Aircraft piston engines, also referred to as reciprocating engines, are those that utilize one or more reciprocating pistons for the means of transforming pressure into a rotating motion. Coming in a variety of forms, piston engines have long served aircraft since the inception of powered flight. Despite their long history, piston engines can still be found on a number of modern models, utilizing their standard operations to drive propeller assemblies for the means of flight. In this blog, we will describe the basic functionality of piston aircraft engine types, allowing you to understand how they work.
While piston engines may come in a variety of forms, there are certain aspects that are common to all types. For one, the pistons are always placed within cylinders, providing a housing for the piston where gas can be introduced, pressurized, ignited, and expelled to create the force necessary to drive the propeller assembly. A majority of piston engines also operate in accordance with the four-stroke cycle, that of which describes the operation of the pistons and the cylinder assembly.
The first step of the four-stroke cycle is the intake stroke, noted by the downward movement of the piston as air and fuel is drawn into the cylinder through an intake valve. After air and fuel enters the cylinder, the compression stroke begins as the piston thrusts upwards, increasing the pressure of the mixture. As the piston begins to reach towards the top of the cylinder assembly, the ignition system will utilize spark plugs to deliver a pulse of electricity capable of igniting the fuel and air mixture. Upon combustion, the rapid expansion of exhaust gases launches the piston downwards once again, causing it to drive the crankshaft so that the propeller assembly may be spun. The final stroke of the cycle is the exhaust stroke, and it occurs after combustion. Once the piston reaches the bottom of the cylinder after combustion, an exhaust valve opens so that the piston can move back up and push all gases out. After the cycle has been completed, it will continue to repeat in rapid succession throughout the entire flight.
Alongside the four-stroke cycle, most aircraft piston engines also contain carburetors and fuel injection systems, those of which facilitate the delivery of fuel and air mixtures to the cylinders. The carburetor is tasked with mixing the fuel and air mixtures, most often being found in smaller aircraft engine types due to their low price point. For larger engines, on the other hand, the fuel-injection system is the most common choice and can provide fuel directly into cylinder assemblies so that they may mix the fuel and air during the intake stroke.
The ignition system is paramount for standard engine operations, ensuring that cylinders are provided with the sparks needed to create a combustive force strong enough to drive the crankshaft. Most aircraft piston engine manufacturers implement magnetos for the means of spark generation, due in part to their ability to create a very hot spark at high engine speeds and their independence from power sources such as batteries, generators, and alternators. To create the spark necessary for ignition, the magneto is rotated. As such, the pilot will rely on a battery-powered starter which causes the magneto to rotate as the engine initiates operations. Once the magneto has begun igniting fuel and air mixtures, the starter may be disengaged as the magneto will continue functionality until the aircraft is powered down.
For redundancy, many piston engines will have a dual ignition system, meaning that two magnetos are used to supply two sparks per cylinder. Both magnetos will induce current to separate plugs, and some aircraft may allow for control over each magneto. The dual ignition system is beneficial due to its safety and efficiency, ensuring that ignition can continue even in the case of one magneto failing. Additionally, having more sparks firing in the cylinders increases the quality of combustion, thus improving engine performance as well.
With the power created through the four stroke cycle, the piston engine operates a propeller assembly that is attached to the nose of the aircraft. Propellers can come in one of two types, those of which are the fixed-pitch and constant-speed propeller. Fixed-pitch propeller assemblies are directly bolted to the engine crankshaft, meaning that their speed is directly tied to the engine. While they may provide less efficiency than other types, they are quite simple to operate as the pilot only needs to monitor tachometer values. The constant-speed propeller, on the other hand, utilizes a governor that manages the blade angle as RPM settings are set. With their method of operation, the constant-speed propeller provides increased efficiency, also allowing for more performance during the takeoff and cruise stages.
Depending on one’s needs, there are various aircraft engine types that one may use. The in-line engine is the earliest piston engine type, featuring a straight line of cylinders such as is seen in various automobiles. Rotary engines were developed after World War I, most notable for their engine that rotates with the propeller to achieve more optimal airflow for reducing heat. The V-type engine followed after and featured a construction reminiscent of two in-line engines joined together to create a “V” shape, and all cylinders share a common crankshaft. Radial engines are one of the newer piston engine types, utilizing odd-numbered cylinders placed in circular rows around a crankshaft. Due to their construction, radial engines feature a much better power-to-weight ratio as compared to their predecessors and have optimal air cooling. The horizontally opposed engine is the final common piston engine variation, featuring a central crankcase and staggered cylinders placed on opposite ends. Due to their simplistic design, such engine types are known for being dependable and easy to maintain.
Piston engines have a long history, and they continue to reliably serve countless aircraft for the means of flight. Just NSN Parts is a leading supplier of aircraft components, and we are your sourcing solution for top quality alignment piston parts, baffle piston rod components, assembly tool piston products, and much more. As you explore our offered parts on our website, you may request a quote for your comparisons at any time through the submission of an Instant RFQ form. Once received, a member of our staff will quickly review and respond to your request in just 15 minutes or less, 24/7x365. Get started today and see how Just NSN Parts can serve as your strategic sourcing partner.
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