variable-cycle engine

Also known as: VCE

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Last updated

July 14, 2026

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A variable-cycle engine (VCE) is designed to operate efficiently across a wide range of flight speeds, from subsonic to supersonic. This is achieved by altering its bypass ratio, a key characteristic of jet engines.

For subsonic flight, a high-bypass ratio is desirable for fuel efficiency and quiet operation. Conversely, supersonic flight requires a low-bypass ratio. A VCE can switch between these configurations using internal valves. When valves are closed, they restrict bypass airflow for supersonic speeds. When open, they increase bypass flow for efficient subsonic flight. This adaptability is crucial for aircraft undertaking mixed missions, such as high-speed commercial airliners.1

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jet engine
Variable-cycle engines
of internal-combustion engine For aircraft designed to fly mixed missions (i.e., at subsonic, transonic, and supersonic flight speeds) with low levels of fuel consumption, it is desirable to have an engine with the characteristics of both a high-bypass engine (for subsonic flight speed) and a low-bypass…
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of internal-combustion engine For aircraft designed to fly mixed missions (i.e., at subsonic, transonic, and supersonic flight speeds) with low levels of fuel consumption, it is desirable to have an engine with the characteristics of both a high-bypass engine (for subsonic flight speed) and a low-bypass…
Read More