Bramo 323

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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.

Development of the 323 started as an enlarged version of the Jupiter, developing it from the original into the "Germanized" Sh.20 and Sh.21 in 1929. 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 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 during introduction.

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 hp at 2,500 RPM for takeoff, improving slightly to 1,000 hp at 10,200 ft. The reduced power at sea level was inevitable for engines with mechanically-driven superchargers when they were regulated to a constant maximum boost pressure below their critical altitude.

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 hp, 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 hp at sea level as in the C/D models, but improved altitude performance considerably, delivering 940 hp at 13,120 ft (4,570 m). The R-2 subtype added MW 50 water-methanol injection for added low-altitude performance, boosting power to 1,200 hp at 2,600 rpm.

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. It's 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 0.50 and 0.54 lb/(hp·h) depending on model, whereas the early versions of the Fafnir got about 0.57 lb/(hp·h), a poor figure for the era. The C/D's, where the supercharger used less power, improved this to 0.51 lb/(hp·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.

[edit] Specifications (BMW 323A)

General characteristics

• Type: 9-cylinder supercharged air-cooled radial engine
• Bore: 154 mm (6.06 in)
• Stroke: 160 mm (6.30 in)
• Displacement: 26.82 litres (1,637 in³)
• Length: 1,420 mm (55.9 in)
• Diameter: 1,388 mm (54.6 in)
• Dry weight: 550 kg (1,210 lb)

Components

• Valvetrain: Pushrod-actuated
• Supercharger: Gear-driven
• Fuel system: Fuel injection
• Cooling system:

Performance

• Power output:
  
  • 670 kW (900 hp) at sea level
  • 745 kW (1,000 hp) 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)