How Radial Engines Function

Since the advent of aviation, a great number of aircraft engine types have come about to achieve heavier-than-air flight. With types such as the turboprop engine, radial engine, and other combustion engines all common to aviation, a variety of aircraft with varying applications and designs may be accommodated for. The radial engine in particular is one of the oldest forms of aircraft engines, and it can still be found on a number of models to this day. Due to its importance and continued use for general aviation, understanding the radial engine’s functionality and make-up can assist in the operation and maintenance of such engines.

As a type of combustion engine, the radial engine utilizes reciprocating cycles to intake, compress, ignite, and expel fuel and air mixtures. With a central crankcase encircled by sets of cylinders, reciprocation of the cylinders is achieved as the crankcase rotates. As cylinders radiate outwards on a set fire order based on the revolution of the crankcase, the process of combusting fuel and air mixtures is very smooth.

While the design of the radial engine is quite simplistic as compared to other aircraft engine types, their operation is still quite reliable and efficient. Furthermore, the low amount of moving parts and components present within the system also lessens the degree of stressors and deterioration that parts face, thus maintenance often proves much easier. As a result, many operators and aircraft manufacturers may choose the radial engine over more powerful turbine and turboprop engines for the ease of repair and maintenance they offer.

As the axes of each cylinder is coplanar, a typical radial engine will utilize a master-and-articulating-rod assembly to connect the pistons and crankshaft together. Generally, the primary piston of the assembly will be directly attached to the crankshaft with a master rod. Meanwhile, the other pistons will be connected to the master rod through rings and connecting rod attachments. If there is a desire to add extra power and operation to the radial engine, more rows of cylinders can be attached without having to extend or adjust the diameter of the assembly.

To ensure that the combustion of gases is smooth and that the firing order follows an “every-other-piston” sequence, an odd number of cylinders are always implemented in each row. As such, there will always be a cylinder between one that is compressing gases and another that is combusting them. The reason that this method and assembly is used is due to the fact that the active stroke assists the compression stroke of another, allowing for the entire process to be more uniform in movement.

As radial engines are typically reserved for smaller aircraft due to their general power output, such combustion engines are often air-cooled. With much of their assembly being placed in the airflow during a flight operation, the cold temperatures of high altitudes will help mitigate heat build-up to protect the engine. While drag may slow the aircraft down slightly and many newer piston powered engine types have come about over the years, the radial engine still serves as one of the best piston-powered options for lighter aircraft.


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