Barrel Aircraft Engines: Historical Anomaly or Stymied Innovation?

Paralleling development of radial and in-line aircraft engines in the period 1910-1940, interesting barrel engine configurations evolved in three distinct forms. One form died of its own complexity, one fell dormant at the start of World War II, and one still lives as a potential light aircraft engine.

Compared to conventional designs, barrel designs promise little vibration, smoother power strokes, and more power and torque for less frontal area, weight, and parts count. Offsetting problems appear to be tricky cooling, lubrication, structural design, and servicing and maintenance challenges. Current design lessons may still be learned from these devices.