FAA Powerplant Written Practice Test

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

1. N1 compressor

2. N2 compressor

3. N3 compressor

4. Fan compressor

The correct answer is: N2 compressor

In a dual axial-flow or twin spool compressor system, the first stage turbine typically drives the second spool, known as the N2 compressor. This is important because the architecture of a dual-spool system allows for independent operation of the low-pressure and high-pressure compressors. In this configuration, the N1 compressor, often referred to as the low-pressure compressor, is usually driven by the fan and connected to the high-pressure turbine, which is the second stage. The first stage turbine is specifically designed to drive the N2 compressor, which is associated with the high-pressure stage of the engine cycle. This separation of duties helps optimize performance, efficiency, and response during various phases of engine operation, such as takeoff and cruising. Understanding this relationship is crucial as it highlights how different components in a turbine engine interact to produce thrust, manage airflow, and ensure the effective operation of the engine at varying speeds and loads. The cooperative nature of the N1 and N2 compressors is critical in maintaining efficient compression ratios and overall performance, particularly at different altitude and power settings.