
Oil system: dry sump, pressure feed with scavenge
Cooling system: air-cooled

Performance

Power output:

65 PS (64 hp; 48 kW) at 2,100 rpm for take-off
60 PS (59 hp; 44 kW) at 2,040 rpm (high power rating) at sea level
55 PS (54 hp; 40 kW) at 1,990 rpm (max. continuous) at sea level

Specific power: 21.8 PS/L (0.35 hp/cu in; 16.03 kW/L)
Compression ratio: 6.2:1
Specific fuel consumption: 0.205 kg/PSh (0.458 lb/(hp⋅h); 0.279 kg/kWh) at max continuous
Oil consumption: 0.001–0.003 kg/PSh (0.002–0.007 lb/(hp⋅h); 0.001–0.004 kg/kWh) at max continuous
Power-to-weight ratio: 0.96 PS/kg (0.43 hp/lb; 0.71 kW/kg)
B.M.E.P.: 9.30 atm (9.42 bar; 136.7 psi)

References

^ "Siebel Si 202 Hummel". www.histaviation.com. Archived from the original on 17 May 2017. Retrieved 4 February 2020.
^ Schneider, Helmut (Dipl.Ing.) (1944). Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944 (in German) (Facsimile reprint 1986 ed.). Leipzig: Herm. Beyer Verlag. p. 396. ISBN 381120484X.