Which term denotes the ratio of mass airflow through the fan to the mass airflow that passes through the gas generator?

• A. Bypass ratio
• B. Block altitude
• C. Calibrated airspeed
• D. Cage

Answer: (A)

This is about how much air bypasses the engine core compared to the air that goes through the core. In a turbofan, the fan moves a large amount of air, some of which goes into the gas generator (the core) to be compressed and burned, while the rest flows around the core through the bypass duct. The bypass ratio is the measure of how much air bypasses the core relative to the air that goes through it. So the term that denotes the ratio of mass airflow through the fan to the mass airflow through the gas generator describes how much of the total air is used to bypass the core versus going through it. A higher bypass ratio means more air bypasses the core, which generally improves fuel efficiency and reduces noise, though it results in a larger engine with lower specific thrust. Other terms like block altitude or calibrated airspeed relate to different flight performance concepts, and a cage isn’t related to this airflow split.