Junkers L5

The Junkers L 5 was a six-cylinder, water-cooled, inline engine for aircraft built in Germany during the 1920s. First run in 1925, it was a much enlarged development of the Junkers L2, in turn a licensed development of the BMW IV.

Junkers L5
Type Inline aircraft engine
Manufacturer Junkers Motorenbau GmbH (Jumo)
First run 1922[1]
Major applications Junkers F.13
Number built >1,000[2]
Variants Junkers L55

Design and development

The Junkers L5 was a development of Junkers' first water-cooled engine, the L2, but at four times the swept volume was a much more powerful engine. It was a water-cooled upright inline 6-cylinder unit, four-stroke and petrol-fuelled, with a capacity of nearly 23 litres. It adopted some of the L2 features, having twin exhaust and inlet valves in each cylinder[2]driven by an overhead camshaft, twin spark plugs and twin magnetos. The splash component of the L2's lubrication was abandoned in favour of a completely forced recirculating system. The twin carburettors of the L2 were replaced with a single float chamber, dual-venturi model. Like the L2, the L5 was a direct drive engine.[2]

The compression ratio of the standard version was 5.5:1, but variants had other ratios to cope with fuels with octane ratings between 76 and 95. The G series introduced carburettor heating together with an hydraulically damped mounting system. There were also choices of starting system, from inertial or compressed air systems to the traditional hand swinging.[2]

Operational history

The L5 proved to be reliable and became the engine of choice for most Junkers aircraft in the mid-1920s as well as powering aircraft from other German manufacturers.[2] Many of these powered the Junkers F.13 and its derivatives like the W 33, which dominated world air transport in the mid-1920s.[3]

The best demonstration of the reliability of the L5 was given by the unit which powered the single-engined W 33 Bremen in the first fixed wing east to west crossing of the Atlantic in April 1928. For this flight the compression ratio was raised to 7:1 to provide sufficient power for the heavily fuelled aircraft at take off. In July 1925 a W 33 powered by a L5 stayed aloft for 65 h 25 min, with a fuel consumption of 35.6 kg/h.[2]


  • L5 many variants including a variety of on compression ratios, power output levels and starting systems.
  • L55 an upright V-12 built from two L5s on a common crankshaft.
  • L8 a significant 1929 development with the same swept volume but cruising at 2,100 rpm and delivering 354 hp; take off power was 413 hp. The output was geared down at ratios between 2.47:1 and 1.44:1 to enhance propeller efficiency. Only a few were produced, powering early configurations of the Junkers G 38 as outer engines, with two L55s inboard.[2]
  • L88 an upright V-12 built from two L8s on a common crankshaft.

Applications (L5)

Specifications (Jumo L 5)

Data from [2]

General characteristics

  • Type: 6-cylinder liquid-cooled inline
  • Bore: 160 mm (6.30 in)
  • Stroke: 190 mm (7.48 in)
  • Displacement: 22.92 l (1,398.66 cu in)
  • Length: 1,750 mm (5 ft 8.90 in)
  • Width: 650 mm (2 ft 1.59 in)
  • Height: 1,265 mm (49.80 in)
  • Dry weight: 334 kg (736.34 lb) dry


  • Valvetrain: large single exhaust and single inlet valves driven by a single overhead camshaft shaft and gear driven from the crankshaft
  • Supercharger: none
  • Fuel system: single float, dual venturi carburettor; twin plugs per cylinder, twin magnetos
  • Fuel type: 95 octane (dependent on compression ratio)
  • Oil system: forced
  • Cooling system: liquid


  • Power output: Take-off - 260 kW (348.7 hp) at 1,450 rpm
Cruise - 208.8 kW (280 hp)

See also

Related lists


  1. Gunston (2006), p. 112
  2. Kay (2004), pp. 264–265
  3. Kay (2004), p. 62


  • Gunston, Bill (2006). World Encyclopedia of Aero Engines: From the Pioneers to the Present Day (5th ed.). Stroud, UK: Sutton. ISBN 0-7509-4479-X.
  • Kay, Antony (2004). Junkers Aircraft & Engines 1913–1945. London: Putnam Aeronautical Books. ISBN 0-85177-985-9.
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