Building Factory: Turbomeca (Francia)

Type: pure turbojet with single faced, single stage centrifugal compressor; annular combustion chamber and single stage turbine.

Weight: 156 (+-3%) kgf.

Rotating sense: hourly, seen from the front.

Compressor: centrifugal single flow, single stage done in aluminum alloy, with axial and radial diffusers. Outer diameter: 382 mm. Theoretical compression ratio: 3.9:1 and air flow volume 8 kgf/seg @ 22 600 static RPMs.

Combustion chamber: annular, Nimonic 75 steel alloy made with centrifugal injection.

Turbine: axial single stage made of steel ATVS-7 alloy with 37 milled blades and 25 hollow stators. Inlet gas temperature: 780 °C. Outer diameter: 339 mm. Coefficient of total expansion in the turbine: 2,20 (What supposes a temperature fall of 150 °C).

Exhaust nozzle: fixed without post-combustion, weight 6 kgf.

Main fuel system: it has a booster pump, a main cut off valve, an up to 20 microns filter , a fuel control unit equipped with a main pump with work pressure of 8 kgf/cm2 and overspeed control, a pressure controller, an accelerator and an altitude control. The fuel feeding system is from centrifugal injection type.

Fuel: aviation kerosene (JPl, JP4, Jet a/b or another one according to norms).

Starting fuel system: it has a micropump with a work pressure of 4 kgf/cm2 and two ignition torches.

Lubrication system: 10 liters oil reserve. It has a gears pump with a pressure of 4 kgf/cm2, filter and recovery circuit.

Lubricant: mineral oil according to norms.

Starting system: DC circuit of 27 Volts (battery or auxiliary starting group). It has an electric starter with a resistance system that allows two starting stages: 1st stage: 8 V, 250 amp. 2nd stage: 17V, 360 amp.

Ignition system: DC circuit of 27 Volts. It has two coils and two torches.

Air extraction system: it has an air derivation from the combustion chamber for the fuel's entrance labyrinth pressurization and two air extraction outlets at the compressor's carter upper side for the airplane systems.

Back bearing refrigeration system: it has a system of atmospheric cold air circulation.

Thermodynamic operation and air circuit*
The atmospheric air is aspired through the entrance conduit by the centrifugal compressor. It undergoes one first compression in the rotor. When coming out of the rotor, a first radial diffuser, reduces the speed of the air, which still plus increases its pressure. A second diffuser, axial, has mainly by purpose straightening the flow.
The compressed air comes around the outer part of the combustion chamber and is divided in two main flows:

1)	The first one, generally called primary flow, constitutes the combustion air. It is divided in two currents: - the first current passes between the cover of the diffusers and the front turbulence plate; the air penetrates in the combustion zone by three rows of radial grooves with tangential exit and inverse sense of exit from a groove to another one, to create a turbulence. - the second current circulates throughout the mixer of the outer part, penetrates in the hollow blades of the turbine stator and flows to the inner part of the combustion air chamber. This air that cools the turbine shaft when passing, arrives to the zone of combustion by hollowed orifices in the inner turbulence plate.
2)	The second, generally called secondary flow, constitutes the dilution air. It penetrates in the interior of the mixer (flame tube), by oval tubes and the four rows of holes perforated in the back part of the mixer. It assures the dilution of combustion gases and cools them.

The relation of the volumes between the primary and secondary flows is approximately one third.

The fuel is lead by a tube to the center of the injection wheel. It is injected in the combustion zone by twelve holes perforated in this wheel. Thanks to the great speed provided by the rotation of the shaft, the fuel undergoes a forced pulverization; it forms with the strongly turbulent air of combustion that arrives by both sides of the injection wheel, a homogenous fuel mixture, inflamed when starting by the two ignition torches.

The calibration of the diverse orifices perforated in the combustion chamber (LDM 5) is such that, in any regime and altitude, it is settled around the injection wheel a center of self-sustaining combustion without neither loosening of flame by insufflated, nor extinction by too rich or too poor mixture. This calibration allows in addition, to have throughout the blades of the turbine a distribution of compatible temperature with its mechanical resistance.

The combustion gases strongly cooled by the dilution air (in such a way that the temperature obtained in front of the blades of the turbine stator does not exceed 800°C), undergo one first expansion crossing the turbine stator. This expansion, that continues through the turbine, provides the necessary energy for the movement of the compressor and the accessories.

The combustion gases escape through the exit diffuser, and a nozzle of calibrated section exit allows to use in optimal way its kinetic energy as a propulsive force under the form of axial push.

PERFORMANCES*
For T.P.N.C. (ambp.=1.033 kgf/cm2 or 1013 mb, ambt.=15°C or 288 K) @ 22 600 rpm (max takeoff) the performances are:
 

Thrust: 400 (+-12) kgf.

Weight/thrust ratio: 0.402 kgf/kgfe.

Jet exhaust speed: 490 m/seg.

Jet exhaust temperature: 620°C.

Fuel consumption: 468 kgf/h (aprox. 585 lts/h).

Specific consumption: 1.090 kgf/kgfe/h.

Oil consuption: 0.2 kgf/h.

*: Data by E.T. Taller Regional Quilmes' courtesy. Cut by Francisco Erjavec's courtesy.