Curtiss Chieftain Engine
Throughout all the 1920s and most of the 1930s, undue emphasis was placed on engine frontal area, resulting in novel approaches to engine design. Development of the Townsend ring and NACA cowl eventually put this concern to rest. In the mean time, several noteworthy engines of small diameter and unusual construction competed with the usual air-cooled radials and liquid-cooled vees. One such engine was the Curtiss Chieftain. The following account is taken from Victor Page’s 1929 work, Modern Aviation Engines, Vol. 2.
Nine Cylinder Single Row Radial.-This type would require an engine of from 1,800 to 1,900 cubic inches to develop about 600 brake-horsepower at a speed in the neighbourhood of 1,900 r.p.m., which is probably a rather optimistic speed at which to expect to run an engine of this power and displacement, owing to the fact that the size of the cylinder bore is reaching a point where cooling is difficult, and the reciprocating weights on one crankpin (even though it may be of the split crankshaft and solid big end type) would be a difficult problem. The outside diameter of a nine cylinder radial engine of this power would be 56 inches to 60 inches in diameter which presents a very large frontal area with severe blanketing of the propeller, resulting in poor propeller efficiency. The added diameter increases the resistance so much that it has been found by experience that the larger radial engines in Pursuit planes make practically no more speed than the lower horsepower radial engines with the smaller diameters. Of course, the rate of climb is increased but this does not offset the disadvantage of carrying high powered engines using more fuel without gaining more top speed.