From automobiles to aircraft, combustion is a powerful force for generating movement in a wide selection of vehicles. To harness enough force to propel a massive metal craft, airplanes rely on one of two types of engines: piston or prop. Though both are frequently used on similar aircraft, the two power sources can be compared for their relative differences in safety, cost, and performance. By knowing these differences along with the general working principles behind these devices, pilots and technicians alike can better understand how to best choose and/or maintain their engine.
How Do Piston Engines and Turboprop Engines Work?
Both turboprop engines and piston engines are similar in that they can be considered air pumps that source energy from combustion to drive propellers. As with all combustion engines, they also follow the same four stages in the engine cycle: intake, compression, combustion, and exhaust. Where the two engines differ is in their mechanical processes.
How Do Piston Engines Work?
Whereas turboprops are relatively new, piston engines have been around since the early days of flight and have persisted in their usage aboard aircraft as a reliable source of power. As stated before, the piston engine follows four basic strokes in its cycle. In the intake stroke, a valve is opened, letting in the fuel-air mixture as the piston moves down to create a large space. Then, in the compression stroke, the piston is forced upwards after the intake valve closes so that it will compress the fuel-air mixture into a much smaller area. Once the piston has completed its upwards stroke, the spark plug ignites the mixture, causing the gas to expand and force the piston back downward. This downwards motion is converted to the rotational motion of the propellers as the piston turns the crankshaft, providing power. Once the engine has harnessed the potential energy from the fuel-air mixture, the cycle must be set up again. To accomplish this, the exhaust valve opens, and the piston moves upwards, pushing the exhaust gas out of the cylinder and into the exhaust system.
How Do Turboprop Engines Work?
While piston engines can be easily separated into distinct processes for each of the four engine cycles, turboprops blur the line between them. First, air is drawn into the compressor of the engine, where it passes through a series of spinning blades, each set smaller than the next, adding more heat and compression to the air. Once the air has passed through the compressor, it is mixed with a precise amount of fuel in the combustion chamber. Rather than relying on spark plugs, the air has become so hot and condensed as a result of its journey through the compressor that it will immediately ignite when mixed with the fuel. After the combustion process, the combusted fuel-air mixture is pulled into the turbine area where the rapidly expanding air rotates the blades, therefore generating thrust. In the final stage, a very small amount of exhaust gas is discharged into the atmosphere.
Piston vs. Turboprop
In general, piston engines are more efficient and less expensive, both to purchase and to operate. However, turboprops are more reliable, have higher efficiencies for higher power outputs, and yield much better performance at high altitudes. They can be more specifically compared by way of the following factors:
1. Safety: While turboprop engines have many more moving parts than a piston engine, those parts rotate in a single direction at a relatively constant speed with well-balanced mass. Moreover, there are virtually no moving parts in a turboprop engine which make contact with one another. Each of these features make for less vibration and fatigue factors which could induce wear and tear on the engine. As a result, turboprops are generally thought of as a safer option and are therefore commonly used in commercial operations that require continual operation.
2. Efficiency: Due to their varying thermodynamic properties, turboprop and piston engines can be more or less efficient depending on the size and weight of the aircraft. In general, turbine engines lose efficiency as they become smaller while piston engines become less efficient as they grow larger. For this reason, piston engines are more often preferred for lighter aircraft just as turboprops are often found in large commercial planes. In terms of efficiency, pistons and turboprops find a crossover point in the 400 HP to 500 HP range.
3. Expense: Purchasing costs for piston engines are much less expensive than turboprops. Whereas a new piston engine could cost between $25,000 and $100,000, turboprop engines regularly cost a minimum of $700,000 and can easily exceed $1,000,0000. They are also much more costly to maintain. However, turboprops have an advantage in that their required maintenance and overhaul schedules are much longer and more predictable which allows operators to more easily manage and predict maintenance intervals. In contrast, piston engines rely much more on mechanical parts and are therefore less predictable in their maintenance. With regards to fuel cost, piston engines are also much less expensive to supply as they use far less fuel per hour and are therefore a good option for lighter planes that do not require a high level of power to fly.
4. Performance: In general, turboprop engines are better suited for higher altitudes and airspeeds, and with weightier aircraft. By comparison, piston engines are limited to lower altitudes and speeds. However, for lower intensity applications, they may be attractive for reducing overall cost where the advantages of a more powerful, but less fuel efficient, turboprop engine are not needed.
In conclusion, the advantages of turboprop and piston engines must be considered based on the aircraft’s weight and necessary power output. NSN Axis is a trusted distributor for all kinds of aircraft parts which have been quality-tested and sourced only from leading manufacturers on our Approved Vendor List. We invite you to browse our inventory of parts in stock and available for purchase on our website. If any of our items pique your interest, you may submit an RFQ to receive a custom quote for your comparisons in just 15 minutes or less!
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