For a long time, from the end of the 19th century until the middle of the 20th century, a piston aircraft engine remained the only engine that provided aircraft flights. And only in the forties of the last century, he gave way to engines with other operating principles - turbojet. But, despite the fact that the piston motors have lost their positions, they have not disappeared from the scene.
Modern applications of piston motors
At present, aircraft piston engines are mainly used on sports aircraft, as well as on small aircraft made to order. One of the main reasons that engines of this type are used very little is that the ratio of the unit of power to the unit mass of the piston engine is significantly less compared to gas turbine ones. Piston speed indicators do not withstand any competition with other engines used in aircraft construction. Moreover, their efficiency does not exceed 30%.
Types of piston aircraft engines
Piston aircraft engines have differences mainly in the arrangement of the cylinders relative to the crankshaft. As a result, there is a fairly large number of different types of piston engines. The most widely used are the following:
- engines with a V-shaped arrangement of cylinders;
- piston radial engine, where the cylinders are star-shaped;
- boxer engine, his cylinders are arranged in rows.
V engines
They are the most famous and used types of internal combustion engines in the aircraft industry and not only. Their name is associated with the characteristic arrangement of the cylinders in relation to the crankshaft. Moreover, they have a different level of inclination in relation to each other. It can range from 10 to 120 degrees. Such engines operate on the same principles as other internal combustion engines.
The advantages of engines with a V-shaped arrangement of cylinders include their relative compactness while maintaining power indicators, as well as the ability to obtain decent torque. The design allows to achieve significant shaft accelerations due to the fact that the inertia created during operation is much higher than that of other types of internal combustion engines. Compared to other types, these are characterized by the smallest height and length.
Motors of this type have high crankshaft rigidity. This provides greater structural strength, which increases the life of the entire engine. The operating frequencies of such motors are large ranges. This allows you to quickly gain momentum, as well as work stably in extreme conditions.
The disadvantages of piston aircraft engines with a V-shaped engine include the complexity of their design. As a result, they cost significantly more than other types. Moreover, they are distinguished by a sufficiently large engine width. Also, V-shaped motors are characterized by a high level of vibration, difficulties in balancing. This leads to the fact that it is necessary to specifically weight their various parts.
Radial Aircraft Piston Engine
Currently, radial piston motors have again become in demand in aviation. They are actively used in sports models of aircraft, or in custom-made ones. All of them are small in size. The device of a radial-looking aircraft piston engine, unlike other engines, consists in the fact that its cylinders are located around the crankshaft through equal angles, like radial rays (asterisks). This gave him the name - star-shaped. Such motors are equipped with an exhaust system that diverges with radial rays. Moreover, an engine of this type may have several star compartments. This is possible due to the fact that the crankshaft is increased in length. Typically, radial engines are made with an odd number of cylinders. This allows a spark to be fed into the cylinder through one. But they also make radial engines with an even number of cylinders, but their number should be more than two.
The biggest drawback of radial type engines is the possibility of oil penetrating the lower engine cylinders when the aircraft is stationary. This problem often enough leads to the occurrence of instant water hammer, which entails the breakdown of the entire crank mechanism. To prevent such problems before starting the engine requires a constant check of the condition of the lower cylinders for the absence of penetration of oil to them.
The advantages of radial type engines include their small size, ease of operation and decent power. Usually they are installed on aircraft of sports models.
Box aircraft piston engine
At present, boxer aircraft engines are beginning to experience their rebirth. Due to their small size and relatively low weight, they are placed on light sports aircraft. They are capable of developing sufficient power and provide very high speeds.
Boxer engines have several types of designs:
1. Motor made by the method of “boxer” (Subaru). In such engines, pistons of cylinders opposed to each other move equidistant. This leads to the fact that in each cycle one is at the top dead center, and the opposite is at the bottom.
2. Engines equipped with an OROS device (Opposed Piston Opposed Cylinder). In such engines, the cylinders are horizontal relative to the crankshaft. In each of them there are two pistons, which during operation move towards. The distant piston is connected to the crankshaft by a special connecting rod.
3. An engine made on the basis of the principle applied in the Soviet 5TDF motor. In this product, the pistons move towards each other, working in pairs in each individual cylinder. When both pistons reach top dead center, fuel is injected between them. Engines of this kind can operate on various types of fuel, from kerosene to gasoline. To increase the power of boxer engines, they are supplied with a turbocharger.
The main advantage in boxer type engines is compactness, small dimensions. They can be used on very small aircraft. Their power is quite high. Currently, they are becoming more common in sports aircraft.
The main disadvantage is the high fuel consumption and especially engine oil. In relation to engines of other types, boxer engines consume fuels and lubricants twice as much. They require a constant oil change.
Modern aircraft engines
Modern piston aircraft engines are very complex systems. They are equipped with modern components and assemblies. Their work is provided and controlled by modern systems and devices. Due to the use of advanced technologies, the weight characteristic of the engine is significantly reduced. Their power has increased, which contributes to widespread use in light-engine - sports aviation.
Aviation oils
Oil in piston aircraft engines operates in fairly difficult conditions. These are high temperatures in the areas of the piston rings, on the internal parts of the pistons, on valves and other components. Therefore, to ensure high-quality operation of the motor in conditions of significant temperatures, pressure, loads, they use high-viscosity oils, which are subjected to special cleaning. They must have high lubricity, remain neutral to metals and other structural materials of the engine. Aviation oils for piston engines must be resistant to oxidation when exposed to high temperatures, not to lose their properties during storage.
Domestic piston aircraft engines
The history of the production of piston engines in Russia begins in 1910. Mass production began during the First World War. In the Soviet Union, Soviet piston aircraft engines of their own design began to be created since 1922. With the growth of industrial production, including aviation, the country began to mass produce piston engines of 4 manufacturers. These were the engines of V. Klimov, A. Shvetsov, plant No. 29, A. Mikulin.
After the war, the process of modernization of aviation of the USSR begins. Aircraft engines for new aircraft are designed and built. Actively developing jet aircraft. In 1947, all military aircraft operating at high speeds switched to jet thrust. Piston aircraft engines are used only on training, sports, passenger and military transport aircraft.
Largest piston aircraft engine
The most powerful piston aircraft engine was created in the USA in 1943. It was called Lycoming XR-7755. It was a thirty-six cylinder engine. Its working volume was 127 liters. He was able to develop a power of 5,000 horsepower. Designed for aircraft Convair B-36. However, the series did not go. It was created in duplicate, as a prototype.