Many experts in the field of aircraft engine overhaul have debated over whether aircraft engines should be air cooled or liquid cooled, although the fact is that both types of systems deliver waste heat into the air eventually. There are pros and cons to both types of engines, and the debate as to which is the better option appears to continue.
Automobile engines, for the most part, are liquid cooled, as fluids run through the engine to keep temperatures at a regulated level. Originally, aircraft engines were also liquid cooled, with the plane engine using water, ethylene glycol or a mixture of the two to cool the engine during flight. Many believe that liquid-cooled engines provide less hazard of shock when cooling the engine, and the ability to direct coolant flows to critical areas of the engine as some of the best reasons to choose a liquid-cooled engine. However, liquid-cooled aircraft engines have added weight, are less adaptable to military applications and their systems are far more complex than air-cooled engines.
As the name implies, air-cooled engines are cooled by air movement through the engine, rather than liquid. Although these engines are considerably lighter and adapt easily to military applications, because air is a gas it does not dissipate heat as rapidly as fluid. To adequately cool an aircraft engine, a significant amount of air is required to cool the engine to acceptable levels. Air-cooled engines have gone through many changes over the years. Over history, air-cooled engines have included:
Inline and V-Type Engines – Glenn Curtiss created the earliest air-cooled aircraft engine in 1908, with an engine consisting of individual cylinders with integral heads and relatively wide spaced fins used to cool the V-8 engine. In 1909, Renault developed an air-cooled V-8 using an engine-driven cooling fan. However, Renault’s version was known for a very short exhaust valve life and high fuel consumption.
- Rotary Radial Engines – Rotary radial engines were used extensively in military aircraft during World War I and the power-to-weight ratio made them extremely attractive to designers. Although an excellent option for military operations, rotary radial aircraft engines were not suitable for commercial purposes. One of the drawbacks to such an engine was that gyroscopic forces created by the engine were a challenge to pilots, and windage losses due to air resistance were significant.
- Static Radial Engines – After World War I, aircraft engine designers saw a need for engines that could be used for both commercial and military usage. Two British designers, Professor A.H. Gibson and Samuel D. Heron, understood that aluminum transferred heat well and learned that bolted joints between the head and barrel of the aircraft engine were frequent sources of gasket failure and leaks. This discovery led to the creation of the static radial engine, a much lighter, more efficient aircraft engine.
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