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Junkers L5 / L 55 / L 8 / L 88

 

Junkers-L5
Junkers L5

 

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 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. First run in 1925, it was a much enlarged development of the Junkers L2, in turn a licensed development of the BMW IV.

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.

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. Many of these powered the Junkers F.13 and its derivatives like the W 33, which dominated world air transport in the mid-1920s.
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.

Overall, less than 1000 were built.

 

The Junkers L55 was Junkers' first V-12 engine, appearing in 1927. The L5 was used in 1927 as the basis of the 665 hp L55, which had two banks of six cylinders aligned at 60°. These banks had the same bore, stroke, camshaft operated twin pairs of valves per cylinder, watercooling etc. as the L5, driving new a common crankshaft in a revised crankcase. A supercharger was added after a year to improve high altitude power.

The L55 is only known to have powered two aircraft for certain, the Junkers G 38 early in its career and the Junkers A 32. The first G 38 originally had two L55s inboard plus two L8 engines. The high altitude research Junkers Ju 49 may have used the L55 at the start of its flight programme. The L55 was rapidly replaced by the L88 in both the G 38 and Ju 49.

 

Variants:

L5 many variants including a variety of on compression ratios, powers 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.
 
L88 an upright V-12 built from two L8s on a common crankshaft.

 

Applications - L5
Albatros L 73
Albatros L 75
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

 

Applications - L55
Junkers A 32
Junkers G 38
Junkers Ju 49, possibly

 

Specifications:

L 5
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 (Bad rounding here5.7 ft)
Width: 650 mm (Bad rounding here2.1 ft)
Height: 1,265 mm (49.80 in)
Dry weight: 334 kg (736.34 lb) dry
Valvetrain: large twin exhaust and twin 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)
Compression ratio: 7:1
Fuel consumption: 61.6 kg/h (136 lb/hr)
Power-to-weight ratio: 1.22 kg/kW (2.01 lb/hp) @ cruise rpm

 

L55
Type: upright V-12 water-cooled 4-stroke piston engine
Bore: 160 mm (6.30 in)
Stroke: 190 mm (7.48 in)
Displacement: 45.84 L (2,797 cu in)
Length: 2.287 m (7 ft 6 in)
Width: 1.273 m (4 ft 2 in)
Height: 0.84 m (2 ft 9 in)
Dry weight: 585 kg (1290 lb)
Valvetrain: two inlet and two exhaust valves per cylinder, one overhead camshaft on each bank
Supercharger: added to rear of engine in 1928
Fuel type: petrol
Oil system: forced
Cooling system: water-cooled
Reduction gear: none; direct drive
Power output: cruise 665 hp (495 kW) at 1,700 rpm, take-off 690 hp (514 kW)
Fuel consumption: 150 kg/h (331 lb/hr)

 

 


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