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Turbine vs. Piston Engines
2001 by Gregory N. Brown


Dear Greg, How does a turbine engine work? And how is it different from the prop airplanes I fly? Amanda


Dear Amanda,

While the reciprocating engine (also known as a piston engine) which powers your airplane has some things in common with turbine (jet) engines, the two types are very different in most respects.

As you can see from the diagrams, both types of engines have the same basic stages of operation, intake, compression, combustion, and exhaust. But the similarities largely end there, the biggest difference being that in a reciprocating engine those stages happen one at a time, while in a turbine engine all of them are continuous.

Instead of compressing intake air with a piston, turbine engines use a series of wheels at the front of the engine known as compressors. Another set of wheels, known as turbines, is driven by exhaust gases departing the combustion section. Both compressor and turbine wheels are somewhat similar in construction, each basically being a sophisticated "fan," composed of high-tolerance blades, and turning at very high speeds inside a tightly-ducted cowl.

The basic operation of all gas turbine engines is the same. Much like a turbocharger, the compressor section and turbine section of a gas turbine engine are mounted on a common shaft. Intake air is compressed by the compressors, and forced into the combustion chamber. Fuel is continuously sprayed into the combustion chamber and ignited, creating exhaust gases that drive the turbines. The turbines, through shafts, drive the compressors, starting the whole process over again. They also harness the engine's energy to drive all of the engine's accessories (such as generators and hydraulic pumps). Finally, the exhausting gases are accelerated through a nozzle at the back of the engine, producing thrust much in the way that air escaping the "nozzle" of an untied balloon causes it to fly across the room.

While the plane you fly has a piston engine turning a propeller to pull it through the air, turbine engines can be designed either to operate as jets, or to drive propellers themselves. As you probably know, a turbine engine driving a propeller is known as a turboprop.

The basic gas turbine engine we've been discussing may be thought of as the "gas generator," or "core turbine engine." Regardless of varying turbine engine types, the basic principles of operation for the core engine are the same. Depending on how the exhaust gases are harnessed, the core turbine engine described above may be applied to turbojet, turbofan, or turboprop engines.

Incidentally, while reciprocating aircraft engines burn gasoline, turbine engines consume jet fuel, which is kerosene. Turbine engines produce a great deal more power for their weight than piston engines, but they burn more fuel and are much more expensive to manufacture.

To learn more about turbine aircraft and how they work, pick up a copy of The Turbine Pilot's Flight Manual by Mark Holt and I. The material is easy for any aviation enthusiast to understand, and I think you'll find it very interesting!


Greg Brown

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