semi-cooled

Updated: May 21, 2025

First made semi-cooled the exhaust valve was left air-cooled, and then entirely water-jacketed this engine demonstrated the advantage of full water cooling, for under the latter condition the same power was developed with cylinders a quarter of an inch less in diameter than in the semi-cooled pattern; at the same time the weight was brought down to 4 1/2 lbs. per horsepower.

W. Lockwood (William Lockwood) Marsh - A History of Aeronautics