The Curtiss Chieftain H-1640 12-cylinder "Hexagon" engine

The Chieftain was an attempt by Curtiss to combine the low frontal area of an in-line engine with the benefits of an air-cooled radial. It was hoped this engine would compete with the wildly successful Wright and Pratt & Whitney air-cooled radials. The Chieftain suffered from rear cylinder cooling problems, gave problems in all its test installations, and never saw production. Still, it makes an interesting study in the numerous engine variations tried in the late 1920s and early 1930s.