The final development of this three-cylinder radial was the 'Y' type of engine, in which the cylinders were regularly disposed at 120 degrees apart, the bore was 4.1, stroke 4.7 inches, and the power developed was 30 brake horse-power at 1,300 revolutions per minute.

Critchley's list of aero engines being constructed in 1910 shows twelve of the radial type, with powers of between 14 and 100 horse-power, and with from three to ten cylinder--this last is probably the greatest number of cylinders that can be successfully arranged in circular form. Of the twelve types of 1910, only two were water-cooled, and it is to be noted that these two ran at the slowest speeds and had the lowest weight per horse-power of any.

The Anzani radial was considerably developed special attention being paid to this type by its makers and by 1914 the Anzani list comprised seven different sizes of air-cooled radials. Of these the largest had twenty cylinders, developing 200 brake horse-power--it was virtually a double radial--and the smallest was the original 30 horse-power three-cylinder design. A six-cylinder model was formed by a combination of two groups of three cylinders each, acting upon a double-throw crankshaft; the two crank pins were set at 180 degrees to each other, and the cylinder groups were staggered by an amount equal to the distance between the centres of the crank pins. Ten-cylinder radial engines are made with two groups of five cylinders acting upon two crank pins set at 180 degrees to each other, the largest Anzani 'ten' developed 125 horsepower at 1,200 revolutions per minute, the ten cylinders being each 4.5 inches in bore with stroke of 5.9 inches, and the weight of the engine being 3.7 lbs. per horse-power. In the 200 horse-power Anzani radial the cylinders are arranged in four groups of five each, acting on two crank pins. The bore of the cylinders in this engine is the same as in the three-cylinder, but the stroke is increased to 5.5 inches. The rated power is developed at 1,300 revolutions per minute, and the engine complete weighs 3.4 lbs. per horse-power.