The BMW 801 twin row radial engine formed the basis of the Focke Wulf fw190 design. This engine has the reputation as being among the better engine designs of WW2 regardless of limitations in German supercharger technology which lead to some failings at high altitude. It also powered many other Luftwaffe aircraft, from the Arado Ar 232A to the Junkers Ju 390.

The Bayerische Motroen Werke (BMW) based in Munich, were manufacturing Pratt and Whitney radials under license in the 1930’s and used this experience to develop its own twin row engine. Despite this, it can be considered an original design incorporating fuel injection and other German features.

A remarkably compact installation, adequate cylinder cooling was obtained using pressure baffling augmented by a magnesium alloy fan geared to turn at 1.72 times engine RPM (3 times propeller speed). An oil tank and cooler are positioned in the nose bowl and are armour plated. The engine mount ring is a sealed unit of square cross-section and also acts as a hydraulic fluid reservoir. Additional streamlining was achieved by the introduction of drag-inducing cowl flaps.

The BMW 801D-2 (fig.6.) was fed by methanol-water injection. Most revolutionary however, was the Kommandogerat. This hydraulicelectric “brain” unit was operated by a single control which was the pilot's throttle lever. It automatically adjusted fuel flow, mixture strength, propeller pitch setting and ignition timing. It also cut in a second stage of the supercharger at the correct altitude. The pilot could, if required, manually set the propeller pitch without altering any of the other settings.

Figure 6: The BMW 801D-2 radial aero engine.

The entire unit had a dry weight of 1,228 kg and an overall diameter of 1,270 mm. With a displacement of 41.8 litres and both a bore and stroke of 156 mm, this “square” engine could develop 1,730 hp at take off.