In a two-spool gas turbine, which statement is true about the LP and HP compressors?

• A. They are both mounted on the same shaft.
• B. The LP compressor handles initial low-pressure air; the HP compressor finishes the compression to higher pressure and drives the gas generator, on separate shafts.
• C. Only the LP compressor drives the gas generator.
• D. HP compressor handles the final stage of heating the air before combustion.

Answer: (B)

In a two-spool gas turbine, there are two separate rotating assemblies: a low-pressure (LP) shaft and a high-pressure (HP) shaft. Air first passes through the LP compressor on its own shaft, which raises it to a moderate pressure. That air then goes to the HP compressor on the separate HP shaft, which finishes the compression to the much higher pressure required for efficient combustion. The HP shaft also drives the gas generator portion of the engine (the core that includes the combustor), so the HP compressor is on the same shaft that powers the gas generator. This setup allows each compressor to operate at speeds optimized for its stage.

So the statement is correct because it reflects the two-spool arrangement with air doing initial compression in the LP stage and final high-pressure compression in the HP stage, with the HP shaft driving the gas generator. The other ideas don’t fit: the compressors aren’t on a single shaft, the LP compressor doesn’t alone drive the gas generator, and heating occurs in the combustor, not in the compressor.