Bypass ratio

The pass ratio ( engl. 'bypass ratio BPR ) is an expression of aeronautical engineering. It describes, in a two -phase jet engine, the ratio between the air mass flow which is routed past by the fan of the gas turbine (low flow or sheath flow ), and the air mass flow inside the combustion chamber of the engine passes, and the shaft provides power ( the core stream ).

Modern civil jet engines have bypass flow ratios from 5:1 to 10:1, military types about to 1.5:1. The next generation of civil engines such as the Pratt & Whitney PW1000G, increases the bypass ratio even up to 12:1.

Military turbofan engines for supersonic range up to about Mach 2.5 typically have a bypass ratio of about 0.4:1, as this represents an optimum between the resistance by the face and the economy through the bypass.

Turboprop engines achieve a fictitious bypass ratio ( prop wash compared to the mass flow through the engine ) of about 100:1.

• Engine technology