6.3.3: Turboprops

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Figure 6.15: Turboprop engines.

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Figure 6.16: A statically mounted Pratt & Whitney J58 engine with full after-burner. Wikimedia Commons / Public Domain.

Many regional aircraft use turboprop engines. There are two main parts in a turboprop engine: the core engine and the propeller. The core engine is very similar to a basic turbojet except that instead of expanding all the hot exhaust gases through the nozzle to produce thrust, most of this energy is used to turn the turbine. The shaft drives the propeller through gear connections and produces most of the thrust (similarly to a propeller). Figure 6.15 illustrates a turboprop.

The thrust of a turboprop is the sum of the thrust of the propeller and the thrust of the core, which is very small. Propellers become less efficient as the speed of the aircraft increases. Thus, turboprops are only used for low subsonic speed regimes aircraft. A variation of the turboprop engine is the turboshaft engine. In a turboshaft engine, the gearbox is not connected to a propeller but to some other drive device. Many helicopters use turboshaft engines.