FAA Powerplant Written Practice Test

Which setup is characteristic of a two-spool gas turbine engine?

1. One turbine drives both compressors

2. Each compressor is driven by its own turbine

3. A single shaft connects both elements

4. The turbines operate at the same speed

The correct answer is: Each compressor is driven by its own turbine

In a two-spool gas turbine engine, the design features two distinct compression stages, each with its own compressor and turbine. This setup is characterized by the fact that each compressor is effectively driven by a separate turbine. The primary advantage of this configuration is that it allows the compressors to operate at different rotational speeds, which can lead to improved efficiency over a broader operational range. In many two-spool designs, the high-pressure compressor is typically driven by the high-pressure turbine, while the low-pressure compressor is driven by the low-pressure turbine. This arrangement enables the engine to optimize performance by tailoring the speeds of the turbines and compressors to suit various phases of operation, such as takeoff and cruise. This structure stands in contrast to setups where a single turbine drives both compressors, which would limit efficiency and operational flexibility. Similarly, while both turbines can be on a single shaft or operate at the same speed in some engine designs, this is not a characteristic feature of a two-spool design. The unique configuration of a two-spool gas turbine engine is crucial for achieving optimal performance across different flight conditions.