|Major applications||Dornier Do 17|
|Developed from||Bristol Jupiter|
The Bramo 323 Fafnir was a 9-cylinder radial aircraft engine of the World War II era. Based heavily on Siemens/Bramo's earlier experience producing the Bristol Jupiter under license, the engine was not particularly modern and saw limited use.
Design and development
Development of the 323 was the end result of a series of modifications to the original Jupiter design, which Siemens licensed in 1929. The first modifications were to "Germanize" the dimensions, producing the Sh.20 and Sh.21. The design was then bored out to produce the 950 hp (708 kW) Sh.22 in 1930. Like the Jupiter, the Sh.22 featured a rather "old" looking arrangement with rather prominent valve pushrods on the front of the engine. In the mid-1930s the Reich Air Ministry (RLM) rationalized engine naming, and Bramo was given the 300-block of numbers, the Sh.14 and Sh.22 becoming the Bramo 314 and 322 respectively. The 322 never matured and remained unreliable.
The team continued work on the basic design, adding fuel injection and a new supercharger. The resulting 323 was just under 27 l in displacement, and produced 900 PS at 2,500 rpm for takeoff, improving slightly to 1,000 PS at 3,100 m (10,200 ft). The reduced power at sea level was inevitable for engines with one-speed mechanically driven superchargers when they were regulated to a constant maximum boost pressure below their critical altitude.
The Fafnir powered a number of German pre-war designs, including the Focke-Wulf Fw 200, Henschel Hs 126, Dornier Do 24 and Dornier Do 17, as well as the Focke Achgelis Fa 223 Drache helicopter. Its fairly poor fuel economy kept it from more widespread use, and most designs chose the similar BMW 132 instead, whose specific fuel consumption varied between 220 and 240 g/(kW•h) depending on model, whereas the early versions of the Fafnir got about 255 g/(kW•h), a poor figure for the era. The C/Ds, where the supercharger used less power, improved this to 230 g/(kW•h), but were only useful at lower altitudes.
BMW bought Bramo in 1939 and continued production to supply the small number of designs that already used it, notably the Do 17. The naming at this point becomes somewhat confusing, with BMW, Bramo and Fafnir being used almost interchangeably. 5,500 were produced before the lines were shut down in 1944.
The original 323 design was produced in A and B models, differing in the direction they turned. The engines were intended to be installed in A/B pairs, thereby eliminating engine torque across a twin-engine aircraft. The similar C and D models featured a lower supercharger gearing for better performance at lower altitudes, improving takeoff power to 1,000 PS, but reducing the critical altitude.
The final versions, P, R and T, featured a two-speed supercharger for better all-round performance. This allowed it to generate 1,000 PS at sea level as in the C/D models, but improved altitude performance considerably, delivering 940 PS at 4,000 m (13,000 ft). The R-2 subtype added MW 50 water-methanol injection for added low-altitude performance, boosting power to 1,200 PS at 2,600 rpm.
- Arado Ar 196
- Arado Ar 232
- Blohm & Voss BV 222
- Dornier Do 17
- Dornier Do 24
- Focke Achgelis Fa 223
- Focke-Wulf Fw 200
- Henschel Hs 126
- Junkers Ju 352
Specifications (BMW 323A)
Data from Jane's
- Type: 9-cylinder supercharged air-cooled radial engine
- Bore: 154 mm (6.06 in)
- Stroke: 160 mm (6.30 in)
- Displacement: 26.82 litres (1,636.8 in³)
- Length: 1,420 mm (55.9 in)
- Diameter: 1,388 mm (54.6 in)
- Dry weight: 550 kg (1,210 lb)
- Valvetrain: Pushrod-actuated overhead valve
- Supercharger: Gear-driven
- Fuel system: Fuel injection
- Fuel type: 87 Octane petrol
- Cooling system: Air-cooled
- Power output:
- 670 kW (900 PS) at 2,500 rpm at sea level for take-off
- 745 kW (1,000 PS) at 3,100 m (10,200 ft)
- Specific power: 27.8 kW/L (0.61 hp/in³)
- Compression ratio: 6.4:1
- Specific fuel consumption: 0.348 kg/(kW·h) (0.572 lb/(hp·h))
- Power-to-weight ratio: 1.36 kW/kg (0.83 hp/lb)
- Gunston 1989, p.30.
- Jane's 1989, p.289.
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