Editing BMW 801 (section)

===Precursor design===
In the 1930s, BMW took out a license to build the [[Pratt & Whitney Hornet]] engines. By the mid-30s they had introduced an improved version, the [[BMW 132]]. The BMW 132 was widely used, most notably on the [[Junkers Ju 52]], which it powered for much of that design's lifetime.

In 1935 the [[Reich Air Ministry|RLM]] funded prototypes of two much larger radial designs, one from [[Bramo]], the Bramo 329, and another from BMW, the [[BMW 139]]. BMW's design used many components from the BMW 132 to create a two-row engine with 14 cylinders,{{citation needed|reason=text documentation is known to exist for it being an 18-cylinder engine|date=January 2015}} supplying 1,550&nbsp;PS (1,529&nbsp;hp, 1,140&nbsp;kW). After BMW bought Bramo in 1939 both projects were merged into the BMW 801, learning from the problems encountered in both projects.

The BMW 139 was originally intended to be used in roles similar to those of the other German radials, namely [[bomber]]s and [[Military transport aircraft|transport aircraft]], but midway through the program the Focke-Wulf firm's chief designer, [[Kurt Tank]] suggested it for use in the [[Focke-Wulf Fw 190]] fighter project. Radial engines were rare in European designs as they were considered to have too large a frontal area for good [[wikt:streamline|streamlining]] and would not be suitable for high speed aircraft. They were most popular on naval aircraft, where their easier maintenance and improved reliability were highly valued. Efforts to improve these designs led to new [[cowling]] designs that reduced the concerns about drag. Tank felt that attention to detail could result in a streamlined radial that would not suffer undue drag, and would be competitive with inlines.

The main concern was providing cooling air over the cylinder heads, which generally required a very large opening at the front of the aircraft. Tank's solution for the BMW 139 was to use an engine-driven fan behind an oversized, flow-through hollow [[Spinner (aeronautics)|prop-spinner]] open at the extreme front, blowing air past the engine cylinders, with some of it being drawn through S-shaped ducts over a [[radiator (engine cooling)|radiator]] for oil cooling. However this system proved almost impossible to operate properly with the BMW 139; early prototypes of the Fw 190 demonstrated terrible cooling problems. Although the problems appeared to be fixable, since the engine was already fairly dated in terms of design, in 1938 BMW proposed an entirely new engine designed specifically for fan-cooling that could be brought to production quickly.