Most modern aircraft, both passenger and military, use gas-powered turbines, also known as jet engines, to create thrust and propel the plane forward and into the air. Turbine engines themselves have various subcategories including turbojet, turbofan, turboshaft and turboprop. Each engine type provides a different amount of power and excels at different speeds and altitudes.
Generally a turbine engine is a rotary engine that uses fluid and air flow for energy. Simple turbines have only one moving part, a rotor assembly, as seen in early turbines such as windmills and water wheels. In turbine engines, a series of drums with blades work to increase the speed of airflow through the engine. Once the engine is spinning, fuel is added and ignited, resulting in very high pressure. This pressure explodes out the rear of the engine and creates the thrust needed to propel the aircraft forward.
A turboprop engine uses the basic design of a turbine except with one defining difference: the presence of a propeller at the front of the engine. Most turbines use the exhaust from the air/fuel mixture to create thrust from the back, but turboprop engines use the energy created from the exhaust to spin the rotor for the propeller. The propeller then creates thrust, which pulls the aircraft forward from the front rather than pushing it from the rear.
Uses of Turboprop Engines
Turboprop engines don't travel as fast as other turbine-propelled aircraft, primarily because the propeller at the front operates back at lower speeds than those powered exclusively by jet exhaust. Turboprop engines are most efficient at 250 to 400 miles per hour and at 18,000 to 30,000 feet in altitude. Because the propellers require less energy to spin at optimal speed than the power turbine can produce, and the engine exhaust is used to spin the propeller rather explode out the back, turboprop engines are more fuel-efficient than other turbine engines. These characteristics make turboprops the preferred engine for small, subsonic aircraft used for shorter trips.
Other Types of Turbines
Turbojet engine are essentially the basic type of turbine engine, accelerating inlet air into the combustion chamber where fuel is added and ignited to expand the air and release it through the exhaust system. Turbofans include features of both turbojet and turboprop engines; the inlet air is diverted into two directions, with one direction used to power spin and accelerate through the rotor while the second stream bypasses the combustion chamber to cool the engine, reduce noise and create additional thrust. The turboshaft engine works much like a turboprop in that the power is used to create spin rather than thrust. Many helicopters use turboshaft engines.