FAA Powerplant Written Practice Test

How is the energy to turn the propeller in a turboprop engine typically produced?

1. Through the combustion chamber

2. By the main fuel pump

3. Additional turbine stages

4. From the electrical starter

The correct answer is: Additional turbine stages

In a turboprop engine, the energy to turn the propeller is primarily produced by additional turbine stages. The design of a turboprop engine involves a gas turbine engine that drives a propeller through a reduction gearbox. The combustion process takes place within the combustion chamber, where fuel is ignited and produces high-temperature, high-pressure gases. These gases then expand and pass through multiple stages of turbines that extract energy from them. After passing through the first turbine stage, a portion of that energy is used to drive the compressor, while the remaining energy is utilized in subsequent turbine stages. It is specifically these additional turbine stages that allow for increased efficiency and enhanced performance in converting thermal energy from the combustion process into mechanical energy that turns the propeller. This setup enables the turboprop engine to produce significant thrust at lower speeds compared to pure jet propulsion systems. By utilizing additional turbine stages, the engine maximizes the utilization of the energy produced from fuel combustion, ensuring that a considerable amount is converted effectively to power the propeller.