Turbomeca Astafan
Encyclopedia
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The Turboméca Astafan is a single-spool, variable-pitch
turbofan engine developed from the Turboméca 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 Turboméca's two test aircraft.
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. The control system also monitors turbine temperature and adjusts blade pitch (and therefore engine load) to maintain it within the preferred range of to . Additionally, the system automatically protects against excessive fuel delivery or unusual changes in blade pitch. Using the thrust lever, pilots can start an Astafan in fine pitch (for minimal resistive torque), select takeoff (coarse) pitch, feather the fan, or even reverse the fan pitch in flight (with the fan providing reverse thrust in lieu of conventional reversers).
to modify each of them to accept two podded Astafan engines inboard of the nacelles. The nacelles were stripped of their turboshaft engines, and converted to carry extra fuel. One of the Turbo Commanders, a model 680V-TU, originally bore the experimental registry F-WSTM, and was later redesignated F-BSTM. The other Turbo Commander, F-BXAS, was either a 690A or B model.
.
). Using this medium-bypass version of the Astafan instead of the Turbomeca Marboré
, the 90 had twice the range of the Magister (with a similar fuel load). Installed in the Fouga 90, and operating at its maximum thrust of , the IIG's specific fuel consumption was . At altitude and Mach 0.5, specific fuel consumption was .
The IIG included the Astafan's characteristic variable-pitch fan, installed in front of an Astazou XVI core (comprising two axial compressor stages preceding a centrifugal compressor on a common shaft). The design also included an annular reverse-flow combustor and a three-stage turbine section. The resulting configuration yielded a bypass ratio of 8.8 and a pressure ratio of 9.1.
The Turboméca Astafan is a single-spool, variable-pitch
Blade pitch
Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power. Wind turbines use this to adjust the rotation speed and the generated power...
turbofan engine developed from the Turboméca Astazou
Turbomeca Astazou
|-References:...
. 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 Turboméca's two test aircraft.
Design
The engine combines an Astazou-derived centrifugal compressorCentrifugal compressor
Centrifugal compressors, sometimes termed radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller...
with up to three axial compressor
Axial compressor
Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...
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. The control system also monitors turbine temperature and adjusts blade pitch (and therefore engine load) to maintain it within the preferred range of to . Additionally, the system automatically protects against excessive fuel delivery or unusual changes in blade pitch. Using the thrust lever, pilots can start an Astafan in fine pitch (for minimal resistive torque), select takeoff (coarse) pitch, feather the fan, or even reverse the fan pitch in flight (with the fan providing reverse thrust in lieu of conventional reversers).
Flying testbeds
Turbomeca owned two Rockwell Turbo Commander aircraft, and arranged for Miles AircraftMiles Aircraft
Miles was the name used to market the aircraft of British engineer Frederick George Miles, who designed numerous light civil and military aircraft and a range of curious prototypes...
to modify each of them to accept two podded Astafan engines inboard of the nacelles. The nacelles were stripped of their turboshaft engines, and converted to carry extra fuel. One of the Turbo Commanders, a model 680V-TU, originally bore the experimental registry F-WSTM, and was later redesignated F-BSTM. The other Turbo Commander, F-BXAS, was either a 690A or B model.
Astafan I
First run as a prototype in 1969, and first flown in 1971, the Astafan I was derived from the core of the Astazou XIV turboshaft. It was capable of outputting of dry thrust at takeoff power, or of thrust with water-methanol injectionWater injection (engines)
In internal combustion engines, water injection, also known as anti-detonant injection, is spraying water into the cylinder or incoming fuel-air mixture to cool the combustion chambers of the engine, allowing for greater compression ratios and largely eliminating the problem of engine knocking...
.
Astafan II
The Astafan II line was based on the Astazou XVI turboshaft engine core with a cooled turbine, and was governed to operate at .Astafan II
The basic Astafan II received its French certification in August 1972. Early Astafan IIs were rated for approximately dry thrust at takeoff power, or with water-methanol injection.Astafan IIA
The Astafan IIA was certified in 1972. It differed from the earlier Astafan II by incorporating a new, larger-diameter fan with blades that had a greater range of motion (improving upon the marginal reverse thrust capability that existed in prior versions). Thrust output of the IIA was .Astafan IIB4
Two IIB4s were installed on F-BSTM and used for testing and demonstration flights. This version was rated at of thrust.Astafan IIG
The IIG was installed on the prototype of Aérospatiale's Fouga 90 jet trainer (a development of the Fouga MagisterFouga Magister
The Fouga Magister is a 1950s French two-seat jet trainer. The related CM.175 Zéphyr was a carrier-capable version for the French Navy....
). Using this medium-bypass version of the Astafan instead of the Turbomeca Marboré
Turbomeca Marboré
|-See also:-References:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:* *...
, the 90 had twice the range of the Magister (with a similar fuel load). Installed in the Fouga 90, and operating at its maximum thrust of , the IIG's specific fuel consumption was . At altitude and Mach 0.5, specific fuel consumption was .
The IIG included the Astafan's characteristic variable-pitch fan, installed in front of an Astazou XVI core (comprising two axial compressor stages preceding a centrifugal compressor on a common shaft). The design also included an annular reverse-flow combustor and a three-stage turbine section. The resulting configuration yielded a bypass ratio of 8.8 and a pressure ratio of 9.1.
Astafan III
The Astafan III used the Astazou XVI core and a cooled turbine. The dry thrust rating at takeoff was , and with water-methanol injection, thrust rose to .Astafan IV
The Astafan IV was based upon the Astazou XX turboshaft's core, and used three axial compressor stages before the Astazou-derived centrifugal compressor. Like the Astafan II, the IV was governed at . The Astafan IV was considered for installation in the Fouga 90, as a more powerful alternative to the IIG.Astafan IVF6
The IVF6 was tested on F-BXAS, and the engines were retained during that aircraft's time as a company transport. This version of the engine output of thrust at takeoff power.Constructed
The Astafan was flown as a developmental engine on two aircraft types:- Rockwell Turbo Commander testbeds (several configurations)
- Fouga 90 (Astafan IIG; prototype built and flown)
Proposed
Despite its many developmental variants, the Astafan was never produced in commercial quantities. Proposed installations included:- Ted SmithTed R. SmithTed R. Smith was an American aircraft designer. He worked for the Douglas Aircraft Company, Aero Design and Engineering Company, and Rockwell Standard Corporation. In 40 years, his designs included the Douglas A-26 Invader , and the first all metal small twin engine business aircraft for Aero...
Super Star 3000 (Astafan II, concept abandoned when Aerostar was sold to Piper Aircraft) - Italair F.22 Jet Condor (Astafan II)
- Fabrica Militar de Aviones IA 58 PucaráFMA IA 58 PucaráThe FMA IA 58 Pucará is an Argentine ground-attack and counter-insurgency aircraft. It is a low-wing two-turboprop-engined all-metal monoplane with retractable landing gear, manufactured by the Fábrica Militar de Aviones.-Development:...
(Astafan IIs to replace turboprop engines)