BMW 801

The BMW 801 was a powerful German air-cooled radial aero engine, found in a number of German military aircraft of World War II.

The engine cylinders were in two rows of seven cylinders each, the bore and stroke were both 156 mm and a capacity of 41.8 litres. The engine generated between 1,600 and 2,000 h.p. The unit (including mounts) weighed around 1,250 kg and was about 1.27 m across, depending on model.

The engine was developed from experience gained when BMW had been manufacturing similar Pratt and Whitney engines under license in the 1930s. An early attempt to make a larger version of these engines resulted in the 1,400hp BMW 139, but the cooling proved problematic and it was decided to start over. The 801 was slightly larger and heavier than the 139, but proved to be much more reliable.

Early versions used a single-stage supercharger with limited capabilities, leading to less than stellar high-altitude performance. A number of solutions were attempted but few saw service. Later models of the basic engine included a system for injecting a water-methanol mixture into the supercharger output to cool the charge and thereby reduce backpressure. Known as MW50 (as in 50-50 methanol-water) the system was fitted to the majority of engines, but the injection systems themselves were rare until the end of the war. Other solutions included powerful turbocharger systems that were too expensive for general use, and a new two-stage supercharger that boosted the later model's emergency power settings to 2,100hp.

Radial engines were uncommon in successful European fighter aircraft until the BMW 801 was used in the Focke-Wulf Fw 190. Originally the 190 mounted the engine behind a completely enclosed engine area, with a fan blowing air into the housing to provide cooling. This proved not to work well and later models left some of the nose area open behind a more traditional looking cowling. In fact this cowling was also fairly complex, included an armoured oil tank and radiator, as well as ducting to move cooling air from the center of the nose to the cylinder heads. Initially the engines had a tendency to overheat and also produced unpleasantly high temperatures in the cockpit, but this was solved via the addition of cooling vents that opened near the rear of the engine cowling. Later Fw 190s, the 'D' model from 1943 and later , tended to use the Junkers Jumo 213 inline, or in the 'Ta' designs of Kurt Tank liquid-cooled Daimler-Benz DB 603 variants.

An additional feature on the BMW engine in the Fw 190 was the Kommandogeraet, a hydraulic-electric unit that automatically adjusted engine fuel flow, mixture and timing with propellor pitch in response to throttle demand and also engaged the supercharger.

• 801A 1,600 h.p.
• 801D 1,730 h.p.
• 801S or TS 2,000 h.p.
• 801F 2,400 h.p., development halted by the end of the war

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