FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesMedium
A high-bypass turbofan engine has a fan (bypass) airflow of 800 lb/sec and a core airflow of 100 lb/sec. What is the engine's bypass ratio?
- A0.8:1
- B8:1
- C1:8
- D9:1
Show answer & explanationAnswer & explanation
Correct answer: B. 8:1
Bypass ratio is defined as bypass (fan) airflow divided by core airflow: 800 ÷ 100 = 8, expressed as 8:1. This means 8 pounds of air bypass the core for every 1 pound that flows through it.
Why the other options are wrong
- A. This results from an incorrect calculation, such as dividing core by fan airflow times 100.
- C. This is the inverse of the correct ratio (core:bypass instead of bypass:core).
- D. This mistakenly uses total airflow (900) divided by core airflow (100).
Bypass Ratio
The ratio of the mass airflow that bypasses the engine core (through the fan duct) to the mass airflow that passes through the engine core.
- High-bypass engines have ratios of 5:1 to over 10:1
- Higher bypass ratio improves fuel efficiency and reduces noise
- Low-bypass turbofans (military) may have ratios below 1:1
Memory trick: Bypass ratio: how much air skips the party (core) versus how much goes through it.