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 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 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.