Quick Facts
- Type
- Engine Parameter
- Definition
- The ratio of air passing around (bypass) a turbofan's core to air passing thr...
- Used By
- Engineers, Pilots
Definition#
Bypass ratio (BPR) is the ratio of the mass of air that flows through the fan duct (bypass stream) to the mass that flows through the engine core. Modern high-bypass turbofans have ratios of 8:1 to 12:1.
Why It Matters Operationally#
Higher bypass ratios improve propulsive efficiency and reduce specific fuel consumption at subsonic speeds. They also lower jet noise. Engine diameter increases with bypass ratio, affecting nacelle drag and ground clearance.