Junkers L5

L5
Junkers L5 on display at the Junkers Museum
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

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.

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]

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 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.

• Albatros L 73
• Albatros L 75
• Albatros L 83 Adler
• Focke-Wulf A 32
• Heinkel HD 42
• Heinkel He 50
• Junkers F 13
• Junkers A 20
• Junkers A 35
• Junkers G 23
• Junkers G 24
• Junkers K 30
• Junkers G 31
• Junkers W 33
• Messerschmitt M 24
• Rohrbach Ro.VIII

Data from ^[2]

• Type: 6-cylinder liquid-cooled inline
• Bore: 160 mm (6.3 in)
• Stroke: 190 mm (7.5 in)
• Displacement: 22.92 L (1,399 cu in)
• Length: 1,750 mm (69 in)
• Width: 650 mm (26 in)
• Height: 1,265 mm (49.8 in)
• Dry weight: 334 kg (736 lb) dry

• Valvetrain: Single exhaust and single inlet valves driven by a single overhead camshaft shaft and gear driven from the crankshaft
• 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 (350 hp) at 1,450 rpm
  

Cruise - 210 kW (280 hp)

• Compression ratio: 7:1
• Fuel consumption: 61.6 kg/h (136 lb/hr)
• Power-to-weight ratio: 0.78 kW/kg (0.47 hp/lb)

Related lists

• List of aircraft engines

• 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.

Wikimedia Commons has media related to Junkers L5.

• The Hugo Junkers Homepage
• http://www.oldengine.org/members/diesel/Duxford/germaer1.htm Archived 2007-08-04 at the Wayback Machine