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During World War I, rotaries attained
tremendous popularity. They were less complex and easier to make than the
water-cooled type. They powered such outstanding fighter planes as
German's Fokker DR-1 and Britain's Sopwith Camel. They used castor oil for
lubrication because it did not dissolve in gasoline. However, they tended
to spray this oil all over, making a smelly mess. Worse, they were limited
in power. The best of them reached 260 to 280 horsepower (190 to 210
kilowatts).
Thus, in 1917 a group of American engine
builders returned to water cooling as they sought a 400-horsepower
(300-kilowatt) engine. The engine that resulted, the Liberty was the most
powerful aircraft engine of its day, with the U.S. auto industry building
more than 20,000 of them. Water-cooled engines built in Europe also
outperformed the air-cooled rotaries, and lasted longer. With the war
continuing until late in 1918, the rotaries lost favour.
Liberty engine
Curtiss OXX-3 Aero Engine
In this fashion, designers returned to
water-cooled motors that again were fixed in position. They stayed cool by
having water or antifreeze flow in channels through the engine to carry
away the heat. A radiator cooled the heated water. In addition to offering
plenty of power, such motors could be completely enclosed within a
streamlined housing, to reduce drag and thus produce higher speeds in
flight. Rolls Royce, Great Britain's leading engine-builder, built only
water-cooled motors.
Inline engines have an advantage of having a small frontal area,
thus drag is reduced. Many however use liquid cooling which increases weight and
make the aircraft more vulnerable to battle damage. |
aviation during World War One
introduction 
