Coomber Rotary Engine

I first learned of this delightful engine while attending a model engineering exhibition. A most prolific modeler, Marlyn Hadley, had one on display. I referred to his excellent book6 to create this illustration.

I have not illustrated the valve linkage, as I’m not exactly sure what it looks like! It appears to be a rotary type, incorporated into the main drive shaft. Steam would be admitted to one end of the cylinder at a time, just as in any other double-acting steam engine.

The inner dimension of the stationary ring is not circular, but is slightly elliptical. The main bearing is situated beneath the center of this ellipse by one half the stroke length.