Turbomeca Astafan
| Company type | Turbofan aircraft engine |
|---|---|
| Industry | Aerospace |
| Predecessor | Turbomeca Astazou |
| Founded | 1969 |
| Headquarters | France |
| Products | Variable-pitch turbofan engines (Astafan series) |
The Turbomeca Astafan is a variable-pitch, single-spool turbofan engine that evolved from the Turbomeca Astazou. Although it demonstrated quiet operation, fuel efficiency, and cleaner emissions compared to traditional turbojets and standard turbofans during flight tests, it never progressed to mass production. While it garnered some commercial interest, its usage was limited to the Fouga 90 prototype and two Turbomeca test aircraft.
Design
This engine integrates a centrifugal compressor derived from the Astazou with up to three axial compressor stages—depending on the specific variant—mounted on a shared shaft. The fan assembly is distinctive for its variable-pitch blades combined with fixed stator vanes at the front. Blade angle adjustments occur hydraulically through a piston located in the fan hub, and the fan itself is driven by the main shaft via reduction gearing.
Engine speed remains constant regardless of thrust demand, achieved through precise fuel flow regulation and fan blade pitch control. Pilots manage engine speed by adjusting a speed lever that regulates fuel supply, then modulate thrust independently using a separate lever that alters fan blade pitch through mechanical and hydraulic linkages. A speed governor ensures steady engine RPM by controlling fuel input. Additionally, the control system continuously monitors turbine temperature, altering blade pitch to maintain it within safe limits and preventing excessive fuel flow or abnormal blade movements. The thrust lever allows pilots to start the engine at fine pitch for low torque, select coarse pitch for takeoff power, feather the fan blades, or reverse blade pitch in flight to generate reverse thrust without requiring conventional thrust reversers.
Flying testbeds
Turbomeca modified two Rockwell Turbo Commander aircraft—originally fitted with turboshaft engines—by removing these engines and converting the nacelles to accommodate two pod-mounted Astafan units placed inboard of the nacelles along with additional fuel capacity. One of these Turbo Commanders was model 680V-TU, initially registered as F-WSTM and later changed to F-BSTM. The second aircraft, registered F-BXAS, was either a 690A or 690B model.
Astafan I
The initial prototype appeared in 1969 and first flew in 1971. It utilized an Astazou XIV turboshaft core and delivered dry thrust of () at takeoff, increasing to () when employing water-methanol injection.
Astafan II
Built around the Astazou XVI core featuring a cooled turbine and governed at , this series improved both thrust output and efficiency.
Astafan II
Achieving French certification in August 1972, early versions of this model produced approximately () of dry thrust at takeoff or () with water-methanol injection.
Astafan IIA
Also certified in 1972, this variant incorporated a larger diameter fan with an expanded blade pitch range that enhanced reverse thrust capability. It generated () of thrust.
Astafan IIB4
Around 1978, two IIB4 engines were fitted on the F-BSTM for evaluation and demonstration purposes, each delivering thrust of ().
Astafan IIG
The IIG engine powered the prototype of the Aérospatiale Fouga 90 jet trainer, replacing the Turbomeca Marboré to achieve twice the range with an equivalent fuel quantity. At its maximum thrust of , the specific fuel consumption measured () while at an altitude of 6000 meters and Mach 0.5, consumption was ().
This model incorporated a variable-pitch fan positioned ahead of an Astazou XVI core, which combined two axial compressor stages with a centrifugal compressor mounted on a shared shaft. The design included an annular reverse-flow combustor and a three-stage turbine, resulting in a bypass ratio of 8.8 and an overall pressure ratio of 9.1.
Astafan III
Utilizing the Astazou XVI core equipped with a cooled turbine, the Astafan III produced a dry takeoff thrust of , which could be enhanced to (lbf) when employing water-methanol injection.
Astafan IV
The Astafan IV was developed around the Astazou XX turboshaft core and featured three axial compressor stages preceding the centrifugal compressor derived from Astazou designs. It was controlled to operate at . This variant was considered as a more powerful alternative for the Fouga 90 compared to the IIG version.
Astafan IVF6
The IVF6 variant, tested on F-BXAS, generated takeoff thrust of and remained in use circa 1987 during the aircraft’s role as company transport.
Built
The Astafan engine served as a developmental powerplant on:
- Various Rockwell Turbo Commander testbed configurations
- Fouga 90 prototype (equipped with Astafan IIG)
Planned
Despite multiple variants being developed, the Astafan did not reach commercial production. Proposed applications included:
- Ted Smith Super Star 3000 (Astafan II; project discontinued following Aerostar’s acquisition by Piper Aircraft)
- Italair F.22 Jet Condor (Astafan II)
- Fabrica Militar de Aviones IA 58 Pucará (Astafan IIs suggested as replacements for turboprop engines)
External links
- Astafan testbed (Airliners.net)