Which statement defines the compressor pressure ratio?

• A. The ratio of engine RPM to propeller pitch.
• B. The ratio of compressor discharge pressure to compressor inlet pressure.
• C. The ratio of fuel flow to air.
• D. The ratio of stall speed to cruise speed.

Answer: (B)

In a jet or turboprop engine, the compressor takes in air at a certain pressure and compresses it to a higher pressure. The compressor pressure ratio is a measure of how much the compressor increases the air pressure, defined as the discharge (outlet) pressure divided by the inlet pressure. This ratio is a key indicator of how effectively the compressor is boosting pressure and, by extension, how the engine will perform.

So, the correct concept is that the compressor pressure ratio equals compressor discharge pressure to compressor inlet pressure. The other ideas involve RPM relative to propeller pitch, the fuel-to-air ratio, or operating speeds like stall and cruise speed, which are not how the compressor pressure ratio is defined.