FAA Powerplant Written Practice Test

In a dual axial-flow or twin spool compressor system, which compressor does the first stage turbine drive?

1. N1 compressor

2. N2 compressor

3. Low-pressure compressor

4. High-pressure compressor

The correct answer is: N2 compressor

In a dual axial-flow or twin spool compressor system, the first stage turbine drives the N2 compressor. The N2 compressor is typically the high-pressure compressor in the system, and it is responsible for compressing the air to a higher pressure before it enters the combustion chamber. In this configuration, the engine consists of two separate shafts: the N1 shaft, which often drives the low-pressure compressor, and the N2 shaft, which is connected to the high-pressure compressor. The reason the first stage turbine specifically drives the N2 compressor relates to the engine's operational efficiency and the design objective of maximizing pressure ratios throughout the compression process. This setup allows for more effective management of airflow and pressure within the engine, enabling better performance across various operating conditions. The high-pressure compressor’s function is critical for producing the necessary conditions for efficient combustion, leading to improved thrust performance of the engine.