Rotary engines were popular on aircraft until the end of World War I, but had serious stability and efficiency problems. Rotary engines have a similar configuration, but the cylinders also continually rotate, creating an air flow even when the vehicle is stationary.Īircraft design more strongly favors lower weight and air-cooled designs. Radial engines allow air to flow around each cylinder directly, giving them an advantage for air cooling over straight engines, flat engines, and V engines.

Higher-power engines generate more waste heat, but can move more weight, meaning they are generally water-cooled. Water has a higher heat capacity than air, and can thus move heat more quickly away from the engine, but a radiator and pumping system add weight, complexity, and cost. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator. Watercraft can use water directly from the surrounding environment to cool their engines. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. System which uses either air or liquid to remove the waste heat from an internal combustion engine

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