NASA Glenn · Guide to Aeronautics
NASA Glenn · Retrieved 2026-09-05
Educational reference; original Owl summariesPROPULSION
Bypass ratio & propulsive efficiency
FLIGHT SCIENCE / CONCEPT REFERENCE
SCIENCEConditions & principles
Bypass ratio compares the mass flow around a turbofan core with the flow through it.
REFERENCE COVERAGE3 / 3 editorial sections
PROVENANCE1 linked source
LAST RETRIEVED2026-09-05
Editorial section coverage describes the article structure, not scientific validation or completeness.
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Source editions
NASA Glenn · Guide to Aeronautics ↗Edition / snapshot: Reference snapshot, September 2026Retrieved: 2026-09-05
Retrieval dates record when Owl obtained the data; they are not publication dates or proof that a specification is current. Where the edition contains only a snapshot date, the original publication date is not recorded.
01
Mechanism
A fan accelerates a large bypass stream while the core provides energy. For a given thrust, moving more air through a smaller velocity change can reduce wasted exhaust kinetic energy.
02
Aircraft response
High bypass architectures can improve subsonic propulsive efficiency, while introducing diameter, nacelle drag and mass tradeoffs.
03
Context & interpretation
Bypass ratio is a flow ratio, not a thrust percentage. The operating condition matters when comparing published ratios.
Physical relationship
BPR = ṁbypass / ṁcoreDimensionless mass-flow ratio; compare values at equivalent conditions.
Sources & context
Educational explanation of physical mechanisms. Aircraft-specific procedures, limitations and current weather information are separate references.