Kroeber M4

M4 Köller
M4 Köller
National origin	Germany
Manufacturer	Dr. Kroeber & Sohn G.m.b.H.
First run	1930s
Major applications	Möller Stomo 3, ITS-8

The Kroeber M4 Köller was a 2-stroke air-cooled horizontally opposed piston engine designed and built by Dr. Kroeber & Sohn G.m.b.H. in Germany in the late 1930s. The M4 proved relatively popular, for powering the ultra-light aircraft and motor-gliders in vogue during the 1920s and 1930s.

Variants

Kroeber M3 Köller: either a typo or a variant of the M4, (only reference is Cynk's Polish aircraft 1893-1939)
Kroeber M4 Köller: Main production variant

Applications

Data from AEHS: HOAE Kroeber

Grunau Motor-Baby – German motor-glider conversion of a Grunau Baby
Kocjan Bąk I – Polish motorglider
Dittmar Condor 'La Falda' (a removable power-egg with M4 and pusher propeller)
Möller Stomo 3 – German high-speed ultralight aircraft
Akaflieg München Mü13M Motormerlin
ITS-8 – Polish motorglider sic Kroeber M3 Köller (only reference to M3)

Engines on display

There are several M4 engines on display, but one of the best preserved and presented is at the Polish Aviation Museum in Kraków.

Specifications (M4)

Data from Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944,

General characteristics

Type: 2-cylinder 2-stroke air-cooled horizontally-opposed
Bore: 75 mm (2.95 in)
Stroke: 72 mm (2.83 in)
Displacement: 0.634 L (38.69 cu in)
Length: 550 mm (21.7 in)
Width: 550 mm (21.7 in)
Height: 646 mm (25.4 in)
Dry weight: 27.8 kg (61 lb)

Components

Fuel system: 2x Meco S1/f carburetor
Fuel type: 1:25 SAE 50 oil / gasoline blend
Oil system: blended with fuel
Cooling system: air-cooled

Performance

Power output:

18 PS (18 hp; 13 kW) at 2,700 rpm (30 minutes) at sea level
16.6 PS (16 hp; 12 kW) at 2,650 rpm (max. continuous / cruise) at sea level

Specific power: 28.4 PS/L (0.46 hp/cu in; 20.89 kW/L)
Compression ratio: 6.2:1
Specific fuel consumption: 0.228 kg/PSh (0.510 lb/(hp⋅h); 0.310 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: 0.645 PS/kg (0.289 hp/lb; 0.474 kW/kg)
B.M.E.P.: 2.55 atm (2.58 bar; 37.5 psi)

References

↑ Cynk, Jerzy B (1971). Polish aircraft 1893-1939. Putnam. p. 652. ISBN 0-370-00085-4.
↑ "Kroeber". www.enginehistory.org. AEHS. Retrieved 5 February 2020.
↑ "Aircraft engine: Köller Kroeber M4". Polish Aviation Museum Kraków. Retrieved 25 December 2023.
↑ 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. 417. ISBN 381120484X. {{cite book}}: ISBN / Date incompatibility (help)
↑ Grey, C.G.; Bridgman, Leonard, eds. (1938). Jane's All the World's Aircraft 1938. London: Sampson Low, Marston & company, ltd. p. 64d.

[Cynk-1] Cynk, Jerzy B (1971). Polish aircraft 1893-1939. Putnam. p. 652. ISBN 0-370-00085-4.

[AEHS-2] "Kroeber". www.enginehistory.org. AEHS. Retrieved 5 February 2020.

[PAM-3] "Aircraft engine: Köller Kroeber M4". Polish Aviation Museum Kraków. Retrieved 25 December 2023.

[schneider-4] 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. 417. ISBN 381120484X. {{cite book}}: ISBN / Date incompatibility (help)

[JAWA1938-5] Grey, C.G.; Bridgman, Leonard, eds. (1938). Jane's All the World's Aircraft 1938. London: Sampson Low, Marston & company, ltd. p. 64d.