What Are Aircraft Reciprocating Engines?
While many modern aircraft now take advantage of advanced and powerful gas turbine engines that have revolutionized flight as we know it, a large number of models still utilize reciprocating engines that have served aviation endeavors since the first powered flight. While the original engines for heavier-than-air aircraft, reciprocating engines are extremely advanced with a number of components that work together to make flight possible. In this blog, we will discuss aircraft reciprocating engines in more detail, allowing you to have a better understanding of their general design, variations, and uses.
Despite there being a few common types of aircraft reciprocating engines that vary in their design, all consist of a basic set of parts, including the crankcase, cylinders, pistons, connecting rods, valves, crankshaft, and valve-operating mechanism. The cylinders are where the combustion of fuel-and-air mixtures takes place, and each is fitted with valves and a spark plug. While one valve permits flow from the induction system, the other leads to the exhaust system. Within each cylinder is also a piston, that of which serves for compression and linear motion.
The crankcase is an important element of the engine as a whole, serving as a housing for the bearings and bearing supports that allow for the crankshaft to revolve. The crankcase also keeps lubricating oil within the assembly, ensuring that various mechanisms are properly lubricated. As misalignments can easily lead to issues, crankcases are often constructed with cast or forged aluminum alloy to achieve sufficient rigidity.
Alongside these basic parts, other various components are often present based on the type of reciprocating engine that one is using. Generally, the most common types include inline, opposed, V-type, and radial engines. Inline engines are commonly designed with an even number of assemblies, and they may be liquid- or air-cooled. While cylinders are generally placed above the crankshaft, inverted engines feature the cylinders below.
Opposed engines, or O-type engines, are those with two sets of cylinders situated opposite of one another with a central crankshaft separating them. Similar to inline engines, opposed engines may either be air- or liquid-cooled, though air-cooled variations are the most prevalent in the aviation industry. While these engines feature a low weight-to-horsepower ratio, their narrow design allows them to be installed on the wings of an aircraft with low vibration.
V-type engines also exhibit two banks of cylinders, though they are set around 60 degrees apart from one another. These cylinder sets may be cooled with air or liquid based on the configuration of the aircraft and its fuselage. Popular during the second World War, V-type engines have become fairly obsolete in recent decades with other options being available.
Radial engines are known for their design where one or more rows of cylinders encircle a central crankcase. Radial engine sets are generally uneven in their cylinder count, some featuring five, seven, or nine cylinders per row. Radial engines are some of the most advanced reciprocating engines available for aircraft, and their popularity has still continued for a number of models since the rise of the gas turbine engine.
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