Turbomeca Astafan
variable-pitch geared turbofan
The Turbomeca Astafan is a single-spool, variable-pitch turbofan engine developed from the Turbomeca Astazou. Despite successful flight-testing, an efficient, quiet and clean design (compared to turbojets and conventional turbofans) and some commercial interest, the Astafan never entered series production. The engines were only flown on the Fouga 90 prototype and Turbomeca's two test aircraft.
Design
The engine combines an Astazou-derived centrifugal compressor with up to three axial compressor stages (depending on the version of the engine), driven by a common driveshaft. The fan section is composed of a unique variable pitch fan and fixed stator blades mounted at the front of the engine. Blade pitch is varied by a hydraulic piston mounted in the fan hub, while the fan itself is powered via a reduction gear from the main driveshaft.
The engine is designed to operate at a constant speed, no matter the thrust output—a characteristic permitted by the Astafan's use of precise fuel metering and fan blade pitch adjustment. To control the engine, the pilot first sets the speed lever, which adjusts fuel flow in proportion to the selected engine speed. Then the pilot moves the thrust lever (analogous to a throttle), actuating the fan pitch piston by way of a mechanical linkage and hydraulic valve, and varying the blade pitch. In response, the speed governor holds engine speed steady by adjusting fuel delivery to the combustor.
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This entry incorporates text from “Turbomeca Astafan” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.