unducted fan

engineering

Also known as: UDF

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Last updated

July 14, 2026

Quick Summary

An unducted fan (UDF) is an advanced propulsion system that utilizes high-efficiency counter-rotating propeller blades. These blades are directly driven by low-pressure turbine stages, eliminating the need for a gearbox. This design aims to achieve higher propulsive efficiency compared to conventional turboprop engines. UDFs are part of a trend in aircraft engine development focused on improving fuel efficiency, particularly for commercial air transport. They represent an evolution in propeller technology, moving towards more efficient operation at higher flight speeds.12

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jet engine
Turboprops, propfans, and unducted fan engines
…engine layout, identified as the unducted fan (or UDF; trademark), provides a set of very high-efficiency counter-rotating propeller blades, each blade mounted on one of either of two sets of counter-rotating low-pressure turbine stages and achieving all the advantages of the arrangement without the use of a gearbox.
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…engine layout, identified as the unducted fan (or UDF; trademark), provides a set of very high-efficiency counter-rotating propeller blades, each blade mounted on one of either of two sets of counter-rotating low-pressure turbine stages and achieving all the advantages of the arrangement without the use of a gearbox.
Read More