TURBO-FANS & -PROPS

Stallfree technology provides an excellent method of blade regulation that can be adapted to the fans of turbofans.

“All commercial aircraft designed in the last 40 years (other than aircraft with fewer than a dozen passengers) are powered by gas turbine engines, either turbofan or turboprop.”

National Academies of Sciences, Engineering, and Medicine. 2016. Commercial Aircraft Propulsion and Energy Systems Research: Reducing Global Carbon Emissions. Washington, DC: The National Academies Press. doi:10.17226/23490.   
https://en.wikipedia.org/wiki/Jet_engine#/media/File:Gas_turbine_efficiency.png
•Turbofans come with low and high bypass ratio (BPR)  . 
•  Fans are somewhere in between axial compressors and propellers.
•Propeller features make the fan perform better at low speed, but at high-speed worse.
•Compressor features are the opposite: improve high-speed efficiency and reduce low speed performance. 
•  Engineers do their best to find the right balance for a good turbofan. 
•  Through fan regulation EFFICIENCY of the engine can be improved.
•  Stallfree technology provides an excellent method of blade regulation that can be adapted to the fans of turbofans.
•  However, effectiveness of regulation is mostly limited to the zones of the flow field where a regime of incompressibility can be retained.

Cutaway view (sketch) of a fan built according to the Stallfree Technology :

•  This is why the efficiency-boost that turbofans can get due to application of the Stallfree technology to their fans, is significant but still not that high as in the case of e.g. the turboprops.
•  On the below chart an estimation of the possible efficiency-boost is shown. This is how an upgrade with Stallfree technology can increase efficiency of a high BPR turbofan.
•  Turboprops are optimally positioned for an upgrade with Stallfree technology.
•All benefits of the new concept materialize in the process at their best.
•If the incompressibility limits are respected (e.g. no supersonic blade tips are allowed) resultant efficiency becomes a flat curve spanning slightly higher (!) than the maximum of the initial propeller characteristic.
Slight gain in the maximum value is expected due to avoidance of traditional trimming techniques aimed at widening the prop’s working speed range by making allowances in peak-efficiency.
•Expected efficiency characteristic of an upgraded turboprop engine is shown on the below figure. Improved chart of the turbofan engine is indicated by transparent shape.
•Upgraded turboprop propulsion has outstanding efficiency features (take-off, climb, cruising, and top speed) in the subsonic speed-range. Most competitive. A propulsion of choice.

Sketch of a fan hub with regulated blades :

Speed-range comparison of propellers and turbofans with and without Stallfree technology :

Example of fan with unregulated blades :

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